Species trait diversity in food webs can reduce the potential for alternative stable states

Vadim Karatayev, School of Environmental Sciences, University of Guelph, Guelph, ON, Canada, Marissa L. Baskett, Environmental Science and Policy, University of California, Davis, Davis, CA and Egbert H. van Nes, Wageningen University, Wageningen, Netherlands

Background/Question/Methods
Alternative stable ecosystem states are possible under the same environmental conditions in many models of 2-3 interacting species and an array of feedback loops. However, multi-species food webs might dissipate the feedback loops that create alternative stable states through species-specific traits and feedbacks. Here we develop a general dynamical model of consumer-resource interactions with two types of processes: either species-specific feedbacks where individual resources become unpalatable at high abundance or aggregate feedbacks where overall resource abundance reduces consumer recruitment. We then quantify how the degree of interconnectedness and species differences in demography affect the potential for either feedback to produce alternative stable consumer- or resource-dominated food web states.
Results/Conclusions
We find that such alternative stable states are likely to happen in many-species food webs when aggregate feedbacks or lower species differences increase redundancy in species contributions to persistence of the consumer guild. Conversely, we show that species-specific palatability feedbacks with distinctive species roles in consumer guild persistence reduce the potential for alternative states but increase the likelihood that losing vulnerable consumers cascades into a food web collapse at low stress levels, a fragility absent in few-species models. Altogether, our results suggest that species trait diversity has a greater impact on whether feedbacks prevent consumer recovery than on the presence of many-species collapses.