Galls as habitats: the inquiline communities of insect galls

Abstract

Gall makers can be considered microhabitat engineers, because their galls provide both a food resource and a habitat that can be exploited by herbivorous and omnivorous organisms that do not feed on the galling insect. We compiled literature data on inquilines of insect-induced galls for 112 galler systems in order to examine physiological, ecological and taxonomic patterns of diversity. We measured inquiline species richness two ways, first as the number of inquiline species/number of natural enemy species + inquiline species for each system in order to attain a measure of relative diversity that was free of sampling bias across different systems, and second as the total number of species. A taxonomic list of gall systems containing inquilines is presented. We conducted quantitative analyses on the following independent variables: host plant architecture, latitude, gall size, gall type and gall maker taxon. Inquiline diversity was significantly correlated only with host plant architecture and latitude; galls on trees support the richest inquiline communities, and inquiline diversity is highest in the temperate zone. However, the relative paucity of inquiline data in the literature is reflected in our results, thus highlighting the need for further study on organisms that are potentially as important a component of galler communities as predators and parasitoids.