There are two key facets to biodiversity: species richness and abundance. Diversity indices are mathematical measures of species diversity in a community. Because there are different facets of diversity, multiple diversity indices have been developed. The Berger-Parker dominance index focuses on quantifying the abundance of individuals of each species observed within an ecological community. The number of individuals per species observed in a community is referred to as 'evenness,' which is a measure of how similar species are in their abundances within a community. Conversely, 'dominance' refers to the extent to which one or a few species are disproportionately abundant in the community. Species abundance may change along environmental gradients or in relation to an environmental impact; thus, measurements of evenness can reveal information about community response to disturbances. For example, disturbed environments often have a high dominance of one species. Species evenness and dominance measures may also be related to net primary productivity of a system, invasion susceptibility, and local extinction patterns.
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