BIOGEOGRAPHICAL GROUPS IN A SOUTHERN AFRICAN, WINTER RAINFALL, DUNG BEETLE ASSEMBLAGE (COLEOPTERA, SCARABAEIDAE) - CONSEQUENCES OF CLIMATIC HISTORY AND HABITAT FRAGMENTATION

A study was made of the effects of climate and habitat fragmentation on the biogeographical composition of the dung beetle fauna (Scarabaeinae, Coprinae) in the southwestern Cape, winter rainfall region of South Africa. The fauna was studied at eleven sites and 45 species were recorded. Three geographical species groups (1, 2, 3) were defined for 38 of the species using multivariate techniques. The other seven species have dissimilar widespread distributions and are treated as a fourth group (4). Two groups (1, 3) comprising 31 and three species, respectively, are either endemic or largely restricted to the winter and bimodal rainfall regions of southern Africa. They show extreme numerical dominance in indigenous shrubland but are also well-represented in pasture. Groups 1 and 3 comprise primarily day-flying taxa with an overall peak in abundance during the moist spring. These endemic groups are probably associated with the inception of winter rainfall climate during the Pliocene rt 3 million years before present. The other two groups (2, 4) have a distribution extending into the adjacent summer rainfall region. In the southwestern Cape, they are found predominantly in recently-created pastures. They include equal numbers of day and dusk/night-flying species with peaks in abundance mainly during the dry summer. Most species of these two groups are taxonomically distant from endemic taxa. Frequency of Group 2 relative to climate was greatest in the westerly summer rainfall region one whereas that of Group 4 was greatest in the south-easterly bimodal rainfall region. As most members of Groups 2 and 4 show limited penetration into indigenous shrubland, the findings suggest that these summer-active groups dispersed from the summer rainfall into the winter rainfall region via western and eastern coastal corridors in response to the thinning or clearance of the formerly ubiquitous native shrubs.