Species coexistence in a variable world


  • Dominique Gravel,

    Corresponding author
    1. Département de biologie, chimie et géographique, Université du Québec à Rimouski, 300 Allée des Ursulines, Québec, Canada. G5L 3A1
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  • Frédéric Guichard,

    1. Biology department, McGill University, 1205 Dr. Penfield avenue, Montréal, Canada. H3A 1B1
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  • Michael E. Hochberg

    1. Université Montpellier 2, CNRS UMR 5554, Institut des Sciences de l’Évolution, CC 065, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France
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E-mail: dominique_gravel@uqar.qc.ca


Ecology Letters (2011) 14: 828–839


The contribution of deterministic and stochastic processes to species coexistence is widely debated. With the introduction of powerful statistical techniques, we can now better characterise different sources of uncertainty when quantifying niche differentiation. The theoretical literature on the effect of stochasticity on coexistence, however, is often ignored by field ecologists because of its technical nature and difficulties in its application. In this review, we examine how different sources of variability in population dynamics contribute to coexistence. Unfortunately, few general rules emerge among the different models that have been studied to date. Nonetheless, we believe that a greater understanding is possible, based on the integration of coexistence and population extinction risk theories. There are two conditions for coexistence in the presence of environmental and demographic variability: (1) the average per capita growth rates of all coexisting species must be positive when at low densities, and (2) these growth rates must be strong enough to overcome negative random events potentially pushing densities to extinction. We propose that critical tests for species coexistence must account for niche differentiation arising from this variability and should be based explicitly on notions of stability and ecological drift.