Dung beetle functions in tropical planted pastures were barely explained by management variables and not at all by community metrics

Abstract

Studies comparing different land covers clearly show that land-use change commonly affects animal communities and the ecological functions they play in ecosystems. However, we lack a good understanding of the effects that more subtle changes, those occurring within a land cover type, can have on ecological functions of animals, and if these are also mediated by shifts in community attributes. We studied two important ecological functions of dung beetles in tropical planted pastures with exotic African grasses. Due to differences in management, pastures varied in grass cover, tree density, pasture age, cattle density, and in the application frequency of veterinary medical products. We sampled beetles and their functions in 24 sites to address two questions: (1) Do management variables known to strongly affect beetle communities also affect their functions?; (2) Are the dung beetle-mediated ecological functions of dung removal and soil excavation correlated, and are they influenced by community attributes? We found no influence of management variables on dung removal, while soil excavation was negatively affected by pasture age, but only weakly. Contrary to our expectations, no community attribute was correlated with either dung removal or soil excavation, but both functions were strongly and positively correlated with each other. Our results indicate that responses of dung beetle communities and their ecological functions to subtle changes within a land cover type, are decoupled, idiosyncratic and context-dependent, making predictions and generalizations difficult. We believe that there is a need of more studies investigating the effects of fine-scale changes within habitats to better understand the consequences of management decisions on ecological processes mediated by animals.

Keywords

• Brazilian savanna
• Dung removal
• Pasture management
• Soil bioturbation