Spatial microdistribution of two introduced dung beetle species Digitonthophagus gazella (F.) and Euoniticellus intermedius (Reiche) (Coleoptera: Scarabaeidae) in an arid region of northern Mexico (Durango, Mexico)

The introduced dung beetle species Digitonthophagus gazella (F.) and Euoniticellus intermedias (Reiche) have become the dominant species into the Scarabaeinae guild of the Mapimí región (Durango, México). The distributions of these two species in an apparently homogeneous environment was analyzed through transects of artificially placed dung pats and pitfall traps baited with cow dung. Both species showed aggregated distnbutions. Aggregation ocurred at high, modérate and low densities and was not affected by emigration, The observed Intraspecific aggregation was probably due to immigration processes: repeated dung beetle selection for the same dung pats and selection of dung pats with larger initial populations. The spatial negativa association between D. gazella and E. intermedius observed at this spatial scale was probably due to differential emigration rates. The rate of emigration of both species depended on the number of the conspecifics into a dung pat, but not on the number of beetles from the other species. We conclude that the competitive interactions among individuáis intraspecifically aggregated ükely ied to differential emigration rafes and caused the observed microspatial segregation.