Dung beetles are highly abundant, species rich, easy to collect, and sensitive to habitat change. To this end, dung beetles are frequently used as a bioindicator for habitat change as surrogates for other species. As detritivores thought to show generalist feeding preferences, their reliance on dung suggests that mammal species composition is an important factor influencing dung beetle species occurrence. Yet the association between dung beetles and mammals is still poorly understood, and mammal data is rarely included in studies of dung beetle distribution.
We used a joint species distribution model to identify the importance of mammal composition, habitat, and abiotic conditions for dung beetle species occurrence. Forty-six dung beetle species collected over old growth forest, secondary forest, and oil palm plantation in Borneo were modelled as a response to both biotic (mammal species composition and forest biomass), and abiotic (soil moisture and temperature) variables. Dung beetle traits (body size, feeding guild and diel activity) and phylogeny were included in the model to relate community level responses to environmental variation. Dung beetle response to mammal composition was then predicted whilst holding other factors constant to identify the effects of mammal species composition on dung beetle communities in different habitat types.
Results/Conclusions
The observed species-specific responses confirmed previous anecdotal associations between dung beetles and environmental variables. Abiotic factors explained 35% of the variation in dung beetle species occurrence, biotic factors explained 41% and the final 24% of variation was explained by spatial factors. The association between explanatory variables and dung beetle species traits was strongly correlated with phylogeny. However less than 1% of the variation in species occurrence in the model was accounted for by dung beetle species traits. This is evidence for niche conservatism within dung beetles and suggests that there are traits influencing dung beetle species distribution that were not accounted for in the model.
In secondary forest, dung beetle species richness and community similarity to old growth forest were positively associated with mammal species related to undisturbed forest. The dung beetle community in oil palm showed low species richness and community similarity with reference to old growth forest, irrespective of how the mammal composition varied. These results are evidence that mammal species composition plays an important role in influencing dung beetle species distribution. This study highlights that biotic factors are equally as important as abiotic and environmental conditions in determining how species are distributed and respond to changing environments.