Species richness measures the number of different species while species evenness tells whether the ecosystem has a dominant species or has similar abundances of all species. Both measures is needed to evaluate the biodiversity of an ecosystem. Biodiversity is defined and measured as an attribute that has two components — richness and evenness. Richness = The number of groups of genetically or functionally related individuals. ... Evenness = Proportions of species or functional groups present on a site. 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. More information was provided from me in this answer. Hope this helps!