Bactra Review
Stability and Complexity in Model
Ecosystems
by Robert M. May
Second Edition, Princeton University Press, 1974
There is, or used to be at any rate, a belief among ecologists that complexity leads to stability. The root of this seems to be the observation that abandoned fields swiftly return to wilderness, whereas forests endure for millennia. (Physics began with timing balls rolling down inclined planes. As Gould says, science is too boring for scientists to be relativists.) The persistence of a forest (or any other natural ecosystem) for hundreds of years, in the face of all the shocks and disturbances that protoplasm is heir to, means that those ecosystems are, in some sense, stable. (One survey of the mathematical literature on stability distinguished about a hundred distinct definitions, leading me to suspect that a supercritical mass of plutonium is, in some sense, stable: but onward.) As all gardeners know to their cost, artificial ecosystems aren't like that. And artificial ecosystems are always much simpler (in the sense of containing fewer species) than natural ones in the same climate: the most extreme case being petri dishes and other laboratory ecosystems, followed by monocultures.
One idea which suggests itself is that complexity leads to stability, and a number of hand-waving reasons have been proposed --- that complexity ``buffers'' or ``spreads out'' shocks, that it increases homeostasis, etc.
May pretty effectively demolishes the idea that any sort of complexity leads to increased stability. His concern, as a mathematical ecologist, is with models of ecosystems, rather than Nature's dirty, bug-filled reality. He examines all the major classes of models popular in mathematical ecology, and shows that
Out of professional parochialism, I note that May's career is yet another heart-warming ``theoretical physicist makes good in the life sciences'' story.
Robert May, Stability and Complexity in Model
Ecosystems [An effective demolition of the idea that, ceteris
paribus, complicated ecosystems are more stable. In fact the reverse
is true --- in general more complicated systems are less stable.
This is good: it allows us to discard hypotheses ``in general'' and focus
on the much smaller set which allow for both complexity and stability.
May is yet another heart-warming ``theoretical-physicist-makes-good'' story.]
vii+265 pp., illus., bibliography, index
No. 6 in the series Monographs in Population Biology
30 August 1995