What does species evenness measure?

Species evenness is a key component of biodiversity that specifically assesses the relative abundance of different species within a community. It provides insight into how evenly individuals are distributed among the various species present in an ecosystem. When species evenness is high, it indicates that the individuals are relatively equally distributed among the species, leading to a more balanced ecosystem. Conversely, low species evenness suggests that a few species dominate in terms of abundance, which can indicate ecological imbalances and reduce resilience against changes.

In the context of biodiversity studies, measuring species evenness helps ecologists understand and compare the structure of different ecosystems, as well as the health and stability of those ecosystems. This measure is distinct from simply counting the total biomass of species, which relates more to the energy flow and productivity within an ecosystem, or from counting total individuals of a single species, which reflects density rather than diversity. Genetic diversity within a population is a different concept focused on the variation of genes within a species, rather than the community composition of multiple species. Thus, species evenness is clearly defined by the relative abundance of different species within a given area.