The Levels of Organization for Biological Diversity

Genetic Diversity: The different forms of a single gene found in an individual and the variation of genes and chromosomes between individuals

Organismal Diversity: Variation in the anatomical, physiological, and behavioral characteristics of individual organisms Population Diversity: Variation in the quantitative and spatial characteristics of populations, such as the numbers of individuals present and the geographic range of the population

Species Diversity: Variation in the number and phylogenetic diversity (or evolutionary relatedness) of species present in an area

Community Diversity: Variation in the ecological interactions between organisms, populations, and species that share an environment and the different types of communities that are formed Ecosystem Diversity: Variation in the interdependence of biotic communities and the abiotic (nonliving) aspects of the environments in which the biotic communities are found

Landscape and Seascape Diversity: Variation between landscapes and seascapes, based on the different types of ecosystems they compose Biogeographic Diversity: Variation of the evolutionary history of the biota of a region (and hence the current species diversity) is related to the geological and geographic history of that region or landscape entific and lay literature (see Gaston, 1996, Table 1.1). For the purposes of this essay, biodiversity is defined as the variety of life on earth at all its levels, from genes to biogeographic regions, and the ecological and evolutionary processes that sustain it.

A comprehensive definition of biodiversity includes several levels of organization, from genetic through landscape (see Figure 1) and encompasses the "functional" aspects of biodiversity. In addition to spanning organizational levels, biodiversity traverses spatial scales (from local through regional and national to global) and times (from daily to seasonal, annual, and evolutionary). Spatial patterns of biodiversity are affected by climate, geology, and physiography (Redford and Richter, 1999).

There are different views on whether one should include the activities of humans in a definition of biodiversity. Some conservation biologists (for example, ibid.) confine biodiversity to the natural variety and variability excluding biotic patterns and ecosystems that result from human activity. Yet it is difficult to assess the "naturalness" of an ecosystem, because human influence is so pervasive and varied (Hunter, 1996; Angermeier, 2000). Many people consider humans to be a part of nature, and therefore a part of biodiversity. If one takes humans as part of nature, then cultural diversity of human populations and the ways that these populations use or otherwise interact with habitats and other species on earth are components of biodiversity, too. Most conservation biologists make a compromise between totally including or excluding human activities as a part of biodiversity. These biologists do not accept all aspects of human activity and culture as part of biodiversity, but they recognize that the ecological and evolutionary diversity of domestic species and the species composition and ecology of agricultural ecosystems are part of biodiversity.

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