Bottom-up and top-down forces structuring consumer communities in an experimental grassland

摘要

After decades of intensive research, the relative importance of top-down and bottom-up control for structuring ecological communities is still a particularly disputed issue among ecologists. In our study, we determine the relative role of bottom-up and top-down forces in structuring the composition of 13 arthropod functional groups (FG) comprising different trophic consumer levels. Based on species-specific plant biomass and arthropod abundance data from 50 plots of a grassland biodiversity experiment, we quantified the proportions of bottom-up and top-down forces on consumer FG composition while taking into account direct and indirect effects of plant diversity, functional diversity, community biomass, soil properties and spatial arrangement of these plots. Variance partitioning using partial redundancy analysis explained 21-44% of total variation in arthropod functional group composition. Plant-mediated bottom-up forces accounted for the major part of the explainable variation within the composition of all FGs. Predator-mediated top-down forces, however, were much weaker, yet influenced the majority of consumer FGs. Plant functional group composition, notably legume composition, had the most important impact on virtually all consumer FGs. Compared to plant species richness and plant functional group richness, plant community biomass explained a much higher proportion of variation in consumer community composition.