BFE - Biodiversity Loss, Conservation, Extinction (Lesson)

Biodiversity Loss, Conservation, Extinction

Biodiversity at all levels is being lost to human impact, most irretrievably in the extinction of species. Extinction occurs when the last member of a species dies and the species ceases to exist. The disappearance of a particular population from a given area, but not the entire species globally, is referred to as extirpation. The International Union for Conservation and Natural Resources (IUCN) maintains The Red List, an updated list of species facing high risks of extinction. The 2010 Red List reported that 21% of mammal species, 12% of bird species, and 30% of amphibian species are threatened with extinction. Among the 1,143 mammals facing extinction, the tiger is one of the most endangered large animals on the planet.

Overall, scientists have identified four primary causes of population decline and species extinction: habitat loss, invasive species, pollution, and overharvesting. Global climate change now is becoming the fifth.

Habitat Loss

Habitat alteration results from any human activity that changes an ecosystem. Deforestation, farming, mining, development, and dams are examples that affect habitats. Habitation alteration is the largest contributor to biodiversity loss and population decline. At one point, there were an estimated 16 million square kilometers of tropical rainforest. Today that number is only 9 million. Additionally, farming and logging have degraded at least 94% of temperate broadleaf forests. In the last 200 years, almost 50% of the natural wetlands in the U.S. have been destroyed. Destruction is not limited to land. Oceans are also experiencing habitat loss. At least one-fifth of coral reefs have been completely destroyed while another one-fifth are severely degraded due to overfishing.

Overharvesting

For most species, high intensity of hunting or harvesting by people will not in itself pose a threat of extinction, but for some, it can. The Siberian Tiger is one of the classic K-selected species impacted by the political freedom that came with the Soviet Union's breakup in 1980. Large in size, few in number, long-lived, and raising few young in its lifetime, this tiger species fell prey to the advent of Russian hunting. The sale of the parts from one tiger fetches at least $15,000 in today's black market- a powerful incentive for poachers in poor regions.

Recently, more attention has been given to overharvesting in the world's oceans. Populations of whales were decimated in the 17th and 18th centuries. More recently, scientists have expressed concern about the overharvesting of large fish such as sharks and tuna. Coral reefs are threatened by excessive tourism and the removal of species for home aquariums. According to a Food and Agriculture Organization (FAO) estimate, over 70% of the world's fish species are either fully exploited or depleted. The dramatic increase of destructive fishing techniques worldwide destroys marine mammals and entire ecosystems. FAO reports that illegal, unreported, and unregulated fishing worldwide appears to be increasing as fishermen seek to avoid stricter rules in many places in response to shrinking catches and declining fish stocks.

Governments have passed laws, signed treaties, and strengthened anti-poaching efforts. Click below to read about the CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) legislation. Scientific tests that use DNA from elephant ivory can determine the geographic location and whether its origin is a natural environment or black market.

Click here to access the CITES and Illegal Ivory site. Links to an external site.

Self-Assessment: Biologists Push to Save Sturgeon

Watch the short documentary using the link below and try the following flashcards to check your understanding.

Click here to watch "Biologists Push to Save Sturgeons." Links to an external site.

 

Pollution

Although pollution is a substantial threat, it tends to be less significant than the public actually believes. The damage to wildlife and ecosystems caused by pollution can be severe, but this tends to be surpassed by the harm caused by habitat alteration or invasive species.

Due to the sensitivity of many amphibian species, their decline and degradation is directly associated with water pollution and agricultural runoff (including fertilizers, pesticides, and sediments).

Investigate the factors listed below in the link to determine the variation and severity of pollution on aquatic and terrestrial amphibians.

 

Effects of Pollution on Amphibians

FACTOR	PROCESS(ES)
Habitat destruction, alteration, and fragmentation	Roads introduced species, or other factors separate remaining populations of amphibians from each other.
Introduced Species	Non-native species prey on or compete with native amphibians.
Over-Exploitation	Amphibians are removed from the wild and sold internationally as food, as pets, or for medicinal and biological supply markets.
Climate Change	Amphibians are extremely sensitive to small changes in temperature and moisture. Changes in global weather patterns (e.g. El Niño events or global warming) can alter breeding behavior, affect reproductive success, decrease immune functions and increase amphibian sensitivity to chemical contaminants.
UV-B Radiation	Levels of UV-B radiation in the atmosphere have risen significantly over the past few decades. Researchers have found that UV-B radiation can kill amphibians directly, cause sublethal effects such as slowed growth rates and immune dysfunction, and work synergistically with contaminants, pathogens, and climate change.
Chemical Contaminants	Chemical stressors (e.g., pesticides, heavy metals, acidification, and nitrogen-based fertilizers) can have lethal, sublethal, direct, or indirect effects on amphibians. These effects may include death, decreased growth rates, developmental and behavioral abnormalities, decreased reproductive success, weakened immune systems, and/or hermaphroditism.
Disease	New diseases (such as chytridiomycosis) or higher susceptibility to existing diseases lead to deaths of adults and larvae.
Deformities	There has been a recent and widespread increase of deformities (or malformations) in natural populations of amphibians; this is now perceived as a major environmental problem.
Synergisms	Multiple factors can act together to cause mortality or sub-lethal effects.

 

Invasive Species

When humans introduce non-invasive species to new environments, some may become invasive and might also push native species toward extinction. These species are so numerous and widespread that it is sometimes difficult to distinguish between a native and invasive species. The invasive species proliferate because there are no known predators to keep the population in check. Kudzu, photo to right, was introduced into the southeast for erosion control in the early 20th century. With the mild winters in the southeastern United States, the vine soon ran rampant and is widespread across the region. Due to the global economy and ease with which goods are transported throughout the world, invasive species are continually being introduced and will continue to be a problem.

 

Please listen to the short video below about the zebra mussels transported in the ballast water of ships.

Click here to watch "Invasive Species" Links to an external site.

 

RESOURCES IN THIS MODULE ARE OPEN EDUCATIONAL RESOURCES (OER) OR CREATED BY GAVS UNLESS OTHERWISE NOTED. SOME IMAGES USED UNDER SUBSCRIPTION.