Abundance
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Abundance is an ecological concept referring to the relative representation of a species in a particular ecosystem. It is usually measured as the large number of individuals found per sample. How species abundances are distributed within an ecosystem is referred to as relative species abundances. Abundance is an important magnitude to study ecosystems but it is challenging to measure.
Abundance is contrasted with, but typically correlates to, incidence, which is the frequency with which the species occurs at all in a sample. When high abundance is accompanied by low incidence, it is considered locally or sporadically abundant.
A variety of sampling methods are used to measure abundance. For larger animals, these may include spotlight counts, track counts and roadkill counts, as well as presence at monitoring stations. In many plant communities the abundances of plant species are measured by plant cover, i.e. the relative area covered by different plant species in a small plot.
Relative species abundance is calculated by dividing the number of species from one group by the total number of species from all groups.