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III.1 Biodiversity: Concepts, Patterns, and Measurement Robert K. Colwell OUTLINE 1. What is biodiversity? 2. Relative abundance: Common species and rare ones 3. Measuring and estimating species richness 4. Species diversity indices 5. The spatial organization of biodiversity 6. Estimating b and g diversity from samples 7. Species–area relations Life on Earth is diverse at many levels, beginning with genes and extending to the wealth and complexity of species, life forms, and functional roles, organized in spatial patterns from biological communities to ecosystems, regions, and beyond. The study of biodiversity encompasses the discovery , description, and analysis of the elements that underlie these patterns as well as the patterns themselves. The challenge of quantifying patterns of diversity at the species level, even when the organisms are known to science , is complicated by the problem of detecting rare species and the underlying complexity of the environmental template. GLOSSARY a, b, and c diversity. The species diversity (or richness) of a local community or habitat (a), the difference in diversity associated with differences in habitat or spatial scale (b), and the total diversity of a region or other spatial unit (g) biodiversity. The variety of life, at all levels of organization , classified both by evolutionary (phylogenetic ) and ecological (functional) criteria diversity index. A mathematical expression that combines species richness and evenness as a measure of diversity evenness. A measure of the homogeneity of abundances in a sample or a community functional diversity. The variety and number of species that fulfill different functional roles in a community or ecosystem rarefaction curve. The statistical expectation of the number of species in a survey or collection as a function of the accumulated number of individuals or samples, based on resampling from an observed sample set relative abundance. The quantitative pattern of rarity and commonness among species in a sample or a community richness estimator. A statistical estimate of the true species richness of a community or larger sampling universe, including unobserved species, based on sample data species accumulation curve. The observed number of species in a survey or collection as a function of the accumulated number of individuals or samples species–area relation. The generally decelerating but ever-increasing number of species as sampling area increases species richness. The number of species in a community , in a landscape or marinescape, or in a region 1. WHAT IS BIODIVERSITY? Although E. O. Wilson first used the term biodiversity in the literature in 1988, the concept of biological diversity from which it arose had been developing since the nineteenth century and continues to be widely used. Biodiversity encompasses the variety of life, at all levels of organization, classified both by evolutionary (phylogenetic ) and ecological (functional) criteria. At the level of biological populations, genetic variation among individual organisms and among lineages contributes to biodiversity as both the signature of evolutionary and ecological history and the basis of future adaptive evolution. Species that lack substantial genetic variation are thought to be more vulnerable to extinction from natural or human-caused changes in their environment. It is at the species level that the term biodiversity is most often applied by ecologists and conservation biologists , although higher levels of classification (genera , families, orders) or patterns of evolutionary diversi fication are sometimes also considered, especially in paleontology. Species richness is the number of species of a particular taxon (e.g., birds or grasses) or life form (e.g., trees or plankton) that characterize a particular biological community, habitat, or ecosystem type. When data are not available at the community, habitat, or ecosystem level, political units (counties, states or provinces, countries) are often used as the basis of statements about species richness. Within biological communities and ecosystems, functional diversity refers to the variety and number of species that fulfill different functional roles. A food web and some measure of its complexity and connectivity is one way to depict the functional diversity of a community. Another is the classification and enumeration of species representing different functional groups, such as primary producers, herbivores, and carnivores. Within forest communities, for example, plant functional groups that are often distinguished include fast-growing pioneer species that quickly colonize disturbed habitats, slower-growing species that characterize mature forests, and plants that fill special functional roles, such as those that fix atmospheric nitrogen. A marine biologist working on soft-bottom communities might categorize benthic organisms by the physical effect they have on the substrate as well as by source of nutrients. In microbial...


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