Spatial and temporal co-occurrence of competitors in southern African dung beetle communities

1. Co-occurrence of 11 species of crepuscular-nocturnal medium-sized tunnelling dung beetles from two core functional groups that vary in their rate of dung burial was examined at a range of spatial and temporal scales to identify the likely extent to which competition for dung might affect the structure of beetle communities of subtropical pasture. 2. At the largest scale, clear seasonal co-occurrence and similar habitat preferences (soil type and vegetation associations) were found amongst the species. 3. Medium- and fine-scale distributions of the species were investigated across nine blocks of dung-baited traps dispersed over a 400 ha tract of open cattle pasture, on deep sandy soil in Natal, South Africa. Traps were baited overnight and cleared in the morning in two series of three successive days. 4. There was marked variation in mean numbers caught within and between each 3-day trapping period, and also between blocks in the total number of beetles (pooled over species) or individual species caught per block. The spatial relationship for total beetles between blocks persisted for several days, but not several weeks. 5. Significant intraspecific aggregation was apparent for all species at the medium spatial scale amongst individual pads and between blocks over the 400 ha, but at the finest spatial scale (within blocks) most species were randomly distributed on most occasions, irrespective of the abundance of the species. The actual level of aggregation was thus found to increase at higher spatial scales. 6. Pairwise species comparisons showed little or no positive association on the majority of occasions and negative pairwise associations were exceedingly rare. Positive association between the two functional groups was stronger, however, and positive species association at the community-wide level was evident on most occasions. 7. There was thus some evidence of independent spatial aggregation patterns amongst individual species on a medium spatial scale (400 ha), but not on a fine scale (100 m2). Intraspecific/functional group aggregation tended to be greater than interspecific/functional group aggregation at all scales of analysis. Despite this, beetle densities in a considerable proportion of pads in the field would indicate, based on previous experimental evidence, that significant levels of inter- and intraspecific/functional group competition for dung is likely to occur. Thus, the aggregative behaviour of species documented here is not predicted to significantly diminish the level of interspecific competition within and between the two functional groups in this system.