Habitat Loss and Species Extinction

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Habitat Loss and Species Extinction

Habitat (natural environment) loss is the number one threat to the survival of many animal species (organisms that share a unique set of characteristics), and water is part of any habitat. Coastal marshes and wetlands in the United States and elsewhere are shrinking every year. Wetlands are areas of land where water covers the surface for at least part of the year and controls the development of soil; marshes are wetlands dominated by grass-like plants. Wetlands in particular support a great variety of bird, fish, and other animal life, and can be used by migrating (periodic traveling) birds as a stop-off point on their long journeys. Without the wetlands, the number of species that can live on the land declines. Habitat loss is primarily caused by human activities, such as logging, development, fishing, and recreation.

Edward Wilson (1929–), a renowned entomologist (scientist who studies insects) has written that the current rate at which life is becoming extinct has not been seen since the time of the dinosaurs 65 million years ago. Wilson estimates that the current rate of extinction (the rate at which every member of a species dies) is 100,000 times faster that what is considered the natural rate and that, in the next 25 years, one of every five species of insect, bird, and animal could die out. Along with the loss of diversity, the possible extinction of even one insect has great importance. Insects, for example, are near the bottom of a natural system of life in which creatures of prey are eaten by predator creatures, called the food web, or the food chain. If the bottom of the food chain is disturbed, it could impact animals along the rest of the chain, including humans.

Development and overuse

Coastal marshes and wetlands in the United States and elsewhere are shrinking in areas where development occurs. The desire for oceanfront property is so great that coastal beaches and the wetland areas where rivers flow into the ocean are often paved over.

Other human activities in coastal areas alter the habitat of the creatures that live near the ocean. Many species of crustaceans, especially ghost crabs, live in the dunes and provide food for birds such as sea gulls and other terns. When plants that naturally grow and strengthen sand dunes are destroyed, the sand is more easily blown away by wind or washed away by waves. Overuse of a beach by people can remove vegetation when beachgoers climb sand dunes. On some beaches, a popular pastime is to drive dune buggies and all-terrain vehicles over the dunes, both of which destroy dune vegetation and eventually, the dune itself.

Fishing and habitat loss

Habitat destruction can also occur underwater. Fishing with dragnets, for example, destroyed underwater habitats in the 1970s. This method involved dragging a huge net along the bottom of the ocean. The front of the net often had a heavy bar attached to it to keep the net open and to deliberately clear out any obstacles that might snag the net, including beneficial plants and coral. The scrapping of the ocean floor completely destroyed habitats of some lobsters, crabs, and fish off the eastern coast of Canada.

In many areas of the United States, the Canadian mid-west, and other countries the small family farm has been largely replaced by farms that are owned and run by large companies. Corporate-owned farms are often thousands of acres (square meters) in size. The plowing under of wetlands to create more land for farming and farming practices such as the use of pesticides has disturbed water habitats. Erosion (wearing away) and the run-off of chemicals from the fields have contaminated both surface and ground waters.

Growth of cities

Most of the world's cities are growing in size and population. Often the most rapid growth takes place on the edges of cities where many people live. Roads and other transportation routes are continually being built to bring suburban commuters closer to the working center of the city. This new development turns fields, forests, and wetlands into more expanses of pavement. In some cities earth and rock is dumped into the water to create new land for housing.

All this change can be bad news for a habitat. In California in the 1990s, growth of cities reduced the amount of a plant called the coastal sage shrub by over 90%. One of the creatures that lives in the coastal sage shrub is the California gnatcatcher, an insect that is now threatened with extinction.

Logging and mining

Logging, or removing trees for wood, can be accomplished in a way that does not harm a habitat. Removing only selected tress and hauling the tress out by horse or small tractor can actually help create more sunlight in a forest, and so encourage growth of new trees. However this does not supply enough trees for the needs of large lumber companies. Instead, often all the trees in an area of a forest are removed and hauled away. This is called clearcutting and it can devastate entire habitats. With no roots left to hold the soil erosion can quickly occur, clogging streams with soil. The biggest threat to the survival of the grizzly bear in Alaska is logging and the building of roads for logging trucks.

Mining, especially where huge pits are dug in the ground, can also destroy natural habitats. The water that runs off from a mine site can contain harmful metals that cause illness if present in the body even in small amounts (heavy metals) and can be so full of acid that it can burn skin and pollute nearby waters. A gold mine located in northern Idaho, for example, is leaking low levels of a toxic (poisonous) chemical called cyanide into a part of the South Fork Salmon River for years. This has contaminated an area of the river where chinook salmon breed, and has threatened the entire salmon population in the South Fork Salmon River.

Kesterson National Wildlife Refuge and Selenium

The Kesterson National Wildlife Refuge is a system of wetlands, grassy regions and surface water pools that cover almost 11,000 acres (4,452 hectares) in the San Joaquin Valley of central California. The refuge was created in 1969 to provide an area where waters draining from surrounding higher land could gather and be protected. The area was also an important stop on the north-south migration route of some birds.

In the 1970s the agriculture nearby began to affect the water draining into the refuge. The agricultural operations removed large amounts of underground freshwater and the water draining into the refuge consisted of more runoff water from the crop fields. By 1981 almost all the water entering the refuge was the leftover agricultural water. This water contained high amounts of an element called selenium. Selenium naturally exists in some soils. As surface water in the refuge evaporated, the selenium that was left behind accumulated to levels that were poisonous. Before scientists learned of the problem and diverted the water away from the refuge, many birds that nested in the refuge died or hatched with physical defects.

The poisoning that occurred at the Kesterson refuge alerted scientists to the fact that along with pesticides and other chemicals in agricultural runoff, naturally occurring compounds could also pose a problem to habitats if the water flow in an area changed.

Changing waterways

Building dams, constructing channels, and changing the direction of a river or stream (diversion) for flood control will all change water habitats, forcing animals to adapt to the changed habitat or find a new home. In the Pacific Northwest, the building of dams on the Columbia River has reduced the number of chinook, coho, chum, sockeye, and pink salmon populations. Two large river fish that were used by Native Americans for food and fertilizer, the bonytail and the razorback sucker, have suffered from changes to the Colorado River imposed by dams and diversion. The bonytail is nearly extinct and the razorback sucker is threatened. In California the use of water for agriculture has caused a toxic compound called selenium to build up in the soil. Runoff (water that flows over ground surface to bodies of water) of selenium into the Kesterson National Wildlife Refuge has caused the deaths of large numbers of birds.

Preventing species loss

Some local governments are working to plan development along coastlines in order to preserve wetland, marsh, beach, and dune habitats. The U.S. Environmental Protection Agency monitors water quality in threatened habitats, and private organizations such as the Nature Conservancy create refuges by buying both wetland habitats and saltwater marshes for conserving as natural areas. So far, several sea turtle species have benefited from these efforts, as well as the dwarf seahorse and the Florida manatee.

Brian Hoyle, Ph.D.

For More Information


Davidson, Olsha Gray. The Enchanted Braid: Coming to Terms with Nature on the Coral Reef. New York: Wiley, 1998.

Kerley, Barbara. A Cool Drink of Water. Washington, DC: National Geographic Society, 2002.

Locker, Thomas. Water Dance. New York: Voyager Books, 2002.


"How You Can Help." National Save the Sea Turtle Foundation.http://www.savetheseaturtle.org/HowYouCanHelp.htm (accessed on September 1, 2004).

"The State of Disappearing Species and Habitat: A Sierra Club Report." Sierra Club.http://www.sierraclub.org/wildlife/species/habitat_report/intro.asp (accessed on September 1, 2004)