Between-group differences in the Iberian dung beetle species-area relationship (Coleoptera : Scarabaeidae)

Between-group alpha- and beta-diversity differences were derived from speci es-area relationships fitted to field data. The accuracy of spatial richnes s variation predictions based on area size was also checked. The log-log mo del (log S = c + z log A) was found to be the best-fit linear model, with s lopes (z) ranging from 0.089 to 0.142. Between-group comparisons of z (slop e) and q (intercept) parameters, using the S = q + cA(Z) curvilinear regres sion model, corroborated early results, indicating a lower beta-diversity ( slope) for Scarabaeinae than for Geotrupinae and Aphodiinae. The latter gro up, probably more sensitive to environmental heterogeneity, should contribu te more to species richness in large areas. alpha-Diversity is greater for Aphodiinae, more relevant to local diversity (1 km(2)), than for Scarabaein ae and considerably greater for these two groups than for Geotrupinae. As e arlier results show that the richness of a single dung pat is rather more a function of the Scarabaeinae species pool, richness on dung pat scales is probably due more to the between-dropping mobile Scarabaeinae, while Aphodi inae contribute mainly to local and regional pool richness. Nearly 88 % of the total richness variance is explained by area size. This percentage decr eases to 37 % when the spatial structure of area size and species number ar e extracted. The corresponding figures for Scarabaeinae, Aphodiinae and Geo trupinae are 44, 22 and 31 %, respectively. (C) 1999 Editions scientifiques et medicales Elsevier SAS.