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Definition: biodiversity from The Penguin Dictionary of Science

The variety among living organisms from all sources, including terrestrial, marine and other aquatic ➤ecosystems of which they are part. The term includes diversity within species, between species and of ecosystems. Ultimately, all biodiversity is determined by ➤genes. Biodiversity is an important concept in planning for conservation of natural resources and was a central theme of the United Nations Conference on the Environment held in Rio de Janeiro in 1992.

Summary Article: Biodiversity from Encyclopedia of Environment and Society

BIODIVERSITY IS GENERALLY used to refer to all aspects of variability evident within the living world, including diversity within and between individuals, populations, species, communities, and ecosystems. Differences in pest resistance among rice varieties, the range of habitats within a forest ecosystem, or the global extinction of species of lake fish all illustrate different aspects of biological diversity. Biodiversity therefore embraces the whole of the incredible variety of life found on earth.

Globally, about 1.75 million species have been described and formally named, and it is believed that millions more species are yet to be discovered and described. In general, biodiversity is highest in and around the equator and continuously decreases toward the poles. The highest terrestrial biodiversity is found in tropical lowland rainforests. They cover only 6–7 percent of the earth’s total land area, but contain probably more than 50 percent of all species. Seasonal variation in climate and any environmental extreme are some other important factors causing a decrease in diversity of plants and animals.


Biodiversity is often described in hierarchical terms including genetic diversity, species diversity, and ecosystem diversity. Genetic diversity refers to the genetic differences between populations of a single species and between individuals within a single population; species diversity refers to the frequency and variety of species within a geographical area; and ecosystem diversity refers to the variety of habitats, the dynamic complexes of plant, animal, and microorganism communities and their nonliving environment, which interact as a functional unit and their change over time.

Varieties of rice, number of plants and animal species coexisting in a geographical area, and number of ecosystems in a forest area exemplify genetic, species, and ecosystem diversity, respectively.

Species diversity can be further distinguished into three types: alpha, beta, and gamma diversities. Alpha diversity refers the diversity at one site, i.e., the number of species coexisting within a single biological community. Beta diversity is species turnover across an environmental or geographical gradient, and gamma diversity refers to the total number of species in all habitats within a region. The “region” means a geographical area that includes no significant barriers to dispersal of organisms.

Some scientists have argued for the necessity of making distinctions between “functional” and “compositional” perspectives in approaching biodiversity, rather than using hierarchical terms. The functional approach is primarily concerned with ecosystem and evolutionary processes, while the compositional approach sees organisms as aggregated into populations, species, higher taxa, communities, and other categories.

Despite a wide range of definitions, biodiversity emerges as a concept linked primarily to the idea of biological variation that is largely unknown in its extent, and its future values.


Biodiversity is important for human beings in a number of ways. First, species have utilitarian (subsistence and commercial) value to humans. Diversity of biological organisms is a crucial component in the livelihood of many poor people, as they often depend on the diversified plants and animals to meet their nutritional, medicinal, and energy needs. Different cultures and societies use, value, and protect these resources and services in a variety of ways. Moreover, there are huge prospects of benefiting from unknown genetic and species diversity. Second, biodiversity represents the natural balance within an ecosystem. Detoxification and decomposition of wastes by biological communities (particularly bacteria and fungi); generation and renewal of soil fertility, including nutrient cycling; and pollination of plants are just a few examples of ecological services associated with biological diversity. As biodiversity is reduced, internal and natural controls must be replaced by more artificial controls (in the form of management and resources), which may not be successful to the same extent. Third, species have intrinsic value. Many argue that protecting them from the terrible finality of extinction by saving their habitats is an ethical responsibility.


Highly valuable biodiversity is being lost at a great rate, and extinction of species is the most serious aspect of this loss. It is estimated that every hour we are losing one species forever; this rate is about 10,000 times higher than the natural rate of extinction. One million species have been estimated to have been lost, and scientists working in this field generally agree that several more million will be lost in the first few decades of the 21st century, unless we have effective measures to control the current rate of species extinction.

Tropical lowland rainforests contain the highest terrestrial biodiversity, with more than 50 percent of all species.

The causes of species extinction can be natural as well as human activities. The causes in prehistoric times were mainly natural, whereas the extinctions in historic and present times are mainly humancaused. Our concern today is related to humancaused extinctions that result from human activities such as destruction, degradation, and fragmentation of natural habitats (e.g., agricultural clearance of forest land); exploitation of species for human use (such as commercial logging); introduction of invasive exotic species, such as certain species of fish; pollution (e.g., pesticides and industrial wastes, particularly sulfur and nitrogen oxides); international trade of wild animals and animal body parts; and increased spread of diseases. Climate change could become the main threat in the future.

These direct or proximate causes of biodiversity loss are considered to be the results of underlying causes, including rapid growth of human population, drive to globalization, and inequality of ownership and property rights. Globalization, for example, has increased reliance on a small number of crop species that can be traded in the global market; for example, demands in industrialized countries encouraged conversion of tropical rainforests into rubber or cocoa plantations, and mangroves into shrimp farms. Overconsumption by developed countries, which acts as a driving force to exploit resources from developing countries for a shortterm gain, exemplifies the inequality of ownership and property rights. Governmental and international support for industrial forestry, agriculture, and energy programs over and above traditional usage patterns, and state subsidies for the cattle industry (e.g., in the Amazon region) and agribusiness (e.g., to grow export crops in Brazil) are some other examples of underlying economic and political causes of the loss of biodiversity.

Concerns are also being expressed in some quarters that the introduction of intellectual property rights, under the aegis of World Trade Organization (WTO) in the biological resources—including agriculture—may lead to erosion of biological diversity in many bioresource zones. The underlying disparity between the private and social costs and benefits of biodiversity use and conservation can be considered as another main reason for the decline of biodiversity. Private costs and benefits refer to losses and gains as perceived by the immediate user, such as the farmer or the industrialist, while social costs and benefits refer to losses and gains that accrue to society (the local area, country, or world). These two interests often do not coincide.

The high rate of biodiversity loss has been a matter of great concern among conservation scientists, especially since the late 1980s. The concern has been increased by our incomplete knowledge of biodiversity: We don’t know the exact number of species on earth, nor do we fully understand the relationships that bind them. The loss of even one species can ruin an entire forest ecosystem of plants and animals because the animals that depended on this vanished species as prey have now lost their food source. In turn, the animals that it fed on have lost a predator, and these species often undergo population explosions that are devastating for the plants or animals that they feed on. The entire ecosystem can collapse in this manner, and will therefore be prevented from performing its usual “ecosystem services” (a utilitarian term for the natural processes that provide rich soil, clean water, and the air we breathe). The seriousness of the problem also lies in the fact that it takes millions of years for new species to evolve in the place of the species that have gone extinct.


The major issue for biodiversity is how its conservation may be integrated with other needs of society. This has become an important issue in the world especially after the Earth Summit held in Rio de Janeiro in 1992. In that summit, more than 150 states signed the Convention on Biological Diversity, acknowledging the sustainable management of the world’s biological resources to be one of the most urgent issues of the modern era, and expressed their commitment to address this collectively. Since then, around 180 countries have ratified the convention. The convention recognizes the need for a multisectoral approach to ensure that biological diversity is conserved and used sustainably, the importance of sharing information and critical technologies, and the benefits that can accrue from use of biological resources. The treaty is considered a landmark in the international community’s approach to environment and development. It has increased the coordination of cross-sectoral action within and between countries for biodiversity conservation, and has also led to the release of substantial international funds to support developing countries. Some international nongovernmental organizations, such as the World Conservation Union (IUCN) and World Wildlife Fund (WWF), are also actively involved in conservation of biodiversity on a global scale.

Investments in public education and awareness, increased stakeholder involvement in decision making, effective implementation of the national biodiversity strategies and action plans, improvement in sectoral and cross-sectoral integration, and strengthening protected area networks are some of the most important priority areas for further action by countries as identified by the Global Biodiversity Outlook 2002. Moreover, it is essential to take a holistic view of biodiversity and address the interactions that species have with each other and their nonliving environment to increase the efficiency of management interventions.

  • Biopiracy; Bioprospecting; Convention on Biodiversity; Cost-Benefit Analysis; Ecosystem; Endangered Species; Extinction of Species; Food Webs (or Food Chains); Genetic Diversity; Invasive Species; Property Rights; World Wildlife Fund.

  • P. L. Angermeier; J. R. Karr, “Biological Integrity vs. Biological Diversity as Policy Directives: Protecting Biotic Resources,” Bioscience (v.44, 1994).
  • James R. Miller, “Biodiversity Conservation and the Extinction of Experience,” TRENDS in Ecology and Evolution (v.20/8, 2005).
  • D. Pearce; Dominic Moran, The Economic Value of Biodiversity (Earthscan, 1995).
  • C. Perrings; D. W. Pearce, “Threshold Effects and Incentives for the Conservation of Biodiversity,” Environmental and Resources Economics (v.4, 1994).
  • Robert E. Ricklefs; Gary L. Miller, Ecology, 4th ed. (W.H. Freeman and Company, 1999).
  • Secretariat of the Convention on Biological Diversity, Global Biodiversity Outlook 2002.
  • Ambika P. Gautam
    Asian Institute of Technology, Thailand
    Copyright © 2007 by SAGE Publications, inc.

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