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polar ice caps, microscopic organisms, soil erosion, tropical rain forests, microorganisms

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Biodiversity or Biological Diversity, sum of all the different species of animals, plants, fungi, and microbial organisms living on Earth and the variety of habitats in which they live. Scientists estimate that upwards of 10 million—and some suggest more than 100 million—different species inhabit the Earth. Each species is adapted to its unique niche in the environment, from the peaks of mountains to the depths of deep-sea hydrothermal vents, and from polar ice caps to tropical rain forests.

Biodiversity underlies everything from food production to medical research. Humans the world over use at least 40,000 species of plants and animals on a daily basis. Many people around the world still depend on wild species for some or all of their food, shelter, and clothing. All of our domesticated plants and animals came from wild-living ancestral species. Close to 40 percent of the pharmaceuticals used in the United States are either based on or synthesized from natural compounds found in plants, animals, or microorganisms.

The array of living organisms found in a particular environment together with the physical and environmental factors that affect them is called an ecosystem. Healthy ecosystems are vital to life: They regulate many of the chemical and climatic systems that make available clean air and water and plentiful oxygen. Forests, for example, regulate the amount of carbon dioxide in the air, produce oxygen as a byproduct of photosynthesis (the process by which plants convert energy from sunlight into carbohydrate energy), and control rainfall and soil erosion. Ecosystems, in turn, depend on the continued health and vitality of the individual organisms that compose them. Removing just one species from an ecosystem can prevent the ecosystem from operating optimally.

Perhaps the greatest value of biodiversity is yet unknown. Scientists have discovered and named only 1.75 million species—less than 20 percent of those estimated to exist. And of those identified, only a fraction have been examined for potential medicinal, agricultural, or industrial value. Much of the Earth’s great biodiversity is rapidly disappearing, even before we know what is missing. Most biologists agree that life on Earth is now faced with the most severe extinction episode since the event that drove the dinosaurs to extinction 65 million years ago. Species of plants, animals, fungi, and microscopic organisms such as bacteria are being lost at alarming rates—so many, in fact, that biologists estimate that three species go extinct every hour. Scientists around the world are cataloging and studying global biodiversity in hopes that they might better understand it, or at least slow the rate of loss.


Eldredge, Niles, A.B., Ph.D.

Curator, Department of Invertebrates, American Museum of Natural History. Author of ''Life in the Balance: Humanity and the Biodiversity Crisis'' and other books.

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