Spatial Patterns and Movements in Coprophagous Beetles

Abstract

Spatial distribution in two groups of dung-inhabiting beetles, Aphodius (Scarabaeidae) and Hydrophilidae, was analysed at two spatial levels, between and within pastures. Long-distance movements in the strictly coprophagous species of Aphodius were studied by trapping beetles in the centre of a town, away from the pastures. In both groups of beetles, and at both spatial levels, a linear relationship was found between log spatial variance and log mean abundance. Between-field variation in numbers was shown to be negatively correlated with the intensity of long-distance movements (interspecific comparison), and between-field variance moreover declined during the seasonal flight period in most species of Aphodius. There was an indication of a negative correlation between spatial variance and the proportion of mature females in the annual catches (Aphodius), which is interpreted as a consequence of interspecific differences in egg-laying habits both in space and time. In species showing little long-distance movements, females predominated among the "migrants" (in the centre of a town), and among the female "migrants" mature individuals were over-represented, compared with the proportion in the pastures. Long-distance movements occurred seasonally in relation to the numbers of beetles in the pastures, which supports the view that in these species there is no important difference between the short-distance and long-distance movements. Modelling of processes important in the dynamics of spatial patterns is discussed, a simple model is proposed, and the advocated universality of the model by Taylor and Taylor is questioned.