Coexistence and emergent neutrality generate synchrony among competitors in fluctuating environments
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Many competitive communities exhibit a puzzling amount of species diversity. In this study, we model a community of symmetric competitors in a fluctuating environment. We use biologically realistic temperature-dependent growth curves with a widely hypothesized trade-off between maximum growth and nice breadth to control the shapes of the curves of different species. We perform three analyses of the community dynamics to investigate the role of environmental fluctuations in community composition and species diversity. We initiate communities with equal abundances of all species and randomize the temperature fluctuations so that there is no correlation between species responses, only noise. We initiate single populations and allow other species to randomly invade the community. We also knock out extant species one by one from an established community and allow them to reinvade after the remaining species have adjusted. We find that competitors with sufficiently different temperature niches coexist via temporal niche differentiation. We also find long-term persistence of species that are very similar to a dominant competitor. This creates communities with species clumped along a temperature niche axis, with stable coexistence between groups and near neutrality within groups. The near neutrality results in interspecific synchrony within the groups, providing an explanation for the maintenance of high diversity in competitive communities where synchrony is commonly observed.
KeywordsCoexistence Competition Emergent neutrality Interspecific synchrony Environmental heterogeneity Thermal performance curve
This work benefitted from discussions with Jeremy Fox, Andre de Roos, Susanna Messinger, and Dan Wieczynski. We thank Jef Huisman for pointing out the link between Eq. 1 and the chemostat model discussed in Appendix A. This work was supported in part by the facilities and staff of the Yale University Faculty of Arts and Sciences High Performance Computing Center. Peter Adler, Jeremy Fox, and Jonathan Levine provided comments on an early draft of this manuscript.
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