Patch size and colonisation patterns: an experimental analysis using northtemperate coprophagous dung beetles

The relationship between dung pad size and both adult colonisation and larv al development was investigated in an assemblage of north temperate dung be etles (Geotrupes, Aphodius and Sphaeridium) using both dung pads and baited pitfall traps. Wet weight of 22-day-old natural dung pads was found to var y widely in the field (<100 g- > 1000 g). Across all sampling dates in fiel d experiments, dung pad size had a significant influence on dung beetle bio mass sampled from pads. Closer examination of experimental dung pads on the second day after deposition, when beetle biomass was at a maximum, reveale d not only a general positive relationship between pad size and dung beetle biomass but, more importantly, a positive relationship between dung pad si ze and dung beetle density (dung beetle biomass per unit dung volume). Ther e was a strong trend for Aphodius species richness to increase, and maintai n higher values for longer periods of time, in larger pads. Although dung p ad and pitfall trap samples could differ in the actual numbers of beetles c aptured, the relationship between different dung sizes and dung beetle biom ass was similar, indicating that the phenomenon is largely related to immig ration processes. Pat residence times of A. rufipes in the laboratory were significantly positively correlated with dung pad size. In two field experi ments, positive correlations were found between dung pad size and numbers o f larvae in pads of different sizes and in one of these experiments, larval densities (numbers per unit dung volume) were significantly and positively correlated with dung pad size. In one experiment, Aphodius larvae in the e arly stages of development were found to preferentially occupy the basal ar ea of dung pads. We discuss the implications of our findings in the context of resource utilisation by north temperate dung beetles.