Food availability, depth, and turbidity drive zooplankton functional diversity over time in a Neotropical floodplain

Abstract

We evaluated temporal trends in zooplankton functional diversity (functional richness—FRic, evenness—FEve divergence—FDiv, and Community-Weighted Means—CWM) in 12 habitats of the Upper Parana River floodplain (Brazil) over 16 years (2000–2016) and their relationships with environmental predictors (chlorophyll-a, water depth, and turbidity). We hypothesized that different environmental drivers affect zooplankton's functional component in a distinct way. We predicted that: (i) FRic is positively related to increases in chlorophyll-a concentration and turbidity associated with impacts of damming on the floodplain and depth. (ii) FEve is negatively related to increases in chlorophyll-a concentration and turbidity, and positively related to depth. (iii) FDiv is negatively related to the increase in chlorophyll-a, depth, and turbidity. (iv) Finally, we asked how do each of the traits change the functional indexes and their relation to environmental predictors. FRic and FEve fluctuated oppositely and cyclically every five years. FDiv showed a trend similar to that of FRic. However, between 2005 and 2010 FDiv only decreased. All functional diversity indexes were explained by temporal variability, depth, and chlorophyll-a concentration. However, the influence of each variable was different for each component of functional diversity. For CWM, turbidity was negatively associated with life span and positively associated with predator escape, and type of reproduction, while predator escape and feeding type were negatively associated with depth. We highlight that, in order to maintain the drivers of zooplankton functional diversity (food availability, turbidity, and depth), it is extremely important to guarantee the floodplain ecosystem's original state of functionality.