Predator Diversity Effects in an Exotic Freshwater Food Web

Rahmat Naddafi,Lars G Rudstam,Sebastian C A Ferse

doi:10.1371/journal.pone.0072599

Rahmat Naddafi, Lars G Rudstam + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0072599

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Abstract

Cascading trophic interactions are often defined as the indirect effects of a predator on primary producers through the effect of the predator on herbivores. These effects can be both direct through removal of herbivores [density-mediated indirect interactions (DMIIs)] or indirect through changes in the behavior of the herbivores [trait-mediated indirect interactions (TMIIs)]. How the relative importance of these two indirect interactions varies with predator diversity remains poorly understood. We tested the effect of predator diversity on both TMIIs and DMIIs on phytoplankton using two competitive invasive dreissenid mussel species (zebra mussel and quagga mussel) as the herbivores and combinations of one, two or all three species of the predators pumpkinseed sunfish, round goby, and rusty crayfish. Predators had either direct access to mussels and induced both TMII and DMII, or no direct access and induced only TMII through the presence of risk cues. In both sets of treatments, the predators induced a trophic cascade which resulted in more phytoplankton remaining with predators present than with only mussels present. The trophic cascade was weaker in three-predator and two-predator treatments than in one-predator treatments when predators had direct access to dreissenids (DMIIs and TMIIs). Crayfish had higher cascading effects on phytoplankton than both pumpkinseed and round goby. Increased predator diversity decreased the strength of DMIIs but had no effect on the strength of TMIIs. The strength of TMIIs was higher with zebra than quagga mussels. Our study suggests that inter-specific interference among predators in multi-species treatments weakens the consumptive cascading effects of predation on lower trophic levels whereas the importance of predator diversity on trait mediated effects depends on predator identity.

Highlights

Indirect effects of predators on basal resources, i.e. top down trophic cascades, are a major driver of the dynamics of ecological communities in both terrestrial and aquatic systems [1,2]
Predator identity, predator diet breadth, abundance and diversity of available prey as well as habitat determine the relative importance of density-mediated indirect interactions (DMIIs) and trait- mediated indirect interactions (TMIIs) [2,9,25]; it is less clear how it is affected by predator diversity
We demonstrated that increased predator diversity decrease the strength of trophic cascades only when predators could kill prey but not when the cascading effect was through trait mediated indirect interactions, increased predator diversity decreased the importance of DMIIs but not TMIIs

Summary

Introduction

Indirect effects of predators on basal resources, i.e. top down trophic cascades, are a major driver of the dynamics of ecological communities in both terrestrial and aquatic systems [1,2]. As there is a trade-off between prey foraging success and risk of predation [14,15] and the non-lethal effect of multiple predators on species interactions can be different from the effect of a single predator [16,17], the diversity of predators may affect the strength of anti-predator behavioural responses and the strength of trait-mediated indirect interactions in both aquatic and terrestrial systems [18,19,20,21]. Predator identity, predator diet breadth, abundance and diversity of available prey as well as habitat determine the relative importance of DMII and TMII [2,9,25]; it is less clear how it is affected by predator diversity. We evaluated how the non-lethal and lethal effects of predators with different hunting modes influence the importance of density- and trait-mediated trophic cascades in a freshwater food web

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