Eichler's rule

Eichler's rule is one of several coevolutionary rules which states that parasites tend to be highly specific to their hosts, and thus it seems reasonable to expect a positive co-variation between the taxonomic richness of hosts and that of their parasites.

A rule to describe the taxonomic relationship between parasites and their hosts was developed in 1942 by Wolfdietrich Eichler (1912–1994), a German authority in zoology and parasitology who served as a professor of parasitology at Leipzig University.

It is one of the first three coevolutionary rules, created in opposition to Heinrich Fahrenholz's research into coevolution.

[3] As a part of their 2012 study, Vas and his co-authors tested Eichler's rule, and concluded that exceptionally strong correlational evidence supports the positive co-variation between the species richness of avian and mammalian families and the generic richness of their parasitic lice.

[4] In volume nine of Advances in Parasitology, parasitologist W. Grant Inglis posited that, when studying the co-variation between the taxonomic richness of hosts and parasites, it is easier to study parasites than free-living host organisms.