what is the single greatest threat to biodiversity according to your textbook?

Chapter 21: Conservation and Biodiversity

Threats to Biodiversity

Learning Objectives

Past the terminate of this section, you will exist able to:

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

Figure 1:Atmospheric carbon dioxide levels fluctuate in a cyclical style. Notwithstanding, the burning of fossil fuels in recent history has caused a dramatic increment in the levels of carbon dioxide in the Earth's temper, which have now reached levels never earlier seen on Earth. Scientists predict that the improver of this "greenhouse gas" to the atmosphere is resulting in climate change that will significantly impact biodiversity in the coming century.

The core threat to biodiversity on the planet, and therefore a threat to human welfare, is the combination of human population growth and the resource used by that population. The human being population requires resources to survive and abound, 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 effect of human population growth and resources use. The third results from increased mobility and trade. A quaternary major cause of extinction, anthropogenic (homo-acquired) climate change, has not yet had a big 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 i]). Environmental issues, such as toxic pollution, have specific targeted furnishings on species, simply are not generally seen as threats at the magnitude of the others.

Habitat Loss

Figure 2: An oil palm plantation in Sabah province Borneo, Malaysia, replaces native forest habitat that a variety of species depended on to live. (credit: Lian Pivot Koh)

Humans rely on technology to change their environment and replace certain functions that were once performed by the natural ecosystem. Other species cannot practice this. Elimination of their habitat—whether it is a forest, coral reef, grassland, or flowing river—volition 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-congenital environments, the species will become extinct. Human destruction of habitats (habitats by and large refer to the function of the ecosystem required past a particular species) accelerated in the latter half of the twentieth century. Consider the infrequent biodiversity of Sumatra: information technology is dwelling house to ane species of orangutan, a species of critically endangered elephant, and the Sumatran tiger, but one-half of Sumatra'south wood is now gone. The neighboring isle of Kalimantan, 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 Kalimantan is listed every bit endangered by the International Marriage for Conservation of Nature (IUCN), only it is simply the well-nigh visible of thousands of species that will non survive the disappearance of the forests of Kalimantan. The forests are removed for timber and to constitute palm oil plantations ([Effigy 2]). Palm oil is used in many products including food products, cosmetics, and biodiesel in Europe. A 5-twelvemonth estimate of global forest comprehend loss for the years from 2000 to 2005 was 3.1 percent. Much loss (ii.four percent) occurred in the humid torrid zone where wood loss is primarily from timber extraction. These losses certainly as well correspond the extinction of species unique to those areas.

Preventing Habitat Destruction with Wise Forest Choices

Most consumers do non imagine that the dwelling house improvement products they purchase might exist contributing to habitat loss and species extinctions. Yet the market place for illegally harvested tropical timber is huge, and the wood products ofttimes find themselves in edifice supply stores in the United States. Ane approximate 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 $three.6 billion in wood products. Virtually of the illegal products are imported from countries that human activity as intermediaries and are not the originators of the wood.

How is it possible to determine if a woods product, such as flooring, was harvested sustainably or fifty-fifty 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 non been taken illegally from a tropical woods. Certification applies to specific products, not to a producer; some producers' products may not have certification while other products are certified. In that location are certifications other than the FSC, only these are run by timber companies creating a conflict of interest. Some other approach is to buy domestic wood species. While it would exist great if there was a list of legal versus illegal woods, it is not that simple. Logging and forest management laws vary from land to country; what is illegal in one land may be legal in another. Where and how a product is harvested and whether the forest from which information technology comes is being sustainably maintained all factor into whether a woods product volition exist certified by the FSC. It is e'er a skillful 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 catamenia government tin can reduce or eliminate populations that are adapted to seasonal changes in catamenia. For instance, 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 admission between them will be lost. This is of detail business concern because amphibians have been declining in numbers and going extinct more apace than many other groups for a diversity of possible reasons.

Overharvesting

Overharvesting is a serious threat to many species, simply peculiarly 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 nearly spectacular recent collapse. While information technology was a hugely productive fishery for 400 years, the introduction of modern factory trawlers in the 1980s and the force per unit area on the fishery led to it becoming unsustainable. The causes of fishery plummet are both economic and political in nature. Most fisheries are managed as a mutual resource, available to anyone willing to fish, even when the fishing territory lies within a country'south territorial waters. Mutual resource are subject field to an economic pressure known every bit the tragedy of the commons, in which fishers have little motivation to do restraint in harvesting a fishery when they do non own the fishery. The general outcome of harvests of resource held in common is their overexploitation. While large fisheries are regulated to endeavor to avoid this pressure, it withal exists in the background. This overexploitation is exacerbated when admission 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 instance—economic forces will drive toward fishing the population to extinction.

Explore a U.South. Fish & Wild fauna Service interactive map of critical habitat for endangered and threatened species in the United States. To brainstorm, select "Visit the online mapper."

For the most part, fishery extinction is non equivalent to biological extinction—the last fish of a species is rarely fished out of the bounding main. But at that place 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 run a 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 confront peril from several processes. Reefs are abode to 1/3 of the world's marine fish species—nearly 4000 species—despite making up simply one percent of marine habitat. Nigh dwelling house 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 merchandise, at that place 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 virtually the effect of the pet trade on some terrestrial species such as turtles, amphibians, birds, plants, and even the orangutans.

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

Bush meat is the generic term used for wild fauna killed for nutrient. Hunting is good 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; all the same, recent commercialization of the practice now has bush-league 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 non being met from agriculture. Species threatened by the bush-league meat trade are mostly mammals including many monkeys and the cracking apes living in the Congo bowl.

Exotic Species

Exotic species are species that take been intentionally or unintentionally introduced by humans into an ecosystem in which they did not evolve. Man transportation of people and goods, including the intentional send 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 depression number of individuals introduced or poor adaptation to the ecosystem they enter. Some species, notwithstanding, 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 atmospheric condition 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.

Effigy 3: The brownish 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, 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 serpent via shipping ([Effigy 3]) from the Solomon Islands to Guam in 1950 has led to the extinction of 3 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; ane was fifty-fifty found on an aircraft arriving in Corpus Christi, Texas. Constant vigilance on the part of airport, military machine, and commercial aircraft personnel is required to preclude the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not brand up a large area of land on the earth, but they practise contain a disproportionate number of owned species considering of their isolation from mainland ancestors.

Figure iv: 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)

Many introductions of aquatic species, both marine and freshwater, have occurred when ships have dumped ballast h2o taken on at a port of origin into waters at a destination port. H2o from the port of origin is pumped into tanks on a transport empty of cargo to increase stability. The water is drawn from the body of water or estuary of the port and typically contains living organisms such as establish parts, microorganisms, eggs, larvae, or aquatic animals. The water is then pumped out before the transport 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 anchor. The zebra mussels in the Groovy Lakes take cost the industry millions of dollars in clean upwardly costs to maintain water intakes and other facilities. The mussels have besides altered the ecology of the lakes dramatically. They threaten native mollusk populations, simply have also benefited some species, such equally smallmouth bass. The mussels are filter feeders and accept dramatically improved water clarity, which in plough 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 declension to Washington. The crabs accept been found to dramatically reduce the abundance of native clams and crabs with resulting increases in the prey of native crabs.

Invading exotic species tin likewise be disease organisms. It at present appears that the global pass up in amphibian species recognized in the 1990s is, in some office, caused by the mucus Batrachochytrium dendrobatidis, which causes the disease chytridiomycosis ([Figure 4]). There is show that the fungus is native to Africa and may accept been spread throughout the earth by send of a usually 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 equally a food fauna but which easily escapes captivity, survives well-nigh infections of B. dendrobatidis and tin human activity as a reservoir for the disease.

Effigy 5: This picayune brown bat in Greeley Mine, Vermont, March 26, 2009, was found to accept white-nose syndrome. (credit: modification of work by Marvin Moriarty, USFWS)

Early testify 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 Land ([Figure five]). The illness 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 ane logical presumption would be that recreational cavers unintentionally brought the mucus on wearing apparel 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 proceed due to past and standing emission of greenhouse gases, primarily carbon dioxide and methane, into the atmosphere caused past the burning of fossil fuels and deforestation. These gases decrease the caste to which World is able to radiate oestrus energy created by the sunlight that enters the temper. The changes in climate and energy residuum caused by increasing greenhouse gases are complex and our agreement of them depends on predictions generated from detailed computer models. Scientists generally hold the present warming tendency is caused by humans and some of the probable effects include dramatic and unsafe climate changes in the coming decades. Still, there is nonetheless debate and a lack of understanding about specific outcomes. Scientists disagree nearly the likely magnitude of the effects on extinction rates, with estimates ranging from 15 to 40 per centum of species committed to extinction past 2050. Scientists do agree that climate change will change regional climates, including rainfall and snowfall patterns, making habitats less hospitable to the species living in them. The warming tendency volition shift colder climates toward the due north and south poles, forcing species to motion with their adapted climate norms, merely also to face habitat gaps along the way. The shifting ranges will impose new competitive regimes on species equally they discover themselves in contact with other species not present in their historic range. Ane such unexpected species contact is between polar bears and grizzly bears. Previously, these 2 species had separate ranges. Now, their ranges are overlapping and there are documented cases of these two species mating and producing feasible offspring. Irresolute climates also throw off the delicate timing adaptations that species have to seasonal food resources and breeding times. Scientists have already documented many gimmicky mismatches to shifts in resource availability and timing.

Range shifts are already being observed: for instance, on boilerplate, European bird species ranges have moved 91 km (56.5 mi) northward. The same report suggested that the optimal shift based on warming trends was double that altitude, suggesting that the populations are not moving speedily 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 charge per unit of warming appears to be accelerated in the arctic, which is recognized as a serious threat to polar behave populations that require sea ice to hunt seals during the winter months: seals are the but source of protein available to polar bears. A tendency to decreasing body of water water ice coverage has occurred since observations began in the mid-twentieth century. The rate of decline observed in contempo years is far greater than previously predicted past climate models ([Figure half dozen]).

Effigy 6: The result of global warming can exist seen in the continuing retreat of Grinnell Glacier. The mean almanac temperature in Glacier National Park has increased 1.33°C since 1900. The loss of a glacier results in the loss of summer meltwaters, sharply reducing seasonal water supplies and severely affecting local ecosystems. (credit: USGS, GNP Archives)

Finally, global warming will enhance ocean levels due to meltwater from glaciers and the greater volume occupied past warmer water. Shorelines volition be inundated, reducing island size, which volition 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 college elevation mountains—a cycle that has provided freshwater to environments for centuries—volition exist altered. This could event in an overabundance of table salt water and a shortage of fresh h2o.

Section Summary

The core threats to biodiversity are human being population growth and unsustainable resource use. To date, the most significant causes of extinction are habitat loss, introduction of exotic species, and overharvesting. Climatic 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 boiling tropics threatens many species in Asia, Africa, and the Americas. Exotic species have been the cause of a number of extinctions and are peculiarly damaging to islands and lakes. Exotic species' introductions are increasing because of the increased mobility of homo 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 climatic change are currently greatest in the arctic. Global warming will too raise sea levels, eliminating some islands and reducing the expanse of all others.

Multiple Selection

Converting a prairie to a subcontract field is an example of ________.

1. overharvesting
2. habitat loss
3. exotic species
4. climate modify

[reveal-answer q="949084″]Testify Answer[/reveal-answer]
[subconscious-answer a="949084″]2[/hidden-answer]

Which 2 extinction risks may exist a direct result of the pet trade?

1. climate change and exotic species introduction
2. habitat loss and overharvesting
3. overharvesting and exotic species introduction
4. habitat loss and climatic change

[reveal-reply q="505566″]Show Answer[/reveal-answer]
[hidden-answer a="505566″]iii[/hidden-respond]

What kind of ecosystem are exotic species especially threatening to?

1. deserts
2. marine ecosystems
3. islands
4. tropical forests

[reveal-answer q="74675″]Show Respond[/reveal-reply]
[hidden-answer a="74675″]3[/subconscious-reply]

Complimentary Response

Describe the mechanisms by which human population growth and resource use causes increased extinction rates.

Human population growth leads to unsustainable resource employ, which causes habitat destruction to build new man settlements, create agricultural fields, and then on. Larger human populations take as well led to unsustainable fishing and hunting of wild animal populations. Excessive use of fossil fuels likewise leads to global warming.

Explain what extinction threats a frog living on a mountainside in Costa rica might face.

The frog is at gamble from global warming shifting its preferred habitat upward the mountain. In addition, it will be at risk from exotic species, either as a new predator or through the touch of transmitted diseases such equally chytridiomycosis. It is likewise possible that habitat destruction volition threaten the species.

Glossary

bush meat

a wild-caught beast used as food (typically mammals, birds, and reptiles); unremarkably referring to hunting in the tropics of sub-Saharan Africa, Asia, and the Americas

chytridiomycosis

a affliction of amphibians acquired by the fungus Batrachochytrium dendrobatidis; thought to be a major cause of the global amphibian decline

exotic species

(likewise, invasive species) a species that has been introduced to an ecosystem in which it did non evolve

tragedy of the commons

an economical principle that resources held in common will inevitably be over-exploited

white-nose syndrome

a affliction of cave-hibernating bats in the eastern United States and Canada associated with the fungus Geomyces destructans

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Source: https://opentextbc.ca/conceptsofbiologyopenstax/chapter/threats-to-biodiversity/

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