Dung beetle - mammal interactions in tropical forests

Dung beetles are functionally-important insects which feed on the faeces of mammals. They are widely studied as biodiversity indicators, and as a model taxon for investigating relationships between biodiversity and ecosystem functioning. In this thesis I explore dung beetle - mammal associations in tropical forests, aiming to place dung beetle resource use in the context of the mammal species on which they rely. In a systematic review of the literature (Chapter 1) I find a growing literature on dung beetle ecology in the context of ecosystem functioning and habitat and land use change; this growth has not been matched by a corresponding increase in research into the associations of dung beetles with mammals. I summarise the methods and findings from previous dung beetle - mammal association studies, finding that the few field studies of dung beetles that include mammal data document a large impact of mammal species presence and species composition on dung beetle species richness and abundance. This highlights a research gap in our understanding of how dung beetles and mammals are associated. In a mesocosm choice experiment (Chapter 2), I find that five dung beetle species from the Atlantic Forest of Brazil vary in their preference towards dung types, but there was no evidence of intraspecific variation in dung choice. In Chapter 3 I assess the magnitude of interactions between dung beetles and dung used either for dung removal (brood ball formation or feeding) or general attraction (liquid feeding or breeding). I show that the trapping method and the type of dung used affect the suite of beetles captured, with the potential to influence the outcome of experiments linking functions to interactions. In Chapter 4 I construct the first quantitative mammal- dung beetle networks and use them to model mammal species extinction scenarios, exploring the consequences for dung beetle populations. I find dung beetle feeding and breeding networks do not differ significantly in structure and show high nestedness and low levels of trophic specialization. Simulations suggest that mammal extinction scenarios based on mammal body mass and mammal dung volume will impact dung beetle populations to a greater extent than random scenarios of mammal loss. Finally (Chapter 5), I use a joint species distribution modelling approach to investigate the role of mammal species composition, abiotic factors and forest structure in determining dung beetle species distributions, using data from Malaysian Borneo. I find that the mammal feeding group biomass explained over half of the variation in dung beetle species occurrence. I show that all 43 dung beetle species are significantly less likely to be observed where carnivore biomass and air temperature are high. Dung beetle species show idiosyncratic responses to the other explanatory variables, and these responses were poorly explained by species traits. Pairwise dung beetle - mammal co-occurrence patterns reveal a higher proportion of positive associations in oil palm compared to old growth and logged forest. Overall, results from this thesis suggest that although dung beetles exhibit generalist intraspecific and interspecific feeding and breeding behaviour, mammal species composition and abundance is a key factor influencing their distribution. Further work is needed to identify the strength and extent of interactions among different dung beetle species and mammal trophic groups to gain an improved understanding of how environmental change will directly and indirectly affect dung beetle species and the ecosystem functions they provide.