Grazing efficiency asymmetry drives zooplankton top-down control on phytoplankton in a subtropical lake dominated by non-toxic cyanobacteria

Abstract

Body size is considered a powerful trait that impacts ecosystem processes and mediates species responses to environmental change. Diversity metrics informed by body size could thus predict ecosystem functions better than taxonomic diversity. However, despite its overwhelming power, the mechanisms by which size drives functions in freshwater ecosystems remain poorly known. Two mechanisms are often hypothesized to explain the relationship between diversity and ecosystem functioning: selection effects and complementarity. Here, we evaluate the relative importance of size-based and taxon-based approaches in explaining the strength of top-down control on phytoplankton and also aimed at disentangling the mechanism by which size operates. We found that size significantly explained the variation in top-down control, but size together with taxonomic diversity provided better predictions. The latter result differs somewhat from those reported in temperate regions and potentially reflects the limited size range that is typical of warmer waters. Our results also reveal the importance of selection effects relative to complementarity as a driver of top-down control. We highlight the importance of considering multiple aspects of biodiversity and recommend that metrics based on body size should complement, rather than replace, metrics of taxonomic diversity to predict ecosystem functions.