Asymmetrical competition between Neotropical dung beetles and its consequences for assemblage structure

1. This study combines the results of laboratory experiments using representative assemblage components and pitfall trapping over a large geographical area to examine the hypothesis that ongoing interspecific competition structures Neotropical dung beetle assemblages. 2. From Guatemala to Panama assemblages of large to medium-sized, fast tunnelling dung beetles include a single large, nocturnal dichotomiine species, Dichotomius annae (Kohlmann & Solı´s, 1997). In competition experiments, this species out-competed the medium-sized coprine species, Copris lugubris Boheman and Phanaeus demon Laporte-Castelnau, for dung and nesting space, in spite of earlier colonisation bythe diurnal species, P. demon. 3. Differences in the abundance of D. annae at Central American sites did not affect total fast-tunnelling dung beetle assemblage richness over the rainy season. However, D. annae rank order was directly related to the probabilityof interspecific encounters (Hurlbert’s D1) among species. These trends were also observed when species lists from published and unpublished studies of other large allopatric dichotomiine species, with a more northerly distribution, were included in the analyses. 4. The results obtained suggest that where large dichotomiine species are abundant, their efficient pre-emption of a considerable proportion of available resources drives all, or most, other fast-tunnelling species to a lower population density, thereby decreasing assemblage diversity.