The Value of Null Theories in Ecology

Reactions to the metabolic theory of ecology (MTE) proposed by Brown et al. (2004, this issue) are likely to fall into the following categories. Enthusiastic support.—MTE persuasively demonstrates how a few simple, well-founded physical principles concerning energy and temperature can explain an impressive fraction of the natural variability in organism-level productivity, developmental rates, mortality, and other life history traits, and in ecosystemlevel carbon turnover, population density, and resource partitioning. This is particularly impressive, given that the theory assumes nothing about many of the concepts that most ecologists had probably thought to be essential input to any comprehensive theory, such as reproductive strategies, succession, stability, food webs, spatial distribution of individuals and species, stochastic and cyclic temporal variability, the influence of disturbance regimes, and organism behavior (including its role in determining effective environmental temperature). MTE will be a major component of a parsimonious theory of nearly everything in ecology. Here at last is an agenda for ecology. Limited admiration.—MTE explains parsimoniously a very limited subset of ecosystem traits, but it cannot hope to say anything useful about most of the things that we care about in ecology, such as reproductive strategies, succession, stability, food webs, spatial distribution of individuals and species, stochastic and cyclic temporal variability, the influence of disturbance regimes, and organism behavior. A parsimonious theory of nearly everything in ecology is, at best, far in the future. In the meantime, there are also critical questions in applied ecology. What will ecosystems look like under global warming? What sustains and what threatens ecosystem services? How can ecosystems be restored and managed? How can we best design reserves? We do not have the luxury of waiting indefinitely for some future comprehensive theory of ecology to answer these practical questions; unfortunately, MTE will not help us here. Skeptical dismissal.—The unexplained variances in MTE are large and all those ignored aspects of ecology (listed in Limited admiration) would have to be ingredients in any theory that would convincingly explain