Following on from the previous post, another way in which community ecologists often misinterpret neutral models is by mixing up neutrality with dispersal limitation. This leads to mistakes like testing for neutrality by testing for a community ecology equivalent of “isolation by distance”, where more widely-separated communities are more different in species composition, independent of any environmental differences.
I honestly have no clue how this zombie idea could’ve gotten started. Sewell Wright’s classic paper defining isolation by distance talks at length about how migration rate among subpopulations affects their isolation, implying that isolation by distance is not a signature of neutrality. Even in a neutral world, different subpopulations can be as different or similar as you want, depending on the migration rate. Neutral models can perfectly well be panmictic. Wright’s paper also has a whole section on how selection affects isolation by distance, showing that you can still have isolation by distance even in a non-neutral world. Much the same is true in the neutral model with which community ecologists are most familiar, Hubbell’s neutral model. That model remains neutral even if the migration rate is set so high that every newborn individual in the local community is an immigrant from the “metacommunity”, so that there’s no “dispersal limitation” at all. More broadly, ecological theorists have for decades considered all sorts of non-neutral models with all sorts of dispersal rates, from completely closed systems (=zero dispersal) to highly open ones. And that’s before we even start talking about things like sophisticated habitat selection behavior on the part of migrants, which can generate isolation by distance in species composition even in non-neutral, drift-free systems. So how did anyone ever get the idea that low migration rates or isolation by distance are synonymous with, or even tend to be associated with, neutrality?
Don’t get me wrong, dispersal limitation is an interesting and important phenomenon. But it has nothing to do with neutrality vs. non-neutrality.
HT to Brian McGill for beating me to the punch on this in a comment on the previous post.