An invasive ant reduces diversity but does not disrupt a key ecosystem function in an African savanna

Understanding the consequences of anthropogenic biodiversity decline has become an increasingly urgent priority for ecologists. Biological invasions are a common result of anthropogenic habitat change, and numerous studies have established the negative impact of invasions on the diversity and abundance of native species. But fewer studies have directly examined the effect of biological invasions on ecosystem functions and services. We leveraged a recent invasion by the big-headed ant (Pheidole megacephala) in an East African savanna to evaluate the impact of invasion on arthropod diversity, and on dung decomposition, an ecosystem function provided by a subset of these arthropods. We found that invaded sites had lower overall arthropod diversity, but these diversity changes did not extend to a functional group of detritivorous insects (e.g., dung beetles and termites), which play key roles in dung decomposition. In a manipulative experiment, we found that rates of dung pile decomposition did not differ significantly in invaded vs. non-invaded sites. Our study provides evidence that these invaded savannas are undergoing large changes in arthropod diversity, while maintaining resilience in decomposition function, suggesting that diversity alone may be an insufficient impact assessment tool. By monitoring functional guilds and their attendant services, we may better understand the broader structural and functional consequences of invasion. © 2016 Milligan et al.