Beard-stoking

The Scientist has a big ol' article, with a fine typo in the last paragraph, on West, Brown, Enquist and their metabolic theory. It's particularly good on recent historical and biographical detail, although a little sketchier on how the idea works, and what else it might apply to besides metabolism.

And I would take issue with the statement that temperature is a "variable necessary to explain the 3/4 scaling of metabolic rates across organisms". It's not, it's an additional variable that explains some of the variation in metabolic rates (between say, reptiles, birds, and mammals, all of which have different body temperatures) not accounted for by size-based 3/4-power scaling.

The article also shows how some of the disagreements about the theory come from differing expectations and goals. WBE are after a theory that gives an abstract, approximate, first-order account of the underlying structure of organisms and ecosystems.

Confronted with Helen Muller-Landau's data on forest population biology that contradicts their predictions they say, well, ok, it shows something else must be going on. Much as, if you see a planet that doesn't follow its predict orbit, you look for something else influencing it before you junk gravity (not that I am saying metabolic theory is as well-established as gravity). Muller-Landau and others, however, see deviation as disproof.

It's a difference partly of philosophy. But it also shows the genuine uncertainty about when you decide that just because a theory can't predict everything doesn't mean it's wrong (as Michael Ruse has written, natural selection's failures are a sign of its strength), and when you decide it's wrong.

WBE's metabolic model is too powerfully predictive, and its foundations make too good sense, to be junked yet. In fact, it seems to be popping up more and more - I have recently spoken to fisheries and foodweb researchers who are using it.

I would also say that people tend not to change their minds, regardless of what data or theory say. A scientific field's centre of gravity depends on when people retire and who gets their job, as much as it does on dialectic.

(The Scientist has published a couple of previous things on metabolic scaling and so on: here and here.)

A GUT of ecological scaling?

OK. I'm not going to pretend that I grasp the details of this, but here goes.

A recent paper in Physical Review Letters by Jayanth Banavar et al. presents a general theory of (macro)ecological scaling.

That is, they offer a common explanation for patterns such as that between the area of a place and the numbers of species that live there, area and total biomass, the number of organisms and species of different sizes, the maximum body size of the biggest species in an ecosystem (see here for another view of maximum carnivore size), and relative abundance — the spread of rare and common species.

All these scaling patterns seem to follow power laws, at least over partially. That is, they take the form y=ax^n, and plot as straight lines on a log/log graph.

Here's the abstract:

Scaling provides an elegant framework for understanding power-law behavior and deducing relationships between critical exponents. We demonstrate that scaling theory can be generalized to develop a framework for the analysis of diverse empirical macroecological relationships traditionally treated as independent. Our mathematical arguments predict links between the species-area relationship, the relative species abundance and community size spectra in excellent accord with empirical data.

As far as I can tell, Banavar et al. present a scaling hypothesis, based on a probability distribution of the mass and abundance of different species. Using this, and a set of reasonable assumptions (such as, that an ecosystem's total population and mass is proportional to its area) they derive the relationships described from a single starting point.

Blimey. If all these things can be brought under the one roof — this is the first such attempt that I know of — that's a big deal, I think. These are fundamental ecological parameters. Together, they pretty much sum up most of the questions that community ecology seeks to answer. Even the metabolic ecology models of West et al. (with which I am more familiar) have steered clear of tackling the relationships between species diversity and area, and between body size and diversity and abundance.

But, although much of the criticism of metabolic ecology focuses on its generality, Banavar and his colleagues have an interesting history of seeking yet more general models for the scaling of metabolic rate with body size. Banavar has also worked with Steve Hubbell to develop the neutral ecological theory. It's interesting that this is in PRL. I wonder what a biology journal would have made of it.

Thanks to Phil Ball for bringing this to my attention. I think. If anyone has any thoughts on this, I'd love to hear them.