Experimental analysis of inter- and intraspecific competition in dung beetle communities

(1) Inter- and intraspecific competition for bovine dung by dung beetles which tunnel and bury dung beneath the dung pad (paracoprids) was examined using co-occurring species which display contrasting patterns of dung use. The coprine species Catharsius tricornutus and Copris elphenor are large fast burying paracoprids and a pair will bury one dung mass (100-300 g) within 24-48 hours of pad colonization. The onitine Onitis alexis is a large slow burying species that buries dung continuously over many days (400-1000 g) following pad colonization. (2) Parallel field and laboratory experiments were conducted using single or coprine/Onitis mixed-species density combinations ranging from one to sixteen pairs per 1.5 kg dung pads. Dung burial by each species was assessed 4 days after pad colonization. (3) Results from field and laboratory experiments were very similar. Strong intraspecific competition for dung was shown by all species at densities greater than two to four pairs per pad. At high densities 70-80% of each pad was removed. O. alexis sequestered all buried dung as a brood mass under the pad, and intraspecific competition led to a reduction in the amount of dung buried per pair. As the density of coprine beetles increased and intraspecific competition intensified, increasing proportions of the dung pad were utilized, but decreasing proportions were converted to buried dung. (4) Strong asymmetric competition was demonstrated between the coprine and onitine species. Dung burial by the coprine species was largely unaffected by the presence of onitine beetles, but the amount of dung buried by O. alexis was markedly reduced in the presence of two to three pairs of coprine beetles, i.e. the rapid resource usage by coprine beetles intensified intraspecific competition in onitine beetles. (5) The coprine and onitine species studied are broadly representative of their groups and colonize fresh dung pads (1-2 days old) at dusk. Hence, strong asymmetric competition (resource pre-emption) is to be expected where members of the two groups occur together. The potential consequences of this for the relative abundance of dung beetle species and hence community organization are considered.