Tuesday, October 30, 2012

The contrasting effects of habitat area and heterogeneity on diversity

ResearchBlogging.org“How extremely stupid not to have thought of that!” (Thomas H. Huxley, commenting on the obviousness of Darwin’s theory of natural selection)

Sometimes I read a paper and Huxley’s famous quote seems exceedingly appropriate. Why I say this is that a new idea or concept is presented which seems both so simple and at the same time a potentially powerful explanation of patterns in nature. This was my reaction to a recent paper from Omri Allouche and colleagues published in the Proceedings ofthe National Academy of Science. The paper presents a simple conceptual model, in the same vein as Connell’s classic intermediate disturbance hypothesis, which accounts for large-scale diversity patterns based on aspects of species niche requirements as well as classic stochastic theory. Merging these two aspects is a critical step forward, as in ecology, there has been a tension in explaining diversity patterns between niche-based processes requiring that species exhibit differences in their needs, and stochastic (or neutral) explanations that ignore these differences, but seem to do well at large scales.

The classic stochastic model in ecology, the theory of island biogeography, simply predicted that the number of species increases with the size of an island or habitat, and ultimately is the balance between species colonizing and going extinct. Allouche et al. also assume this stochastic colonization and extinction, such that in a uniform environment, the number of species increases with area. However, they then add the fact that species do not do equally well in different habitats, that is they have specific environmental niches associated with a particular environment. Thus as you increase the amount of heterogeneity in a landscape, you increase the total number of species, because you’ve captured more niches. However, there is a trade-off here. Namely, as you increase the heterogeneity in a landscape, the amount of area for the dominant habitat type decreases, thus reducing the number of species. So if you increase the heterogeneity too much, the individual habitat types will be too small to support large numbers of species and the numbers of species will be less than regions with less heterogeneity –paradoxically.

Their heuristic prediction is that diversity is maximized at intermediate levels of heterogeneity, as long as species have intermediate niche breadths (i.e., they could perhaps use a couple of different habitats). However, if their niche breadth is too narrow (i.e., they can only exist in a single habitat type), then diversity may only decline with increasing heterogeneity. Conversely, if species have very broad niche breadths (i.e., can survive in many different habitats) then the tradeoff vanishes and heterogeneity has little effect on diversity.

They tested this exceedingly simple prediction using European bird data and found that species richness was maximized at intermediate heterogeneity (measured by the variation in elevation). Further, when they classified species into different niche width classes, they found that the relationship between richness and heterogeneity changed was predicted (i.e., strongest for intermediate breadth).

This is a great paper and should have a large impact. It will be exciting to see what other systems fit this pattern and how specific studies later the interpretation or mechanisms in this model.

Allouche, O., Kalyuzhny, M., Moreno-Rueda, G., Pizarro, M., & Kadmon, R. (2012). Area-heterogeneity tradeoff and the diversity of ecological communities Proceedings of the National Academy of Sciences, 109 (43), 17495-17500 DOI: 10.1073/pnas.1208652109

Friday, October 26, 2012

Open access: where to from here?

Undoubtedly, readers of this blog have: a) published in an open access (OA) journal; b) debated the merits of an OA journal; and/or c) received spam from shady, predatory OA journals (I know when my grad students have 'made it' when they tell me they got an e-mail invite to submit to the Open Journal of the Latest Research Keyword). Now that we have had OA journals operating for several years, it is a good time to ask about their meaningfulness for research and researchers. Bob O'Hara has recently published an excellent reflection on OA in the Guardian newspaper, and it deserves to be read and discussed. Find it here.

Thursday, October 18, 2012

Amusing titles for papers - the crowning touch?

I'll try for a more content-full blog post in the near future, but I couldn't help noticing that there are a number of papers in my reader this month with amusing titles. Titles are always one of the most difficult parts of writing a paper - how do you capture the important aspects of your paper in a minimum of words, while avoiding the usual traps of colons, question marks, and cliches (not to mention the urge to throw in buzzwords)? For that reason, I always appreciate authors willing to be a little intriguing, whether with metaphors, puns, or clever references.

(As an anecdote, I was in a reading group a week ago where we were discussing a paper about turtle movements. People couldn't stop making Ninja Turtle jokes throughout the meeting (academics are cool like that), and I'll admit I had a moment of jealousy over people who work with charismatic creatures which lend themselves to amusing references in papers and talks. There aren't too many jokes about computer models.)

Some amusing titles in the last month or two:

Taxonomy versus phylogeny: evolutionary history of marsh rabbits without hopping to conclusions

Declining woodland birds in North America: should we blame Bambi?

Dragonflies: climate canaries for river management

Bayesian transmogrification of clade divergence dates: a critique 

A slightly older but still excellent title:

The well-temperatured biologist

Although this study suggests that a clever titles will get cited less, I am at least more likely to read the abstract...

There are lots of classic titles I've overlooked, feel free to add them to the comments.