Interaction strength and stability in stage‐structured food web modules

Karin A Nilsson,Amanda L Caskenette,Kevin S Mccann

doi:10.1111/oik.05029

Abstract

There has been a long‐standing debate on what creates stability in food webs. One major finding is that weak interactions can mute the destabilizing potential of strong interactions. Considering that stage structure is common in nature, that existing studies on stability that include population stage structure point in different directions, and the recent theoretical developments in the area of stage structure, there is a need to address the effects of population stage structure in this context. Using simple food web modules, with stage structure in an intermediate consumer, we here begin to theoretically investigate the effects of stage structure on food web stability. We found a general correspondence to previous results such that strong interactions had destabilizing effects and weak interactions that result in decreased energy flux had stabilizing effects. However, we also found a number of novel results connected to stage structure. Interestingly, weak interactions can be destabilizing when they excite other interactions. We also found that cohort cycles and predator–prey cycles did not respond in the same way to increasing interactions strength. We found that the combined effects of two predators feeding on the same prey can strongly destabilize a system. Consistent with previous studies, we also found that stage‐specific feeding can create a refuge effect that leads to a lack of strong destabilization at high interaction strength. Overall, stage structure had both stabilizing and destabilizing aspects. Some effects could be explained by our current understanding of energetic processes; others need additional consideration. Additional aspects such as shunting of energy between stages, control of biomass fluxes, and interactions between lags and energy flux, should be considered.

Highlights

Ecologists have sought to understand the relationship between food web complexity and stability for over 40 years (Elton 1958, May 1973, McCann 2000)
Specific question we address include: 1) do cohort cycles respond to increasing interaction strength in the same way as predator–prey cycles? 2) Does increasing interaction strength in a food chain with a size-selective predator yield the same stability response as in the unstructured case, i.e. is there a transition from a stabilizing effect to a destabilizing effect as interaction strength is increased? 3) Is there a transition from a stabilizing to a destabilizing effect as interaction strength is increased in a scenario with two predators present? For this case we had the specific goal to test if weak interactions can be destabilizing for cases when emergent facilitation is present
We have shown that our results using stage-structured populations resonate with previous findings on interaction strength and stability, in that weak interactions caused stabilization, and that we see a transition from a stabilizing effect to an destabilizing effect as interaction strength is increased

Summary

Introduction

Ecologists have sought to understand the relationship between food web complexity and stability for over 40 years (Elton 1958, May 1973, McCann 2000) This issue has become more pressing in light of human impact that is altering the food web structure underlying natural systems. During this time, researchers have put forward a number of consistent theoretical arguments for specific ecosystem properties that govern food web stability (May 2006). This result appears to be consistent over different scales of food web resolution (Rooney et al 2008), but has largely ignored the role of stage structure in mediating dynamics and stability

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Conclusion