Metabolic theories of ecology are based on fractal scaling laws, or the observation that various biological metrics are constant across species, and indeed across phyla. In the 1990's Kleiber's fractal scaling law for animals was extrapolated to ecosystems.
This is a slide from an awesome presentation at the Kavli Institute for Theoretical Physics. The presentation, by Geoffrey West, does an excellent job describing the scope and excitement of this approach. Someday they will be teaching this new theory to school children. The theory was developed by James Brown (UNM), Geoffrey West (Santa Fe Institute), and Brian Enquist (UA). The theory is critically reviewed here.
The original paper is: West, G. B., Brown, J. H. & B. J.Enquist (1997) A general model for the origin of allometric scaling laws in biology. Science 276:122-126.
I will tackle the larger question of linking these organism-centric ideas with ideas about the larger efficiency of communities and ecosystems in a second post...