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.

Intermediate Disturbance Hypothesis, Fractal landscapes, and heterogeneity

A pretentious title of sorts, but... I was reading through "the effect of landscape structure on community self-organization and critical biodiversity" (With 2004), which is quite interesting, and noticed a connection between her landscape structure creations and disturbance maps. Her fractal landscapes (ranging from random to highly ordered) look just like different disturbance maps, corresponding to small, frequent disturbances to rare, large disturbances. The connection wasn't made in her paper, but it's still kind of cool. Then, thinking about how landscape biodiversity is usually a simple function of the amount of habitat available, I put together a graph combining those two ideas, mostly for myself to try and clarify the relationship. Hopefully it makes sense. The boxes on the left show the types of habitat in the different setups, I didn't indicate edge on the two lower ones, but they are there. It requires not thinking about edges as "effected interior habitat," but rather considering them unique habitat in their own right, which is a fair statement, I imagine. Second, all of those boxes on the left are supposed to have the same amount of black and white (before edges are taken into account) so there's no change in the amount of habitat before edges from highly clumped (top) to highly fragmented (bottom). This would also place Kendi's invasibility work right in the middle too.

Note that landscape heterogeneity peaks in the middle. Forgot to put that line in.



Now that I post that, I think it's probably a pretty trivial and obvious relationship. But... it's there now, and I need to go vote, so it's staying up. Cheers.

On the importance of landscape history for assessing extinction risk, Schrott (2005), Ecological Applications

Pretty interesting paper detailing the risk of extinction in various landscape situations over time, and showing the potential for lagged responses in population size. If there's a lagged response, then any population viability assessment could be quite erroneous if based on only the current situtation, and not looking at the past history. Makes sense. It's pretty theoretical, so there are several arbitrary deliniations for a viable population, threshold values, etc, but that's fine. Of course, there is a caveat that extinction thresholds are so different for individual species that a cookbook approach (i.e. how much habitat is "enough") is to be avoided- but then the whole paper is "strategic," in that it's meant to be applicable broadly... So when calculating suitable and unsuitable habitat, aren't you more or less calculating what is "enough?" Perhaps splitting hairs and being unfair to a theoretical argument, I suppose.

One problem is the way they calculate spread. Both the persistence and the "invasion" calculations are the same, i.e. the species has the same chance at persistence in suitable habitat as it does spread into neighboring suitable habitat. Work by Kendi has shown that in many cases, it's more difficult to spread then persist, and some sort of favorable conditions need to exist before a species spreads into neighboring habitats, even if that habitat would be perfectly suitable once the species arrives (like an activation energy barrier from chemistry or something), mainly due to competition, low initial population sizes, stochastic issues, etc.

While this is based entirely from the conservation viewpoint, there's no reason the same ideas wouldn't be directly applicable to invasions... for an invader to invade, it's got to avoid going extinct when colonizing. Makes sense for the bark beetle too- they are effectivly destroying their own habitat as they go along, changing the landscape structure and therefore altering the environment in which the next generation has to make a living. Finally, how do you do this assessment on a species intitially? If you haven't made repeated population and landscape assessments over the last 20 years, then this analysis doesn't seem to help, unless we can find some clever way to circumvent that problem...

Invasion in a heterogeneous world: resistance, coexistence or hostile takeover?
Melbourne, et al. Ecology Letters (2007) 10:77-94