Conservation biology is concerned with the application of ecological and biological science to the conservation and protection of Earth's biodiversity . Conservation biology is a relatively recent field of scientific activity, having emerged during the past several decades in response to the accelerating biodiversity crisis. Conservation biology represents an integration of theory, basic and applied research, and broader educational goals. It includes much of ecology but extends it with social sciences, policy, and management.
The most important cause of the biodiversity crisis is the disturbance of natural habitats, particularly through the conversion of tropical forests into agricultural habitats. Biodiversity is also greatly threatened by the excessive hunting of certain species , by commercial forestry, by climate change, and by other stressors associated with human activities, such as air and water pollution . A central goal of conservation biology is to discover ways of avoiding or repairing the damages that human influences are causing to biodiversity. Important considerations include the development of science-based methods for conserving endangered populations of species on larger landscapes (or seascapes, in marine environments), and of designing systems of protected areas where natural ecosystems and indigenous species can be conserved.
Biodiversity and its importance
Biodiversity can be defined as the total richness of biological variation. The scope of biodiversity ranges from the genetic variation of individuals within and among populations of species, to the richness of species that co-occur in ecological communities. Some ecologists also consider biodiversity to include the spatial and temporal changes of communities on the greater landscape or seascape.
About 1.7 million of Earth's species have been identified and given a scientific name. However, biologists have not yet "discovered" most species, especially those living in tropical habitats. According to some estimates, Earth may support as many as 30–50 million species, of which 90% occur in tropical ecosystems, particularly in old-growth rainforests. Biologists believe that most of the unknown species are invertebrates, especially species of beetles and other insects. Compared with invertebrates, the numbers of species of plants and vertebrate animals are relatively well known.
Biodiversity is valuable for many reasons, but these can be grouped into the following three classes:
- Intrinsic value. Regardless of its worth in terms of the needs of humans, biodiversity has its own, intrinsic value .
- Utilitarian value. Humans have an undeniable need to harvest wild and domesticated species and their communities as sources of food, materials, and energy. Although harvests of biodiversity can be conducted in ways that foster renewal, these potentially renewable resources are often harvested or managed too intensively, resulting in degradation or extinction of the resource.
- Provision of ecological services. Biodiversity provides numerous ecological services that are directly and indirectly important to human welfare. These services include biological productivity, nutrient cycling, cleansing of water and air, control of erosion , provision of atmospheric oxygen and removal of carbon dioxide , and other functions related to the health and integrity of ecosystems. According to the American biologist Peter Raven: "Biodiversity keeps the planet habitable and ecosystems functional."
Threats to biological diversity
Biodiversity at local, regional, continental, and global scales is critically threatened by human activities. The damages that are being caused to Earth's species and ecosystems are so severe that they are referred to by ecologists as a biodiversity crisis. Many permanent losses of biodiversity have already been caused by human influences, including the extinctions of numerous species and the losses of distinctive, natural communities. Unless there are substantial changes in the ways that humans affect ecosystems, there will be enormously greater losses of biodiversity in the near future.
Earth's natural biodiversity has always been subjected to extinction (that is, the permanent loss of species and other groups) The fossil record shows that species, families, and even entire phyla have appeared and disappeared on Earth. For example, many invertebrate phyla proliferated during an evolutionary radiation at the beginning of the Cambrian era about 570 million years ago, but most of these are now extinct.
Many of the natural extinctions occurred simultaneously, apparently as a result of an unpredictable catastrophe. For instance, about 65 million years ago a mass extinction occurred that resulted in the loss of the last of the dinosaurs and as many as 76% of the then-existing species. That catastrophe is believed to have been caused by a meteorite impacting Earth. In other cases, natural extinctions have been caused by more gradual environmental changes, for example in climate or in the intensity of disease or predation.
More recently, however, humans have been responsible for almost all of the extinctions that are occurring. In fact, species are now being lost so quickly that the changes represent a modern mass extinction. Well-known examples of extinctions caused by humans include the dodo , passenger pigeon , and great auk. Numerous other species have been taken to the brink of extinction, including the plains bison , whooping crane , ivory-billed woodpecker , and right whale. These losses have been caused by over-hunting and the disturbance and conversion of natural habitats.
In addition to these famous cases involving large animals, an even more ruinous damage to Earth's biodiversity is being caused by extensive losses of tropical ecosystems, particularly the conversion of tropical rain forests into agricultural habitats. Because tropical ecosystems are particularly rich in numbers of species, loss of natural tropical habitat causes extinctions of numerous species. Many of those species occurred nowhere else but in particular tropical locales.
The mission of conservation biology is to understand the causes and consequences of the modern crisis of extinction and degradation of Earth's biodiversity, and then to apply scientific principles to preventing or repairing the damages. This is largely done by conserving populations and by protecting natural areas.
Conservation at the population level
In some cases, endangered species can be enhanced by special programs that increase their breeding success and enhance the survival of their populations. Usually, a variety of actions is undertaken, along with the preservation of appropriate habitat, under a scheme that is known as a population recovery plan. Components of a population recovery plan may include such actions as (1) the careful monitoring of wild populations and the threats that they face; (2) research into the specific habitat needs of the endangered species; (3) the establishment of a captive-breeding program and the release of surplus individuals into the wild; (4) research into genetic variation within the species; and (5) other studies of basic biology and ecology that are considered necessary for preservation of the species, particularly in its natural habitats. Unfortunately, population recovery plans have only been developed for a small fraction of endangered species, and most of these have been prepared for species that occur in relatively wealthy countries.
One example involves the whooping crane (Grus americana ), an endangered species in North America. Because of excessive hunting and critical habitat loss, this species declined in abundance to the point where as few as only 15 individuals were alive in 1941. Since then, however, the wild population of whooping cranes has been vigorously protected in the United States and Canada, and their critical breeding, migratory, and wintering habitats have been preserved. In addition, the basic biology and behaviour of whooping cranes have been studied, and some wild birds have been taken into captivity and used in breeding programs to increase the total population of the species. Some of the captive-bred animals have been released to the wild, and whooping crane eggs have also been introduced into the nests of the closely related sandhill crane (Grus canadensis ), which serve as foster parents. These applications of conservation biology have allowed the critically endangered population of whooping cranes to increase to more than 150 individuals in the mid-1980s, and to about 300 birds in 1997, of which about half were in captivity. Because of these actions, there is now guarded optimism for the survival of this endangered species.
Protected areas such as parks and ecological reserves are necessary for the conservation of biodiversity in wild, natural ecosystems. Most protected areas are established for the preservation of natural values, particularly the known habitats of endangered species, threatened ecological communities, or representative examples of widespread communities. However, many protected areas (particularly parks) are also used for human activities, as long as they do not severely threaten the ecological values that are being conserved. These uses can include ecotourism , and in some cases fishing, hunting, and even timber harvesting. In 1993 there were about 9,000 protected areas globally, with a total area of almost two million acres (792 million ha). Of this total, about 2,500 sites comprising 1.15 million acres (464 million ha) were fully protected, and could be considered to be ecological reserves.
Ideally, a national system of protected areas would provide for the longer-term conservation of all native species and their natural communities, including terrestrial, freshwater, and marine ecosystems. So far, however, no country has implemented a comprehensive system of ecological reserves to fully protect the natural biodiversity of the region. Moreover, many existing reserves are relatively small and are threatened by environmental changes and other disturbances, such as illegal hunting of animals and plants and sometimes intensive tourism.
Ecological knowledge has allowed conservation biologists to make important contributions to the optimized design of networks of protected areas. Important considerations include: (1) the need to protect areas that provide adequate representation of all types of natural ecosystems; (2) the need to preserve all endangered ecosystems and the habitats of threatened species; (3) the requirement of redundancy, so that if one example of an endangered ecosystem becomes lost through an unavoidable natural disturbance (such as a hurricane or wildfire ), the type will continue to survive in another protected area; (4) the need to decide whether or not the network of protected areas should be linked by corridors, a matter of some controversy among ecologists.
Conservation biology has also made important contributions towards the spatial design of individual protected areas. Important considerations include (1) the need to make protected areas as large as possible, which will help to allow species and ecosystems to better cope with disturbances and environmental changes; (2) a preference for smaller reserves to have a minimal amount of edge, which helps to avoid damages that can be caused by certain predators and invasive species; (3) the need to take an ecosystem approach which ensues that the reserve and its surrounding area will be managed in an integrated manner.
Although conservation biology is a relatively young field, important progress is being made towards development of the effective ecological and biological tools necessary to preserve biodiversity.
[Bill Freedman Ph.D. ]
Freedman, B. Environmental Ecology, 2nd edition. Academic Press, San Diego, 1995.
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Wilson, E.O. (ed.). Biodiversity. Washington, D.C: National Academy Press, 1988.
CONSERVATION BIOLOGY, an interdisciplinary, mission-oriented science with the goal of alleviating the extinction crisis and fostering biological diversity. Conservation biologists include researchers and managers from fields as varied as ecology, genetics, evolution, biogeography, wildlife biology, forestry, captive species breeding, and restoration ecology. Scientists hope that by studying why species become extinct, they can improve the management of natural areas and endangered species in ways that will prevent further extinctions.
The groundwork for the modern field of conservation biology was laid in the early 1900s with the development of the fields of fisheries, forestry, and wildlife management, along with the first modern formulation of a land ethic, generally credited to Aldo Leopold. Tremendous theoretical progress in community ecology and biogeography during the 1960s and 1970s established a scientific foundation for conservation. At the same time, growing evidence of the massive extinction of species was raising concern within the biological community. Experts estimated that as many as a quarter of all surviving species could be doomed to extinction by the year 2025 if current trends continued. As many as 20,000 species could be lost or doomed every year, most of them unknown to Western science, and virtually all of them victims of human activity.
According to Harvard professor E. O. Wilson, a leader in the field, the current rate of extinction (the number of species lost each year) is between 1,000 and 10,000 times greater than the estimated rate of extinction before the evolution of humans. A species may be vulnerable to extinction for many reasons. Small populations can be wiped out by random local events, social dysfunction, or genetic deterioration. Species that cannot disperse well or that reproduce slowly are in danger. Those exploited by humans are particularly vulnerable because harvesting may drive populations too low, either inadvertently or intentionally. Species dependent on a threatened habitat will suffer the fate of that habitat. Species with large home ranges, such as elk, caribou, bears, and wolves, are also vulnerable because it is difficult for conservationists to protect a land area large enough to support a viable population. (A viable population has a 95 percent probability or better of surviving for more than 100 years.)
From its inception, two core goals of conservation biology have been to preserve functioning samples of all global ecosystems in their natural range and to maintain viable populations of all native species within those ecosystems. Part of the challenge to conservation biologists has been to use scientific principles to select and manage wildlife reserves that meet these two goals. Historically, most parks and other protected areas were chosen for aesthetic or recreational value or because they appeared to have no desirable extractable resources. Conservation biologists now help to choose and redesign protected areas to foster biological diversity.
In practice, this has meant developing a few rules for designing refuges. First, large areas are preferable to small ones because larger areas are more likely to support species with extensive home ranges, and the larger area provides more of a buffer between the refuge and human activities on surrounding lands. Natural disturbances, such as fires and floods, are also less likely to cause extinctions when species can move away from the disturbance yet still remain on protected lands. This is particularly important because some ecosystems require periodic disturbances to maintain their integrity. Some tree species in Yellowstone National Park, for example, require fire to establish seedlings and regenerate the forest. Conversely, periodic fires help maintain midwestern prairie ecosystems where most tree species are not well-adapted to fire. Second, protected zones should have few roads, because they en-courage increased human activities, such as logging, trampling, hunting, and dumping, which may be detrimental to native flora and fauna, and because even the mere presence of roads themselves can affect the suitability of an ecosystem for certain species, especially certain birds. Third, protected zones should be close together and connected. Linkages increase the effective size of protected areas by permitting seasonal movements or migrations, dispersal to prevent inbreeding or to recolonize other sites, and long-distance range shifts in response to climate change.
Because of the sweeping ecological change that has already occurred, in addition to preventing further extinctions, many conservation biologists argue that attempts must be made to restore threatened and endangered ecosystems, populations, and species. Restoration ecology has been the subject of considerable controversy. Questions central to the debate include whether current levels of scientific knowledge and technology make restoration feasible, how scientists can measure the successes and failures of restoration projects, whether preservation is more cost-effective than restoration, and whether it is appropriate to remove preservationist constraints on one site, thus allowing rapid environmental change, on the promise that another site will be restored to a former habitat, a process often fraught with problems, delays, and unforeseen expenses.
While these issues remain unresolved, majority opinions within the world of conservation biology have emerged. First, preservation is generally more cost-effective than restoration. Second, because ecological change and damage are ongoing, restoration projects must be attempted despite failures. Third, it is unwise to allow the possibility of restoration to support the continued expansion of ecologically destructive practices. Fourth, measurement of restoration must include scrutiny of ecosystem function over the long term.
At the start of the twenty-first century, the Society for Conservation Biology (SCB), one of the most prominent organizations in the field of conservation biology, brought together a wide range of interested people, including resource managers, public and private conservation workers, and students and educators from around the world to study—and take action to solve—the problems associated with protecting biological diversity. Because the goals and purposes of conservation biology are political in addition to scientific, research in the field typically is linked to an explicit ecological agenda. Michael Soule, a cofounder of SCB, described conservation biology as a "crisis discipline," in which it is sometimes necessary to make tactical decisions without information. He proposes that in crisis disciplines "the risks of nonaction may be greater than the risks of inappropriate action."
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Susan J.Cooper/c. w.
Conservation biology is the study of the biological diversity—biodiversity for short—of Earth. Biodiversity is the variety of different living creatures, both plants and animals. Conservation biology is a relatively new field of study, having its start in the 1980s. It applies the principles of many sciences in order to preserve biodiversity throughout the world.
While at the end of the twentieth century the number of described species was about 1.7 million, estimates put the total number of species at 5 to 30 million. Many scientists believe that Earth is experiencing the greatest episode of mass extinction since the extinction of the dinosaurs 65 million years ago. Current rates of species extinctions throughout the world are believed to be 50 to 100 times greater than rates prior to human impact. In tropical forests, the extinction rates are believed to be 1,000 to 10,000 times higher than the expected rate. Given the current rates of extinction, by the year 2020, 30 to 70 percent of the world's species will be extinct. This crisis is thought to be due largely to human activities. Human population reached 6 billion in September 1999. Every day, this number increases by an estimated 250,000 (an extra 87 million people per year). This huge human population is straining Earth's natural resources in many ways.
The leading factor in the increasing rate of species extinctions has been the human destruction of natural areas where plants and animals live. Since 1950, one-third of the world's forests have been destroyed. Loss of tropical rain forest is estimated at an acre every second. It is estimated that humans consumed one-third of the world's natural resources during the period 1970 to 1995. It has also been estimated that the United States, with only about 5 percent of the world's population, consumes 25 percent of the world's resources and generates 25 to 30 percent of the world's waste.
Other human activities that are increasing species extinctions are the pollution of the environment and the overexploitation of animals, such as whales and tigers, that have commercial value.
There are many reasons to conserve and protect biodiversity. New species could provide new food sources for humans. Genes from wild plants are used to improve food crops. New plants and animals can be used as biological control agents to control pests. Nearly all the medicines used today were derived from plants or animals, and other species may provide important new medicines. Plants and animals carry out many functions in the environment that are critical to humans. For example, bees and bats pollinate flowering plants, and green plants provide oxygen.
There are other less practical reasons to preserve biodiversity. Plants and animals are beautiful and interesting. Humans gain much pleasure and peace of mind interacting with the natural world. In addition, there is the argument that all species have value regardless of their worth to humans.
Meffe, Gary K., C. Ronald Carroll, et al. Principles of Conservation Biology, 2nd ed. Sunderland, MA: Sinauer Associates, Inc., 1997.
Bryant, Peter J. Biodiversity and Conservation: A Hypertext Book. <http://darwin.bio.uci.edu/~sustain/bio65/lec01/b65lec01.htm>.