Dispersal limitation and habitat connectivity drive patterns of genetic and species diversity of invertebrate metacommunities in river systems

Background/Question/Methods

Understanding how habitat structure affects population dynamics and diversity is of high current interest in ecology. Until recently, studies on biodiversity and dispersal have minimally considered the specific structure of landscapes, or were done using landscapes with simplified spatial structure. However, the spatial structures of many natural systems are complex. This is especially true for river ecosystems, which are bifurcating in a hierarchical way, creating well-defined dendritic networks. Relative to their area, freshwater rivers are among the most diverse habitats on earth. However, diversity and species composition in many river systems is rapidly declining, often due to species invasions and habitat changes. Therefore, understanding diversity patterns at several fundamental levels (genetic, species, and functional diversity) and how river-network structure affects community composition is a high priority. A recently initiated large-scale (>40,000 km2), randomized monitoring program in Central Europe, has been collecting data on diversity of all macroinvertebrates across several river systems. From these data, we analysed species diversity of macroinvertebrates and genetic diversity (microsatellites) of Amphipods, with respect to local habitat characteristics and connectivity within the aquatic metacommunity. Using a spatially explicit metacommunity framework, we suggest how dispersal along the river system is affecting local and among-community diversity (alpha and beta diversity respectively).

Results/Conclusions

We found that the network structure had strong and consistent effects on diversity patterns, both on the species and genetic level. Dispersal-limitation along the river network resulted in a distance-dependent decay in community similarity, which didn’t match the decay when using Euclidian distance as a Null model. Clusters of haplotype populations of Amphipods were confined to individual drainage areas, suggesting stable and long-lasting dispersal limitation. Besides spatial connectivity, however, local environmental factors, such as altitude, were also affecting community composition and diversity. Headwaters harbored specialised invertebrate communities, including endemic species, due to the high spatial isolation of headwater branches and their high altitude in alpine streams (up to 2500 m). Contrarily, communities at lower altitudes and confluences were less diversified. Our findings confirm the key role of dispersal directionality in dendritic metacommunities and help to direct conservation actions in alpine river systems.