Scaling local abundance determinants in mediterranean dung beetles

Abstract. 1. We study the factors that contribute to the variation in the local abundance of dung beetle species inhabiting Cabañeros National Park, a Mediterranean reserve in Central Spain. The relative roles of five different groups of explanatory variables (climatic, local-scale vegetation, landscape-scale vegetation, landscape connectivity and trophic resources) were assessed for 27 sampling sites established by a nested hierarchical sampling design that considered three regional landscapes (woodland, scrubland, grassland) and three local habitat types (forest, scrub, pasture) within each landscape. 2. Connectivity variables related to the spatial configuration of closed vegetation and distance to patches of open or closed vegetation were the best predictors of the species abundance. Precipitation was the most important climatic variable, whereas grassland area at the local- or landscape-scale and woodland area at the landscape-scale were the most important vegetation variables. Dung resources variables had the lowest explanatory ability. 3. More than 60% of the models explained more than 70% of the total variability. Observed and predicted abundance were highly and positively correlated and the mean percentage of absolute predictive errors was approximately 50%. Low-abundance observations had higher predictive errors and model accuracies seemed to be lower for species with narrow distributional ranges and presence in a high number of sampling localities. 4. Mediterranean ecosystems contain a diverse assemblage of dung beetle species whose composition and abundance are influenced by a variety of factors operating across different spatial scales. The most important variables are the spatial configuration and the habitat connectivity around each locality.