Effects of prey density, temperature and predator diversity on nonconsumptive predator-driven mortality in a freshwater food web

Lukáš Veselý,Miloš Buřič,Pavel Kozák,David S Boukal,Arnaud Sentis,Antonín Kouba

doi:10.1038/s41598-017-17998-4

Abstract

Nonconsumptive predator-driven mortality (NCM), defined as prey mortality due to predation that does not result in prey consumption, is an underestimated component of predator-prey interactions with possible implications for population dynamics and ecosystem functioning. However, the biotic and abiotic factors influencing this mortality component remain largely unexplored, leaving a gap in our understanding of the impacts of environmental change on ecological communities. We investigated the effects of temperature, prey density, and predator diversity and density on NCM in an aquatic food web module composed of dragonfly larvae (Aeshna cyanea) and marbled crayfish (Procambarus fallax f. virginalis) preying on common carp (Cyprinus carpio) fry. We found that NCM increased with prey density and depended on the functional diversity and density of the predator community. Warming significantly reduced NCM only in the dragonfly larvae but the magnitude depended on dragonfly larvae density. Our results indicate that energy transfer across trophic levels is more efficient due to lower NCM in functionally diverse predator communities, at lower resource densities and at higher temperatures. This suggests that environmental changes such as climate warming and reduced resource availability could increase the efficiency of energy transfer in food webs only if functionally diverse predator communities are conserved.

Highlights

Investigating the effects of environmental drivers on food webs is crucial to better understand global change impacts on energy and nutrient fluxes across trophic levels
We experimentally investigated the effects of temperature, resource availability, and predator density and diversity on Nonconsumptive predator-driven mortality (NCM) strengths
While prey mortality was negligible in controls without predators (0–2% of the initial prey died during the experiment, mean ± SD = 0.84 ± 1.06%), the proportion of dead uneaten prey per predator was significantly positive in treatments with predators

Summary

Introduction

Investigating the effects of environmental drivers on food webs is crucial to better understand global change impacts on energy and nutrient fluxes across trophic levels. While surplus killing is well documented and relatively common, cases of prey mortality linked to high stress levels and unsuccessful predator attacks remain largely unexplored All these phenomena contribute to nonconsumptive predator-driven mortality (hereafter NCM) in food webs. Human activities lead to rapid environmental changes including pollution, habitat alteration, nutrient enrichment, and global warming Understanding how these drivers impact organisms and their interactions, including surplus killing and other processes affecting energy transfer across trophic levels, is important to better predict global change consequences on Earth’s biota[4,37,38,39,40]. One study reported a decrease in surplus killing with warming[34], possibly due to higher metabolic demands of predators at warmer temperatures and higher ingestion rates required to fulfil these demands[23]

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Results

Discussion

Conclusion