Biodiversity

The study of biodiversity began in the later part of the twentieth century. The word was coined by Edward O. Wilson to explain the biological living resources and wealth lost when whole areas of tropical rainforest were destroyed by clear-cutting and burning. Many, if not all, of these tropical rainforests were in remote areas, often in developing countries, untouched by modern civilization, and relatively unstudied by scientists. As a result, many of the plants and animals, especially insects, were unknown to scientists. Many of the species lived nowhere else on earth and once destroyed, became extinct. Scientists realized that these tropical rainforests held a great wealth of species and that their destruction was removing large numbers, perhaps millions, of species, along with the DNA that made each species unique. Wilson referred to this loss of species as a loss of the forests’ biological diversity, or biodiversity. The loss is not merely of the species that become extinct but also of the combination of highly specific genetic material in each species.

Because the study of biodiversity involves the study of individual species, their loss, and their habitat, the subject is closely tied to endangered species, ecology, and conservation biology. Endangered species are those plants and animals that are nearly extinct; threatened species are not yet at the point of being endangered but will be if measures are not taken soon. Both plants and animals, including insects, worms, clams, crayfish, and other creatures, may be considered either threatened or endangered. Specific habitats, especially those that are unique and found in only one location on earth, can also be considered threatened. Protecting individual species often means protecting the habitat the species needs for survival.

During the nineteenth century and the first part of the twentieth, some animals were hunted to extinction. Several other species were hunted to near extinction or were extirpated (removed) from large areas, largely by extensive changes to their habitats. As a result of the losses and near losses, some scientists, resource managers, and political leaders instituted programs and activities to prevent extinction and to restore species that were near extinction. Animals (and later plants) that were near extinction were officially designated as endangered and given legal protection to prevent their extinction. Eventually, these efforts grew to encompass a much broader field of work by experts in many fields.

One of the more difficult aspects of protecting a single species is the importance of the habitat to the well-being of the species. This fact is one of the underlying principles driving the whole study of biodiversity. Scientists have learned that the habitat is critical for restoration of a species and that protecting the habitat is a powerful means of preventing species loss and protecting biodiversity. As a result, programs and individuals trying to protect or restore biodiversity or individual species have come into conflict with those who use or plan to use large areas of land and whole habitats for purposes such as housing or industrial development, harvesting, and aquaculture.

Threats to Biodiversity

Scientists generally believe that three major factors cause the loss of biodiversity: resource overharvesting, habitat loss, and introduction of exotic species. Overharvesting or excessive hunting and catching caused the loss of species such as the great auk, passenger pigeon, and Steller’s sea cow. Some species of whales nearly suffered the same fate. However, for most animals and plants, overharvesting is not a major cause of endangerment or extinction. Many animals that are commonly harvested have large and dispersed populations, so harvesting stops before it causes populations to decline to the point of endangerment and extinction. This does not mean that overharvesting is not a problem, but that it is seldom the sole cause of population declines and not the most frequent cause.

Several international controls have been implemented to prevent, limit, or discourage the killing of some of the animals that are threatened by overharvesting in many countries around the world. Many such controls ban the import or shipping of either live animals (tropical birds such as parrots) or parts of them (elephant ivory and rhinoceros horn). The animals endangered by overharvesting—the rhinoceros, elephant, and parrot—tend to be long-lived and restricted in distribution. Their reproductive rates are low, and populations often require a large habitat. The habitats of many of these animals are threatened by human activities, which makes the effect of their being slaughtered for commercial reasons much more pronounced. In 1997, one of the major international treaties governing commercial transactions in rare and endangered species was modified to permit some African nations to sell stocks of certain animal products that had been previously prohibited. Some experts worried that the change in the laws would again provoke illegal overharvesting.

Many animals are threatened in their native habitats by exotic species introduced into the area. These exotic species often cause biological pressures that the native species cannot handle. They may threaten native species directly by competing for food, living space, critical habitat (such as nesting space), or other necessary environmental resources. Some exotic animals are aggressive and drive away or attack the native ones. In the United States, sea lamprey were introduced into the Great Lakes and have driven populations of many native species to precipitously low levels or even extirpated them.

Exotic species may also present indirect threats by introducing diseases, parasites, or hitchhiker species that arrive with the exotic. In South Carolina and Texas, exotic shrimp are used in aquaculture, and they can carry a deadly virus that may threaten native shrimp if released into the wild by accident. Zebra mussels were carried into the Great Lakes water system in the ballast water of ocean tankers. With no natural controls, zebra mussels have multiplied to the point that they are not only a nuisance to human activities but also serious competition for native aquatic animals.

Habitat Loss and Degradation

The most significant threat to biodiversity, as occurs in tropical deforestation, is habitat loss or degradation, including poisoning. Habitat loss is the elimination of a habitat, often by cutting, plowing, filling, or other construction or harvesting methods. When all the trees in a forest area are felled for wood (a practice known as clear-cutting), the habitat is lost until the trees regrow, an event that may never take place. Degradation is the elimination or lessening of some characteristic of the habitat that is critical for one or more species. Changing the temperature or speed of the water flowing in a stream can render it no longer suitable for a particular fish or mussel. Filling or draining a wetland alters the moisture content of the soil and changes its suitability for plants or animals.

One of the earliest examples of habitat degradation was the poisoning of bald eagles and peregrine falcons in the United States by the pesticide dichloro-diphenyl-trichloroethane (DDT). DDT was widely used throughout the world (and still is in some countries), is highly persistent, and accumulates in animals at ever-increasing levels in a trophic system (a system in which one animal feeds on another that feeds on another, and so on). Falcons and eagles were some of the birds of prey that took in so much DDT that they were poisoned, and their eggs became too thin-shelled to survive. Their populations began to decline from reproductive failure. Many species of freshwater mussels are highly sensitive to chemicals and do not survive even low levels in the water. Many of the mussel species have become rare and endangered as a result of this poisoning, and they are not the only species to suffer from environmental poisons.

Altering stream and river flow via dams, diversions, withdrawals, and dredging is another form of habitat degradation that can dramatically change the way animals and plants use the aquatic system. In river systems throughout the Pacific Northwest, salmon return from the ocean to spawn (lay eggs and reproduce) in the river, where they grew from egg to fish before migrating to the open ocean. If a dam blocks the river or if the conditions in the river are no longer suitable, the salmon are not able to spawn. In salmon, the fish that spawn in each river are distinct and genetically identifiable, almost forming a subspecies. Therefore, authorities in the Pacific Northwest have had to determine the relationship between individual spawning groups and the watershed habitat before altering streams and rivers.

The cutting of mature forests in the Pacific Northwest and in Alaska eliminated the habitat for the spotted owl. Great controversy resulted from limits, restrictions, or bans on logging in these forests, which were prized for the high-quality lumber that could be made from the trees. These and similar conflicts formed the basis for many studies on scientific, legal, and policy matters concerning the Endangered Species Act in the United States.

Controversies have arisen over habitat protection programs and laws in the United States and other countries because of the restrictions and limitations imposed on development, logging, and other human activities. People on one side argue that the potential benefits from protecting a species are greater than any inconvenience or costs that might ensue, and those on the other side argue that the economic benefit from the activity that threatens the species outweighs any ecological concerns. Significant protests have taken place in some places, such as the large June 2024 march in London, in which thousands of people and 350 environmental groups came together to protest the lack of action by United Kingdom leaders to protect the loss of wildlife in that region. However, in some cases, companies and governments have worked hard to preserve species believed to be of economic value.

Biodiversity Research

Biodiversity is studied at the level of populations, of individuals (including molecular biology), and in the interactions between organisms and their environment. Research on biodiversity includes genetic, ecological, and behavioral studies and investigations focusing on diseases and life histories.

Much of the work on any specific species, especially large vertebrates, is conducted in the field, using techniques for observing, counting, tracking, and monitoring the population. Most invertebrates cannot be studied other than by observation and counting. One of the goals of ecological research on biodiversity is to understand the life histories and ecology of individual species. Scientists seek to explain life span, reproductive patterns and strategies, food preferences, environmental requirements, and limits. Other major goals are to describe the habitat requirements and better understand the relationship between the species and the habitat.

The management and legal aspects of various programs are included in biodiversity studies. This research is closely related to the field of conservation biology. Such study entails examining areas such as how programs work; what money is spent, by whom, how, and for what use; whether habitats or species are protected, restored, or lost; and the time required for various activities. These considerations are generally part of program evaluation, a topic that can be more thoroughly researched in the field of management science. The legal aspects of preserving biodiversity and protecting endangered species have been studied by a number of legal and policymaking organizations, including the Environmental Law Institute and Environmental Defense Fund, both of Washington, DC. The National Research Council, the operating arm of the National Academy of Sciences, has published several reports on the Endangered Species Act, and these usually address legal, policy, and science issues.

Modern molecular genetic techniques are applied to the study of individual species of plants and animals and their restoration. Tissue, often a blood sample, taken from a single individual, is analyzed to determine the genetic relations among members of a population. Scientists may then assess the potential of the remaining individuals to act as the beginning or nucleus for a new population. Modern techniques can determine the genetic makeup of animals and whether the individuals are distantly related enough to form a breeding pair without suffering the adverse consequences of inbreeding.

Artificial breeding and culture are techniques often employed with the few remaining members of a population. These animals may be brought in from the wild and confined, as were the last remaining California condors. The animals are kept in captivity so that artificial breeding and maintenance techniques can be used to raise additional members of the population. Once the population is large enough for release or other factors are favorable, reintroduction into the wild may be attempted.

Zoological parks and botanical gardens have been involved in maintaining the few remaining specimens of some species. With the help of such facilities, animal tissue has been stored in culture, and sperm have been frozen for later use in breeding. Zoos and gardens now play an active role in species propagation and husbandry through breeding, nourishment programs, studying and preventing disease, and behavioral training to reintroduce zoo animals into the wild.

Increasing Awareness of Biodiversity’s Importance

Human activities eliminated more than a few animals from the face of the earth before the second half of the twentieth century, when national and international laws were enacted to protect endangered species and the modern environmental movement began. Among the animals lost were the great auk in 1844, and the passenger pigeon in 1914. These animals were hunted to extinction under the mistaken belief that extinction could not happen, and because authorities lacked a way to limit the hunting of the animals. Despite international efforts to protect animals from extinction, in the latter part of the twentieth century, many countries allowed or encouraged the wholesale destruction of tropical rainforests, along with the animals that lived there.

In 1973, amid growing awareness of the need to prevent further extinctions, the Endangered Species Act was passed by the Congress of the United States. The act gave the US Fish and Wildlife Service the responsibility for enforcing the law and setting procedures for determining which species should be listed as endangered. The act also established the category of threatened species to protect those that were close to becoming endangered. Subsequently, this protection was extended to the habitats on which the animals depend.

Studies by academic and government scientists revealed that most species are threatened by habitat loss or degradation, overharvesting, or exotic species. Most of the problems arise from habitat loss or degradation rather than overharvesting, which had been the cause in several of the cases that prompted passage of the Endangered Species Act. Scientifically, and eventually legally, one of the most difficult tasks is to determine habitat requirements and then ensure that the required habitat is protected. Identifying and protecting habitats became an important part of all programs aimed at protecting biodiversity. Loss or degradation of habitat became one of the criteria that federal agencies used to take legal action or make official decisions.

Many human activities—logging, building, mining, and farming—can destroy or degrade valuable habitats on which endangered species depend. As a result, endangered species protection programs and activities have conflicted with some business interests seeking to carry out activities that threaten species or their habitats. According to the World Wildlife Fund's Living Planet Report 2022, conservation efforts launched in the 1970s have done little to slow the decline of biodiversity and mitigate human damage to the global ecosystem. The report found that, between 1970 and 2022, monitored wildlife populations declined by 69 percent. Freshwater species experienced the greatest loss, seeing an 83 percent decline in population. Marine and terrestrial species populations both declined by more than 35 percent. Species population and biodiversity decline were greatest in Latin America and the Caribbean—a region rich in rainforest ecosystems—where species populations declined by an average of around 94 percent.

Efforts, activities, and programs to protect biodiversity rely on the latest techniques and methods. These include electronic tracking of large animals, molecular analysis of genetic material, and cellular studies of tissues to help determine actual or potential threats to animals. Ecologists investigate life histories, including feeding habits, environmental requirements and limits, and migration patterns.

Principal Terms

Aquaculture: The artificial growth of animals or plants that live in the water; the culture of something living in water

Biodiversity: The number and kinds of animals and plants and the variations in genetic material they possess

Exotic Species: Organisms that are not naturally found in a place but have been artificially introduced, whether by accident or intentionally

Extinct: No longer found anywhere on earth

Extirpated: Not found in an immediate local area but found elsewhere on earth

Habitat: An assemblage of plants, animals, and the physical land, water, minerals, and other elements that support a life-form; usually refers to a single species

Invertebrate: An animal without a backbone; for example, worms, clams, crabs, insects, and jellyfish

Species: A group or groups of interbreeding natural populations of organisms that are reproductively isolated from other such groups

Subspecies: A group or groups of interbreeding organisms that are distinct and separated from similar related groups but not fully reproductively isolated

Threatened Species: Animals or plants so few in number that they may soon be endangered and then extinct

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