High temperature, predation, nutrient, and food quality drive dominance of small-sized zooplankton in Neotropical lakes

Body size plays a key role in the functioning of communities and ecosystems. However, this ecological trait is commonly under strong selection pressure by environmental drivers, such as temperature, nutrients, predation, and food quality. Understanding how environmental factors interact to shape the body size structure of communities is, therefore, of fundamental and applied interest. Using a unique database from 12 Neotropical lakes, we quantified the community-weighted mean trait (CWM) of zooplankton body size. We investigated how temperature, total phosphorus, abundance of predators (planktivorous fish) and food availability (abundance of edible and inedible algae) affect CWM of zooplankton body size. We also analyzed the interactions among these environmental predictors, and their cascading effects on zooplankton body size. We found that planktivorous fish, inedible algae, and edible algae had strong direct impacts on CWM of zooplankton body size. In particular, planktivorous fish and inedible algae decreased the CWM of body size, whereas edible algae increased it. Temperature and total phosphorus indirectly affected CWM of body size by increasing the abundance of planktivorous fish and inedible algae, and decreasing the abundance of edible algae. Our findings illustrate that environmental factors act in combination and affect zooplankton body size through multiple pathways. Therefore, focusing on the interaction between environmental predictors rather than just their isolated effects may provide a more mechanistic understanding of how environmental changes drive the body size structure of biotic communities.