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44756_Ward's World+MGH Biodiversity

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1 Biodiversity Article by: Michelle A. Marvier, Department of Environmental Studies and Sciences, Santa Clara University, Santa Clara, California, and Donald W. Linzey, Wytheville Community College, Wytheville, Virginia. Access to this content is available to Ward's World readers for free from McGraw Hill's AccessScience, an award-winning, digital STEM resource that provides immediate, authoritative answers to students' thirst for scientific knowledge on topics such as climate change, virology, pollution, and more. Ward's World and McGraw Hill have partnered to offer educators a no-obligation, free trial subscription to this product. Request your free trial today and discover how valuable AccessScience can be for you and your students. The number of different plant and animal species living in a defined ecosystem or study area; a contrac- tion of biological diversity. Bio- diversity includes genetic diversity (variability in the genetic makeup among individuals in a single species), species diversity (the variety of species in different habitats on the Earth), and ecological diversity (the variety of biological communities that inter- act with one another and with their nonliving environments). Biodiversity can be expressed mathematically as an index that includes both the number of different species in a particular ecosys- tem (species richness) and the relative abundance of each species present (species equitability). In addition, biodiversity across the world can be af- fected detrimentally by human activity, especially by human-caused habitat loss and degradation. The biodiversity of these regions, known as biological hotspots (Fig. 1), is a great concern of conservationists. + ward ' s science Key Concepts • Biological diversity, or biodiversity, is a measurement of the number of different plant and animal species living in a particular ecosystem. • Biodiversity has many aspects, including genetic diversity, species diversity, and ecological diversity. • Mathematically, biodiversity is expressed as species richness and species equitability. • The greatest biodiversity occurs in warm, wet climates, such as tropical rainforests. • Human activities can cause rapid, dramatic decreases in biodiversity, leading to decreased ecosystem stability in biological hotspots, and a decline in genetic protection against natural extinctions. Fig. 1: Global biodiversity hotspots. There are more than 30 biodiversity hotspots located around the world. These areas have experienced severe habitat losses (at least 70%) as the result of human activities, hampering the work of conservationists in their attempts to preserve endemic species. (Credit: Conservation International Foundation) Global biodiversity Most estimates of the total number of global species range from 3 to 30 million, but some researchers indicate that this number may be greater than 100 million. Out of the total number, though, only about 1.75 million species have been scientifically described. The best-studied groups include plants and vertebrates (phylum Chordata), whereas poorly described groups include fungi, nematodes, and arthropods. Species that live in the ocean (Fig. 2) and in soils remain poorly known. Abiotic factors, such as

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