Measurement of Biodiversity: Richness and Evenness

Abstract

Evidence about the health of ecosystems is often thought to be related to biodiversity. Traditional attempts to define biodiversity consider two components: richness—the number of species in the ecosystem—and evenness—the extent to which species are evenly distributed. This chapter studies attempts to make both concepts precise using mathematical approaches. It describes a number of evenness indices that have been widely used, studies axioms for evenness that an index could be required to satisfy, and explores which evenness indices satisfy those axioms. The chapter also considers evenness indices that ``preserve'' certain partial orders. The relationship between richness and evenness and attempts to derive measures of biodiversity based on both richness and evenness are explored.