Rabbit Advocacy Animal Matters
Bagheera: In the Wild
VANISHING IN THE WILD
The current endangered species and extinction crisis is unique, in that the loss of biodiversity is occurring very rapidly, and the causes of the crisis are the activities of a single species: human beings. Some scientists believe the current crisis began when humans and their domestic animals first began to colonize the various parts of the globe.
Others believe it began around 1600, when human population growth exploded, and the level of per capita resource consumption began to rise dramatically in some parts of the world.
The Extinction Crisis
Note: Emphasized words can be found in the Glossary.
The human species, one of millions of life forms on this planet, is threatening the very existence of many other species. Biological diversity, or biodiversity, is the variety of life forms that interact tosupport and sustain the balance of nature.
As the human population grows, more and more of the Earth's living space, food, and other resources are consumed. Explosive human population growth and consumption are causing loss of biological diversity at an ever-increasing pace, an extinction crisis that threatens to surpass the mass extinctions that have occurred periodically during the Earth's history.
Never before have so many species been threatened with extinction in so short a period of time. In fact, some scientists estimate that species are disappearing at the rate of one every day, hundreds of times faster than the background rate of extinction. (See discussion of extinction rates in "IN THE WILD: Extinct".)
What else is different about this mass extinction, in addition to how fast it is happening? Scientists believe that other extinction events were caused by phenomena such as climate change and collisions of asteroids or meteors with the Earth. After these events, new species evolved that were adapted to the changed conditions. In contrast, modern extinctions are being caused by human use of the Earth's resources.
If humans continue to destroy, degrade, and fragment the habitat that for millions of years has supported other life forms, it will be difficult for new species to evolve. Only species that are adapted to human-altered landscapes will be able to survive or evolve.
Why It Matters
Should it matter to humans that other life forms are disappearing? Many people think so. Human populations depend on plants and animals for much of their food, medicines, clothing, and shelter.
Perhaps even more important, intact ecosystems perform many vital functions, like purifying the air, filtering harmful substances out of water, turning decayed matter into nutrients, preventing erosion and flooding, and moderating climate. It is not known how many species can be eliminated from an ecosystem without its functioning being impaired.
It is likely that an ecosystem with more species is more stable than one that has lost some species. For example, research has shown that grassland plots with a greater number of plant species are better able to withstand drought than those with less species diversity. This stability may well be important in the future, as changes in precipitation brought on by global warming stress ecosystems.
Some species are particularly important to the health of their ecosystems. These are called "keystone species", because like the center stone in an arch, their removal can greatly affect the entire system. A classic example of the consequences of removing a keystone species occurred when fur hunters eliminated sea otters from some Pacific kelp beds. Otters eat sea urchins, which eat kelp. With its major predator gone, urchin populations exploded and consumed most of the kelp. Fish and other animals associated with kelp beds disappeared.
In many cultures, humans value animals for reasons other than maintaining ecosystem health. Animals play a prominent role in the religions or belief systems of many cultures. Many people value other species for the enjoyment they give. Still others believe humans have a moral obligation to live in harmony with other life forms. Whatever their reasons, most people agree that it is important to try to prevent species extinction. Not all people agree on how to do this, however, or what to do when human needs conflict with needs of other species.
It is only recently that people have begun to be concerned about the decline of wildlife that has no commercial value to humans. Wildlife laws originally were passed to control exploitation of animals that people hunted. For example, international regulation of whaling started after hunting had depleted many whale populations.
Whalers were worried that soon no more whales would be left and their livelihood would disappear. In the United States, the first wildlife laws regulated hunting of game animals to preserve populations large enough for people to continue hunting.
Now, our concern has expanded to include animals that have little or no obvious economic value, like songbirds, as well as those we value for food or other uses.
Threatened and Endangered Species
Under the Endangered Species Act in the United States, a species or subspecies is regarded as "endangered" when it is in danger of extinction throughout all or a significant part of its normal range. A species is considered "threatened" when it is likely to become an endangered species in the foreseeable future.
A species does not have to be in danger of global extinction in order to be regarded as endangered. For example, many species that are endangered or threatened in the lower 48 states of the United States still thrive in Alaska, which is largely still wilderness. These include the grizzly bear, bald eagle, and gray wolf, among others.
It makes sense to protect a species before it has declined too far. When its populations have become small or isolated, it is harder and more expensive to help the species recover. In addition, many plants and animals play an important role in their ecosystems, such as that of a keystone species. It is important to conserve species in many parts of their range so ecosystems remain healthy.
The most common cause of endangerment is habitat loss. Plants and animals need space to live and energy provided by food, just as humans do.
As human population and consumption increase, wildlife habitat is converted to houses and highways. Forests are cut down for building materials, fuel, and paper. Prairies and forest land are turned into crop land and grazing land for our livestock, and shopping malls stand where wetlands once existed. The damming of rivers to create hydropower has flooded river valleys, making it hard for ocean-going fish to migrate.
Even if habitat is not completely destroyed, it can be fragmented or degraded so much that it can no longer support the species it once did.
Many species, particularly large mammals, need large areas of habitat to survive and reproduce. Patches of forest or grassland surrounded by farms or cities, or divided by roads, will not support these species. (For more discussion of the effects of fragmentation, see Island Biogeography).
A significant percentage of many habitats in North America that are important for wildlife have been destroyed or degraded since the time of European colonization. Over 50 percent of wetlands are gone, 90 percent of ancient forest in the Northwest has been logged, and millions of acres of grasslands have disappeared.
Humans also deplete wildlife populations by capturing or killing individuals for their own use. Animals are killed for food, fur, feathers, oil, medicines, crafts, and a host of other uses. They are also shot to stop them from killing livestock, or simply for sport.
Animal eggs are taken for food, and species are captured for pets or to use in medical experiments. Sophisticated technology allows ever-increasing numbers of animals to be captured *at once, depleting seemingly limitless species like ocean fish.
As the developing nations of the world accumulate more wealth, the demand for animal products grows. The international market for animals and animal parts is a huge and growing cause of wildlife endangerment.
Humans often move species around, introducing species that are not native to an ecosystem and disrupting the delicate balance that evolved among species in that ecosystem. Species can be moved both accidentally and intentionally. The introduced species may compete with native species for food or nest sites, or they may prey on native species.
As humans penetrate into more remote places, we allow other species to do the same by using the roads we build. In addition, we transport species by sea. Ships take on water in one location for ballast, travel across the ocean, and then dump the ballast water, carrying new aquatic life forms to habitats already occupied by other species.
We travel from island to island for trade or recreation, taking foreign species with us. Islands are particularly vulnerable because they are isolated and native species have nowhere to go when other species move in.
One of the ways habitat is degraded is by pollution. Creatures that depend on either freshwater or saltwater for all or part of their life cycles, like fish, frogs, marine mammals, and many invertebrates, are especially vulnerable to pollution.
Water is polluted by things like run-off of fertilizers and pesticides from farms, oil and other chemicals from roads, and human sewage that flows untreated into rivers, lakes, and oceans. In addition to polluting waterways, we divert fresh water from rivers and lakes for irrigation, drinking water, and industrial uses. There is less water left in the rivers and lakes to dilute the polluting chemicals.
Ships pollute saltwater by dumping waste. Oil spills, like the big spill from the oil tanker Exxon Valdez in Alaska in 1989, kill large numbers of animals. Many smaller spills and leaks go relatively undetected, but their cumulative effects over the years also can injure wildlife.
Water is not the only element that suffers from pollution. Factories and cars release chemicals into the air. The chemicals are deposited on land by rain, causing pollution, including what is known as acid rain. Acid rain weakens and kills plant life, decreasing the food supply for animals that eat the plants.
Pesticides are another source of pollution. Farmers use pesticides to keep insects from eating crops. Pesticides remain in crops and in wild plants eaten by herbivores (plant eaters). Insects also carry pesticides. Animals that eat herbivores (like predatory birds) and insects (like birds and amphibians) get high concentrations of these chemicals in their systems. The chemicals can disrupt physical functions like reproduction in these animals.
We know less about other factors that probably contribute to the decline of biological diversity. We know little about how changes in our atmosphere, such as global warming or ozone depletion, is affecting other life forms.
Disease and insect infestations, which are natural and nonthreatening phenomena in many ecosystems, can deal a death blow to populations weakened or depleted by other pressures.
We know very little about how all these factors interact to affect plant and animal populations. We do know, however, that these "natural" changes are becoming proportionately less significant as human impacts increase in magnitude, intensity, and duration
Conservation Biology: A Response to the Extinction Crisis
The new discipline of conservation biology has developed to respond to the increased threats to biological diversity. Its main goals are to determine human impacts on other species and to develop practical solutions to reduce the extinction rate.
Conservation biologists draw on knowledge from a broad range of fields. They apply the natural and social sciences, law, economics, ethics, resource management, veterinary medicine, and many other kinds of knowledge to individual conservation challenges.
Scientists, political leaders, resource managers, economists, lawyers, educators, anthropologists, engineers, and many others cooperate to solve these difficult problems. Solutions often require compromises between conservation and short-term human needs.
Conservation biology is called a "crisis discipline" because decisions must be made under severe time pressures, often with incomplete information. We can not afford to wait to take action until we have all the information we would like.
There are many ways conservation biologists are addressing the extinction crisis. These include:
Questions for Thought
1. Society does not have the resources to save every species from human-caused extinction. How should we decide where to put our energy and resources in conserving species? Should we concentrate on the species people like best, the "charismatic megafauna?" What other criteria might we use?
2. Should our primary aim be to preserve a maximum amount of biodiversity? Or, in light of what we know about ecosystem interactions, should we concentrate on ecosystems and try to maintain ecological processes?
3. In a few decades, your children or other young people may ask you what you did in the 1990's, when the full extent of the biodiversity crisis became known. What will your answer be?
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