Patterns in the evenness of gastrointestinal helminth communities

Within a parasite community, the relative abundance of each parasite species, or species evenness, is a key component of the structure of that community. However, little is known about which, if any, ecological factors determine the evenness of the parasite community in a given host. Here, the associations between selected ecological variables and the evenness of gastrointestinal helminth communities were evaluated across species of vertebrate hosts. Using host species as statistically independent observations, evenness correlated negatively with parasite abundance in fish hosts, and positively with community richness in bird hosts. After controlling for host-phylogenetic effects, the correlation between evenness and parasite abundance in fish hosts was still present. In addition, a link between parasite community evenness and host body size became apparent among fish hosts, and evenness correlated positively with richness in mammal hosts. These trends lack solid explanations, and point to new directions in the study of parasite community ecology.