The loss of habitats, the contamination of water and food supplies, poaching, and indiscriminate hunting and fishing have depleted the population of many species. Most scientists agree that prospects for the survival of many species of wildlife, and hence biodiversity, are worsening. The expansion of human development into wildlife habitats has resulted in some animals being squeezed into cities and suburbs where encounters between humans and wildlife have become increasingly common.
Species loss and habitat loss are related. Scientists have recognized for some 150 years the connection between the size of an area and the number of species it contains—as large tracts of land are lost, so are some species that make their homes there. Other major causes of animal extinction are hunting and invasive (nonnative) species.
An invasive species is one that is not native to a particular ecosystem and whose presence there causes environmental or economic harm or harm to human health. This includes species purposely introduced (such as the plant saltcedar, which was brought to the United States to control erosion) and unintentionally introduced (such as zebra mussels, which are thought to have arrived in the ballast water of ships). Invasive species often have high reproductive rates and lack predators in their new environments. They can choke out or "out-compete" native species.
Many scientists consider invasive species to be one of the most serious issues threatening the environment. In response to this threat, the National Invasive Species Council was established by the U.S. government in 1997. The council includes members from a variety of agencies including the EPA, the USDA, and the U.S. Department of the Interior. In 2001 the council issued its management plan for dealing with the invasive species problem in Meeting the Invasive Species Challenge.
The report states that invasive plants infest approximately 100 million acres in the United States and cost around $137 billion annually for prevention and control. Zebra mussels, which are believed to have arrived in the ballast of ships in the Great Lakes, are one invasive species that has spread rapidly. By 1999 zebra mussel populations extended all the way to the Gulf Coast. The zebra mussel is considered so permanently entrenched that wholesale eradication would be virtually impossible. Instead, authorities are concentrating on limiting further spread of the pests, which clog water intake pipes.
In addition, authorities are increasingly concerned about the West Nile virus, an invasive pathogen that is thought to have originated in Africa. The virus was first detected in the United States in 1999 in New York. It infected animals and birds throughout the East and spread west quickly, carried by migratory birds. The virus can be transmitted to humans by mosquitoes that have bitten infected animals and birds. In 1999 there were 62 human cases reported to the Centers for Disease Control and Prevention (CDC), and 7 people died from the virus. The number of human cases and deaths grew steadily each following year. In 2003 there were 9,858 cases reported to the CDC and 262 deaths. Figure 9.8 shows the counties as of March 24, 2004 that have experienced positive test results for West Nile virus in humans.
Sharing the Planet
In the nineteenth century, miners took parakeets with them into the mines. If a bird died, they knew they were in danger from noxious gases. While more scientific and humane procedures now exist to determine how dangerous the situation is, some scientists believe that plants and animals may still serve as indicators of the safety of the world. When biologists discover toxic amounts of poisons in wildlife, they ask whether human beings are also ingesting these poisons.
Some observers believe that animals should be protected out of an intrinsic respect for life, aside from any market value or use to humans. Others contend that humankind must manage wildlife correctly because biodiversity makes good economic and survival sense. Still others believe that there is no species-loss "problem," that species loss is a natural part of evolution. All of these issues are being deliberated as the people of the world
Counties with cases of West Nile Virus in humans, as of March 24, 2004
struggle to decide how best to live with the other animals and plants that populate the Earth.
A 1996 study by the Nature Conservancy on more than 20,000 American plant and animal species found that about one-third of species were rare or imperiled, a larger fraction than some scientists had expected. The study, the most comprehensive assessment to date of the state of American plants and animal species, found that mammals and birds were doing relatively well compared to other groups, but that a high proportion of flowering plants and freshwater marine species, like mussels, crayfish, and fish, were in trouble. Of the 20,481 species examined, about two-thirds were secure, 1.3 percent were extinct or possibly extinct, 6.5 percent were critically imperiled, 8.9 percent were imperiled, and 15 percent were considered vulnerable. The destruction or degradation of habitat was considered to be the main threat.
City Life Collides with Wilderness
The growth of urban areas has resulted in a collision between city life and wildlife. Increasingly, humans are encountering wild animals in their communities. The 600,000-acre Angeles National Park in the Los Angeles out-back of the San Gabriel Mountains has been the site of numerous attacks on visitors by snakes and wild animals. In addition humans are using some areas designed for wildlife for undesirable purposes; poachers and some hunters shoot deer out of season and prey on the endangered Nelson bighorn sheep. During Christmas season trees are cut down. Crowds of picnickers and hikers often swell to music-festival size and clog roads. Toxic-waste outlaws heave garbage and poisons into creeks and abandoned mine shafts. Criminals sell drugs in the forest and even have small marijuana plantations located there. The Angeles National Park has also become a well-known dumping ground for homicide victims—eight bodies were found in the forest in 1995.
Some Cases of Threatened Species
Almost daily the decline or threat to some plant or animal is reported. Scientists attribute the decline of salmon on the West Coast to spoiled habitat and disruption of river flow. Erosion of the coastline in Florida has left no place for sea turtles to dig their nests, and they are dying off.
Peregrine falcons, one of the first species to be listed on the Endangered Species List, were dying because they were consuming DDT in the food chain. Following their listing under the ESA, and the banning of DDT in 1972, the falcon population has rebounded. In 1999 they were officially removed from the Endangered Species List.
The ivory tusks of African elephants are very valuable as they can be fashioned into jewelry and artwork. In the mid-twentieth century African elephants were so extensively hunted for their ivory that their population dropped to dangerous levels. The international community responded in 1990 by banning trade in African elephant ivory under the Convention on the International Trade in Endangered Species. Poaching of elephants continued but their population began to rebound. By 1999 there were so many elephants in Zimbabwe, Namibia, and Botswana that those countries (unsuccessfully) requested permission to resume limited trade in ivory.
Dolphins tend to swim with schools of tuna in the Pacific Ocean and nets used by commercial fisheries to catch tuna also entrap dolphins. Since netting began in 1958 an estimated seven million dolphins have been killed. In 1972 Congress passed the Marine Mammal Protection Act (PL 92-522) to reduce the deaths of the dolphins. The law was amended in 1985 and 1988 to regulate tuna imported from other countries. Trade groups have challenged these regulations by pointing to the economic losses of companies and nations that abide by the law. Some companies ignore the law, while other companies have printed a "Dolphin Safe" label on their tuna products to show that they obey the law.
Environmentalists have long argued with government and industry over the question of logging in the Pacific Northwest forests. Environmentalists claim that the biological health of the ecosystem is in decline and more than 100 species of plants and animals are threatened with extinction, while the timber industry responds that the forest provides jobs for thousands of Americans and lumber for millions of people.
The argument came to a head in 1990 when the spotted owl—which lived only in this particular region—was added to the list of endangered species. Logging was halted and a succession of lawsuits was filed against the Forest Service and the Department of the Interior. In 1992 President Bush grudgingly restricted logging in that area but, at the same time, moved to amend the law to allow economic considerations to be taken into account. In 1994 President Clinton worked out what was claimed to be a compromise between environmentalists and business interests, allowing logging to resume with restrictions on the size, number, and distribution of trees to be cut.
Scientists investigating a worldwide decline in frogs and other amphibians have found evidence identifying a number of factors that have contributed to the decline: ultraviolet radiation caused by the thinning of the ozone layer, chemical pollution, and a human taste for frog meat. These species are considered indicator species because their sensitivity makes them early indicators of environmental damage. Butterflies, another creature considered an indicator species, are also disappearing in many areas.
Roads and Wildlife
Almost four million miles of public roads cross the 48 contiguous states. As roadways reach further and further into undeveloped areas, encounters with wildlife are inevitable. In Critter Crossing: Linking Habitats and Reducing Roadkill (2000) the U.S. Department of Transportation reported that roads impact wildlife in several ways:
- Roadkill—Vehicles traveling U.S. roads kill millions of birds, mammals, reptiles, and amphibians every year. The ocelot, an already endangered cat, is in further jeopardy due to highway kills. In addition humans are sometimes killed or injured in animal-vehicle collisions. The insurance industry estimates the cost of these fatalities and injuries is about $200 million; motorists pay at least $2,000 in vehicle repair when they hit a large animal.
- Habitat loss—When humans build highways and develop areas, they destroy habitat. This forces animals into smaller and smaller areas and into areas inhabited by humans. Some species cannot migrate, and therefore die; others are forced to compete for fewer resources to live and breed.
- Habitat fragmentation—When roads cut through wild areas, they divide wildlife populations into smaller, more isolated, and less stable groups. These animals become more vulnerable to predators and are given to inbreeding with its resulting genetic defects.
Under the 1998 Transportation Equity Act for the Twenty-First Century (PL 105-178), the Federal Highway Administration can provide wildlife crossings—"habitat connectivity measures"—for new and existing roads. Among the strategies used to counteract habitat loss and roadkill are overpasses and underpasses, tunnels, and culverts.
Worldwide, after centuries of steady growth, the total catch of wild fish peaked in the early 1990s and has
declined ever since. In State of World Fisheries and Aquaculture, 2002, the FAO reported that approximately 47 percent of all commercial fish stocks have been fully exploited. A further 18 percent of stocks were reported to be overexploited.
A result of the declining catches of fish in shallow fisheries is the recent scouring of the deep seas for other varieties of fish such as the nine-inch-long royal red shrimp, rattails, skates, squid, red crabs, orange roughy, oreos, hoki, blue ling, southern blue whiting, and spiny dogfish. Although limited commercial fishing of the deep has been practiced for decades, new sciences and technologies are making it more practical and efficient. As stocks of better-known fish shrink and international quotas tighten, experts say the deep ocean waters will increasingly be targeted as a source of seafood. Scientists worry that the rush for deep-sea food will upset the ecology of the ocean.
A Blue Revolution?
The decline in the availability of fish has produced the growth of aquaculture, or farmed fish. Worldwide, one in every five fish eaten is raised on a farm, a share that is expected to rise in the years ahead. Aquaculture is one of the fastest growing sectors in world food production.
As a source of animal protein, farmed fish are an economical alternative to beef or pork and are on par with chicken. While 4 kilograms of grain are required to produce each kilogram of pork and 7 for each kilogram of beef, only 2 kilograms of grain are needed for a kilogram of chicken or fish. In addition only 40 percent of the weight of sheep is eaten and 50 percent of pigs and chicken, while 65 percent of finfish (as opposed to shellfish) is actually consumed. (Because fish are supported by water they have little bone structure; therefore, more of their weight is edible.) Fish are also low in fat and cholesterol, an advantage over other meats.
Contamination of Fish
Noncommercially caught fish and wildlife are sometimes contaminated with chemicals, such as mercury, polychlorinated biphenyls (PCBs), and DDT. In order to protect consumers from health risks associated with consuming such pollutants, the EPA and the states issue consumption advisories to inform the public that high concentrations of contaminants have been found in local specimens. In May 2003 the EPA published its annual publication Update: National Listing of Fish and Wildlife Advisories. During 2002 there were 2,800 fish consumption advisories in effect around the country. (See Figure 6.11 in Chapter 6.)