Landscape effects on taxonomic and functional diversity of dung beetle assemblages in a highly fragmented tropical forest

Abstract

We evaluated how the taxonomic and functional diversity of dung beetles responds to landscape fragmentation in Los Tuxtlas Biosphere Reserve (LTBR). We sampled dung beetle assemblages in 15 landscapes (spatial windows) representing a gradient of forest cover loss and evaluated the degree of forest fragmentation in each landscape. The percentage of forest coverage of each landscape had a significant positive effect on species richness (0D), Shannon diversity (1D), and functional divergence of dung beetles. Forest fragmentation was negatively related to Simpson diversity (2D), biomass, and functional evenness of dung beetles, whereas their functional richness expanded as forest fragmentation increased. Taxonomic and functional beta diversity were positively correlated; the former was driven mainly by species replacement and the latter by nestedness. Functional alpha and beta diversities varied mostly at random, as did the probability of co-occurrence between species. However, the few non-random positive associations between species involved small-bodied forest dung beetles. Species and their ecological traits are lost randomly in the landscape, suggesting a surprising resilience of dung beetle assemblages to forest cover loss. Nevertheless, loss and fragmentation of forest coverage had an unbalancing effect on dung beetle abundance and trait distribution, reducing their functional evenness, and divergence while favoring the establishment of small-sized species. In conclusion, although the LTBR has buffered further loss of dung beetle species and functional richness, it cannot effectively safeguard all aspects of their functional diversity. Our results suggest that the recovery of the original forest cover and large mammals is crucial for maintaining the taxonomic and functional diversity of dung beetles in tropical rainforests.