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How interplay between positive and negative feedback influences the persistence of consumer-resource and mutualistic interactions


Investigating the mechanisms by which species persist within complex ecological communities and in variable environments is critical for understanding how biodiversity is maintained in the face of perturbations in the biotic (e.g., invasive species) and abiotic (e.g., climate change) environment. Persistence arises from the interplay between species interactions (e.g., consumer-resource, mutualism, competition) and species' responses to environmental variability. My objectives are to investigate the mechanisms promoting the persistence of consumer-resource (e.g., predator-prey) and mutualistic (e.g., plant-pollinator) interactions and to understand how species respond to environmental variation. From a theoretical perspective, I develop conceptual frameworks to investigate how tension between stabilizing negative feedback and destabilizing positive feedback affects the persistence of (i) consumer-resource and (ii) mutualistic interactions. (i) The stability of consumer-resource interactions arises from the tension between within-species interactions inducing negative feedback (e.g., resource self-limitation due to intraspecific competition) and between-species interactions inducing positive feedback (e.g., consumer overcompensation due to saturating functional responses). I derive an empirically quantifiable metric that incorporates positive and negative feedback effects, and thus, the net effect of within- and between-species interactions on a focal species' per capita growth rate. (ii) Mutualistic interactions are characterized by positive feedback that should make them extinction prone. Yet, mutualisms are widespread and persistent in nature. Empirical data suggests that competition for the benefits given by mutualistic partners may induce negative feedback. I develop a theoretical framework that incorporates competition for benefits within mutualistic interactions and find that competition for benefits alone promotes the assembly and persistence of mutualistic communities. Finally, I use a combination of theoretical and empirical approaches to investigate the population dynamics of the bordered plant bug (Largus californicus), a Hemipteran herbivore inhabiting the California coastal sage scrub. I find that both temperature and resource variation interact with development-induced delays in the operation of negative feedback to drive the observed dynamics. These frameworks yield testable predictions about the mechanisms promoting the persistence of consumer-resource and mutualistic interactions and the dynamics of species inhabiting variable environments. The results illustrate how considering positive and negative feedback effects offer key insights into the mechanisms underlying the generation and maintenance of biodiversity.

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