Local distribution and coexistence of Digitonthophagus gazella (Fabricius, 1787) and Onthophagus batesi Howden and Cartwright 1963 (Coleoptera: Scarabaeidae)

With data coming from two Mexican Neotropical localities, an analysis of the main niche dimensions of two potential competitors was carried out: an introduced Indoafrican species (D. gazella) and a native one (O. batesi). Both species show similar daily activity. They coexist in grasslands bordering on tropical forest opened for cattle activity. Results show spatial segregation at local level: both species inhabit open areas but O. batesi less so. This latter species also inhabits the forest, mainly at the edge zones. The possible causes of this spatial segregation along the environmental gradient could be related with a different detection capacity of the two species. Since their flying activity occurs at dusk and dawn, we suggest that the detection of humidity has an important role in the observed segregation. We propose that the adults colonize dung pats located in places with suitable environmental conditions that secure progeny survivorship. However. the possibility of competition between these species, cannot be ruled out. From a historic-evolutive perspective the coexistence of both species is recent. It is necessary to determine the spatial behavior of either species where the other one is missing. What happens with possible interactions in overlapping zones (edge-grassland) and studies about immigration-emigration rates from dung pats in these zones, where the two species coexist, are questions for future research.