Species coexistence in a variable world |
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Authors: | Gravel Dominique Guichard Frédéric Hochberg Michael E |
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Institution: | Département de biologie, chimie et géographique, Université du Québec à Rimouski, 300 Allée des Ursulines, Québec, Canada G5L 3A1. dominique_gravel@uqar.qc.ca |
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Abstract: | 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. |
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Keywords: | Coexistence ecological drift extinction risk neutral theory niche nonlinear averaging stability stochasticity |
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