Evidence of competition in a herbivorous, gall-inhabiting moth (Lepidoptera) community

The larvae of a number of Lepidoptera species inhabit galls induced by the rust fungus Ravenelia macowaniana on Acacia karroo in South Africa, and the community appears to fulfill the conditions required for interspecific competition. Therefore, the aim of this study was to determine if the predominantly polyphagous moth community utilizing this ephemeral, patchily distributed, yet high quality, resource, showed evidence of exploitative instraspecific and interspecific competition. The galls were found to be extensively utilized with over 93% of galls occupied and between 50-80% of gall tissue consumed. Fewer than 0.6% of the larvae were parasitized. Significant, positive intra- and interspecific aggregation occurred in the gals and the mean number of species per gall was consistently greater than one. A threshold density of 13 individuals, representing a total month biomass of 12.74 mg, was found above which body mass compensation occurred. Resources are therefore limited in the community. The species were positively associated as a result of a common habitat affinity. Species abundances also covaried positively in a common response to resource conditions. Resource limitation and 'non-specific' exploitative competition was thus found on the Lepidoptera community.