Anthropogenic stress alters community concordance at the river-riparian interface

Organisms often respond in similar ways to environmental or spatial gradients, particularly at large spatial scales, but patterns at finer scales and across ecotones are less certain. It is important to understand these relationships at multiple spatial scales, as managers often need suitable surrogate taxa for conservation and monitoring purposes. We explored whether community concordance at the river-riparian interface was decoupled by increasing anthropogenic stress (a gradient of local land-use intensity) at 15 sites over three years within the LTER site, Rhine-Main Observatory, a low mountain river system in central Germany. We assessed concordance between four organism groups: riparian spiders and carabid beetles, benthic macroinvertebrates, and combined aquatic macrophytes and riparian plants. This represented three different linkages: (1) predator-prey, (2) direct competition, and (3) habitat associations. While there were no correlations in richness patterns, multivariate community structure was highly concordant between all groups. Anthropogenic stress strongly reduced links between riparian spiders and carabid beetles, likely resulting from their shared resource requirements. However, increasing concordance occurred between plants and other groups. We posit that patterns may be resulting from two processes: (1) linkages between directly competing species decouple with increasing anthropogenic stress, and (2) stronger coupling may occur between habitat providers and dependent species when overall habitat complexity is reduced. These results highlight the complex manner in which anthropogenic stress can influence ecosystems and the importance of considering community structure when exploring biodiversity patterns in basic and applied ecological research, particularly at small scales and for surrogate taxa development.

Anthropogenic stress alters community concordance at the river-riparian interface

Organisms often respond in similar ways to environmental or spatial gradients, particularly at large spatial scales, but patterns at finer scales and across ecotones are less certain. It is important to understand these relationships at multiple spatial scales, as managers often need suitable surrogate taxa for conservation and monitoring purposes. We explored whether community concordance at the river-riparian interface was decoupled by increasing anthropogenic stress (a gradient of local land-use intensity) at 15 sites over three years within the LTER site, Rhine-Main Observatory, a low mountain river system in central Germany. We assessed concordance between four organism groups: riparian spiders and carabid beetles, benthic macroinvertebrates, and combined aquatic macrophytes and riparian plants. This represented three different linkages: (1) predator-prey, (2) direct competition, and (3) habitat associations. While there were no correlations in richness patterns, multivariate community structure was highly concordant between all groups. Anthropogenic stress strongly reduced links between riparian spiders and carabid beetles, likely resulting from their shared resource requirements. However, increasing concordance occurred between plants and other groups. We posit that patterns may be resulting from two processes: (1) linkages between directly competing species decouple with increasing anthropogenic stress, and (2) stronger coupling may occur between habitat providers and dependent species when overall habitat complexity is reduced. These results highlight the complex manner in which anthropogenic stress can influence ecosystems and the importance of considering community structure when exploring biodiversity patterns in basic and applied ecological research, particularly at small scales and for surrogate taxa development.

Spatial community concordance of summer phytoplankton and profundal macroinvertebrates in boreal lakes

Reliance of profundal benthic macroinvertebrate assemblages on epilimnetic algal production — a key element of pelagic–benthic coupling — is a well-recognized phenomenon in the literature but the details are still poorly understood. In particular, the importance of taxonomic composition of algal communities and associated qualitative aspects of the settling material to benthic invertebrates is poorly known. We addressed this issue by investigating concordance of summer phytoplankton and profundal macroinvertebrate community composition using data from 47 boreal lakes. We examined community variation and environmental correlates of phytoplankton and macroinvertebrates with nonmetric multidimensional scaling ordinations. We also used cluster analysis to group sites according to their macroinvertebrate assemblages and evaluated the differences in phytoplankton composition and class-specific relative abundance among the clusters. Community concordance was evaluated with Procrustes rotation and partial Mantel tests, using oxygen concentration and phytoplankton biomass — the main drivers of macroinvertebrate community structure — as controlling factors. Procrustes and Mantel tests suggested congruence between macroinvertebrate and summer phytoplankton community composition. The concordance remained significant even after controlling for oxygen and biomass, by partial Mantel tests, suggesting a unique effect of phytoplankton species composition on macroinvertebrate assemblages. The four groups of lakes clustered by their macroinvertebrate assemblages also differed significantly in their phytoplankton taxa composition, and there were among-cluster differences in relative abundance of the seven most abundant phytoplankton classes. Our findings of community concordance of phytoplankton and profundal macroinvertebrates suggest a functional dependency of these two components, but further studies are needed to verify the actual causal mechanisms.

Regional-scale patterns in community concordance: testing the roles of historical biogeography versus contemporary abiotic controls in determining stream community composition

The determinants of a local-scale biological community can include both abiotic and biotic factors acting at a variety of spatial and temporal scales. Previous studies have shown that the Precambrian Shield, a broad-scale geological feature, has distinct abiotic conditions and aquatic communities in lotic systems as compared with systems off-Shield. The relative importance of historical biogeography and postglacial colonization in Ontario versus the role of contemporary abiotic conditions has been debated in determining fish community composition. In this study, we sampled fish and macroinvertebrate community data from south-central Ontario streams to examine the degree of community concordance between fishes and macroinvertebrates and to determine the main abiotic drivers for this biological distinction between Shield and off-Shield areas. This study shows that low-order lotic systems on the Shield differ both abiotically and biotically from adjacent off-Shield systems and that similar abiotic drivers are responsible for structuring both groups of taxa. However, water chemistry and land-use variables are the most important in structuring macroinvertebrate communities, whereas physical habitat plays a larger role for fish communities.