Response of dung beetle assemblages to grazing intensity in two distinct bioclimatic contexts

Abstract

Given the impact of livestock on ecosystems worldwide, it is necessary to understand the effects of grazing practices on biodiversity in order to improve the sustainability of pasture management practices. In a pasture, spatio-temporal variability in livestock activity results in a heterogeneous distribution of defoliation, trampling and excreta. To date, fine-scale analyses of grazing intensity have been rare, and the geographical extent of the studies often limited. In this study, we addressed this gap by analysing the influence of contrasting intra-pasture grazing intensity on the structure and composition of dung beetle assemblages. To do this, we studied a three-level grazing intensity gradient in two distinct bioclimatic contexts, a Mediterranean steppe and the Alps, which also allowed us to determine if dung beetle responses to grazing intensity are related to bioclimatic conditions. The observed dung beetle responses showed an imprint of the bioclimatic context and the local pasture conditions, and species composition and relative abundance showed strong variations along the grazing intensity gradient in both study areas. Species assemblages from the most and least grazed parts of pastures differed strongly. By altering habitat conditions, changing dung availability and modifying competitive interactions, fine-scale heterogeneity in grazing intensity led to substantial variations in the abundance of dung beetle nesting guilds. In both study areas an increase in grazing intensity was detrimental to the largest species and the soil-digging species (which bury dung in underground nests), whereas dung-dwelling species (which reproduce inside dung pads) were favoured. We discuss the combined use of nesting guilds and body mass as potential features to generalize the application of dung beetles as indicators of grazing practices.