Alpha diversity is a measure of species diversity within a specific, homogeneous habitat or area. It is used to describe the number of different species present in a particular community or ecosystem. Alpha diversity is often calculated by various indices, such as the Simpson index, the Shannon index, or the Simpson reciprocal index, which take into account the number of species present, as well as how evenly the individuals are distributed among the species in a given area.
Because alpha diversity measures species richness and evenness in a specific habitat or area, it can be a good estimate for understanding differences in community structure, as it enables scientists to compare the diversity of species among several different sites or communities. Alpha diversity can also provide an indication of how stable or resilient an ecosystem might be over time, as higher diversity tends to be correlated with a more resilient ecosystem. For example, a higher alpha diversity index in an area of a forest might suggest that there are a greater number of different species present and better ecological processes taking place.