Consumer‐mediated recycling and cascading trophic interactions

Leroux, Shawn J.; Loreau, Michel

doi:10.1890/09-0133.1

Cited by 46 publications

(61 citation statements)

References 44 publications

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“…elemental C : N contents) of their prey. This shows further that consumer-mediated recycling can be a key mechanism determining the nature of cascading trophic effects within ecosystems [26,33,44,54]. Our results demonstrate the need for caution in interpreting findings that are based on the commonly used C : N ratio.…”

Section: Discussionmentioning

confidence: 58%

Predation risk, stoichiometric plasticity and ecosystem elemental cycling

2012

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It is widely held that herbivore growth and production is limited by dietary nitrogen (N) that in turn constrains ecosystem elemental cycling. Yet, emerging evidence suggests that this conception of limitation may be incomplete, because chronic predation risk heightens herbivore metabolic rate and shifts demand from N-rich proteins to soluble carbohydrate -carbon (C). Because soluble C can be limiting, predation risk may cause ecosystem elemental cycling rates and stoichiometric balance to depend on herbivore physiological plasticity. We report on a stoichiometrically explicit ecosystem model that investigates this problem. The model tracks N, and soluble and recalcitrant C through ecosystem compartments. We evaluate how soluble plant C influences C and N stocks and flows in the presence and absence of predation risk. Without risk, herbivores are limited by N and respire excess C so that plant-soluble C has small effects only on elemental stocks and flows. With predation risk, herbivores are limited by soluble C and release excess N, so plant-soluble C critically influences ecosystem elemental stocks flows. Our results emphasize that expressing ecosystem stoichiometric balance using customary C : N ratios that do not distinguish between soluble and recalcitrant C may not adequately describe limitations on elemental cycling.

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Section: Discussionmentioning

confidence: 58%

Predation risk, stoichiometric plasticity and ecosystem elemental cycling

2012

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“…Such trophic cascades have been widely described in aquatic systems [13]. While crayfish nutrient excretion could also be contributing to increasing primary production by increasing the availability of potentially limiting nutrients, an often overlooked potential mechanism by which consumers can increase primary productivity [55], [56], we did not observe significant relationships between crayfish density and nutrient concentrations in the experiment (Electronic supplemental material Table S1). There were no significant associations between crayfish and algal accrual on control tiles in the experiment (Electronic supplemental material Table S1).…”

Section: Discussionmentioning

confidence: 60%

Trophic Tangles through Time? Opposing Direct and Indirect Effects of an Invasive Omnivore on Stream Ecosystem Processes

et al. 2012

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Omnivores can impact ecosystems via opposing direct or indirect effects. For example, omnivores that feed on herbivores and plants could either increase plant biomass due to the removal of herbivores or decrease plant biomass due to direct consumption. Thus, empirical quantification of the relative importance of direct and indirect impacts of omnivores is needed, especially the impacts of invasive omnivores. Here we investigated how an invasive omnivore (signal crayfish, Pacifastacus leniusculus) impacts stream ecosystems. First, we performed a large-scale experiment to examine the short-term (three month) direct and indirect impacts of crayfish on a stream food web. Second, we performed a comparative study of un-invaded areas and areas invaded 90 years ago to examine whether patterns from the experiment scaled up to longer time frames. In the experiment, crayfish increased leaf litter breakdown rate, decreased the abundance and biomass of other benthic invertebrates, and increased algal production. Thus, crayfish controlled detritus via direct consumption and likely drove a trophic cascade through predation on grazers. Consistent with the experiment, the comparative study also found that benthic invertebrate biomass decreased with crayfish. However, contrary to the experiment, crayfish presence was not significantly associated with higher leaf litter breakdown in the comparative study. We posit that during invasion, generalist crayfish replace the more specialized native detritivores (caddisflies), thereby leading to little long-term change in net detrital breakdown. A feeding experiment revealed that these native detritivores and the crayfish were both effective consumers of detritus. Thus, the impacts of omnivores represent a temporally-shifting interplay between direct and indirect effects that can control basal resources.

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“…They are based on fundamental principles of elemental flux and storage among different trophic levels in an ecosystem, based on known mechanisms for their action (Leroux and Loreau 2010; Schmitz et al. 2010).…”

Section: The Theoretical Frameworkmentioning

confidence: 99%

“…1) often used when examining organismal effects on ecosystem functioning (Hall et al. 2007; Leroux and Loreau 2010; Loreau 2010; Bassar et al. 2012; Leroux et al.…”

Section: The Theoretical Frameworkmentioning

confidence: 99%

Predator‐driven elemental cycling: the impact of predation and risk effects on ecosystem stoichiometry

Leroux

Schmitz

2015

Ecology and Evolution

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Empirical evidence is beginning to show that predators can be important drivers of elemental cycling within ecosystems by propagating indirect effects that determine the distribution of elements among trophic levels as well as determine the chemical content of organic matter that becomes decomposed by microbes. These indirect effects can be propagated by predator consumptive effects on prey, nonconsumptive (risk) effects, or a combination of both. Currently, there is insufficient theory to predict how such predator effects should propagate throughout ecosystems. We present here a theoretical framework for exploring predator effects on ecosystem elemental cycling to encourage further empirical quantification. We use a classic ecosystem trophic compartment model as a basis for our analyses but infuse principles from ecological stoichiometry into the analyses of elemental cycling. Using a combined analytical‐numerical approach, we compare how predators affect cycling through consumptive effects in which they control the flux of nutrients up trophic chains; through risk effects in which they change the homeostatic elemental balance of herbivore prey which accordingly changes the element ratio herbivores select from plants; and through a combination of both effects. Our analysis reveals that predators can have quantitatively important effects on elemental cycling, relative to a model formalism that excludes predator effects. Furthermore, the feedbacks due to predator nonconsumptive effects often have the quantitatively strongest impact on whole ecosystem elemental stocks, production and efficiency rates, and recycling fluxes by changing the stoichiometric balance of all trophic levels. Our modeling framework predictably shows how bottom‐up control by microbes and top‐down control by predators on ecosystems become interdependent when top predator effects permeate ecosystems.

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Consumer‐mediated recycling and cascading trophic interactions

Cited by 46 publications

References 44 publications

Predation risk, stoichiometric plasticity and ecosystem elemental cycling

Predation risk, stoichiometric plasticity and ecosystem elemental cycling

Trophic Tangles through Time? Opposing Direct and Indirect Effects of an Invasive Omnivore on Stream Ecosystem Processes

Predator‐driven elemental cycling: the impact of predation and risk effects on ecosystem stoichiometry

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