Spatial and Temporal Variation in Species Composition, Diversity, and Structure of Mediterranean Dung Beetle Assemblages (Coleoptera: Scarabaeidae) Across a Bioclimatic Gradient

Both spatial (bioclimatic stages) and temporal (seasons) analyses were contemplated to estimate the influence of Mediterranean bioclimate on dung beetle assemblage's distribution. Insects were pitfall trapped once per season from 2008 to 2009 at eight bioclimatic sites from north to south of Tunisia. In total, 3,278 specimens and 39 species (18 Aphodiinae and 21 Scarabaeinae) were collected and the completeness of sampling was of 76.81%. Along the bioclimatic gradient species richness of these two families were of the same order (Scarabaeinae/Aphodiinae ratio 1.16). The highest value of species richness occurs in subhumid site (27 species) and the lowest in the arid sites (5 species). More beetles were captured in spring and few beetles in autumn. However, more Scarabaeinae were captured in summer and more Aphodiinae in winter. Humid and subhumid sites were more diverse with high temporal turnover and, 80% of species occur in this area of the north-west of Tunisia. Conversely, the arid sites have the lowest values of alpha- and beta-diversity. The highest spatial turnover occurs between semiarid middle and semiarid inferior. Several factors could explain these results such as the soil nature, the geographical position, and latitude. Multivariate analyses showed that: 1) latitude greatly influenced the assemblage organization than bioclimate; 2) spatial factors (soil, bioclimate, latitude, altitude, marine influence) have greater effect than temporal factors (season); and 3) the Tunisian Dorsale is a stronger determinant where it act as a barrier or a filter that limit the colonization of arid sites by dung beetles and species occurred in these sites were those locally abundant an largely distributed. Results indicate that there were no spatio-temporal patterns according to bioclimate, but the influence of local and regional factors predominates on the dung beetle assemblages distribution.