Stability, abundance, and niche width in the beetle community inhabiting cow dung

The relative frequency of different species in two extensive sets of data, collected for 2-3 yr at two localities in southern Finland, was examined to assess the numerical stability in the community structure. Carnivores and coprophages were equally stable, but dung specialist coprophages were more unstable than microhabitat generalist coprophages. Low abundance, instability and specialization (i.e. narrow niche) were all positively correlated with each other; the strongest correlation in the coprophages was that between abundance and stability, whilst in the carnivores it was between abundance and niche width. The idea that niche width is a result of opposing forces of intra- and interspecific competition is supported by the results. On the assumption that total niche overlap is correlated with diffuse competition, an increase in interspecific competition seems to decrease abundance in the coprophages, whilst in the carnivores just the opposite was indicated. It is pointed out that in Aphodius species, which are dung specialists, species turn-over in geographical scale (gamma diversity) is much greater than in microhabitat generalist Cercyon species.