Temperature boosts and constrains dung beetle diversity along an Andean-Amazonian elevation gradient

In the light of a warming climate, it is becoming increasingly urgent to understand the factors that influence biodiversity. Temperature can have a positive effect on species diversity by influencing diversification and ecological rates, but temperatures exceeding thermal tolerance limits of organisms may also restrict species distributions. We tested the influence of temperature, moisture, and energy resources on biodiversity, by assessing the diversity and thermal limits of dung beetles (Scarabaeidae) collected with baited (dung, carrion, fermented fruit) pitfall traps at 26 study plots along a complete, forested Andean-Amazonian elevation gradient from 250–3500 meters above sea level (masl). As a proxy for dung availability, we recorded mammal activity for predicting mammalian biomass at each plot. We found that dung beetle diversity was not correlated with mammalian biomass but decreased exponentially with temperature from 500–3500 masl, with a pronounced drop of diversity in Amazonian lowland forests (250 masl). In accordance with the sharp lowland decline, thermal safety margins decreased exponentially towards the lowlands with ambient temperatures partly being high enough to cause thermal injuries and heat coma in less than one minute. Furthermore, dung beetle communities showed a decreasing degree of resource specialization with increasing elevation. Our findings highlight temperature as the primary driver of dung beetle diversity, with upper thermal limits acting as a key constraint in lowland areas. Our data suggests that additional warming of the Amazonian lowlands may have detrimental consequences for dung beetle communities and their ecosystem functions, even in intact rainforests.