Neutral theory tested by birds, Ostling 2006 and Coexistence of Neutral and Niche Perspectives, Liebold 2006

Ostling presents a case study on birds testing neutral theory over the whole of South America, and finds it lacking. No real surprise there, on a regional scale differences in habitat and niches should predominate in determining species communities. But on a smaller scale, neutral theory isn't ruled out either, as Liebold makes the point of noting (of course, niche theory isn't excluded either). Both papers seem to make the point that a blend of the two views is appropriate (usually), and the degree of blending depends on the community in question, the scale of investigation, and the evolutionary history of the species.

I'm wondering if it's fair to say that if within species phenotypic variation (averaged over all ecologically important traits) is greater than between species variation in a given ecological setting then neutral interactions will predominate, and if between species variation is greater then niche differentiation will predominate. Neither excludes the other completely, of course.

I also found this prediction by Liebold pretty interesting- equivalent species should be more prevalent in areas more recently subjected to ecological upheavals. If that's the case, we should have a lot of evidence around us from the recent glaciation of N America. Second, I wonder if species previously considered "recently speciated" or "on their way to divergence" might actually be endpoints (i.e. ecological selection forces are no longer actively driving the two species apart), different species maintained by neutral interactions, rather then simply species on their way to more dramatic speciation.

This neutral theory stuff is intersting to me- I don't have a lot of background in it. Apparently it was popularized after I finished my undergrad. I always thought of it more as a foil, a null model like the Hardy-Weinburg, to test more robust theories against. Cool to read about it's actual application, and even if it turns out to be just a null model in the end, it's still certainly generated a lot of good thought.