Resource quality and the colonisation and succession of coprophagous dung beetles

In order to examine the degree of resource selectivity in a north temperate dung beetle assemblage and to identify major parameters that influence such selectivity, the occurrence of adult dung beetles (Aphodius, Geotrupes and Sphaeridium) in up to five different types of dung over a period of up to 25 d was examined in a series of field experiments using standardised dung pats. There were significant physical and chemical differences in dung quality between dung types and over time during succession. Dung beetle species showed distinct preferences for particular types of dung which were generally similar in data sets from both pitfall traps and dung pat samples. Species also showed distinct patterns of successional occurrence. Ordinations produced by Canonical Correspondence Analysis, based on species occurrences in dung types and over time, usually selected dung pat age as the most important environmental variable influencing dung beetle assemblages. Dung quality parameters contributed a significant element of structure to the species ordinations but ordinations using dung types or dung quality parameter values as the environmental variables were very similar in terms of sample and species placement within the ordination for each data set. Most importantly the CCA ordinations clearly grouped species according to their breeding behaviour. Early-successional species laid eggs in the soil, or in silken egg cocoons, which allowed them to exploit wet dung. Mid and late-successional species laid eggs in the dung pat; late-successional species could exploit normally wetter dung types than mid-successional species, probably due to increased crust formation and drying as the dung pat ages. Thus, species appear to be differentially adapted to exploit varying types of dung microhabitats. Therefore, where two or more species of large herbivores are present, dung quality preferences probably constitute an important niche dimension.