Scale dependent biodiversity patterns in Mediterranean river catchments: a multi taxa approach

Although the important contribution of beta-diversity to regional (gamma) diversity is increasingly recognised, our understanding of how the spatial scaling of beta-diversity differs among taxonomic groups is still limited, especially in dynamic lotic ecosystems. In this study, we assessed the difference in the partitioning of diversity at nested spatial scales, from reach to catchment, among riparian birds, fish and benthic macroinvertebrates in Mediterranean river systems. Fish and macroinvertebrates showed similar scaling patterns, with beta-diversity always larger than expected by a random distribution of individuals at all spatial scales (among reaches, rivers and catchments), and local (alpha) diversity always lower than expected. Conversely, beta-diversity of riparian birds appeared larger than expected only at the largest scale (among catchments), while local diversity did not differ from random expectation. For birds, however, results partly depended on the weighting of abundant and rare species. Although the relative contribution of beta to gamma-diversity did not differ substantially among groups (with multiplicative beta representing five to six distinct communities), its deviation from random expectations showed marked differences indicating that functionally different groups exhibit distinct spatial patterns. This study is among the first to investigate scaling patterns in beta-diversity across taxonomic groups with different ecological requirements and dispersal ability, and provides a holistic picture of riverine biodiversity. From a conservation perspective, the results suggest that, in these river systems, flexible conservation strategies are required in order to protect multiple taxonomic groups.