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

Body size is considered a powerful traitthat impacts ecosystem processes and mediatesspecies responses to environmental change. Diversitymetrics informed by body size could thus predictecosystem functions better than taxonomic diversity.However, despite its overwhelming power, the mechanismsby which size drives functions in freshwaterecosystems remain poorly known. Two mechanismsare often hypothesized to explain the relationshipbetween diversity and ecosystem functioning: selectioneffects and complementarity. Here, we evaluate the relative importance of size-based and taxon-basedapproaches in explaining the strength of top-downcontrol on phytoplankton and also aimed at disentanglingthe mechanism by which size operates. Wefound that size significantly explained the variation intop-down control, but size together with taxonomicdiversity provided better predictions. The latter resultdiffers somewhat from those reported in temperateregions and potentially reflects the limited size rangethat is typical of warmer waters. Our results also revealthe importance of selection effects relative to complementarityas a driver of top-down control. Wehighlight the importance of considering multipleaspects of biodiversity and recommend that metricsbased on body size should complement, rather thanreplace, metrics of taxonomic diversity to predictecosystem functions.