Rapid evolution of multiple species as the origin of functional groups and ecological neutrality

Background/Question/Methods   
For decades, ecologists have struggled to determine the mechanisms that control diversity in natural communities.  Niche partitioning, in which species evolve to use different resources to avoid competitive exclusion, has served as the foundation for most theories of biodiversity, but requires significant niche space.  In contrast, the neutral theory of biodiversity posits that species may coexist because their similarity precludes competitive dominance, allowing species to share niches.  Intra and interspecific competition among neutral species are similar, thus precluding competitive exclusion of any one species.  Yet, current neutral theory, while explaining ecological patterns, provides no mechanism for the origin or maintenance of species equivalence over evolutionary time.  We simulate the evolution of suites of species using substitutable, discrete resources to follow the simultaneous evolution of multiple competitors.
Results/Conclusions

The model demonstrates that both convergence and divergence may occur and the evolutionary outcomes depend on the interaction between species initial similarity in resource use and the rate of evolution.   Species using similar resources compete strongly and are likely to suffer extinction unless they evolve sufficiently fast to converge in resource use.  Convergence leads to ecological neutrality and species avoid competitive exclusion.  Although it is rarely considered in ecological models, convergence proves to be a viable evolutionary strategy, and may be especially common when considering the simultaneous evolution of multiple competitors.  Such evolution in a community context is rarely considered theoretically or experimentally, but is commonplace in natural communities since few species exist in isolation from other species.  Niche and neutral theories are typically thought of as opposing theories, but recent work has tried to reconcile how both niche (i.e. coexistence mechanisms) and neutral processes (i.e. stochastic ecological drift) are likely to control diversity in the same community.  We suggest that neutral processes may be important for determining diversity within functionally similar groups, while niche processes drive diversity among functional groups.