The influence of the metacommunity state on neutral theory predictions for the local community

Background/Question/Methods

Ecologists have been testing the predictions of a neutral theory of community structure in hopes of detecting departures from it as an indication of other community assembly mechanisms at work. This neutral theory assumes species coexist due to similarities in fitness in a given environment, in which case demographic stochasticity and dispersal are the dominant influences on patterns in community structure. The theory is often tested in its ability to generate species abundance distribution predictions that can be fit to species abundance distributions observed in a given local community.  These local community predictions are generated in a model framework that assumes a neutral local community experiences immigration from a regional pool, called the metacommunity, which is also modeled as neutral, but which gets its input of species through a process of speciation. The predictions do not use information about the actual regional pool, instead assuming that the metacommunity could be in any one of the many possible states it might achieve at equilibrium, and hence integrates over the relative probability of that variety of states. But how much does the actual state of the metacommunity affect the predicted species abundance distribution of the local community?

Results/Conclusions

We find that the average species abundance distribution in a local community, predicted from a particular equilibrium state of the metacommunity, can vary from the average predicted assuming that any equilibrium state of the metacommunity is possible.  In particular, we find that metacommunities with more dominant species engender local communities with fewer rare species.  We are currently carrying out analyses to quantify this effect and further explicate the influence of the metacommunity on local community predictions.