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 — was 3. In the humid tropics where forest loss is primarily from timber extraction, , km 2 was lost out of a global total of 11,, km 2 or 2.
In the tropics, these losses certainly also represent the extinction of species because of high levels of endemism. Figure 2. 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.
Lian Pin Koh. 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.
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.
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 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 years, the introduction of modern factory trawlers in the s and the pressure on the fishery led to it becoming unsustainable. The causes of fishery collapse are both economic and political in nature.
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. Explore a U. 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. 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. One approach is environmental management, which is based largely on information gained from earth science, environmental science, and conservation biology.
A second approach is management of human consumption of resources, which is based largely on information gained from economics. A third, more recent, approach adds cultural and political concerns into the sustainability matrix. Loss of biodiversity stems largely from the habitat loss and fragmentation produced by human appropriation of land for development, forestry and agriculture as natural capital is progressively converted to human-made capital.
At the local human scale, sustainability benefits accrue from the creation of green cities and sustainable parks and gardens. Similarly, environmental problems associated with industrial agriculture and agribusiness are now being addressed through such movements as sustainable agriculture, organic farming, and more-sustainable business practices. Overharvesting threatens biodiversity by degrading ecosystems and eliminating species of plants, animals, and other organisms.
Overharvesting, also called overexploitation, refers to harvesting a renewable resource to the point of diminishing returns. Ecologists use the term to describe populations that are harvested at a rate that is unsustainable, given their natural rates of mortality and capacities for reproduction. The term applies to natural resources such as wild medicinal plants, grazing pastures, game animals, fish stocks, forests, and water aquifers.
Sustained overharvesting can lead to the destruction of the resource, and is one of the five main activities — along with pollution, introduced species, habitat fragmentation, and habitat destruction — that threaten global biodiversity today. All living organisms require resources to survive. Overharvesting these resources for extended periods of time can deplete natural resources to the point where they are unable to recover within a short time frame. Humans have always harvested food and other resources they have needed to survive; however, human populations, historically, were small and methods of collection limited to small quantities.
Exponential increase in human population, expanding markets, and increasing demand, combined with improved access and techniques for capture, are causing the exploitation of many species beyond sustainable levels.
As mentioned above, sustained overharvesting is one of the primary threats to biodiversity. Overharvesting can lead to resource destruction, including extinction at the population level and even extinction of whole species. Depleting the numbers or amount of certain resources can also change their quality; for example, the overharvesting of footstool palm a wild palm tree found in Southeast Asia, the leaves of which are used for thatching and food wrapping has resulted in its leaf size becoming smaller.
Overharvesting not only threatens the resource being harvested, but can directly impact humans as well — for example by decreasing the biodiversity necessary for medicinal resources.
A significant proportion of drugs and medicines are natural products which are derived, directly or indirectly, from biological sources. However, unregulated and inappropriate harvesting could potentially lead to overexploitation, ecosystem degradation, and loss of biodiversity; further, it can negatively impact the rights of the communities and states from which the resources are taken.
Overharvesting is a serious threat to many species, especially aquatic ones. The natural outcome of harvesting common resources is their overexploitation. 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 for example, whales economic forces will always drive toward fishing the population to extinction. Cod trawler and net : Overharvesting fisheries is an especially salient problem because of a situation termed the tragedy of the commons.
In this situation, fishers have no real incentive to practice restraint when harvesting fish because they do not own the fisheries. Overexploitation of species can also result in cascade effects, particularly if a habitat loses its apex predator. Because of the loss of the top predator, a dramatic increase in their prey species can occur.
In turn, the unchecked prey can then overexploit their own food resources until population numbers dwindle, possibly to the point of extinction. Exotic species introduced into foreign ecosystems can threaten native species through competition for resources, predation, and disease. Exotic species are those that have been intentionally or unintentionally introduced by humans into an ecosystem in which they did not evolve.
Such introductions probably occur frequently as natural phenomena. For example, Kudzu Pueraria lobata , which is native to Japan, was introduced in the United States in It was later planted for soil conservation.
Problematically, it grows too well in the southeastern United States: up to one foot each day. It is now a pest species, covering over seven 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. Exotic threats : 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 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, resetting the ecological conditions in the new environment, while threatening the species that exist there. For this reason, exotic species, also called invasive species, can threaten other species through competition for resources, predation, or disease.
Invasive species can change the functions of ecosystems. For example, invasive plants can alter the fire regimen, nutrient cycling, and hydrology in native ecosystems. Invasive species that are closely related to rare native species have the potential to hybridize with the native species. Harmful effects of hybridization have led to a decline and even extinction of native species. For example, hybridization with introduced cordgrass, Spartina alterniflora , threatens the existence of California cordgrass in San Francisco Bay.
Invasive species cause competition for native species. Four hundred of the endangered species under the Endangered Species Act are at risk due to this competition. Global decline in amphibian species : This Limosa Harlequin Frog Atelopus limosus , an endangered species from Panama, died from a fungal disease called chytridiomycosis.
In addition, chemical pollutants such as pesticides and herbicides leach into soils and watersheds. Some fish species, such as salmonids , require small freshwater streams to spawn.
Polluted streams result in the abandonment of traditional spawning areas and ultimately in the loss of salmon populations. However, many species are vulnerable to the indirect effects of pollution through the concentration of toxic chemicals in top predators of food chains and disruption of predator-prey interactions.
With the increase in temperature expected from increasing greenhouse gases, there will be higher levels of air pollution, greater variability in weather patterns, and changes in the distribution of vegetation in the landscape. Some species will not be able to adapt to these changes in the environment and will become extinct.
However, it is expected that many plant and animal species will attempt to disperse to higher latitudes and altitudes as the temperature increases. Therefore, any barriers in the landscape, such as highways and urban areas that prevent movement to more hospitable environments, will result in loss of biodiversity.
Such threats to biodiversity may cause the extinction of many species. Maintaining the connectivity of the landscape could offset their impacts on biodiversity. The corridor concept proposes that refuges connected by corridors will have higher immigration rates than isolated patches of natural habitat. This can offset extinction by promoting gene flow and preventing inbreeding. Corridors composed of naturally occurring or restored strips of land that connect large habitat patches may facilitate the movement of species between patches, and decrease the effects of threats to biodiversity.
Habitat patches connected by corridors must always be large enough to maintain populations of species, especially for large-bodied vertebrates. The effectiveness of wildlife corridors depends on many corridor design parameters, which include habitat type and structural stage, length and width, and level of human activity in and around the corridor.
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