Direct, water-chemistry mediated, and cascading effects of human-impact intensification on multitrophic biodiversity in ponds

There is a consensus that human activities affect biodiversity in pond ecosystems. However, the majority of studies have mainly focused on the direct effect of human activities on a single group, despite the fact that anthropogenically induced biodiversity loss in ecosystems occurs across multiple trophic levels and may depend on both altered habitat (e.g., water chemistry) and on trophic interactions cascading up the trophic network. In this study, we analyzed the simultaneous direct, water-chemistry mediated and trophic network cascading effects of the overall human-impact intensification on density (biomass/abundance) and richness (number of taxa) across all trophic levels in pond ecosystems. For this, we collected and combined multi-taxon data (341 taxa) for macrophytes, phytoplankton, zooplankton, benthic and epiphytic macroinvertebrates, and fishes. We showed that human-impact intensification affected the densities and richness of almost all trophic levels across the study ecosystems, and resulted in an overall negative effect on the multitrophic diversity of the entire community. We detected direct effect of human-impact intensification, but no indirect effects, on the richness of primary producers. In contrast, the indirect effects mediated through the nutrient content in the water were the most influential drivers of multitrophic diversity in the invertebrate communities. At the same time, the indirect effects through the trophic network cascades were detected mainly within the fish community. Our findings improve the mechanistic understanding of multitrophic diversity responses in ponds under the ongoing intensification of anthropogenic pressure.