these two elements threaten ecosystem biodiversity

Want to create or adapt books like this? Learn more about how Pressbooks supports open publishing practices.

124 Threats to Biodiversity

By the end of this section, you will be able to do the following:

• Identify significant threats to biodiversity
• Explain the effects of habitat loss, the introduction of exotic species, and hunting on biodiversity
• Identify the early and predicted effects of climate change on biodiversity

The core threat to biodiversity on the planet, and therefore a threat to human welfare, is the combination of human population growth and resource exploitation. The human population requires resources to survive and grow, and those resources are being removed unsustainably from the environment. The three greatest proximate threats to biodiversity are habitat loss, overharvesting, and the introduction of exotic species. The first two of these are a direct result of human population growth and resource use. The third results from increased mobility and trade. A fourth major cause of extinction, anthropogenic climate change, has not yet had a large impact, but it is predicted to become significant during this century. Global climate change is also a consequence of human population needs for energy and the use of fossil fuels to meet those needs (Figure 1). Environmental issues, such as toxic pollution, have specific targeted effects on species, but they are not generally seen as threats at the magnitude of the others.

Habitat Loss

Humans rely on technology to modify their environment and replace certain functions that were once performed by the natural ecosystem. Other species cannot do this. Elimination of their ecosystem—whether it is a forest, a desert, a grassland, a freshwater estuarine, or a marine environment—will kill the individuals belonging to the species. The species will become extinct if we remove the entire habitat within the range of a species. Human destruction of habitats accelerated in the latter half of the twentieth century. Consider the exceptional biodiversity of Sumatra: it is home to one species of orangutan, a species of critically endangered elephant, and the Sumatran tiger, but half of Sumatra’s forest is now gone. The neighboring island of Borneo, home to the other species of orangutan, has lost a similar area of forest. Forest loss continues in protected areas of Borneo. All three species of orangutan are now listed as endangered by the International Union for Conservation of Nature (IUCN), but they are simply the most visible of thousands of species that will not survive the disappearance of the forests in Sumatra and Borneo. The forests are removed for timber and to plant palm oil plantations (Figure 2). Palm oil is used in many products including food products, cosmetics, and biodiesel in Europe. A five-year estimate of global forest cover loss for the years 2000–2005 was 3.1 percent. In the humid tropics where forest loss is primarily from timber extraction, 272,000 km 2 was lost out of a global total of 11,564,000 km 2 (or 2.4 percent). In the tropics, these losses certainly also represent the extinction of species because of high levels of endemism —species unique to a defined geographic location, and found nowhere else.

EVERYDAY CONNECTION

Preventing habitat destruction with wise wood choices.

Most consumers are not aware that the home improvement products they buy might be contributing to habitat loss and species extinctions. Yet the market for illegally harvested tropical timber is huge, and the wood products often find themselves in building supply stores in the United States. One estimate is that 10 percent of the imported timber stream in the United States, which is the world’s largest consumer of wood products, is potentially illegally logged. In 2006, this amounted to $3.6 billion in wood products. Most of the illegal products are imported from countries that act as intermediaries and are not the originators of the wood.

How is it possible to determine if a wood product, such as flooring, was harvested sustainably or even legally? The Forest Stewardship Council (FSC) certifies sustainably harvested forest products, therefore, looking for their certification on flooring and other hardwood products is one way to ensure that the wood has not been taken illegally from a tropical forest. Certification applies to specific products, not to a producer; some producers’ products may not have certification while other products are certified. While there are other industry-backed certifications other than the FSC, these are unreliable due to lack of independence from the industry. Another approach is to buy domestic wood species. While it would be great if there was a list of legal versus illegal wood products, it is not that simple. Logging and forest management laws vary from country to country; what is illegal in one country may be legal in another. Where and how a product is harvested and whether the forest from which it comes is being maintained sustainably all factor into whether a wood product will be certified by the FSC. If you are in doubt, it is always a good idea to ask questions about where a wood product came from and how the supplier knows that it was harvested legally.

Habitat destruction can affect ecosystems other than forests. Rivers and streams are important ecosystems that are frequently modified through land development, damming, channelizing, or water removal. Damming affects the water flow to all parts of a river, which can reduce or eliminate populations that had adapted to the natural flow of the river. For example, an estimated 91 percent of United States rivers have been altered in some way. Modifications include dams, to create energy or store water; levees, to prevent flooding; and dredging or rerouting, to create land that is more suitable for human development. Many fish and amphibian species and numerous freshwater clams in the United States have seen declines caused by river damming and habitat loss.

Overharvesting

Overharvesting is a serious threat to many species, but particularly to aquatic (both marine and freshwater) species. Despite regulation and monitoring, there are recent examples of fishery collapse. The western Atlantic cod fishery is the among the most significant. While it was a hugely productive fishery for 400 years, the introduction of modern factory trawlers in the 1980s caused it to become unsustainable. Fisheries collapse as a result of both economic and political factors. Fisheries are managed as a shared international resource even when the fishing territory lies within an individual country’s territorial waters. Common resources are subject to an economic pressure known as the tragedy of the commons , in which essentially no fisher has a motivation to exercise restraint in harvesting a fishery when it is not owned by that fisher. Overexploitation is a common outcome. This overexploitation is exacerbated when access to the fishery is open and unregulated and when technology gives fishers the ability to overfish. In a few fisheries, the biological growth of the resource is less than the potential growth of the profits made from fishing if that time and money were invested elsewhere. In these cases—whales are an example—economic forces will always drive toward fishing the population to extinction.

LINK TO LEARNING

Explore a U.S. Fish & Wildlife Service interactive map of critical habitat for endangered and threatened species in the United States.

For the most part, fishery extinction is not equivalent to biological extinction—the last fish of a species is rarely fished out of the ocean. At the same time, fishery extinction is still harmful to fish species and their ecosystems. There are some instances in which true extinction is a possibility. Whales have slow-growing populations due to low reproductive rates, and therefore are at risk of complete extinction through hunting. There are some species of sharks with restricted distributions that are at risk of extinction. The groupers are another population of generally slow-growing fishes that, in the Caribbean, includes a number of species that are at risk of extinction from overfishing.

Coral reefs are extremely diverse marine ecosystems that face immediate peril from several processes. Reefs are home to 1/3 of the world’s marine fish species—about 4,000 species—despite making up only 1 percent of marine habitat. Most home marine aquaria are stocked with wild-caught organisms, not cultured organisms. Although no species is known to have been driven extinct by the pet trade in marine species, there are studies showing that populations of some species have declined in response to harvesting, indicating that the harvest is not sustainable at those levels. There are concerns about the effect of the pet trade on some terrestrial species such as turtles, amphibians, birds, plants, and even the orangutan.

View a brief video discussing the role of marine ecosystems in supporting human welfare and the decline of ocean ecosystems .

Bush meat is the generic term used for wild animals killed for food. Hunting is practiced throughout the world, but hunting practices, particularly in equatorial Africa and parts of Asia, are believed to threaten a number of species with extinction. Traditionally, bush meat in Africa was hunted to feed families directly; however, recent commercialization of the practice now has bush meat available in grocery stores, which has increased harvest rates to the level of unsustainability. Additionally, human population growth has increased the need for protein foods that are not being met from agriculture. Species threatened by the bush meat trade are mostly mammals including many primates living in the Congo basin.

Exotic Species

Exotic species are species that have been intentionally or unintentionally introduced into an ecosystem in which they did not evolve. For example, Kudzu ( Pueraria lobata ), which is native to Japan, was introduced in the United States in 1876. It was later planted for soil conservation. Problematically, it grows too well in the southeastern United States—up to a foot a day. It is now an invasive pest species and covers over 7 million acres in the southeastern United States. If an introduced species is able to survive in its new habitat, that introduction is now reflected in the observed range of the species. Human transportation of people and goods, including the intentional transport of organisms for trade, has dramatically increased the introduction of species into new ecosystems, sometimes at distances that are well beyond the capacity of the species to ever travel itself and outside the range of the species’ natural predators.

Most exotic species introductions probably fail because of the low number of individuals introduced or poor adaptation to the ecosystem they enter. Some species, however, possess pre-adaptations that can make them especially successful in a new ecosystem. These exotic species often undergo dramatic population increases in their new habitat and reset the ecological conditions in the new environment, threatening the species that exist there. For this reason, exotic species are also called invasive species. Exotic species can threaten other species through competition for resources, predation, or disease. For example, the Eurasian star thistle, also called spotted knapweed, has invaded and rendered useless some of the open prairies of the western states. However, it is a great nectar-bearing flower for the production of honey and supports numerous pollinating insects, including migrating monarch butterflies in the north-central states such as Michigan.

Explore an interactive global database of exotic or invasive species .

Lakes and islands are particularly vulnerable to extinction threats from introduced species. In Lake Victoria, as mentioned earlier, the intentional introduction of the Nile perch was largely responsible for the extinction of about 200 species of endemic cichlids. The accidental introduction of the brown tree snake via aircraft ( Figure 3 ) from the Solomon Islands to Guam in 1950 has led to the extinction of three species of birds and three to five species of reptiles endemic to the island. Several other species are still threatened. The brown tree snake is adept at exploiting human transportation as a means to migrate; one was even found on an aircraft arriving in Corpus Christi, Texas. Constant vigilance on the part of airport, military, and commercial aircraft personnel is required to prevent the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not make up a large area of land on the globe, but they do contain a disproportionate number of endemic species because of their isolation from mainland ancestors.

It now appears that the global decline in amphibian species recognized in the 1990s is, in some part, caused by the fungus Batrachochytrium dendrobatidis , which causes the disease chytridiomycosis (Figure 4). There is evidence that the fungus is native to Africa and may have been spread throughout the world by transport of a commonly used laboratory and pet species: the African clawed toad ( Xenopus laevis ). It may well be that biologists themselves are responsible for spreading this disease worldwide. The North American bullfrog, Rana catesbeiana , which has also been widely introduced as a food animal but which easily escapes captivity, survives most infections of Batrachochytrium dendrobatidis , and can act as a reservoir for the disease. It also is a voracious predator in freshwater lakes.

Early evidence suggests that another fungal pathogen, Geomyces destructans , introduced from Europe is responsible for white-nose syndrome , which infects cave-hibernating bats in eastern North America and has spread from a point of origin in western New York State (Figure 5). The disease has decimated bat populations and threatens extinction of species already listed as endangered: the Indiana bat, Myotis sodalis , and potentially the Virginia big-eared bat, Corynorhinus townsendii virginianus . How the fungus was introduced is unclear, but one logical presumption would be that recreational cavers unintentionally brought the fungus on clothes or equipment from Europe.

Climate Change

Climate change , and specifically the anthropogenic (meaning, caused by humans) warming trend presently escalating, is recognized as a major extinction threat, particularly when combined with other threats such as habitat loss and the expansion of disease organisms. Scientists disagree about the likely magnitude of the effects, with extinction rate estimates ranging from 15 percent to 40 percent of species destined for extinction by 2050. Scientists do agree, however, that climate change will alter regional climates, including rainfall and snowfall patterns, making habitats less hospitable to the species living in them, in particular, the endemic species. The warming trend will shift colder climates toward the north and south poles, forcing species to move with their adapted climate norms while facing habitat gaps along the way. The shifting ranges will impose new competitive regimes on species as they find themselves in contact with other species not present in their historic range. One such unexpected species contact is between polar bears and grizzly bears. Previously, these two distinct species had separate ranges. Now, their ranges are overlapping and there are documented cases of these two species mating and producing viable offspring, which may or may not be viable crossing back to either parental species. Changing climates also throw off species’ delicate timed adaptations to seasonal food resources and breeding times. Many contemporary mismatches to shifts in resource availability and timing have already been documented.

Range shifts are already being observed: for example, some European bird species ranges have moved 91 km northward. The same study suggested that the optimal shift based on warming trends was double that distance, suggesting that the populations are not moving quickly enough. Range shifts have also been observed in plants, butterflies, other insects, freshwater fishes, reptiles, and mammals.

Climate gradients will also move up mountains, eventually crowding species higher in altitude and eliminating the habitat for those species adapted to the highest elevations. Some climates will completely disappear. The accelerating rate of warming in the arctic significantly reduces snowfall and the formation of sea ice. Without the ice, species like polar bears cannot successfully hunt seals, which are their only reliable source of food. Sea ice coverage has been decreasing since observations began in the mid-twentieth century, and the rate of decline observed in recent years is far greater than previously predicted.

Finally, global warming will raise ocean levels due to meltwater from glaciers and the greater volume of warmer water. Shorelines will be inundated, reducing island size, which will have an effect on some species, and a number of islands will disappear entirely. Additionally, the gradual melting and subsequent refreezing of the poles, glaciers, and higher elevation mountains—a cycle that has provided freshwater to environments for centuries—will also be jeopardized. This could result in an overabundance of salt water and a shortage of fresh water.

Threats to Biodiversity Copyright © by Various Authors - See Each Chapter Attribution. All Rights Reserved.

Share This Book

WWF: These are the biggest threats to the Earth's biodiversity

Climate change was ranked as a 6% risk to Earth's biodiversity. Image:  Unsplash/Sid Balachandran

.chakra .wef-1c7l3mo{-webkit-transition:all 0.15s ease-out;transition:all 0.15s ease-out;cursor:pointer;-webkit-text-decoration:none;text-decoration:none;outline:none;color:inherit;}.chakra .wef-1c7l3mo:hover,.chakra .wef-1c7l3mo[data-hover]{-webkit-text-decoration:underline;text-decoration:underline;}.chakra .wef-1c7l3mo:focus,.chakra .wef-1c7l3mo[data-focus]{box-shadow:0 0 0 3px rgba(168,203,251,0.5);} Carmen Ang

.chakra .wef-9dduvl{margin-top:16px;margin-bottom:16px;line-height:1.388;font-size:1.25rem;}@media screen and (min-width:56.5rem){.chakra .wef-9dduvl{font-size:1.125rem;}} Explore and monitor how .chakra .wef-15eoq1r{margin-top:16px;margin-bottom:16px;line-height:1.388;font-size:1.25rem;color:#F7DB5E;}@media screen and (min-width:56.5rem){.chakra .wef-15eoq1r{font-size:1.125rem;}} Nature and Biodiversity is affecting economies, industries and global issues

.chakra .wef-1nk5u5d{margin-top:16px;margin-bottom:16px;line-height:1.388;color:#2846F8;font-size:1.25rem;}@media screen and (min-width:56.5rem){.chakra .wef-1nk5u5d{font-size:1.125rem;}} Get involved with our crowdsourced digital platform to deliver impact at scale

Stay up to date:, nature and biodiversity.

• WWF’s Living Planet Report 2020 has ranked the biggest threats to Earth's biodiversity.
• The list includes climate change, changes in land and sea use and pollution.
• The WWF used data from over 4,000 different species.

The biggest threats to Earth’s biodiversity

Biodiversity benefits humanity in many ways.

It helps make the global economy more resilient, it functions as an integral part of our culture and identity, and research has shown it’s even linked to our physical health.

However, despite its importance, Earth’s biodiversity has decreased significantly over the last few decades. In fact, between 1970 and 2016, the population of vertebrate species fell by 68% on average worldwide. What’s causing this global decline?

Today’s graphic uses data from WWF’s Living Planet Report 2020 to illustrate the biggest threats to Earth’s biodiversity, and the impact each threat has had globally.

Measuring the loss of biodiversity

Before looking at biodiversity’s biggest threats, first thing’s first—how exactly has biodiversity changed over the years?

WWF uses the Living Planet Index (LPI) to measure biodiversity worldwide. Using data from over 4,000 different species, LPI tracks the abundance of mammals, birds, fish, reptiles, and amphibians across the globe.

Here’s a look at each region’s average decline between 1970 and 2016:

Latin America & Caribbean has seen the biggest drop in biodiversity at 94% . This region’s drastic decline has been mainly driven by declining reptile, amphibian, and fish populations.

Despite varying rates of loss between regions, it’s clear that overall, biodiversity is on the decline. What main factors are driving this loss, and how do these threats differ from region to region?

Biggest threats to biodiversity, overall

While it’s challenging to create an exhaustive list, WWF has identified five major threats and shown each threats proportional impact, averaged across all regions:

Across the board, changes in land and sea use account for the largest portion of loss, making up 50% of recorded threats to biodiversity on average. This makes sense, considering that approximately one acre of the Earth’s rainforests is disappearing every two seconds .

Species overexploitation is the second biggest threat at 24% on average, while invasive species takes the third spot at 13% .

Biggest threats to biodiversity, by region

When looking at the regional breakdown, the order of threats in terms of biodiversity impact is relatively consistent across all regions—however, there are a few discrepancies:

In Latin America and Caribbean, climate change has been a bigger biodiversity threat than in other regions, and this is possibly linked to an increase in natural disasters. Between 2000 and 2013, the region experienced 613 extreme climate and hydro-meteorological events, from typhoons and hurricanes to flash floods and droughts.

Another notable variation from the mean is species over-exploitation in Africa, which makes up 35% of the region’s threats. This is higher than in other regions, which sit around 18-27%.

While the regional breakdowns differ slightly from place to place, one thing remains constant across the board—all species, no matter how small, play an important role in the maintenance of Earth’s ecosystems.

Will we continue to see a steady decline in Earth’s biodiversity, or will things level out in the near future?

Don't miss any update on this topic

Create a free account and access your personalized content collection with our latest publications and analyses.

License and Republishing

World Economic Forum articles may be republished in accordance with the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Public License, and in accordance with our Terms of Use.

The views expressed in this article are those of the author alone and not the World Economic Forum.

Related topics:

The agenda .chakra .wef-n7bacu{margin-top:16px;margin-bottom:16px;line-height:1.388;font-weight:400;} weekly.

A weekly update of the most important issues driving the global agenda

.chakra .wef-1dtnjt5{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;-webkit-flex-wrap:wrap;-ms-flex-wrap:wrap;flex-wrap:wrap;} More on Nature and Biodiversity .chakra .wef-17xejub{-webkit-flex:1;-ms-flex:1;flex:1;justify-self:stretch;-webkit-align-self:stretch;-ms-flex-item-align:stretch;align-self:stretch;} .chakra .wef-nr1rr4{display:-webkit-inline-box;display:-webkit-inline-flex;display:-ms-inline-flexbox;display:inline-flex;white-space:normal;vertical-align:middle;text-transform:uppercase;font-size:0.75rem;border-radius:0.25rem;font-weight:700;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;line-height:1.2;-webkit-letter-spacing:1.25px;-moz-letter-spacing:1.25px;-ms-letter-spacing:1.25px;letter-spacing:1.25px;background:none;padding:0px;color:#B3B3B3;-webkit-box-decoration-break:clone;box-decoration-break:clone;-webkit-box-decoration-break:clone;}@media screen and (min-width:37.5rem){.chakra .wef-nr1rr4{font-size:0.875rem;}}@media screen and (min-width:56.5rem){.chakra .wef-nr1rr4{font-size:1rem;}} See all

Critical minerals demand has doubled in the past five years – here are some solutions to the supply crunch

Emma Charlton

May 16, 2024

The fascinating link between biodiversity and mental wellbeing

Andrea Mechelli

May 15, 2024

These Japanese volunteers are planting seagrass to fight climate change

Scientists expect global heating to exceed 1.5°C, and other nature and climate stories you need to read this week

May 13, 2024

Scientists have found 700 species in a Cambodian mangrove forest

Funding the green technology innovation pipeline: Lessons from China

May 8, 2024

Want to create or adapt books like this? Learn more about how Pressbooks supports open publishing practices.

The core threat to biodiversity on the planet, and therefore a threat to human welfare, is the combination of human population growth and the resources used by that population. The human population requires resources to survive and grow, and many of those resources are being removed unsustainably from the environment. The three greatest proximate threats to biodiversity are habitat loss, overharvesting, and the introduction of exotic species. The first two directly result from human population growth and resource use. The third results from increased mobility and trade. A fourth major cause of extinction, anthropogenic (human-caused) climate change, has not yet had a large impact, but it is predicted to become significant during this century. Global climate change is also a consequence of the human population’s need for energy and the use of fossil fuels to meet those needs (Figure 1). Environmental issues, such as toxic pollution, have specific targeted effects on species but are not generally seen as threats at the magnitude of the others.

Habitat Loss

Humans rely on technology to modify their environment and make it habitable. Other species cannot do this. Eliminating their habitat—whether it is a forest, coral reef, grassland, or flowing river—will kill the individuals in the species. Remove the entire habitat, and the species will become extinct unless they are among the few species that do well in human-built environments. Human destruction of habitats ( habitat  generally refers to the part of the ecosystem required by a particular species) accelerated in the latter half of the twentieth century.

Consider the exceptional biodiversity of Sumatra: it is home to one species of orangutan, a species of critically endangered elephant, and the Sumatran tiger, but half of Sumatra’s forest is now gone. The neighboring island of Borneo, home to other orangutan species, has lost a similar forest area. Forest loss continues in protected areas of Borneo. The orangutan in Borneo is listed as endangered by the International Union for Conservation of Nature (IUCN). Still, it is simply the most visible of thousands of species that will not survive the disappearance of the forests of Borneo. The forests are removed for timber and to plant palm oil plantations (Figure 2). Palm oil is used in many products, including food products, cosmetics, and biodiesel in Europe. A 5-year estimate of global forest cover loss from 2000 to 2005 was 3.1%. Much loss (2.4%) occurred in the tropics, where forest loss is primarily from timber extraction. These losses certainly also represent the extinction of species unique to those areas.

Most consumers do not imagine their home improvement products might contribute to habitat loss and extinction of species. Yet the market for illegally harvested tropical timber is huge, and the wood products often find themselves in building supply stores in the United States. One estimate is that up to 10% of the imported timber in the United States, the world’s largest consumer of wood products, is illegally logged. In 2006, this amounted to $3.6 billion in wood products. Most illegal products are imported from countries that act as intermediaries and are not the originators of the wood.

How is it possible to determine if a wood product, such as flooring, was harvested sustainably or legally? The Forest Stewardship Council (FSC) certifies sustainably harvested forest products. Looking for their certification on flooring and other hardwood products is one way to ensure that the wood has not been taken illegally from a tropical forest. There are certifications other than the FSC, but these are run by timber companies, thus creating a conflict of interest. Another approach is to buy domestic wood species. While it would be great if there was a list of legal versus illegal woods, it is not that simple. Logging and forest management laws vary from country to country; what is illegal in one country may be legal in another. Where and how a product is harvested and whether the forest from which it comes is being sustainably maintained all factor into whether a wood product will be certified by the FSC. It is always a good idea to ask where a wood product came from and how the supplier knows it was harvested legally.

Habitat destruction can affect ecosystems other than forests. Rivers and streams are important ecosystems and are frequently the target of habitat modification. Damming of rivers affects flow and access to habitat. Altering a flow regime can reduce or eliminate populations adapted to seasonal flow changes. For example, an estimated 91% of riverways in the United States have been modified with damming or stream bank modification. Many fish species in the United States, especially rare species or species with restricted distributions, have seen declines caused by river damming and habitat loss. Research has confirmed that species of amphibians that must carry out parts of their life cycles in aquatic and terrestrial habitats are at greater risk of population declines and extinction because of the increased likelihood that one of their habitats or access between them will be lost. This is of particular concern because amphibians have been declining in numbers and going extinct more rapidly than many other groups for various reasons.

Overharvesting

Overharvesting is a serious threat to many species, particularly to aquatic species. Many examples of regulated fisheries (including hunting marine mammals and harvesting crustaceans and other species) monitored by fisheries scientists have nevertheless collapsed. The western Atlantic cod fishery is the most spectacular recent collapse. While it was a hugely productive fishery for 400 years, the introduction of modern factory trawlers in the 1980s and the pressure on the fishery made it unsustainable. The causes of fishery collapse are both economic and political in nature.

Most fisheries are managed as a common resource, available to anyone willing to fish, even when the fishing territory lies within a country’s territorial waters. Common resources are subject to an economic pressure known as the tragedy of the commons, in which fishers have little motivation to exercise restraint in harvesting a fishery when they do not own the fishery. The general outcome of harvests of resources held in common is their overexploitation. While large fisheries are regulated to attempt to avoid this pressure, it still exists in the background. This overexploitation is exacerbated when access to the fishery is open and unregulated, and technology allows fishers to overfish. In a few fisheries, continuing overfishing is more profitable than waiting for the fishery to recover. In these cases—whales are an example—economic forces will drive the fishing population to extinction.

Explore a U.S. Fish & Wildlife Service interactive map ( http://openstaxcollege.org/l/habitat_map2 ) of critical habitats for endangered and threatened species in the United States. To begin, select “Visit the online mapper.”

Coral reefs are extremely diverse marine ecosystems that face peril from several processes. Reefs are home to 1/3 of the world’s marine fish species—about 4000 species—despite making up only one percent of marine habitat. Most home marine aquaria house coral reef species that are wild-caught organisms—not cultured organisms. Although no marine species are known to have been driven extinct by the pet trade, studies show that some species’ populations have declined in response to harvesting, indicating that the harvest is not sustainable at those levels. There are also concerns about the effect of the pet trade on some terrestrial species, such as turtles, amphibians, birds, plants, and even the orangutans.

Bush meat is the generic term used for wild animals killed for food. Hunting is practiced worldwide, but hunting practices, particularly in equatorial Africa and parts of Asia, are believed to threaten several species with extinction. Traditionally, bush meat in Africa was hunted to feed families directly. However, recent commercialization of the practice now has bush meat available in grocery stores, which has increased harvest rates to the level of unsustainability. Additionally, human population growth has increased the need for protein foods that agriculture does not meet. Species threatened by the bush meat trade are mostly mammals, including many monkeys and the great apes in the Congo basin.

Invasive Species

Exotic species are species that humans have intentionally or unintentionally introduced into an ecosystem in which they did not evolve. Human transportation of people and goods, including the intentional transport of organisms for trade, has dramatically increased the introduction of species into new ecosystems. These new introductions are sometimes at distances well beyond the species’ capacity to ever travel itself and outside the range of the species’ natural predators.

Most exotic species introductions probably fail because of the low number of individuals introduced or poor adaptation to the ecosystem they enter. Some species, however, have characteristics that can make them especially successful in a new ecosystem. These exotic species often undergo dramatic population increases in their new habitat and reset the ecological conditions in the new environment, threatening their species. When this happens, the exotic species also become an invasive species . Invasive species can threaten other species through resource competition, predation, or disease.

Explore this interactive global database ( http://openstaxcollege.org/l/exotic_invasiv2 ) of exotic or invasive species.

Lakes and islands are particularly vulnerable to extinction threats from introduced species. In Lake Victoria, the intentional introduction of the Nile perch was largely responsible for the extinction of about 200 species of cichlids. The accidental introduction of the brown tree snake via aircraft (Figure 4) from the Solomon Islands to Guam in 1950 has led to the extinction of three species of birds and three to five species of reptiles endemic to the island. Several other species are still threatened. The brown tree snake is adept at exploiting human transportation to migrate; one was found on an aircraft arriving in Corpus Christi, Texas. Constant vigilance on the part of the airport, military, and commercial aircraft personnel is required to prevent the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not comprise a large area of land on the globe, but they contain a disproportionate number of endemic species because of their isolation from mainland ancestors.

Many introductions of marine and freshwater aquatic species have occurred when ships have dumped ballast water taken on at a port of origin into waters at a destination port. Water from the port of origin is pumped into tanks on a ship empty of cargo to increase stability. The water is drawn from the ocean or estuary of the port and typically contains living organisms such as plant parts, microorganisms, eggs, larvae, or aquatic animals. The water is pumped out before the ship takes on cargo at the destination port, which may be on a different continent. The zebra mussel was introduced to the Great Lakes from Europe before 1988 in ballast water. The zebra mussels in the Great Lakes have created millions of dollars in clean-up costs to maintain water intakes and other facilities. The mussels have also altered the ecology of the lakes dramatically. They threaten native mollusk populations but have benefited some species, such as smallmouth bass. The mussels are filter feeders and have dramatically improved water clarity, which has allowed aquatic plants to grow along shorelines, providing shelter for young fish where they did not exist before. The European green crab, Carcinus maenas , was introduced to San Francisco Bay in the late 1990s, likely in ship ballast water, and has spread north along the coast to Washington. The crabs have been found to dramatically reduce the abundance of native clams and crabs, increasing the prey species of those native crabs.

Invading exotic species can also be disease organisms. It now appears that the global decline in amphibian species recognized in the 1990s is, in some parts, caused by the fungus Batrachochytrium dendrobatidis , which causes the disease chytridiomycosis (Figure 5). Evidence shows that the fungus is native to Africa and may have been spread worldwide by transporting a commonly used laboratory and pet species: the African clawed frog, Xenopus laevis . It may well be that scientists themselves are responsible for spreading this disease worldwide. The North American bullfrog, Rana catesbeiana , which has been widely introduced as a food animal but which easily escapes captivity, survives most infections of B. dendrobatidis and can act as a reservoir for the disease.

Early evidence suggests that another fungal pathogen, Geomyces destructans , introduced from Europe, is responsible for white-nose syndrome, which infects cave-hibernating bats in eastern North America and has spread from the point of origin in western New York State (Figure 6). The disease has decimated bat populations and threatens the extinction of species already listed as endangered: the Indiana bat, Myotis sodalis , and potentially the Virginia big-eared bat, Corynorhinus townsendii virginianus . How the fungus was introduced is unknown, but one logical presumption would be that recreational cavers unintentionally brought the fungus onto clothes or equipment from Europe.

Climate Change

Climate change, specifically the anthropogenic warming trend presently underway, is recognized as a major extinction threat, particularly when combined with other threats such as habitat loss. Anthropogenic warming of the planet has been observed. It is due to past and continuing emissions of greenhouse gases, primarily carbon dioxide, and methane, into the atmosphere caused by burning fossil fuels and deforestation. Scientists overwhelmingly agree humans cause the present warming trend, and some of the likely effects include dramatic and dangerous climate changes in the coming decades. Scientists predict that climate change will alter regional climates, including rainfall and snowfall patterns, making habitats less hospitable to the species living in them. The warming trend will shift colder climates toward the north and south poles, forcing species to move (if possible) with their adapted climate norms.

The shifting ranges will impose new competitive regimes on species as they are in contact with other species not in their historic range. One such unexpected species contact is between polar bears and grizzly bears. Previously, these two species had separate ranges. Their ranges overlap, and there are documented cases of these two species mating and producing viable offspring. Changing climates also reduce species’ delicate timing adaptations to seasonal food resources and breeding times. Scientists have already documented many contemporary mismatches to resource availability and timing shifts.

Other shifts in the range have been observed. For example, one study indicates that, on average, European bird species ranges have moved 91 km (56.5 mi) northward. The same study suggested that the optimal shift based on warming trends was double that distance, suggesting that the populations are not moving quickly enough. Range shifts have also been observed in plants, butterflies, other insects, freshwater fishes, reptiles, amphibians, and mammals.

Climate gradients will also move up mountains, eventually crowding species higher in altitude and eliminating the habitat for those species adapted to the highest elevations. Some climates will completely disappear. The rate of warming appears to be accelerated in the Arctic, which is recognized as a serious threat to polar bear populations that require sea ice to hunt seals during the winter months. Seals are a critical source of protein for polar bears. A decreasing sea ice coverage trend has occurred since observations began in the mid-twentieth century. The rate of decline observed in recent years is far greater than previously predicted by climate models.

Finally, global warming will raise ocean levels due to meltwater from glaciers and the greater volume occupied by warmer water. Shorelines will be inundated, reducing island size, which will affect some species, and a number of islands will disappear entirely. Additionally, the gradual melting and subsequent refreezing of the poles, glaciers, and higher-elevation mountains—a cycle that has provided freshwater to environments for centuries—will be altered. This could result in an overabundance of salt water and a shortage of fresh water.

Suggested Supplementary Reading:

Hall. S. 2017. Could Genetic Engineering Save the Galápagos? Scientific American . December.  p. 48-57.

       This article explores the destructive nature of invasive species in the Galápagos Islands. Traditional efforts to eradicate invasive species, such as rats, can be expensive and cause ecological harm through the widespread distribution of poison. An alternate approach is genetic engineering in the form of a “gene drive,” an emerging technology that could be better – or worse – for the environment. 

Introduction to Environmental Sciences and Sustainability Copyright © 2023 by Emily P. Harris is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

Share This Book

47.3 Threats to Biodiversity

Learning objectives.

• Identify significant threats to biodiversity
• Explain the effects of habitat loss, exotic species, and hunting on biodiversity
• Identify the early and predicted effects of climate change on biodiversity

The core threat to biodiversity on the planet, and therefore a threat to human welfare, is the combination of human population growth and resource exploitation. The human population requires resources to survive and grow, and those resources are being removed unsustainably from the environment. The three greatest proximate threats to biodiversity are habitat loss, overharvesting, and introduction of exotic species. The first two of these are a direct result of human population growth and resource use. The third results from increased mobility and trade. A fourth major cause of extinction, anthropogenic climate change, has not yet had a large impact, but it is predicted to become significant during this century. Global climate change is also a consequence of human population needs for energy and the use of fossil fuels to meet those needs ( Figure 47.10 ). Environmental issues, such as toxic pollution, have specific targeted effects on species, but they are not generally seen as threats at the magnitude of the others.

Habitat Loss

Humans rely on technology to modify their environment and replace certain functions that were once performed by the natural ecosystem. Other species cannot do this. Elimination of their ecosystem—whether it is a forest, a desert, a grassland, a freshwater estuarine, or a marine environment—will kill the individuals in the species. Remove the entire habitat within the range of a species and, unless they are one of the few species that do well in human-built environments, the species will become extinct. Human destruction of habitats accelerated in the latter half of the twentieth century. Consider the exceptional biodiversity of Sumatra: it is home to one species of orangutan, a species of critically endangered elephant, and the Sumatran tiger, but half of Sumatra’s forest is now gone. The neighboring island of Borneo, home to the other species of orangutan, has lost a similar area of forest. Forest loss continues in protected areas of Borneo. The orangutan in Borneo is listed as endangered by the International Union for Conservation of Nature (IUCN), but it is simply the most visible of thousands of species that will not survive the disappearance of the forests of Borneo. The forests are removed for timber and to plant palm oil plantations ( Figure 47.11 ). Palm oil is used in many products including food products, cosmetics, and biodiesel in Europe. A five-year estimate of global forest cover loss for the years 2000–2005 was 3.1 percent. In the humid tropics where forest loss is primarily from timber extraction, 272,000 km 2 was lost out of a global total of 11,564,000 km 2 (or 2.4 percent). In the tropics, these losses certainly also represent the extinction of species because of high levels of endemism.

Everyday Connection

Preventing Habitat Destruction with Wise Wood Choices Most consumers do not imagine that the home improvement products they buy might be contributing to habitat loss and species extinctions. Yet the market for illegally harvested tropical timber is huge, and the wood products often find themselves in building supply stores in the United States. One estimate is that 10 percent of the imported timber stream in the United States, which is the world’s largest consumer of wood products, is potentially illegally logged. In 2006, this amounted to $3.6 billion in wood products. Most of the illegal products are imported from countries that act as intermediaries and are not the originators of the wood.

How is it possible to determine if a wood product, such as flooring, was harvested sustainably or even legally? The Forest Stewardship Council (FSC) certifies sustainably harvested forest products, therefore, looking for their certification on flooring and other hardwood products is one way to ensure that the wood has not been taken illegally from a tropical forest. Certification applies to specific products, not to a producer; some producers’ products may not have certification while other products are certified. While there are other industry-backed certifications other than the FSC, these are unreliable due to lack of independence from the industry. Another approach is to buy domestic wood species. While it would be great if there was a list of legal versus illegal wood products, it is not that simple. Logging and forest management laws vary from country to country; what is illegal in one country may be legal in another. Where and how a product is harvested and whether the forest from which it comes is being maintained sustainably all factor into whether a wood product will be certified by the FSC. It is always a good idea to ask questions about where a wood product came from and how the supplier knows that it was harvested legally.

Habitat destruction can affect ecosystems other than forests. Rivers and streams are important ecosystems and are frequently modified through land development and from damming or water removal. Damming of rivers affects the water flow and access to all parts of a river. Differing flow regimes can reduce or eliminate populations that are adapted to these changes in flow patterns. For example, an estimated 91percent of river lengths in the United States have been developed: they have modifications like dams, to create energy or store water; levees, to prevent flooding; or dredging or rerouting, to create land that is more suitable for human development. Many fish species in the United States, especially rare species or species with restricted distributions, have seen declines caused by river damming and habitat loss. Research has confirmed that species of amphibians that must carry out parts of their life cycles in both aquatic and terrestrial habitats have a greater chance of suffering population declines and extinction because of the increased likelihood that one of their habitats or access between them will be lost.

Overharvesting

Overharvesting is a serious threat to many species, but particularly to aquatic species. There are many examples of regulated commercial fisheries monitored by fisheries scientists that have nevertheless collapsed. The western Atlantic cod fishery is the most spectacular recent collapse. While it was a hugely productive fishery for 400 years, the introduction of modern factory trawlers in the 1980s and the pressure on the fishery led to it becoming unsustainable. The causes of fishery collapse are both economic and political in nature. Most fisheries are managed as a common (shared) resource even when the fishing territory lies within a country’s territorial waters. Common resources are subject to an economic pressure known as the tragedy of the commons in which essentially no fisher has a motivation to exercise restraint in harvesting a fishery when it is not owned by that fisher. The natural outcome of harvests of resources held in common is their overexploitation. While large fisheries are regulated to attempt to avoid this pressure, it still exists in the background. This overexploitation is exacerbated when access to the fishery is open and unregulated and when technology gives fishers the ability to overfish. In a few fisheries, the biological growth of the resource is less than the potential growth of the profits made from fishing if that time and money were invested elsewhere. In these cases—whales are an example—economic forces will always drive toward fishing the population to extinction.

Link to Learning

Explore a U.S. Fish & Wildlife Service interactive map of critical habitat for endangered and threatened species in the United States. To begin, select “Visit the online mapper.”

For the most part, fishery extinction is not equivalent to biological extinction—the last fish of a species is rarely fished out of the ocean. At the same time, fishery extinction is still harmful to fish species and their ecosystems. There are some instances in which true extinction is a possibility. Whales have slow-growing populations and are at risk of complete extinction through hunting. There are some species of sharks with restricted distributions that are at risk of extinction. The groupers are another population of generally slow-growing fishes that, in the Caribbean, includes a number of species that are at risk of extinction from overfishing.

Coral reefs are extremely diverse marine ecosystems that face peril from several processes. Reefs are home to 1/3 of the world’s marine fish species—about 4,000 species—despite making up only 1 percent of marine habitat. Most home marine aquaria are stocked with wild-caught organisms, not cultured organisms. Although no species is known to have been driven extinct by the pet trade in marine species, there are studies showing that populations of some species have declined in response to harvesting, indicating that the harvest is not sustainable at those levels. There are concerns about the effect of the pet trade on some terrestrial species such as turtles, amphibians, birds, plants, and even the orangutan.

View a brief video discussing the role of marine ecosystems in supporting human welfare and the decline of ocean ecosystems.

Bush meat is the generic term used for wild animals killed for food. Hunting is practiced throughout the world, but hunting practices, particularly in equatorial Africa and parts of Asia, are believed to threaten several species with extinction. Traditionally, bush meat in Africa was hunted to feed families directly; however, recent commercialization of the practice now has bush meat available in grocery stores, which has increased harvest rates to the level of unsustainability. Additionally, human population growth has increased the need for protein foods that are not being met from agriculture. Species threatened by the bush meat trade are mostly mammals including many primates living in the Congo basin.

Exotic Species

Exotic species are species that have been intentionally or unintentionally introduced by humans into an ecosystem in which they did not evolve. Such introductions likely occur frequently as natural phenomena. For example, Kudzu ( Pueraria lobata ), which is native to Japan, was introduced in the United States in 1876. It was later planted for soil conservation. Problematically, it grows too well in the southeastern United States—up to a foot a day. It is now a pest species and covers over 7 million acres in the southeastern United States. If an introduced species is able to survive in its new habitat, that introduction is now reflected in the observed range of the species. Human transportation of people and goods, including the intentional transport of organisms for trade, has dramatically increased the introduction of species into new ecosystems, sometimes at distances that are well beyond the capacity of the species to ever travel itself and outside the range of the species’ natural predators.

Most exotic species introductions probably fail because of the low number of individuals introduced or poor adaptation to the ecosystem they enter. Some species, however, possess preadaptations that can make them especially successful in a new ecosystem. These exotic species often undergo dramatic population increases in their new habitat and reset the ecological conditions in the new environment, threatening the species that exist there. For this reason, exotic species are also called invasive species. Exotic species can threaten other species through competition for resources, predation, or disease.

Explore an interactive global database of exotic or invasive species.

Lakes and islands are particularly vulnerable to extinction threats from introduced species. In Lake Victoria, as mentioned earlier, the intentional introduction of the Nile perch was largely responsible for the extinction of about 200 species of cichlids. The accidental introduction of the brown tree snake via aircraft ( Figure 47.12 ) from the Solomon Islands to Guam in 1950 has led to the extinction of three species of birds and three to five species of reptiles endemic to the island. Several other species are still threatened. The brown tree snake is adept at exploiting human transportation as a means to migrate; one was even found on an aircraft arriving in Corpus Christi, Texas. Constant vigilance on the part of airport, military, and commercial aircraft personnel is required to prevent the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not make up a large area of land on the globe, but they do contain a disproportionate number of endemic species because of their isolation from mainland ancestors.

It now appears that the global decline in amphibian species recognized in the 1990s is, in some part, caused by the fungus Batrachochytrium dendrobatidis , which causes the disease chytridiomycosis ( Figure 47.13 ). There is evidence that the fungus is native to Africa and may have been spread throughout the world by transport of a commonly used laboratory and pet species: the African clawed toad ( Xenopus laevis ). It may well be that biologists themselves are responsible for spreading this disease worldwide. The North American bullfrog, Rana catesbeiana , which has also been widely introduced as a food animal but which easily escapes captivity, survives most infections of Batrachochytrium dendrobatidis and can act as a reservoir for the disease.

Early evidence suggests that another fungal pathogen, Geomyces destructans , introduced from Europe is responsible for white-nose syndrome , which infects cave-hibernating bats in eastern North America and has spread from a point of origin in western New York State ( Figure 47.14 ). The disease has decimated bat populations and threatens extinction of species already listed as endangered: the Indiana bat, Myotis sodalis , and potentially the Virginia big-eared bat, Corynorhinus townsendii virginianus . How the fungus was introduced is unclear, but one logical presumption would be that recreational cavers unintentionally brought the fungus on clothes or equipment from Europe.

Climate Change

Climate change, and specifically the anthropogenic (meaning, caused by humans) warming trend presently underway, is recognized as a major extinction threat, particularly when combined with other threats such as habitat loss. Scientists disagree about the likely magnitude of the effects, with extinction rate estimates ranging from 15 percent to 40 percent of species committed to extinction by 2050. Scientists do agree, however, that climate change will alter regional climates, including rainfall and snowfall patterns, making habitats less hospitable to the species living in them. The warming trend will shift colder climates toward the north and south poles, forcing species to move with their adapted climate norms while facing habitat gaps along the way. The shifting ranges will impose new competitive regimes on species as they find themselves in contact with other species not present in their historic range. One such unexpected species contact is between polar bears and grizzly bears. Previously, these two species had separate ranges. Now, their ranges are overlapping and there are documented cases of these two species mating and producing viable offspring. Changing climates also throw off species’ delicate timing adaptations to seasonal food resources and breeding times. Many contemporary mismatches to shifts in resource availability and timing have already been documented.

Range shifts are already being observed: for example, some European bird species ranges have moved 91 km northward. The same study suggested that the optimal shift based on warming trends was double that distance, suggesting that the populations are not moving quickly enough. Range shifts have also been observed in plants, butterflies, other insects, freshwater fishes, reptiles, and mammals.

Climate gradients will also move up mountains, eventually crowding species higher in altitude and eliminating the habitat for those species adapted to the highest elevations. Some climates will completely disappear. The rate of warming appears to be accelerated in the arctic, which is recognized as a serious threat to polar bear populations that require sea ice to hunt seals during the winter months: seals are the only source of protein available to polar bears. A trend to decreasing sea ice coverage has occurred since observations began in the mid-twentieth century. The rate of decline observed in recent years is far greater than previously predicted by climate models.

Finally, global warming will raise ocean levels due to melt water from glaciers and the greater volume of warmer water. Shorelines will be inundated, reducing island size, which will have an effect on some species, and a number of islands will disappear entirely. Additionally, the gradual melting and subsequent refreezing of the poles, glaciers, and higher elevation mountains—a cycle that has provided freshwater to environments for centuries—will also be jeopardized. This could result in an overabundance of salt water and a shortage of fresh water.

As an Amazon Associate we earn from qualifying purchases.

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Access for free at https://openstax.org/books/biology/pages/1-introduction

• Authors: Connie Rye, Robert Wise, Vladimir Jurukovski, Jean DeSaix, Jung Choi, Yael Avissar
• Publisher/website: OpenStax
• Book title: Biology
• Publication date: Oct 21, 2016
• Location: Houston, Texas
• Book URL: https://openstax.org/books/biology/pages/1-introduction
• Section URL: https://openstax.org/books/biology/pages/47-3-threats-to-biodiversity

© Feb 14, 2022 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.

• school Campus Bookshelves
• menu_book Bookshelves
• perm_media Learning Objects
• login Login
• how_to_reg Request Instructor Account
• hub Instructor Commons

Margin Size

• Download Page (PDF)
• Download Full Book (PDF)
• Periodic Table
• Physics Constants
• Scientific Calculator
• Reference & Cite
• Tools expand_more
• Readability

selected template will load here

This action is not available.

17.2: Threats to Biodiversity

• Last updated
• Save as PDF
• Page ID 52701

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)

\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)

( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)

\( \newcommand{\Span}{\mathrm{span}}\)

\( \newcommand{\id}{\mathrm{id}}\)

\( \newcommand{\kernel}{\mathrm{null}\,}\)

\( \newcommand{\range}{\mathrm{range}\,}\)

\( \newcommand{\RealPart}{\mathrm{Re}}\)

\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

\( \newcommand{\Argument}{\mathrm{Arg}}\)

\( \newcommand{\norm}[1]{\| #1 \|}\)

\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)

\( \newcommand{\vectorA}[1]{\vec{#1}}      % arrow\)

\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}}      % arrow\)

\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

\( \newcommand{\vectorC}[1]{\textbf{#1}} \)

\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)

\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)

\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)

The core threat to biodiversity on the planet, and therefore a threat to human welfare, is the combination of human population growth and the resources used by that population. The human population requires resources to survive and grow, and those resources are being removed unsustainably from the environment. The three greatest proximate threats to biodiversity are habitat loss, overharvesting, and introduction of exotic species. The first two of these are a direct result of human population growth and resource use. The third results from increased mobility and trade. A fourth major cause of extinction, anthropogenic (human-caused) climate change, has not yet had a large impact, but it is predicted to become significant during this century. Global climate change is also a consequence of human population needs for energy and the use of fossil fuels to meet those needs (Figure \(\PageIndex{1}\)). Environmental issues, such as toxic pollution, have specific targeted effects on species, but are not generally seen as threats at the magnitude of the others.

Habitat Loss

Humans rely on technology to modify their environment and replace certain functions that were once performed by the natural ecosystem. Other species cannot do this. Elimination of their habitat—whether it is a forest, coral reef, grassland, or flowing river—will kill the individuals in the species. Remove the entire habitat within the range of a species and, unless they are one of the few species that do well in human-built environments, the species will become extinct. Human destruction of habitats (habitats generally refer to the part of the ecosystem required by a particular species) accelerated in the latter half of the twentieth century. Consider the exceptional biodiversity of Sumatra: it is home to one species of orangutan, a species of critically endangered elephant, and the Sumatran tiger, but half of Sumatra’s forest is now gone. The neighboring island of Borneo, home to the other species of orangutan, has lost a similar area of forest. Forest loss continues in protected areas of Borneo. The orangutan in Borneo is listed as endangered by the International Union for Conservation of Nature (IUCN), but it is simply the most visible of thousands of species that will not survive the disappearance of the forests of Borneo. The forests are removed for timber and to plant palm oil plantations (Figure \(\PageIndex{2}\)). Palm oil is used in many products including food products, cosmetics, and biodiesel in Europe. A 5-year estimate of global forest cover loss for the years from 2000 to 2005 was 3.1 percent. Much loss (2.4 percent) occurred in the humid tropics where forest loss is primarily from timber extraction. These losses certainly also represent the extinction of species unique to those areas.

BIOLOGY IN ACTION: Preventing Habitat Destruction with Wise Wood Choices

Most consumers do not imagine that the home improvement products they buy might be contributing to habitat loss and species extinctions. Yet the market for illegally harvested tropical timber is huge, and the wood products often find themselves in building supply stores in the United States. One estimate is that 10 percent of the imported timber stream in the United States, which is the world’s largest consumer of wood products, is potentially illegally logged. In 2006, this amounted to $3.6 billion in wood products. Most of the illegal products are imported from countries that act as intermediaries and are not the originators of the wood.

How is it possible to determine if a wood product, such as flooring, was harvested sustainably or even legally? The Forest Stewardship Council (FSC) certifies sustainably harvested forest products; therefore, looking for their certification on flooring and other hardwood products is one way to ensure that the wood has not been taken illegally from a tropical forest. Certification applies to specific products, not to a producer; some producers’ products may not have certification while other products are certified. There are certifications other than the FSC, but these are run by timber companies creating a conflict of interest. Another approach is to buy domestic wood species. While it would be great if there was a list of legal versus illegal woods, it is not that simple. Logging and forest management laws vary from country to country; what is illegal in one country may be legal in another. Where and how a product is harvested and whether the forest from which it comes is being sustainably maintained all factor into whether a wood product will be certified by the FSC. It is always a good idea to ask questions about where a wood product came from and how the supplier knows that it was harvested legally.

Habitat destruction can affect ecosystems other than forests. Rivers and streams are important ecosystems and are frequently the target of habitat modification through building and from damming or water removal. Damming of rivers affects flows and access to all parts of a river. Altering a flow regime can reduce or eliminate populations that are adapted to seasonal changes in flow. For example, an estimated 91 percent of river lengths in the United States have been modified with damming or bank modifications. Many fish species in the United States, especially rare species or species with restricted distributions, have seen declines caused by river damming and habitat loss. Research has confirmed that species of amphibians that must carry out parts of their life cycles in both aquatic and terrestrial habitats are at greater risk of population declines and extinction because of the increased likelihood that one of their habitats or access between them will be lost. This is of particular concern because amphibians have been declining in numbers and going extinct more rapidly than many other groups for a variety of possible reasons.

Overharvesting

Overharvesting is a serious threat to many species, but particularly to aquatic species. There are many examples of regulated fisheries (including hunting of marine mammals and harvesting of crustaceans and other species) monitored by fisheries scientists that have nevertheless collapsed. The western Atlantic cod fishery is the most spectacular recent collapse. While it was a hugely productive fishery for 400 years, the introduction of modern factory trawlers in the 1980s and the pressure on the fishery led to it becoming unsustainable. The causes of fishery collapse are both economic and political in nature. Most fisheries are managed as a common resource, available to anyone willing to fish, even when the fishing territory lies within a country’s territorial waters. Common resources are subject to an economic pressure known as the tragedy of the commons, in which fishers have little motivation to exercise restraint in harvesting a fishery when they do not own the fishery. The general outcome of harvests of resources held in common is their overexploitation. While large fisheries are regulated to attempt to avoid this pressure, it still exists in the background. This overexploitation is exacerbated when access to the fishery is open and unregulated and when technology gives fishers the ability to overfish. In a few fisheries, the biological growth of the resource is less than the potential growth of the profits made from fishing if that time and money were invested elsewhere. In these cases—whales are an example—economic forces will drive toward fishing the population to extinction.

CONCEPT IN ACTION

Explore a U.S. Fish & Wildlife Service interactive map of critical habitat for endangered and threatened species in the United States. To begin, select “Visit the online mapper.”

For the most part, fishery extinction is not equivalent to biological extinction—the last fish of a species is rarely fished out of the ocean. But there are some instances in which true extinction is a possibility. Whales have slow-growing populations and are at risk of complete extinction through hunting. Also, there are some species of sharks with restricted distributions that are at risk of extinction. The groupers are another population of generally slow-growing fishes that, in the Caribbean, includes a number of species that are at risk of extinction from overfishing.

Coral reefs are extremely diverse marine ecosystems that face peril from several processes. Reefs are home to 1/3 of the world’s marine fish species—about 4000 species—despite making up only one percent of marine habitat. Most home marine aquaria house coral reef species that are wild-caught organisms—not cultured organisms. Although no marine species is known to have been driven extinct by the pet trade, there are studies showing that populations of some species have declined in response to harvesting, indicating that the harvest is not sustainable at those levels. There are also concerns about the effect of the pet trade on some terrestrial species such as turtles, amphibians, birds, plants, and even the orangutans.

Bush meat is the generic term used for wild animals killed for food. Hunting is practiced throughout the world, but hunting practices, particularly in equatorial Africa and parts of Asia, are believed to threaten several species with extinction. Traditionally, bush meat in Africa was hunted to feed families directly; however, recent commercialization of the practice now has bush meat available in grocery stores, which has increased harvest rates to the level of unsustainability . Additionally, human population growth has increased the need for protein foods that are not being met from agriculture. Species threatened by the bush meat trade are mostly mammals including many monkeys and the great apes living in the Congo basin.

Exotic Species

Exotic species are species that have been intentionally or unintentionally introduced by humans into an ecosystem in which they did not evolve. Human transportation of people and goods, including the intentional transport of organisms for trade, has dramatically increased the introduction of species into new ecosystems. These new introductions are sometimes at distances that are well beyond the capacity of the species to ever travel itself and outside the range of the species’ natural predators.

Most exotic species introductions probably fail because of the low number of individuals introduced or poor adaptation to the ecosystem they enter. Some species, however, have characteristics that can make them especially successful in a new ecosystem. These exotic species often undergo dramatic population increases in their new habitat and reset the ecological conditions in the new environment, threatening the species that exist there. When this happens, the exotic species also becomes an invasive species. Invasive species can threaten other species through competition for resources, predation, or disease.

Explore this interactive global database of exotic or invasive species.

Lakes and islands are particularly vulnerable to extinction threats from introduced species. In Lake Victoria, the intentional introduction of the Nile perch was largely responsible for the extinction of about 200 species of cichlids . The accidental introduction of the brown tree snake via aircraft (Figure \(\PageIndex{3}\)) from the Solomon Islands to Guam in 1950 has led to the extinction of three species of birds and three to five species of reptiles endemic to the island. Several other species are still threatened. The brown tree snake is adept at exploiting human transportation as a means to migrate; one was even found on an aircraft arriving in Corpus Christi, Texas. Constant vigilance on the part of airport, military, and commercial aircraft personnel is required to prevent the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not make up a large area of land on the globe, but they do contain a disproportionate number of endemic species because of their isolation from mainland ancestors.

Many introductions of aquatic species, both marine and freshwater, have occurred when ships have dumped ballast water taken on at a port of origin into waters at a destination port. Water from the port of origin is pumped into tanks on a ship empty of cargo to increase stability. The water is drawn from the ocean or estuary of the port and typically contains living organisms such as plant parts, microorganisms, eggs, larvae, or aquatic animals. The water is then pumped out before the ship takes on cargo at the destination port, which may be on a different continent. The zebra mussel was introduced to the Great Lakes from Europe prior to 1988 in ship ballast. The zebra mussels in the Great Lakes have cost the industry millions of dollars in clean up costs to maintain water intakes and other facilities. The mussels have also altered the ecology of the lakes dramatically. They threaten native mollusk populations, but have also benefited some species, such as smallmouth bass. The mussels are filter feeders and have dramatically improved water clarity, which in turn has allowed aquatic plants to grow along shorelines, providing shelter for young fish where it did not exist before. The European green crab, Carcinus maenas , was introduced to San Francisco Bay in the late 1990s, likely in ship ballast water, and has spread north along the coast to Washington. The crabs have been found to dramatically reduce the abundance of native clams and crabs with resulting increases in the prey of native crabs.

Invading exotic species can also be disease organisms. It now appears that the global decline in amphibian species recognized in the 1990s is, in some part, caused by the fungus Batrachochytrium dendrobatidis , which causes the disease chytridiomycosis (Figure \(\PageIndex{4}\)). There is evidence that the fungus is native to Africa and may have been spread throughout the world by transport of a commonly used laboratory and pet species: the African clawed frog, Xenopus laevis . It may well be that biologists themselves are responsible for spreading this disease worldwide. The North American bullfrog, Rana catesbeiana , which has also been widely introduced as a food animal but which easily escapes captivity, survives most infections of B. dendrobatidis and can act as a reservoir for the disease.

Early evidence suggests that another fungal pathogen, Geomyces destructans , introduced from Europe is responsible for white-nose syndrome, which infects cave-hibernating bats in eastern North America and has spread from a point of origin in western New York State (Figure \(\PageIndex{5}\)). The disease has decimated bat populations and threatens extinction of species already listed as endangered: the Indiana bat, Myotis sodalis , and potentially the Virginia big-eared bat, Corynorhinus townsendii virginianus . How the fungus was introduced is unknown, but one logical presumption would be that recreational cavers unintentionally brought the fungus on clothes or equipment from Europe.

Climate Change

Climate change, and specifically the anthropogenic warming trend presently underway, is recognized as a major extinction threat, particularly when combined with other threats such as habitat loss. Anthropogenic warming of the planet has been observed and is hypothesized to continue due to past and continuing emission of greenhouse gases, primarily carbon dioxide and methane, into the atmosphere caused by the burning of fossil fuels and deforestation. These gases decrease the degree to which Earth is able to radiate heat energy created by the sunlight that enters the atmosphere. The changes in climate and energy balance caused by increasing greenhouse gases are complex and our understanding of them depends on predictions generated from detailed computer models. Scientists generally agree the present warming trend is caused by humans and some of the likely effects include dramatic and dangerous climate changes in the coming decades. However, there is still debate and a lack of understanding about specific outcomes. Scientists disagree about the likely magnitude of the effects on extinction rates, with estimates ranging from 15 to 40 percent of species committed to extinction by 2050. Scientists do agree that climate change will alter regional climates, including rainfall and snowfall patterns, making habitats less hospitable to the species living in them. The warming trend will shift colder climates toward the north and south poles, forcing species to move with their adapted climate norms, but also to face habitat gaps along the way. The shifting ranges will impose new competitive regimes on species as they find themselves in contact with other species not present in their historic range. One such unexpected species contact is between polar bears and grizzly bears. Previously, these two species had separate ranges. Now, their ranges are overlapping and there are documented cases of these two species mating and producing viable offspring. Changing climates also throw off the delicate timing adaptations that species have to seasonal food resources and breeding times. Scientists have already documented many contemporary mismatches to shifts in resource availability and timing.

Range shifts are already being observed: for example, on average, European bird species ranges have moved 91 km (56.5 mi) northward. The same study suggested that the optimal shift based on warming trends was double that distance, suggesting that the populations are not moving quickly enough. Range shifts have also been observed in plants, butterflies, other insects, freshwater fishes, reptiles, amphibians, and mammals.

Climate gradients will also move up mountains, eventually crowding species higher in altitude and eliminating the habitat for those species adapted to the highest elevations. Some climates will completely disappear. The rate of warming appears to be accelerated in the arctic, which is recognized as a serious threat to polar bear populations that require sea ice to hunt seals during the winter months: seals are the only source of protein available to polar bears. A trend to decreasing sea ice coverage has occurred since observations began in the mid-twentieth century. The rate of decline observed in recent years is far greater than previously predicted by climate models (Figure \(\PageIndex{6}\)).

Finally, global warming will raise ocean levels due to meltwater from glaciers and the greater volume occupied by warmer water. Shorelines will be inundated, reducing island size, which will have an effect on some species, and a number of islands will disappear entirely. Additionally, the gradual melting and subsequent refreezing of the poles, glaciers, and higher elevation mountains—a cycle that has provided freshwater to environments for centuries—will be altered. This could result in an overabundance of salt water and a shortage of fresh water.

The core threats to biodiversity are human population growth and unsustainable resource use. To date, the most significant causes of extinction are habitat loss, introduction of exotic species, and overharvesting. Climate change is predicted to be a significant cause of extinction in the coming century. Habitat loss occurs through deforestation, damming of rivers, and other activities. Overharvesting is a threat particularly to aquatic species, but the taking of bush meat in the humid tropics threatens many species in Asia, Africa, and the Americas. Exotic species have been the cause of a number of extinctions and are especially damaging to islands and lakes. Exotic species’ introductions are increasing because of the increased mobility of human populations and growing global trade and transportation. Climate change is forcing range changes that may lead to extinction. It is also affecting adaptations to the timing of resource availability that negatively affects species in seasonal environments. The impacts of climate change are currently greatest in the arctic. Global warming will also raise sea levels, eliminating some islands and reducing the area of all others.

Contributors and Attributions

Samantha Fowler (Clayton State University), Rebecca Roush (Sandhills Community College), James Wise (Hampton University). Original content by OpenStax (CC BY 4.0; Access for free at https://cnx.org/contents/b3c1e1d2-83...4-e119a8aafbdd ).

ENCYCLOPEDIC ENTRY

Biodiversity.

Biodiversity refers to the variety of living species on Earth, including plants, animals, bacteria, and fungi. While Earth’s biodiversity is so rich that many species have yet to be discovered, many species are being threatened with extinction due to human activities, putting the Earth’s magnificent biodiversity at risk.

Biology, Ecology

grasshoppers

Although all of these insects have a similar structure and may be genetic cousins, the beautiful variety of colors, shapes, camouflage, and sizes showcase the level of diversity possible even within a closely-related group of species.

Photograph by Frans Lanting

Biodiversity is a term used to describe the enormous variety of life on Earth. It can be used more specifically to refer to all of the species  in one region or ecosystem . Bio diversity refers to every living thing, including plants, bacteria, animals, and humans. Scientists have estimated that there are around 8.7 million species of plants and animals in existence. However, only around 1.2 million species have been identified and described so far, most of which are insects. This means that millions of other organisms remain a complete mystery.

Over generations , all of the species that are currently alive today have evolved unique traits that make them distinct from other species . These differences are what scientists use to tell one species from another. Organisms that have evolved to be so different from one another that they can no longer reproduce with each other are considered different species . All organisms that can reproduce with each other fall into one species .

Scientists are interested in how much biodiversity there is on a global scale, given that there is still so much biodiversity to discover. They also study how many species exist in single ecosystems, such as a forest, grassland, tundra, or lake. A single grassland can contain a wide range of species, from beetles to snakes to antelopes. Ecosystems that host the most biodiversity tend to have ideal environmental conditions for plant growth, like the warm and wet climate of tropical regions. Ecosystems can also contain species too small to see with the naked eye. Looking at samples of soil or water through a microscope reveals a whole world of bacteria and other tiny organisms.

Some areas in the world, such as areas of Mexico, South Africa, Brazil, the southwestern United States, and Madagascar, have more bio diversity than others. Areas with extremely high levels of bio diversity are called hotspots . Endemic species — species that are only found in one particular location—are also found in hotspots .

All of the Earth’s species work together to survive and maintain their ecosystems . For example, the grass in pastures feeds cattle. Cattle then produce manure that returns nutrients to the soil, which helps to grow more grass. This manure can also be used to fertilize cropland. Many species provide important benefits to humans, including food, clothing, and medicine.

Much of the Earth’s bio diversity , however, is in jeopardy due to human consumption and other activities that disturb and even destroy ecosystems . Pollution , climate change, and population growth are all threats to bio diversity . These threats have caused an unprecedented rise in the rate of species extinction . Some scientists estimate that half of all species on Earth will be wiped out within the next century. Conservation efforts are necessary to preserve bio diversity and protect endangered species and their habitats.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Production Managers

Program specialists, last updated.

March 11, 2024

User Permissions

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text on this page is printable and can be used according to our Terms of Service .

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources

Which Are the Threats to Biodiversity? It’s Conservation and Sustainability

• First Online: 11 October 2023

Cite this chapter

• Kodoth Prabhakaran Nair 2  

86 Accesses

It is a very vexing scientific question, and, that concerns the severe threats biodiversity is now facing globally. When a very valuable species is threatened, it has a chain reaction. Many species have become extinct and many more are soon to follow this fate. The former chapter (Chap. 4 ) has elaborately discussed the threats which the hydrothermal vents, on the ocean bed, are now facing globally. The effect of this, is that, a very valuable process of synthesizing energy, the chemosynthesis, unlike the photosynthesis, is being now threatened by human greed.

This is a preview of subscription content, log in via an institution to check access.

Access this chapter

• Available as PDF
• Read on any device
• Instant download
• Own it forever
• Available as EPUB and PDF
• Durable hardcover edition
• Dispatched in 3 to 5 business days
• Free shipping worldwide - see info

Tax calculation will be finalised at checkout

Purchases are for personal use only

Institutional subscriptions

Anubhav, K. S., Rastogi, A., & Singh, V. (2009). Sacred groves in India: Celebrating sanctity of life through biodiversity conservation. In P. L. Gautam, V. Singh, & U. Melkania (Eds.), Ecosystem diversity and carbon sequestration: Climate change challenges and a way out for ushering in a sustainable future (pp. 89–101). Daya Publishing House.

Google Scholar  

IUCN-UNEP-WWF. (1980). World conservation strategy: Living resource conservation for sustainable development (77 pp). IUCN.

IUCN. (2019). Guidelines for using the IUCN red list categories and criteria: Version 14 (113 pp). IUCN.

Mittermeir, R. A., Myers, N., & Gil, P. R., & Mittermeir, C. G. (1999). Hotspots: Earth’s biologically richest and most endangered terrestrial ecoregions . Cemex, Conservation International and Agrupacion Sierra Madre.

Myers, N. (1988). Threatened biotas: “Hot spots” in tropical forests. The Environmentalist, 8 , 187–208. https://doi.org/10.1007/BF02240252

Article   CAS   PubMed   Google Scholar  

Myers, N. (1990). The biodiversity challenge: Expanded hotspots analysis. Environmentalist, 8 , 187–208. https://doi.org/10.1007/BFO2240252 .

Myers, N., Mittermeir, R. A., Mittermeir, C. G., da Fonseca, G. A. B., & Kent, J. (2000). Biodiversity hotspots for conservation priorities. Nature, 403 , 853–858. https://doi.org/10.1038/35002501

Nair, K. P. P. (2019a). Intelligent soil management for sustainable agriculture—The nutrient buffer power concept . Springer Nature Switzerland AG.

Nair, K. P. P. (2019b). Utilizing crop wild relatives to combat global warming. Advances in Agronomy, 153 , 175–258.

Article   Google Scholar  

Nair, K. P. P. (2019c). Combating global warming—The role of crop wild relatives for food security . Springer Nature Switzerland AG.

Nair, K. P. P. (2023a). The living soil: A lifetime journey in understanding it for human sustenance. SpringerBriefs in Environmental Science . Springer Nature Switzerland AG.

Nair, K. P. P. (2023b). Extractive farming or Bio farming? Making a better choice for the 21st century. SpringerBriefs in Environmental Science . Springer Nature Switzerland AG.

Ormsby, A. A., & Bhagavat, S. A. (2010). Sacred forests of India: A strong tradition of community-based natural resource management. Environmental Conservation, 37 (3), 320–326. https://doi.org/10.1017/S0376892910000651

Singh, V. (2019). Fertilizing the universe: A new chapter of unfolding evolution (285 pp). Cambridge Scholars Publishing.

Singh, V. (2020). Environmental plant physiology: Botanical strategies for a climate smart planet (230 pp). Taylor and Francis (CRC Press).

Download references

Author information

Authors and affiliations.

International Agricultural Scientist, Malaparamba, Kerala, India

Kodoth Prabhakaran Nair

You can also search for this author in PubMed   Google Scholar

Rights and permissions

Reprints and permissions

Copyright information

© 2023 The Author(s), under exclusive license to Springer Nature Switzerland AG

About this chapter

Nair, K.P. (2023). Which Are the Threats to Biodiversity? It’s Conservation and Sustainability. In: Biodiversity in Agriculture . Springer, Cham. https://doi.org/10.1007/978-3-031-44252-0_5

Download citation

DOI : https://doi.org/10.1007/978-3-031-44252-0_5

Published : 11 October 2023

Publisher Name : Springer, Cham

Print ISBN : 978-3-031-44251-3

Online ISBN : 978-3-031-44252-0

eBook Packages : Biomedical and Life Sciences Biomedical and Life Sciences (R0)

Share this chapter

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

• Publish with us

Policies and ethics

• Find a journal
• Track your research

Threatened species have declined 2% a year since 2000. Nature positive? Far from it.

Senior Lecturer, Public Sector Management, School of Business, UNSW Sydney

Professor in Conservation Science, School of Ecosystem and Forest Science, The University of Melbourne

Professor of Conservation Biology, The University of Queensland

Disclosure statement

Megan C Evans has received funding from various sources, including the Australian Research Council through a Discovery Early Career Research Award (2020-2023), the Australian Conservation Foundation, the Department of Agriculture, Water and the Environment, WWF Australia, and the National Environmental Science Program's Threatened Species Recovery Hub.

Brendan Wintle has received funding from The Australian Research Council, the Victorian State Government, the NSW State Government, the Queensland State Government, the Commonwealth National Environmental Science Program, the Ian Potter Foundation, the Hermon Slade Foundation, and the Australian Conservation Foundation. Wintle is a Board Director of Zoos Victoria and a lead councillor of the Biodiversity Council.

Hugh Possingham works for the University of Queensland, Accounting for Nature, and the Biodiversity Council. He currently receives grant funding from the Australian Research Council. He is affiliated with over 20 organisations providing pro-bono or limited renumeration, board or committee level advice. These include: BirdLife Australia (vice-President), The University of Adelaide (Environment Institute Board Chair), various state and federal governments, the Terrestrial Ecosystem Research Network (Board Chair), AgForce, and several NGOs, etc.

University of Melbourne provides funding as a founding partner of The Conversation AU.

UNSW Sydney and University of Queensland provide funding as members of The Conversation AU.

View all partners

Our government has great aspirations. It has committed to end extinctions and expand our protected areas to cover 30% of every Australian ecosystem by 2030. This is part of its Nature Positive Plan , aligned with the 2022 Kunming-Montreal global biodiversity pact . The goal is not just to conserve nature but to restore what is being lost.

But how can these goals be reconciled with a budget that allocated more public money to carbon capture and storage than biodiversity?

This week’s federal budget was a new low point for investment in nature. Environmental groups roundly criticised the “ bad budget for nature ”, which delivered next-to-no money to protect and recover Australia’s unique and threatened biodiversity.

Research has shown Australians want at least 2% of the federal budget spent on nature. Instead, less than 0.1% of the budget spend will support biodiversity in some way. Over the past decade, biodiversity funding has gone down 25% relative to GDP.

Let’s say the government decided it was finally time to roll up the sleeves and do something. How would they go about it? What would it take to actually reverse the decline, as the government says it wants to in its Nature Positive approach?

Our threatened species populations have been declining by about 2-3% a year over the past 20 years. The first step is to stop the fall. Then the challenge is to restore dwindling species and ecosystems.

The Dow Jones for threatened species goes down, down, down

Australia now has a Threatened Species Index . Think of it like the Dow Jones for wildlife. It uses trend data from bird, mammal and plant species collected from over 10,000 sites to measure progress for nature in Australia.

Last year, Treasurer Jim Chalmers talked up the index as part of the first national “wellbeing budget” , which aimed to measure Australia’s progress across a range of social, health and sustainability indicators.

What does the index tell us? You can see for yourself. The health of our threatened species has fallen by about 2-3% a year since the turn of the century.

If, as is likely, the trend continues, it will lead to the extinction of many more of our unique native animals and plant species. It will signal the failure of the government’s Nature Positive policy and a global biodiversity tragedy.

Given we have had decades of successive decline, what would be needed to reach the goal of nature positive?

Nature positive actually has a very specific meaning . It would:

halt and reverse nature loss measured from a baseline of 2020, through increasing the health, abundance, diversity and resilience of species, populations and ecosystems so that by 2030 nature is visibly and measurably on the path of recovery.

This definition gives us a clear, measurable timeline for action, often described as nature’s answer to net zero .

To reach nature positive means halting biodiversity loss by 2030 so that in the future there is much more biodiversity, relative to a 2020 baseline.

What would that look like using the Threatened Species Index? To get on track with nature positive, we would have to stop the index declining, stabilise, and then increase from 2030 onwards.

Of course, strong environmental laws and aligned policies are needed to effectively prevent further loss of habitat.

But we also need to invest in restoring what has been lost. Scientists think this is possible with $2 billion a year to recover our most threatened native plants and animals, and another $2 billion annually to drive ecosystem restoration across Australia.

The budget is not nature positive

In the budget papers , the government uses the Threatened Species Index as a performance measure for its nature positive goal. It expects the trajectory of the index to be “maintained or improved” out to 2027-28.

But given our species and ecosystems are steadily declining, year after year, to maintain a trajectory is simply to embrace the decline. It’s not nature positive at all. The government could make minor improvements, slowing the collapse, and claim it was improving the lot of nature.

Imagine if our GDP growth was negative and the government’s goal was merely to slow its decline over the next five years – there would be national uproar.

If the government is serious about nature positive – which is an excellent goal – it would be setting more ambitious targets. For instance, the goal could be for the index to climb back up to 2020 levels by the end of the decade.

Instead, Labor is planning for biodiversity decline to continue, while describing it as “nature positive”.

Watching over the steady decline of our species and calling it nature positive makes about as much sense as opening up new gas fields and calling it net zero.

Greenwashing Nature Positive

Unfortunately, this is not the first time the government has engaged in nature positive greenwash .

In coming weeks, the government will introduce bills to parliament to establish two new agencies, Environment Information Australia and Environmental Protection Australia. But there will be one bill missing – the reformed federal environment laws , intended to give teeth to the nature positive push.

The laws were pushed back indefinitely , to the shock of scientists and environmental groups.

But let’s be generous and say these laws finally make it to parliament after the next election. Would they be enough to stop our species losses and put the Threatened Species Index onto a nature positive trajectory?

It’s unlikely .

The consultation documents show the government is aiming to deliver “net positive outcomes”, whereby development impacts to threatened species and ecosystems are more than compensated for.

But we don’t know the detail. How much improvement is the government aiming for? In the draft laws, this figure is listed simply as “at least X%”.

Time to aim higher

It is hard not to feel dispirited over the government’s backtracking on its promise to:

not shy away from difficult problems or accept environmental decline and extinction as inevitable.

But we cannot give up. As the plight of nature worsens, even iconic species such as the koala and platypus are now at risk. As ecosystems collapse , our food security, health and wellbeing, communities and businesses will suffer.

Perhaps one day we will have a government able to grasp the nettle and actually tackle the nature crisis – for the sake of all of us.

Read more: Australia's long-sought stronger environmental laws just got indefinitely deferred. It's back to business as usual

• Conservation
• Biodiversity
• Environment
• Endangered species
• Nature positive
• Federal budget 2024

Case Management Specialist

Lecturer / Senior Lecturer - Marketing

Assistant Editor - 1 year cadetship

Executive Dean, Faculty of Health

Lecturer/Senior Lecturer, Earth System Science (School of Science)

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

• View all journals
• Explore content
• About the journal
• Publish with us
• Sign up for alerts
• Review Article
• Published: 19 March 2024

Invasive species drive cross-ecosystem effects worldwide

• Tianna Peller   ORCID: orcid.org/0000-0002-7131-2066 1 , 2 &
• Florian Altermatt   ORCID: orcid.org/0000-0002-4831-6958 1 , 2  

Nature Ecology & Evolution ( 2024 ) Cite this article

2171 Accesses

94 Altmetric

Metrics details

• Biodiversity
• Community ecology
• Conservation biology
• Ecosystem ecology
• Invasive species

Invasive species are pervasive around the world and have profound impacts on the ecosystem they invade. Invasive species, however, can also have impacts beyond the ecosystem they invade by altering the flow of non-living materials (for example, nutrients or chemicals) or movement of organisms across the boundaries of the invaded ecosystem. Cross-ecosystem interactions via spatial flows are ubiquitous in nature, for example, connecting forests and lakes, grasslands and rivers, and coral reefs and the deep ocean. Yet, we have a limited understanding of the cross-ecosystem impacts invasive species have relative to their local effects. By synthesizing emerging evidence, here we demonstrate the cross-ecosystem impacts of invasive species as a ubiquitous phenomenon that influences biodiversity and ecosystem functioning around the world. We identify three primary ways by which invasive species have cross-ecosystem effects: first, by altering the magnitude of spatial flows across ecosystem boundaries; second, by altering the quality of spatial flows; and third, by introducing novel spatial flows. Ultimately, the strong impacts invasive species can drive across ecosystem boundaries suggests the need for a paradigm shift in how we study and manage invasive species around the world, expanding from a local to a cross-ecosystem perspective.

This is a preview of subscription content, access via your institution

Access options

Access Nature and 54 other Nature Portfolio journals

Get Nature+, our best-value online-access subscription

24,99 € / 30 days

cancel any time

Subscribe to this journal

Receive 12 digital issues and online access to articles

111,21 € per year

only 9,27 € per issue

Buy this article

• Purchase on Springer Link
• Instant access to full article PDF

Prices may be subject to local taxes which are calculated during checkout

Similar content being viewed by others

A large invasive consumer reduces coastal ecosystem resilience by disabling positive species interactions

Invasive alien species of policy concerns show widespread patterns of invasion and potential pressure across European ecosystems

Risks posed by invasive species to the provision of ecosystem services in Europe

Global Assessment Report on Biodiversity and Ecosystem Services (IPBES Secretariat, 2019).

Summary for Policymakers of the Thematic Assessment Report on Invasive Alien Species and their Control of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES Secretariat, 2023).

Gallardo, B., Clavero, M., Sánchez, M. I. & Vilà, M. Global ecological impacts of invasive species in aquatic ecosystems. Glob. Change Biol. 22 , 151–163 (2016).

Article   ADS   Google Scholar  

Walsh, J. R., Carpenter, S. R. & Zanden, M. J. V. Invasive species triggers a massive loss of ecosystem services through a trophic cascade. Proc. Natl Acad. Sci. USA 113 , 4081–4085 (2016).

Article   ADS   CAS   PubMed   PubMed Central   Google Scholar  

Hejda, M., Pyšek, P. & Jarošik, V. Impact of invasive plants on the species richness, diversity and composition of invaded communities. J. Ecol. 97 , 393–403 (2009).

Article   Google Scholar  

Bradley, B. A. et al. Disentangling the abundance–impact relationship for invasive species. Proc. Natl Acad. Sci. USA 116 , 9919–9924 (2019).

Cameron, E. K., Vilà, M. & Cabeza, M. Global meta-analysis of the impacts of terrestrial invertebrate invaders on species, communities and ecosystems. Glob. Ecol. Biogeogr. 25 , 596–606 (2016).

Vilà, M. et al. Ecological impacts of invasive alien plants: a meta-analysis of their effects of species, communities and ecosystems. Ecol. Lett. 14 , 702–708 (2011).

Article   PubMed   Google Scholar  

Linders, T. E. W. et al. Direct and indirect effects of invasive species: biodiversity loss is a major mechanism by which an invasive tree affects ecosystem functioning. J. Ecol. 107 , 2660–2672 (2019).

Polis, G. A., Anderson, W. B. & Holt, R. D. Towards an integration of landscape and food web ecology: the dynamics of spatially subsidized food webs. Annu. Rev. Ecol. Evol. Syst. 28 , 289–316 (1997).

Gounand, I., Harvey, E., Little, C. J. & Altermatt, F. Meta-ecosystems 2.0: rooting the theory into the field. Trends Ecol. Evol. 33 , 36–46 (2018).

Montagano, L., Leroux, S. J., Giroux, M. A. & Lecomte, N. The strength of ecological subsidies across ecosystems: a latitudinal gradient of direct and indirect impacts on food webs. Ecol. Lett. 22 , 265–274 (2019).

Peller, T., Andrews, S., Leroux, S. & Guichard, F. From marine metacommunities to meta-ecosystems: examining the nature, scale and significance of resource flows in benthic marine environments. Ecosystems 24 , 1239–1252 (2021).

Richardson, J. S. & Wipfli, M. S. Getting quantitative about consequences of cross-ecosystem resource subsidies on recipient consumers. Can. J. Fish. Aquat. Sci. 73 , 1609–1615 (2016).

Graham, N. A. J. et al. Seabirds enhance coral reef productivity and functioning in the absence of invasive rats. Nature 559 , 250–253 (2018).

Article   ADS   CAS   PubMed   Google Scholar  

Swain, N. R., Hocking, M. D., Harding, J. N. & Reynolds, J. D. Effects of salmon on the diet and condition of stream-resident sculpins. Can. J. Fish. Aquat. Sci. 71 , 521–532 (2014).

Article   CAS   Google Scholar  

Marcarelli, A. M., Baxter, C. V., Mineau, M. M. & Hall, R. O. Quantity and quality: unifying food web and ecosystem perspectives on the role of resource subsidies in freshwaters. Ecology 92 , 1215–1225 (2011).

Peller, T., Guichard, F. & Altermatt, F. The significance of partial migration for food web and ecosystem dynamics. Ecol. Lett. 26 , 3–22 (2023).

Knight, T. M., McCoy, M. W., Chase, J. M., McCoy, K. A. & Holt, R. D. Trophic cascades across ecosystems. Nature 437 , 880–883 (2005).

Harvey, E., Gounand, I., Ganesanandamoorthy, P. & Altermatt, F. Spatially cascading effect of perturbations in experimental meta-ecosystems. Proc. R. Soc. B 283 , 20161496 (2016).

Article   PubMed   PubMed Central   Google Scholar  

Mineau, M. M., Baxter, C. V., Marcarelli, A. M. & Minshall, G. W. An invasive riparian tree reduces stream ecosystem efficiency via a recalcitrant organic matter subsidy. Ecology 93 , 1501–1508 (2012).

Wasserman, R. J., Sanga, S., Buxton, M., Dalu, T. & Cuthbert, R. N. Does invasive river red gum ( Eucalyptus camaldulensis ) alter leaf litter decomposition dynamics in arid zone temporary rivers? Inland Waters 11 , 104–113 (2020).

Hladyz, S., Åbjörnsson, K., Giller, P. S. & Woodward, G. Impacts of an aggressive riparian invader on community structure and ecosystem functioning in stream food webs. J. Appl. Ecol. 48 , 443–452 (2011).

Gunn, R. L. et al. Terrestrial invasive species alter marine vertebrate behaviour. Nat. Ecol. Evol. 7 , 82–91 (2023).

Benkwitt, C. E., Wilson, S. K. & Graham, N. A. J. Seabird nutrient subsidies alter patterns of algal abundance and fish biomass on coral reefs following a bleaching event. Glob. Change Biol. 25 , 2619–2632 (2019).

Koel, T. M. et al. Predatory fish invasion induces within and across ecosystem effects in Yellowstone National Park. Sci. Adv. 5 , eaav1139 (2019).

Article   ADS   PubMed   PubMed Central   Google Scholar  

Kurle, C. M., Croll, D. A. & Tershy, B. R. Introduced rats indirectly change marine rocky intertidal communities from algae- to invertebrate-dominated. Proc. Natl Acad. Sci. USA 105 , 3800–3804 (2008).

Kurle, C. M. et al. Indirect effects of invasive rat removal result in recovery of island rocky intertidal community structure. Sci. Rep. 11 , 5395 (2021).

Baxter, C. V., Fausch, K. D., Murakami, M. & Chapman, P. L. Fish invasion restructures stream and forest food webs by interrupting reciprocal prey subsidies. Ecology 85 , 2656–2663 (2004).

Epanchin, P. N., Knapp, R. A. & Lawler, S. P. Nonnative trout impact an alpine-nesting bird by altering aquatic-insect subsidies. Ecology 91 , 2406–2415 (2010).

Benjamin, J. R., Fausch, K. D. & Baxter, C. V. Species replacement by a nonnative salmonid alters ecosystem function by reducing prey subsidies that support riparian spiders. Oecologia 167 , 503–512 (2011).

Article   ADS   PubMed   Google Scholar  

Merkley, S. S., Radar, R. B. & Schaalje, G. B. Introduced western mosquitofish ( Gambusia affinis ) reduce the emergence of aquatic insects in a desert spring. Freshw. Sci. 34 , 564–573 (2015).

Jackson, M. C. et al. Trophic overlap between fish and riparian spiders: potential impacts of an invasive fish on terrestrial consumers. Ecol. Evol. 6 , 1745–1752 (2016).

Collins, S. F. & Wahl, D. H. Invasive planktivores as mediators of organic matter exchanges within and across ecosystems. Oecologia 184 , 521–530 (2017).

Gergs, R., Koester, M., Schulz, R. S. & Schulz, R. Potential alteration of cross-ecosystem resource subsidies by an invasive aquatic macroinvertebrate: implications for the terrestrial food web. Freshw. Biol. 59 , 2645–2655 (2014).

Finlay, J. C. & Vredenburg, V. T. Introduced trout sever trophic connections in watersheds: consequences for a declining amphibian. Ecology 88 , 2187–2198 (2007).

McCauley, D. J. et al. From wing to wing: the persistence of long ecological interaction chains in less-disturbed ecosystems. Sci. Rep. 2 , 409 (2012).

Wang, B. et al. Long-distance facilitation of coastal ecosystem structure and resilience. Proc. Natl Acad. Sci. USA 119 , e2123274119 (2022).

Article   CAS   PubMed   PubMed Central   Google Scholar  

Novais, A., Souza, A. T., Ilarri, M., Pascoal, C. & Sousa, R. From water to land: how an invasive clam may function as a resource pulse to terrestrial invertebrates. Sci. Total Environ. 538 , 664–671 (2015).

Crait, J. R., Regehr, E. V. & Ben-David, M. Indirect effects of bioinvasions in Yellowstone Lake: the response of river otters to declines in native cutthroat trout. Biol. Conserv. 191 , 596–605 (2015).

Middleton, A. D. et al. Grizzly bear predation links the loss of native trout to the demography of migratory elk in Yellowstone. Proc. R. Soc. B 280 , 20130870 (2013).

Burkle, L. A., Mihaljevic, J. R. & Smith, K. G. Effects of an invasive plant transcend ecosystem boundaries through a dragonfly-mediated trophic pathway. Oecologia 170 , 1045–1052 (2012).

Ertel, B. D., McMahon, T. E., Koel, T. M., Gresswell, R. E. & Burckhardt, J. C. Life history migrations of adult Yellowstone cutthroat trout in the upper Yellowstone River. N. Am. J. Fish. Manag. 37 , 743–755 (2017).

Sousa, R. et al. Massive die-offs of freshwater bivalves as resource pulses. Int. J. Limnol. 48 , 105–112 (2012).

Bódis, E., Tóth, B. & Sousa, R. Massive mortality of invasive bivalves as a potential resource subsidy for the adjacent terrestrial food web. Hydrobiologia 735 , 253–262 (2014).

Larsen, S., Muehlbauer, J. D. & Marti, E. Resource subsidies between stream and terrestrial ecosystems under global change. Glob. Change Biol. 22 , 2489–2504 (2015).

Schulz, R. et al. Review on environmental alterations propagating from aquatic to terrestrial ecosystems. Sci. Total Environ. 538 , 246–261 (2015).

López, B. E. et al. Global environmental changes more frequently offset than intensify detrimental effects of biological invasions. Proc. Natl Acad. Sci. USA 119 , e2117389119 (2022).

Riedl, H. L., Stinson, L., Pejchar, L. & Clements, W. H. An introduced plant affects aquatic-derived carbon in the diets of riparian birds. PLoS ONE 13 , e0207389 (2018).

Julian, P., Everham, E. M. & Main, M. B. Influence of a large-scale removal of an invasive plant ( Melaleuca quinquenervia ) on home-range size and habitat selection by female Florida panthers ( Puma concolor coryi ) within Big Cypress National Preserve, Florida. Southeast. Nat. 11 , 337–348 (2012).

Hardesty-Moore, M., Orr, D. & McCauley, D. J. Invasive plant Arundo donax alters habitat use by carnivores. Biol. Invasions 22 , 1983–1995 (2020).

Lym, R. G. & Kirby, D. R. Cattle foraging behaviour in leafy spurge-infested rangeland. Weed Technol. 1 , 314–318 (1987).

Natusch, D. J. D., Mayer, M., Lyons, J. A. & Shine, R. Interspecific interactions between feral pigs and native birds reveal both positive and negative effects. Austral Ecol. 42 , 479–485 (2017).

Tarr, M. D. Effects of non-native shrubs on caterpillars and shrubland-dependent passerines within three transmission line rights-of-way in southeastern New Hampshire. Northeast. Nat. 29 , 1–43 (2022).

Peller, T., Marleau, J. & Guichard, F. Traits affecting nutrient recycling by mobile consumers can explain coexistence and spatially heterogeneous trophic regulation across a meta-ecosystem. Ecol. Lett. 25 , 440–452 (2022).

Roon, D. A., Wipfli, M. S., Wurtz, T. L. & Blanchard, A. L. Invasive European bird cherry ( Prunus padus ) reduces terrestrial prey subsidies to urban Alaskan salmon streams. Can. J. Fish. Aquat. Sci. 73 , 1679–1690 (2016).

Roon, D. A., Wipfli, M. S. & Kruse, J. J. Riparian defoliation by the invasive green alder sawfly influences terrestrial prey subsidies to salmon streams. Ecol. Freshw. Fish. 27 , 963–975 (2018).

Riedl, H. L., Clements, W. H. & Pejchar, L. An introduced plant is associated with declines in terrestrial arthropods, but no change in stream invertebrates. Can. J. Fish. Aquat. Sci. 76 , 1314–1325 (2019).

Rundio, D. E. & Lindley, S. T. Importance of non-native isopods and other terrestrial prey resources to steelhead/rainbow trout Oncorhynchus mykiss in coastal streams in Big Sur, California. Ecol. Freshw. Fish. 30 , 419–432 (2021).

Baxter, C. V., Fausch, K. D. & Saunders, W. C. Tangled webs: reciprocal flows of invertebrate prey link stream and riparian zones. Freshw. Biol. 50 , 201–220 (2005).

Vitousek, P. M., Walker, L. R., Whiteaker, L. D., Mueller-dombois, D. & Matson, P. A. Biological invasion by Myrica faya alters ecosystem development in Hawaii. Science 238 , 802–804 (1987).

Atkinson, C. L., Opsahl, S. P., Covich, A. P., Golladay, S. W. & Conner, L. M. Stable isotopic signatures, tissue stoichiometry, and nutrient cycling (C and N) of native and invasive freshwater bivalves. J. N. Am. Benthol. Soc. 29 , 496–505 (2010).

Kennedy, T. A. & Hobbie, S. E. Saltcedar ( Tamarix ramosissima ) invasion alters organic matter dynamics in a desert stream. Freshw. Biol. 49 , 65–76 (2004).

Lecerf, A. et al. Stream ecosystems respond to riparian invasion by Japanese knotweed ( Fallopia japonica ). Can. J. Fish. Aquat. Sci. 64 , 1273–1283 (2007).

Hladyz, S., Gessner, M. O., Giller, P. S., Pozo, J. & Woodward, G. Resource quality and stoichiometric constraints on stream ecosystem functioning. Freshw. Biol. 54 , 957–970 (2009).

Stephens, J. P., Berven, K. A. & Tiegs, S. D. Anthropogenic changes to leaf litter input affect the fitness of a larval amphibian. Freshw. Biol. 58 , 1539–1565 (2013).

Leonard, N. E. The Effects of the Invasive Exotic Chinese Tallow Tree ( Triadica sebifera ) on Amphibians and Aquatic Invertebrates. PhD thesis, Univ. New Orleans (2008).

Kuglerova, L., Garcia, L., Pardo, I., Mottiar, Y. & Richardson, J. S. Does leaf litter from invasive plants contribute the same support of a stream ecosystem function as native vegetation. Ecosphere 8 , e01779 (2017).

Stewart, S. D., Young, M. B., Harding, J. S. & Horton, T. W. Invasive nitrogen-fixing plant amplifies terrestrial–aquatic nutrient flow and alters ecosystem function. Ecosystems 22 , 587–601 (2019).

Heinrich, K. K., Baxter, C. V., Bell, A. T. C. & Hood, J. M. Of olives and carp: interactive effects of an aquatic and a terrestrial invader on a stream–riparian ecosystem. Ecosphere 12 , e03789 (2021).

Ferreira, V., Figueiredo, A., Graça, M. A. S., Marchante, E. & Pereira, A. Invasion of temperate deciduous broadleaf forests by N-fixing tree species – consequences for stream ecosystems. Biol. Rev. 96 , 877–902 (2021).

Atwood, T. B., Wiegner, T. N., Turner, P. & MacKenzie, R. A. Potential effects of an invasive nitrogen-fixing tree on a Hawaiin stream food web. BioOne 64 , 367–379 (2010).

CAS   Google Scholar  

Maerz, J. C., Cohen, J. S. & Blossey, B. Does detritus quality predict the effect of native and non-native plants on the performance of larval amphibians. Freshw. Biol. 55 , 1694–1704 (2010).

Cohen, J. S., Maerz, J. C. & Blossey, B. Traits, not origin, explain impacts of plants on larval amphibians. Ecol. Appl. 22 , 218–228 (2012).

Milanovich, J. R., Barrett, K. & Crawford, J. A. Detritus quality and locality determines survival and mass, but no export, of wood frogs at metamorphosis. PLoS ONE 11 , e0166296 (2016).

Rodrigues, A. C. M. et al. Invasive species mediate insecticide effects on community and ecosystem functioning. Environ. Sci. Technol. 52 , 4889–4900 (2018).

Krumhasl, K. A. & Scheibling, R. E. Detrital subsidy from subtidal kelp beds is altered by the invasive green alga Codium fragile ssp. fragile . Mar. Ecol. Prog. Ser. 456 , 73–85 (2012).

Rodil, I. F., Olabarria, C., Lastra, M. & López, J. Differential effects of native and invasive algal wrack on macrofaunal assemblages inhabiting exposed sandy beaches. J. Exp. Mar. Biol. Ecol. 358 , 1–13 (2008).

Suárez-Jiménez, R. et al. Importance of the invasive macroalga Undaria pinnatifida as trophic subsidy for a beach consumer. Mar. Biol . 164 , 113 (2017).

Bishop, M. J. & Kelaher, B. P. Replacement of native seagrass with invasive algal detritus: impacts to estuarine sediment communities. Biol. Invasions 15 , 45–59 (2013).

Jiménez, R. S., Hepburn, C. D., Hyndes, G. A., McLeod, R. J. & Hurd, C. L. Contributions of an annual invasive kelp to native algal assemblages: algal resource allocation and seasonal connectivity across ecotones. Phycologia 54 , 530–544 (2015).

Sitters, J., Atkinson, C. L., Guelzow, N., Kelly, P. & Sullivan, L. L. Spatial stoichiometry: cross-ecosystem material flows and their impact on recipient ecosystems and organisms. Oikos 124 , 920–930 (2015).

Taylor, S. L., Bishop, M. J., Kelaher, B. P. & Glasby, T. M. Impacts of detritus from the invasive alga Caulerpa taxofolia on a soft sediment community. Mar. Ecol. Prog. Ser. 420 , 73–81 (2010).

Schmitz, O. J. et al. Animals and the zoogeochemistry of the carbon cycle. Science 362 , eaar3213 (2018).

Capps, K. A. & Flecker, A. S. Invasive fishes generate biogeochemical hotspots in a nutrient-limited system. PLoS ONE 8 , e54093 (2013).

Huser, B. J., Bajer, P. G., Kittelson, S., Christenson, S. & Menken, K. Changes to water quality and sediment phosphorus forms in a shallow, eutrophic lake after removal of common carp ( Cyprinus carpio ). Inland Waters 12 , 33–46 (2020).

Li, J. et al. Benthic invaders control the phosphorus cycle in the world’s largest freshwater ecosystem. Proc. Natl Acad. Sci. USA 118 , e2008223118 (2021).

Cappuccino, N. & Arnason, J. T. Novel chemistry of invasive exotic plants. Biol. Lett. 2 , 189–193 (2006).

Diller, J. G. P., Hüftlein, F., Lücker, D., Feldhaar, H. & Laforsch, C. Allelochemical run-off from the invasive terrestrial plant Impatiens glandulifera decreases defensibility in Daphnia . Sci. Rep. 13 , 1207 (2023).

Diller, J. G. P. et al. The beauty is a beast: does leachate from the invasive terrestrial plant Impatiens glandulifera affect aquatic food webs? Ecol. Evol. 12 , e8781 (2022).

Griffiths, M. R., Strobel, B. W., Hama, J. R. & Cedergreen, N. Toxicity and risk of plant-produced alkaloids to Daphnia magna . Environ. Sci. Eur. 33 , 10 (2021).

Custer, K. W., Borth, E. B., Mahoney, S. D. & McEwan, R. W. Lethal and sublethal effects of novel terrestrial subsidies from an invasive shrub ( Lonicera maackii ) on stream macroinvertebrates. Freshw. Sci. 36 , 750–759 (2017).

McNeish, R. E., Benbow, M. E. & McEwan, R. W. Removal of the invasive shrub, Lonicera maackii (Amur honeysuckle), from a headwater stream riparian zone shifts taxonomic and functional composition of the aquatic biota. Invasive Plant Sci. Manag. 10 , 232–246 (2017).

Watling, J. I., Hickman, C. R., Lee, E., Wang, K. & Orrock, J. L. Extracts of the invasive shrub Lonicera maackii increase mortality and alter behaviour of amphibian larvae. Oecologia 165 , 153–159 (2011).

Hickman, C. R. & Watling, J. I. Leachates from an invasive shrub causes risk-prone behaviour in a larval amphibian. Behav. Ecol. 25 , 300–305 (2008).

Iglesias-Carrasco, M., Cabido, C. & Ord, T. J. Natural toxins leached from Eucalyptus globulus plantations affect the development and life-history of anuran tadpoles. Freshw. Biol. 67 , 278–388 (2022).

Maerz, J. C., Brown, C. J., Chapin, C. T. & Blossey, B. Can secondary compounds of an invasive plant affect larval amphibians? Funct. Ecol. 19 , 970–975 (2005).

Sato, T., El-Sabaawi, R. W., Campbell, K., Ohta, T. & Richardson, J. S. A test of the effects of timing of a pulsed resource subsidy on stream ecosystems. J. Anim. Ecol. 85 , 1136–1146 (2016).

Rossi, F., Olabarria, C., Incera, M. & Garrido, J. The trophic significance of the invasive seaweed Sargassum muticum in sandy beaches. J. Sea Res. 63 , 52–61 (2010).

Kuebbing, S. E. & Nuñez, M. A. Negative, neutral, and positive interactions among nonnative plants: patterns, processes, and management implications. Glob. Change Biol. 21 , 926–934 (2014).

Fryxell, D. X., Diluzio, A. R., Friedman, M. A., Menge, N. A. & Palkovacs, E. P. Cross-habitat effects shape the ecosystem consequences of co-invasion by a pelagic and a benthic consumer. Oecologia 182 , 519–528 (2016).

Fontoura, L. et al. Protecting connectivity promotes successful biodiversity and fisheries conservation. Science 375 , 336–340 (2022).

Benkwitt, C. E., Gunn, R. L., Le Corre, M., Carr, M. & Graham, N. A. J. Rat eradication restores nutrient subsidies from seabirds across terrestrial and marine ecosystems. Curr. Biol. 31 , 2704–2711 (2021).

Article   CAS   PubMed   Google Scholar  

Guzman, L. M. et al. Towards a multi-trophic extension of metacommunity ecology. Ecol. Lett. 22 , 19–33 (2019).

Fortin, M.-J., Dale, M. R. T. & Brimacombe, C. Network ecology in dynamic landscapes. Proc. R. Soc. B 288 , 20201889 (2021).

Bauer, S. & Hoye, B. J. Migratory animals couple biodiversity and ecosystem functioning worldwide. Science 344 , 1242552 (2014).

Krumhansl, K. A., Lee, J. M. & Scheibling, R. E. Grazing damage and encrustation by an invasive bryozoan reduce the ability of kelps to withstand breakage by waves. J. Exp. Mar. Biol. Ecol. 407 , 12–18 (2011).

Aiyer, A., Shine, R., Somaweera, R., Bell, T. & Ward-Fear, G. Shifts in the foraging tactics of crocodiles following invasion by toxic prey. Sci. Rep. 12 , 1267 (2022).

Crain, C. M., Kroeker, K. & Halpern, B. S. Interactive and cumulative effects of multiple human stressors in marine systems. Ecol. Lett. 11 , 1304–1315 (2008).

Tockner, K., Pusch, M., Borchardt, D. & Lorang, M. S. Multiple stressors in coupled river–floodplain ecosystems. Freshw. Biol. 55 , 135–151 (2010).

Download references

Acknowledgements

The authors thank M. Brosse for preparing Fig. 1 and the figure in Box 1 . Funding is from the Swiss National Science Foundation (grant no. 10030_197410) and the University of Zurich Research Priority Programme on Global Change and Biodiversity (URPP GCB) to F.A.

Author information

Authors and affiliations.

Department of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland

Tianna Peller & Florian Altermatt

Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland

You can also search for this author in PubMed   Google Scholar

Contributions

T.P. conceptualized the study, carried out the synthesis and led the writing of the manuscript, with substantial contributions from F.A. on all elements.

Corresponding authors

Correspondence to Tianna Peller or Florian Altermatt .

Ethics declarations

Competing interests.

The authors declare no competing interests.

Peer review

Peer review information.

Nature Ecology & Evolution thanks Montserrat Vilà and Stefano Larsen for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary information.

Supplementary information describing search strategy.

Supplementary Table

Supplementary Table 1. List of studies included in the qualitative and quantitative data synthesis. All studies in this list were included in the qualitative synthesis. Studies included in the quantitative synthesis are indicated in the quantitative synthesis column.

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Cite this article.

Peller, T., Altermatt, F. Invasive species drive cross-ecosystem effects worldwide. Nat Ecol Evol (2024). https://doi.org/10.1038/s41559-024-02380-1

Download citation

Received : 19 June 2023

Accepted : 13 February 2024

Published : 19 March 2024

DOI : https://doi.org/10.1038/s41559-024-02380-1

Share this article

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

Quick links

• Explore articles by subject
• Guide to authors
• Editorial policies

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Module 26: Ecology and the Environment

Threats to biodiversity, learning outcomes.

• Identify significant threats to biodiversity

The core threat to biodiversity on the planet, and therefore a threat to human welfare, is the combination of human population growth and resource exploitation. The human population requires resources to survive and grow, and those resources are being removed unsustainably from the environment. The three greatest proximate threats to biodiversity are habitat loss, overharvesting, and the introduction of exotic species. The first two of these are a direct result of human population growth and resource use. The third results from increased mobility and trade. A fourth major cause of extinction, anthropogenic climate change, has not yet had a large impact, but it is predicted to become significant during this century. Global climate change is also a consequence of human population needs for energy and the use of fossil fuels to meet those needs (Figure 1). Environmental issues, such as toxic pollution, have specific targeted effects on species, but they are not generally seen as threats at the magnitude of the others.

Figure 1. Atmospheric carbon dioxide levels fluctuate in a cyclical manner. However, the burning of fossil fuels in recent history has caused a dramatic increase in the levels of carbon dioxide in the Earth’s atmosphere, which have now reached levels never before seen in human history. Scientists predict that the addition of this “greenhouse gas” to the atmosphere is resulting in climate change that will significantly impact biodiversity in the coming century.

Habitat Loss

Humans rely on technology to modify their environment and replace certain functions that were once performed by the natural ecosystem. Other species cannot do this. Elimination of their ecosystem—whether it is a forest, a desert, a grassland, a freshwater estuarine, or a marine environment—will kill the individuals belonging to the species. The species will become extinct if we remove the entire habitat within the range of a species. Human destruction of habitats accelerated in the latter half of the twentieth century. Consider the exceptional biodiversity of Sumatra: it is home to one species of orangutan, a species of critically endangered elephant, and the Sumatran tiger, but half of Sumatra’s forest is now gone. The neighboring island of Borneo, home to the other species of orangutan, has lost a similar area of forest. Forest loss continues in protected areas of Borneo. All three species of orangutan are now listed as endangered by the International Union for Conservation of Nature (IUCN), but they are simply the most visible of thousands of species that will not survive the disappearance of the forests in Sumatra and Borneo. The forests are removed for timber and to plant palm oil plantations (Figure 2). Palm oil is used in many products including food products, cosmetics, and biodiesel in Europe. A five-year estimate of global forest cover loss for the years 2000–2005 was 3.1 percent. In the humid tropics where forest loss is primarily from timber extraction, 272,000 km 2  was lost out of a global total of 11,564,000 km 2  (or 2.4 percent). In the tropics, these losses certainly also represent the extinction of species because of high levels of  endemism —species unique to a defined geographic location, and found nowhere else.

Figure 2. (a) One of three species of orangutan, Pongo pygmaeus, is found only in the rainforests of Borneo, and an other species of orangutan (Pongo abelii) is found only in the rainforests of Sumatra. These animals are examples of the exceptional biodiversity of (c) the islands of Sumatra and Borneo. Other species include the (b) Sumatran tiger (Panthera tigris sumatrae) and the (d) Sumatran elephant (Elephas maximus sumatranus), both critically endangered species. Rainforest habitat is being removed to make way for (e) oil palm plantations such as this one in Borneo’s Sabah Province. (credit a: modification of work by Thorsten Bachner; credit b: modification of work by Dick Mudde; credit c: modification of work by U.S. CIA World Factbook; credit d: modification of work by “Nonprofit Organizations”/Flickr; credit e: modification of work by Dr. Lian Pin Koh)

Preventing Habitat Destruction with Wise Wood Choices

Most consumers are not aware that the home improvement products they buy might be contributing to habitat loss and species extinctions. Yet the market for illegally harvested tropical timber is huge, and the wood products often find themselves in building supply stores in the United States. One estimate is that 10 percent of the imported timber stream in the United States, which is the world’s largest consumer of wood products, is potentially illegally logged. In 2006, this amounted to $3.6 billion in wood products. Most of the illegal products are imported from countries that act as  intermediaries  and are not the originators of the wood.

How is it possible to determine if a wood product, such as flooring, was harvested sustainably or even legally? The  Forest Stewardship Council  (FSC) certifies sustainably harvested forest products, therefore, looking for their certification on flooring and other hardwood products is one way to ensure that the wood has not been taken illegally from a tropical forest. Certification applies to specific products, not to a producer; some producers’ products may not have certification while other products are certified. While there are other industry-backed certifications other than the FSC, these are unreliable due to lack of independence from the industry. Another approach is to buy domestic wood species. While it would be great if there was a list of legal versus illegal wood products, it is not that simple. Logging and forest management laws vary from country to country; what is illegal in one country may be legal in another. Where and how a product is harvested and whether the forest from which it comes is being maintained sustainably all factor into whether a wood product will be certified by the FSC. If you are in doubt, it is always a good idea to ask questions about where a wood product came from and how the supplier knows that it was harvested legally.

Habitat destruction can affect ecosystems other than forests. Rivers and streams are important ecosystems that are frequently modified through land development, damming, channelizing, or water removal. Damming affects the water flow to all parts of a river, which can reduce or eliminate populations that had adapted to the natural flow of the river. For example, an estimated 91 percent of United States rivers have been altered in some way. Modifications include dams, to create energy or store water; levees, to prevent flooding; and dredging or rerouting, to create land that is more suitable for human development. Many fish and amphibian species and numerous freshwater clams in the United States have seen declines caused by river damming and habitat loss.

Overharvesting

Overharvesting is a serious threat to many species, but particularly to aquatic (both marine and freshwater) species. Despite regulation and monitoring, there are recent examples of fishery collapse. The western Atlantic cod fishery is the among the most significant. While it was a hugely productive fishery for 400 years, the introduction of modern factory trawlers in the 1980s caused it to become unsustainable. Fisheries collapse as a result of both economic and political factors. Fisheries are managed as a shared international resource even when the fishing territory lies within an individual country’s territorial waters. Common resources are subject to an economic pressure known as the  tragedy of the commons , in which essentially no fisher has a motivation to exercise restraint in harvesting a fishery when it is not owned by that fisher. Overexploitation is a common outcome. This overexploitation is exacerbated when access to the fishery is open and unregulated and when technology gives fishers the ability to overfish. In a few fisheries, the biological growth of the resource is less than the potential growth of the profits made from fishing if that time and money were invested elsewhere. In these cases—whales are an example—economic forces will always drive toward fishing the population to extinction.

For the most part, fishery extinction is not equivalent to biological extinction—the last fish of a species is rarely fished out of the ocean. At the same time, fishery extinction is still harmful to fish species and their ecosystems. There are some instances in which true extinction is a possibility. Whales have slow-growing populations and are at risk of complete extinction through hunting. There are some species of sharks with restricted distributions that are at risk of extinction. The groupers are another population of generally slow-growing fishes that, in the Caribbean, includes a number of species that are at risk of extinction from overfishing.

Coral reefs are extremely diverse marine ecosystems that face peril from several processes. Reefs are home to 1/3 of the world’s marine fish species—about 4,000 species—despite making up only 1 percent of marine habitat. Most home marine aquaria are stocked with wild-caught organisms, not cultured organisms. Although no species is known to have been driven extinct by the pet trade in marine species, there are studies showing that populations of some species have declined in response to harvesting, indicating that the harvest is not sustainable at those levels. There are concerns about the effect of the pet trade on some terrestrial species such as turtles, amphibians, birds, plants, and even the orangutan.

Bush meat is the generic term used for wild animals killed for food. Hunting is practiced throughout the world, but hunting practices, particularly in equatorial Africa and parts of Asia, are believed to threaten several species with extinction. Traditionally, bush meat in Africa was hunted to feed families directly; however, recent commercialization of the practice now has bush meat available in grocery stores, which has increased harvest rates to the level of unsustainability. Additionally, human population growth has increased the need for protein foods that are not being met from agriculture. Species threatened by the bush meat trade are mostly mammals including many primates living in the Congo basin.

Exotic Species

Exotic species  are species that have been intentionally or unintentionally introduced into an ecosystem in which they did not evolve. For example, Kudzu ( Pueraria lobata ), which is native to Japan, was introduced in the United States in 1876. It was later planted for soil conservation. Problematically, it grows too well in the southeastern United States—up to a foot a day. It is now an invasive pest species and covers over 7 million acres in the southeastern United States. If an introduced species is able to survive in its new habitat, that introduction is now reflected in the observed range of the species. Human transportation of people and goods, including the intentional transport of organisms for trade, has dramatically increased the introduction of species into new ecosystems, sometimes at distances that are well beyond the capacity of the species to ever travel itself and outside the range of the species’ natural predators.

Most exotic species introductions probably fail because of the low number of individuals introduced or poor adaptation to the ecosystem they enter. Some species, however, possess pre-adaptations that can make them especially successful in a new ecosystem. These exotic species often undergo dramatic population increases in their new habitat and reset the ecological conditions in the new environment, threatening the species that exist there. For this reason, exotic species are also called invasive species. Exotic species can threaten other species through competition for resources, predation, or disease. For example, the Eurasian star thistle, also called spotted knapweed, has invaded and rendered useless some of the open prairies of the western states. However, it is a great nectar-bearing flower for the production of honey and supports numerous pollinating insects, including migrating monarch butterflies in the north-central states such as Michigan.

Figure 3. The brown tree snake, Boiga irregularis , is an exotic species that has caused numerous extinctions on the island of Guam since its accidental introduction in 1950. (credit: NPS)

Lakes and islands are particularly vulnerable to extinction threats from introduced species. In Lake Victoria, as mentioned earlier, the intentional introduction of the Nile perch was largely responsible for the extinction of about 200 species of cichlids. The accidental introduction of the brown tree snake via aircraft (Figure 3) from the Solomon Islands to Guam in 1950 has led to the extinction of three species of birds and three to five species of reptiles endemic to the island. Several other species are still threatened.

The brown tree snake is adept at exploiting human transportation as a means to migrate; one was even found on an aircraft arriving in Corpus Christi, Texas. Constant vigilance on the part of airport, military, and commercial aircraft personnel is required to prevent the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not make up a large area of land on the globe, but they do contain a disproportionate number of endemic species because of their isolation from mainland ancestors.

Figure 4. This Limosa Harlequin Frog ( Atelopus limosus ), an endangered species from Panama, died from a fungal disease called chytridiomycosis. The red lesions are symptomatic of the disease. (credit: Brian Gratwicke)

It now appears that the global decline in amphibian species recognized in the 1990s is, in some part, caused by the fungus  Batrachochytrium dendrobatidis , which causes the disease  chytridiomycosis  (Figure 4). There is evidence that the fungus is native to Africa and may have been spread throughout the world by transport of a commonly used laboratory and pet species: the African clawed toad ( Xenopus laevis ). It may well be that biologists themselves are responsible for spreading this disease worldwide. The North American bullfrog,  Rana catesbeiana , which has also been widely introduced as a food animal but which easily escapes captivity, survives most infections of  Batrachochytrium dendrobatidis , and can act as a reservoir for the disease. It also is a voracious predator in freshwater lakes.

Early evidence suggests that another fungal pathogen,  Geomyces destructans , introduced from Europe is responsible for  white-nose syndrome , which infects cave-hibernating bats in eastern North America and has spread from a point of origin in western New York State (Figure 5). The disease has decimated bat populations and threatens extinction of species already listed as endangered: the Indiana bat,  Myotis sodalis , and potentially the Virginia big-eared bat,  Corynorhinus townsendii virginianus . How the fungus was introduced is unclear, but one logical presumption would be that recreational cavers unintentionally brought the fungus on clothes or equipment from Europe.

Figure 5. This little brown bat in Greeley Mine, Vermont, March 26, 2009, was found to have white-nose syndrome. (credit: Marvin Moriarty, USFWS)

In Summary: Threats to Biodiversity

The core threats to biodiversity are human population growth and unsustainable resource use. To date, the most significant causes of extinctions are habitat loss, introduction of exotic species, and overharvesting. Climate change is predicted to be a significant cause of extinctions in the coming century. Habitat loss occurs through deforestation, damming of rivers, and other activities. Overharvesting is a threat particularly to aquatic species, while the taking of bush meat in the humid tropics threatens many species in Asia, Africa, and the Americas. Exotic species have been the cause of a number of extinctions and are especially damaging to islands and lakes. Exotic species’ introductions are increasing because of the increased mobility of human populations and growing global trade and transportation. Climate change is forcing range changes that may lead to extinction. It is also affecting adaptations to the timing of resource availability that negatively affects species in seasonal environments. The impacts of climate change are greatest in the arctic. Global warming will also raise sea levels, eliminating some islands and reducing the area of all others.

• Biology 2e. Provided by : OpenStax. Located at : http://cnx.org/contents/[email protected] . License : CC BY: Attribution . License Terms : Access for free at https://openstax.org/books/biology-2e/pages/1-introduction

Threats to Biodiversity

The core threat to biodiversity on the planet, and therefore a threat to human welfare, is the combination of human population growth and resource exploitation. The human population requires resources to survive and grow, and those resources are being removed unsustainably from the environment. The three greatest proximate threats to biodiversity are habitat loss, overharvesting, and the introduction of exotic species. The first two of these are a direct result of human population growth and resource use. The third results from increased mobility and trade. A fourth major cause of extinction, anthropogenic climate change, is predicted to become significant during this century. Global climate change is also a consequence of the human population’s need for energy and the use of fossil fuels to meet those needs ( Figure 1 ). Environmental issues, such as toxic pollution, have specific targeted effects on species, but they are not generally seen as threats at the magnitude of the others.

Habitat Loss

Habitat loss is a major threat to biodiversity. Remove the entire habitat within the range of a species and, unless they are one of the few species that do well in human-built environments, the species will become extinct. Human destruction of habitats accelerated in the latter half of the twentieth century. Consider the exceptional biodiversity of Sumatra: it is home to one species of orangutan, a species of critically endangered elephant, and the Sumatran tiger, but half of Sumatra’s forest is now gone. The neighboring island of Borneo, home to the other species of orangutan, has lost a similar area of forest. Forest loss continues even in protected areas of Borneo. The orangutan in Borneo is listed as endangered by the International Union for Conservation of Nature (IUCN), but it is simply the most visible of thousands of species that will not survive the disappearance of the forests of Borneo. The forests are removed for timber and to plant palm oil plantations ( Figure 2 ). Palm oil is used in many products including food products, cosmetics, and biodiesel in Europe. A five-year estimate of global forest cover loss for the years 2000–2005 was 3.1 percent. In the humid tropics where forest loss is primarily from timber extraction, 272,000 km 2 was lost out of a global total of 11,564,000 km 2 (or 2.4 percent). In the tropics, these losses certainly also represent the extinction of species because of high levels of endemism.

Preventing Habitat Destruction with Wise Wood Choices

Most consumers do not imagine that the home improvement products they buy might be contributing to habitat loss and species extinctions. Yet the market for illegally harvested timber is huge, and the wood products often find themselves in building supply stores in the United States. One estimate is that 10 percent of the imported timber stream in the United States, which is the world’s largest consumer of wood products, is potentially illegally logged. In 2006, this amounted to $3.6 billion in wood products. Most of the illegal products are imported from countries that act as intermediaries and are not the originators of the wood.

How is it possible to determine if a wood product, such as flooring, was harvested sustainably or even legally? The Forest Stewardship Council (FSC) certifies sustainably harvested forest products, therefore, looking for their certification on flooring and other hardwood products is one way to ensure that the wood has not been taken illegally from a tropical forest. Certification applies to specific products, not to a producer; some producers’ products may not have certification while other products are certified. While there are other industry-backed certifications other than the FSC, these are unreliable due to lack of independence from the industry. Another approach is to buy domestic wood species. While it would be great if there was a list of legal versus illegal wood products, it is not that simple. Logging and forest management laws vary from country to country; what is illegal in one country may be legal in another. Where and how a product is harvested and whether the forest from which it comes is being maintained sustainably all factor into whether a wood product will be certified by the FSC. It is always a good idea to ask questions about where a wood product came from and how the supplier knows that it was harvested legally.

Habitat destruction can affect ecosystems other than forests. Rivers and streams are important ecosystems and are frequently modified through land development and from damming or water removal. Damming of rivers affects the water flow and access to all parts of a river. Differing flow regimes can reduce or eliminate populations that are adapted to these changes in flow patterns. For example, an estimated 91 percent of river lengths in the United States have been developed: they have modifications like dams, to create energy or store water; levees, to prevent flooding; or dredging or rerouting, to create land that is more suitable for human development. Many fish species in the United States, especially rare species or species with restricted distributions, have seen declines caused by river damming and habitat loss. Research has confirmed that species of amphibians that must carry out parts of their life cycles in both aquatic and terrestrial habitats have a greater chance of suffering population declines and extinction because of the increased likelihood that one of their habitats or access between them will be lost.

Overharvesting

Overharvesting is a serious threat to many species, but particularly to aquatic species. There are many examples of regulated commercial fisheries monitored by fisheries scientists that have nevertheless collapsed. The western Atlantic cod fishery is the most spectacular recent collapse. While it was a hugely productive fishery for 400 years, the introduction of modern factory trawlers in the 1980s and the pressure on the fishery led to it becoming unsustainable. The causes of fishery collapse are both economic and political in nature. Most fisheries are managed as a common (shared) resource even when the fishing territory lies within a country’s territorial waters. Common resources are subject to an economic pressure known as the tragedy of the commons in which essentially no fisher has a motivation to exercise restraint in harvesting a fishery when it is not owned by that fisher. The natural outcome of harvests of resources held in common is their overexploitation . While large fisheries are regulated to attempt to avoid this pressure, it still exists in the background. This overexploitation is exacerbated when access to the fishery is open and unregulated and when technology gives fishers the ability to overfish. In a few fisheries, the biological growth of the resource is less than the potential growth of the profits made from fishing if that time and money were invested elsewhere. In these cases—whales are an example—economic forces will always drive toward fishing the population to extinction.

For the most part, fishery extinction is not equivalent to biological extinction—the last fish of a species is rarely fished out of the ocean. At the same time, fishery extinction is still harmful to fish species and their ecosystems. There are some instances in which true extinction is a possibility. Whales have slow-growing populations and are at risk of complete extinction through hunting. There are some species of sharks with restricted distributions that are at risk of extinction. The groupers are another population of generally slow-growing fishes that, in the Caribbean, includes a number of species that are at risk of extinction from overfishing.

Coral reefs are extremely diverse marine ecosystems that face peril from several processes. Reefs are home to 1/3 of the world’s marine fish species—about 4,000 species—despite making up only 1 percent of marine habitat. Most home marine aquaria are stocked with wild-caught organisms, not cultured organisms. Although no species is known to have been driven extinct by the pet trade in marine species, there are studies showing that populations of some species have declined in response to harvesting, indicating that the harvest is not sustainable at those levels. There are concerns about the effect of the pet trade on some terrestrial species such as turtles, amphibians, birds, plants, and even the orangutan.

Bush meat is the generic term used for wild animals killed for food. Hunting is practiced throughout the world, but hunting practices, particularly in equatorial Africa and parts of Asia, are believed to threaten several species with extinction. Traditionally, bush meat in Africa was hunted to feed families directly; however, recent commercialization of the practice now has bush meat available in grocery stores, which has increased harvest rates to the level of unsustainability. Additionally, human population growth has increased the need for protein foods that are not being met from agriculture. Species threatened by the bush meat trade are mostly mammals including many primates living in the Congo basin.

Exotic Species

Exotic species are species that have been intentionally or unintentionally introduced by humans into an ecosystem in which they did not evolve. Such introductions likely occur frequently as natural phenomena. For example, Kudzu ( Pueraria lobata ), which is native to Japan, was introduced in the United States in 1876. It was later planted for soil conservation. Problematically, it grows too well in the southeastern United States—up to a foot a day. It is now a pest species and covers over 7 million acres in the southeastern United States. If an introduced species is able to survive in its new habitat, that introduction is now reflected in the observed range of the species. Human transportation of people and goods, including the intentional transport of organisms for trade, has dramatically increased the introduction of species into new ecosystems, sometimes at distances that are well beyond the capacity of the species to ever travel itself and outside the range of the species’ natural predators.

Most exotic species introductions probably fail because of the low number of individuals introduced or poor adaptation to the ecosystem they enter. Some species, however, possess preadaptations that can make them especially successful in a new ecosystem. These exotic species often undergo dramatic population increases in their new habitat and reset the ecological conditions in the new environment, threatening the species that exist there. For this reason, exotic species are also called invasive species. Exotic species can threaten other species through competition for resources, predation, or disease.

Lakes and islands are particularly vulnerable to extinction threats from introduced species. In Lake Victoria, the intentional introduction of the Nile perch was largely responsible for the extinction of about 200 species of cichlids. The accidental introduction of the brown tree snake via aircraft ( Figure 3 ) from the Solomon Islands to Guam in 1950 has led to the extinction of three species of birds and three to five species of reptiles endemic to the island. Several other species are still threatened. The brown tree snake is adept at exploiting human transportation as a means to migrate; one was even found on an aircraft arriving in Corpus Christi, Texas. Constant vigilance on the part of airport, military, and commercial aircraft personnel is required to prevent the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not make up a large area of land on the globe, but they do contain a disproportionate number of endemic species because of their isolation from mainland ancestors.

It now appears that the global decline in amphibian species recognized in the 1990s is, in some part, caused by the fungus Batrachochytrium dendrobatidis , which causes the disease chytridiomycosis ( Figure 4 ). There is evidence that the fungus is native to Africa and may have been spread throughout the world by transport of a commonly used laboratory and pet species: the African clawed toad ( Xenopus laevis ). It may well be that biologists themselves are responsible for spreading this disease worldwide. The North American bullfrog, Rana catesbeiana , which has also been widely introduced as a food animal but which easily escapes captivity, survives most infections of Batrachochytrium dendrobatidis and can act as a reservoir for the disease.

Early evidence suggests that another fungal pathogen, Geomyces destructans , introduced from Europe is responsible for white-nose syndrome , which infects cave-hibernating bats in eastern North America and has spread from a point of origin in western New York State ( Figure 5 ). The disease has decimated bat populations and threatens the extinction of species already listed as endangered: the Indiana bat, Myotis sodalis , and potentially the Virginia big-eared bat, Corynorhinus townsendii virginianus . How the fungus was introduced is unclear, but one logical presumption would be that recreational cavers unintentionally brought the fungus on clothes or equipment from Europe.

Climate Change

Climate change , and specifically the anthropogenic (meaning, caused by humans) warming trend presently underway, is recognized as a major extinction threat, particularly when combined with other threats such as habitat loss. Scientists disagree about the likely magnitude of the effects, with extinction rate estimates ranging from 15 percent to 40 percent of species committed to extinction by 2050. Scientists do agree, however, that climate change will alter regional climates, including rainfall and snowfall patterns, making habitats less hospitable to the species living in them. The warming trend will shift colder climates toward the north and south poles, forcing species to move with their adapted climate norms while facing habitat gaps along the way. The shifting ranges will impose new competitive regimes on species as they find themselves in contact with other species not present in their historic range. One such unexpected species contact is between polar bears and grizzly bears ( Figure 6 ). Previously, these two species had separate ranges. Now, their ranges are overlapping and there are documented cases of these two species mating and producing viable offspring. Changing climates also throw off species’ delicate timing adaptations to seasonal food resources and breeding times. Many contemporary mismatches to shifts in resource availability and timing have already been documented.

Range shifts are already being observed: for example, some European bird species ranges have moved 91 km northward. The same study suggested that the optimal shift based on warming trends was double that distance, suggesting that the populations are not moving quickly enough. Range shifts have also been observed in plants, butterflies, other insects, freshwater fishes, reptiles, and mammals.

Climate gradients will also move up mountains, eventually crowding species higher in altitude and eliminating the habitat for those species adapted to the highest elevations. Some climates will completely disappear. The rate of warming appears to be accelerated in the arctic, which is recognized as a serious threat to polar bear populations that require sea ice to hunt seals during the winter months: seals are the only source of protein available to polar bears. A trend to decreasing sea ice coverage has occurred since observations began in the mid-twentieth century. The rate of decline observed in recent years is far greater than previously predicted by climate models.

Finally, global warming will raise ocean levels due to melt water from glaciers and the greater volume of warmer water. Shorelines will be inundated, reducing island size, which will have an effect on some species, and a number of islands will disappear entirely. Additionally, the gradual melting and subsequent refreezing of the poles, glaciers, and higher elevation mountains—a cycle that has provided freshwater to environments for centuries—will also be jeopardized. This could result in an overabundance of salt water and a shortage of fresh water.

The core threats to biodiversity are human population growth and unsustainable resource use. To date, the most significant causes of extinctions are habitat loss, introduction of exotic species, and overharvesting. Climate change is predicted to be a significant cause of extinctions in the coming century. Habitat loss occurs through deforestation, damming of rivers, and other activities. Overharvesting is a threat particularly to aquatic species, while the taking of bush meat in the humid tropics threatens many species in Asia, Africa, and the Americas. Exotic species have been the cause of a number of extinctions and are especially damaging to islands and lakes. Exotic species’ introductions are increasing because of the increased mobility of human populations and growing global trade and transportation. Climate change is forcing range changes that may lead to extinction. It is also affecting adaptations to the timing of resource availability that negatively affects species in seasonal environments. The impacts of climate change are greatest in the arctic. Global warming will also raise sea levels, eliminating some islands and reducing the area of all others.

OpenStax , Biology. OpenStax CNX. June 26, 2020. https://cnx.org/contents/[email protected]:noBcfThl@7/Understanding-Evolution .

Principles of Biology Copyright © 2017 by Lisa Bartee, Walter Shriner, and Catherine Creech is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

Share This Book