Background/Question/Methods
A central question in the study of community ecology is the means by which multiple species coexist.  Many mechanisms explaining coexistence have been developed, usually depending on species having differential responses, or trade-offs, in their ability to respond to other organisms or their environment.  While it is well documented that many such mechanisms allow multiple species to coexist ecologically, the evolutionary origin and stability of coexistence is rarely considered.  Using the framework of adaptive dynamics, we analyze the evolutionary properties of a specific coexistence mechanism, including the evolutionary route to multispecies coexistence and the maximum diversity supported at evolutionary stability.  We are also concerned with the sensitivity of these properties to changes in the components of coexistence, namely, the environmental conditions and the strength of the trade-off between species’ responses to their environment.  In particular, we examine the evolutionary stability of a mechanism that has been shown to permit the ecological coexistence of competing phytoplankton species.  This “gleaner-opportunist” mechanism relies on a trade-off between the competitive ability and the maximum growth rate of interacting species subjected to an environment with periodically fluctuating resource levels.
Results/Conclusions
We find that the ecologically stable multispecies coalitions attributed to this coexistence mechanism are also evolutionarily stable.  The region of parameter space in which multispecies solutions are achieved depends significantly on the proportion of time that resources are available relative to the period of the environmental fluctuation, with the highest number of species supported at intermediate levels of resource availability.  The strength of the trade-off between maximum growth rate and ability to compete for resources also strongly influences the potential for multispecies coexistence, with more severe trade-off curves increasing the range of environmental conditions over which coexistence occurs, and the number of species present in evolutionarily stable coalitions.  The evolutionary stability of other coexistence mechanisms should be similarly evaluated, to better understand the general significance of trade-off strengths and environmental conditions, and to locate any discrepancies between ecologically and evolutionarily stable coexistence.