Is dung removal a good proxy for other dung beetle functions when monitoring for conservation? A case study from the Brazilian Amazon

Abstract

Dung beetles are increasingly used as a focal taxon for conservation monitoring. Dung removal is the most commonly quantified ecological function performed by dung beetles, since it is assumed to be strongly related to many other functions, such as soil excavation, pest control, nutrient cycling, secondary seed dispersal, etc. However, results of some studies suggest that this assumption may not always hold. We carried out a field study in the Brazilian Amazon to address four questions: (1) Does dung removal explain soil excavation and seed dispersal of small, medium and large seeds?; (2) Does soil excavation explain seed dispersal?; (3) Does land-use type affect the relationships between functions?; (4) Do the relationships between dung beetle functions and community attributes help us understand the relationships between functions? We sampled dung beetles and their functions in 58 transects distributed across four land-use types: primary forest, secondary forest, agriculture and pasture. Dung removal did not explain soil excavation or seed dispersal, except the dispersal of small seeds in the primary forest; the latter result indicates that land-use can affect the relationships between functions. The dispersal of small, medium and large seeds was explained by soil excavation, and these relationships were not affected by land-use type. In general, the relationships between functions and community attributes that we assessed had little value in helping us interpret the relationships between functions. Our results indicate that dung removal may not always be a good proxy for other dung-beetle mediated functions; furthermore, the relationship between dung removal and other functions (e.g. small-seed dispersal) can vary depending on environmental conditions (e.g. land-use). When dung beetles are used for conservation monitoring, we recommend that ecological functions of interest be quantified empirically, in addition to dung removal. Studies that have a particular interest in the function of secondary seed dispersal, or other dung-beetle functions associated with bioturbation (e.g. soil aeration), may consider using soil excavation as a proxy variable.