The geographic gradients of diversity have fascinated ecologists and biogeographers for the last two centuries, and their variations have been related to several factors; current climate, topography, quality and structure of the habitats, human disturbance or historical climate changes are known to affect the distribution of diversity in different ways. However, the concurrent effects of these factors, together with evolutionary processes and historical contingencies, make difficult disentangling the specific effects of each one of them on diversity gradients.
Another key question in ecology is whether communities are either relatively fixed structures that tend to persist through time or highly dynamic structures resulting from the mere coincidence of species’ distributions in space and time. In spite of the importance of this question, most knowledge on diversity gradients is based on the study of variations in species richness; little is known about other aspects of diversity, such as the functional and evolutionary structure of communities.
Here we propose to study the determinants of the diversity and the structure of the communities of Scarabaeoidea dung beetles (scarabs) in the Western Palearctic (WP), aiming to understand how they interact in time and space. The Western Palearctic is perhaps the region where determining the different roles of climate, local habitat and historical processes in determining large-scale diversity gradients is most difficult, due to the complexity of its recent history, the long-term impacts of human populations, the importance of the glacial processes on its territory and its topographical complexity. The diversity, thermal adaptations, dispersal ability and ecological specialization of scarabs make them ideal candidates to disentangle the different roles of each of the determinants acting over the geographic gradients of diversity, because their distributions are expected to be mainly constrained by temperature gradients but not by post-glacial dispersal processes or resource availability, and their diversity allows studying the responses coming from a range of physiological and ecological adaptations.
More precisely, we aim to disentangle the effects of the processes and/or factors that have determined (a) the evolution of the whole WP dung beetle fauna; (b) current geographic gradients of diversity; and (c) the structure of local communities. To achieve these three objectives we will: (i) construct a phylogeny of the lineages of Scarabaeoidea dung beetles present in WP; (ii) gather a database of functional traits for all WP scarab species; (iii) analyze the evolution of both these traits and the responses to environmental gradients; (iv) compile information on the distribution of all WP scarab species and data on the composition of local communities; (v) study the deteminants of the geographic gradients of the diversity, evolutionary structure and functional structure of WP scarab assemblages, with an additional emphasis on arid zones; and (vi) assess how these effects scale down from regional to local scales.
Through this comprehensive approach we seek reaching a thorough understanding on the processes driving the biogeographic and evolutionary dynamics of Western Palearctic dung beetles, from the build-up of regional faunas to the assembly of local communities.