Parallel assemblage structures in Mediterranean marine amphipods revealed by beta diversity partitioning

Abstract

Relying on a purely taxonomic view of diversity may ignore the fact that ecological communities can be constituted of species having both distinct evolutionary histories and functional characteristics. Thus, considering how the multiple facets of diversity vary along environmental and geographic gradients may provide insights into the role of historic processes and current environmental conditions in determining the distribution of species, lineages and functions across space. By using distributional, taxonomic-distance and traits information, we explore the role of spatial/environmental gradients and of biogeographic subdivision of Mediterranean Sea on the different facets of beta diversity components in seagrass amphipods. Beta diversity partitioning and correlation analyses showed a nearly equal contribution of the replacement and richness components on total beta diversity for all facets, although the influence of environmental and geographic distance differs among components. While the replacement was mainly related to a pure spatial gradient, both the environmental and geographic distance were correlated with the richness component of beta diversities. Our results are in line with the complex paleobiogeographic history of the Mediterranean Sea, with the replacement component likely to be related to the progressive substitution of species of Atlantic origin with Mediterranean endemics along the west-east geographic gradient, and the richness component to the marked environmental difference between different basins. Moreover, the influence of biogeographic partition on the richness components suggests the role of spatially structured gradients at biogeographic level in determining the net loss/gain of species, lineages and functions, possibly influencing the assembly processes of passive dispersal organisms.