Persistent disruption of interspecific competition after ultra-low esfenvalerate exposure

TL;DR

This study shows that ultra-low concentrations of esfenvalerate can significantly disrupt interspecific competition in aquatic species, highlighting the need to include ecological interactions in pesticide risk assessments.

Contribution

It demonstrates that environmentally relevant pesticide levels can alter species interactions, emphasizing the importance of ecological complexity in toxicity evaluations.

Findings

Disruption of competition occurs at concentrations 3-4 orders of magnitude below EC50.

Significant population perturbations are only observed near the EC50.

Ecological interactions are sensitive indicators of pesticide effects at low concentrations.

Abstract

Field and mesocosm studies repeatedly show that higher tier process reduce the predictive accuracy of toxicity evaluation and consequently their value for pesticide risk assessment. Therefore, understanding the influence of ecological complexity on toxicant effects is crucial to improve realism of aquatic risk assessment. Here we investigate the influence of repeated exposure to ecologically realistic concentrations of esfenvalerate on the similarly sensitive species Daphnia magna and Culex pipiens in a food limited and highly competitive environment. We show that significant perturbations in population development are only present close to the EC50. In contrast, interspecific competition between species is already reduced at concentrations 3-4 orders of magnitude below the acute EC50. We conclude that extremely low, environmentally relevant concentrations can disrupt species interactions. This toxicant mediated alteration of competitive balances in ecological communities may be the underlying mechanism for shifts in species distribution at ultra-low pesticide concentrations. A realistic risk assessment should therefore consider these processes in order to predict potential pesticide effects on the structure of communities.