The role of diversity, body size and climate in dung removal: a correlative and experimental approach

The mechanisms by which climatic changes influence ecosystem functions,
i.e. by a direct climatic control of ecosystem processes or by modifying
richness and trait compositions of species communities, remain unresolved.
This study is a contribution to this discourse by elucidating the linkages
between climate, land use, biodiversity, body size and ecosystem
functions. We disentangled direct climatic from biodiversity-mediated
effects by using dung removal by dung beetles as a model system and by
combining correlative field data and exclosure experiments along an
extensive elevational gradient on Mt. Kilimanjaro, Tanzania. Dung removal
declined with increasing elevation, being associated with a strong
reduction in the richness and body size traits of dung beetle communities.
Climate influenced dung removal rates by modifying biodiversity rather
than by direct effects. The biodiversity-ecosystem effect was driven by a
change in the mean body size of dung beetles. Dung removal rates were
strongly reduced when large dung beetles were experimentally excluded.
This study underscores that climate influences ecosystem functions mainly
by modifying biodiversity and underpins the important role of body size
for dung removal.