The role of stochastic vs. deterministic processes in affecting the structure and composition of ecological communities has recently received much attention, because discussions regarding the importance of neutral- and niche-based models of community assembly are largely discussions of the relative importance of stochasticity and determinism.  Community size, defined as the number of individuals in a local community, is an important determinant of the degree to which stochastic and deterministic forces affect competition: stochasticity plays a greater role in determining victory when local communities are small, whereas deterministic outcomes are more likely when communities are large.  Using a combination of analytical models and numerical simulations, I examined how community size affects the outcome of competition within metacommunities.
Results/Conclusions

I find that, due to increased ecological drift, inferior competitors are more likely to persist in metacommunities composed of small local communities.  Although the persistence of inferior competitors is often assumed to require colonization abilities greater than the superior competitor (i.e. the competition-colonization tradeoff), my results demonstrate that greater colonization ability is not necessary, as long as the size of local communities is small enough that inferior competitors are likely to achieve victory by chance alone in some of the patches where they coincide with superior competitors.  In addition to demonstrating conditions under which inferior competitors may persist, these results suggest that the characteristics of local communities are extremely important in determining metacommunity dynamics: in otherwise identical metacommunities, local community size can determine which competitors persist and which competitors become extinct.