Rarefaction (ecology)

Rarefaction, in the context of ecology, is a statistical technique used to estimate species richness for a given number of sampled individuals. It addresses the issue that species richness is highly dependent on sampling effort, meaning that a larger sample size will almost invariably yield a higher number of observed species. Rarefaction allows researchers to standardize samples to a common abundance, enabling meaningful comparisons of species richness among communities or across different studies, even when sampling effort varies.

The core principle of rarefaction involves repeatedly drawing random subsamples from a larger sample and then plotting the average number of species found in each subsample as a function of subsample size. This generates a "rarefaction curve." By comparing rarefaction curves of different communities, one can determine which community is likely to be more diverse, independent of the size of the original sample.

Mathematically, rarefaction is often based on hypergeometric probability. It estimates the expected number of species, E(S), in a smaller subsample of size n, drawn from a larger sample of size N containing S species, where n < N. The calculation is based on the abundances of each species in the larger sample.

Rarefaction is particularly valuable when comparing communities that have been sampled unevenly, which is a common occurrence in ecological studies. It can be applied to various types of organisms, including plants, animals, and microorganisms. However, it is important to note that rarefaction only estimates richness, not evenness or other aspects of community structure. Furthermore, it is sensitive to the assumptions of random sampling and accurate species identification.