Abstract:
AIM : Aridity gradients are of great interest for understanding the responses of biodiversity
to water availability and water stress. However, little is known about the responses
of many animal groups, which are crucial for assessing the effects of climate
change. Here, we study the effects of aridity on dung beetle communities, a group
with well-known
responses to large-scale
environmental gradients.
LOCATION : Sahara, Kalahari and Chihuahuan deserts.
TAXA : Dung beetles of the family Scarabaeidae.
METHODS : We conducted standardized surveys along approximately 400 km aridity
gradients in each of the three deserts, and measured species richness, abundance,
evenness and three aspects of trait-based
functional diversity (functional richness,
functional evenness and functional dispersion). By using randomization tests and linear
mixed models, we compared observed with expected values for functional diversity
indices from null models that hierarchically incorporate additional assembly
constraints.
RESULTS : Overall, we found a decrease of both taxonomic richness and functional dispersion
along the three aridity gradients. Also, aridity seems to have mild effects on
functional richness and functional evenness. Besides these general trends, we identified
differences between deserts in the responses of both taxonomic and functional
diversity.
MAIN CONCLUSIONS : Aridity shows greater importance than competition and other processes
of limiting similarity or stochastic processes in community assembly. Also, the
functional hypervolume of dung beetle desert communities decreases with aridity not
only due to species loss, but also because of selection of a few distinct phenotypes
under harsh environmental conditions. Last, we observed that the different regional
pools respond to aridity in different ways. Therefore, understanding future responses
of dung beetle communities to the progressive decreases in water availability driven
by climate change requires determining how the characteristics of the species in the
regional pool interact with aridity-driven
assembly processes.
