Conservation of temporary streams: The relevance of spatiotemporal variation in beta diversity

1. Temporary streams are affected by increasing human alterations, and this situation is expected to worsen under global change. Understanding biodiversity trends and the contribution of sites and species to beta-diversity is of high importance in establishing conservation priorities at a regional scale. 2. This paper focuses on aquatic macroinvertebrate biodiversity in temporary streams on the island of Mallorca, using a space-time framework. Differences in alpha-diversity, spatial-temporal fluctuations of beta-diversity, local contribution to beta-diversity (LCBD) and species contribution to beta-diversity (SCBD) were examined. 3. Data analysis shows that only the space-time approach to beta-diversity can capture the full variation of macroinvertebrate composition in temporary streams. This confirmed our hypothesis that beta-diversity patterns are better explained by incorporating the temporal dimension to the space-time approach. 4. Regarding beta-diversity components, species replacement components always dominate over richness difference. These results imply that beta-diversity variability is mainly caused by differences in species composition, while the relative difference in richness among sites has a minor role. Consequently, the optimal conservation strategy requires the protection of several undisturbed sites. 5. Although the LCBD analysis did not detect any keystone sites, it helped to identify those sites that should be prioritized for restoration efforts (sites with high LCBD values and low alpha-diversity). We also concluded that SCBD analysis should be interpreted carefully, as rare endemic species had low SCBD values. 6. This study demonstrated the need for incorporating temporal variability in the analysis of biodiversity patterns in highly dynamic ecosystems, such as temporary streams. It also revealed the urgency of preserving a spatial network of temporary streams under non-impaired conditions that can act as dispersal point sources to other streams for biodiversity conservation. These insights are relevant for Mallorca and other Mediterranean islands, and for the protection of temporary rivers elsewhere.