| There has been growing interest in the idea that the mass- and temperature-dependence of organism metabolism, coupled with considerations of biological stoichiometry, can be scaled up to predict patterns in the structure and function of populations, communities, and ecosystems at ecological and evolutionary time scales. Although some empirical evidence has been presented in support of this hypothesis, the "metabolic theory of ecology" remains largely untested. Using a combination of empirical and computational approaches, this dissertation examines the extent to which the mass- and temperature-dependence of organism metabolism determines patterns in population density, population energy use, and whole-ecosystem respiration rate. I found that whole-ecosystem respiration rate scaled with temperature and resource availability in 29 natural, aquatic, "rock pool" microcosm ecosystems, but that the patterns observed differed significantly from the expectations derived using metabolic theory. In further contrast to the expectations of metabolic theory, the amount of energy used by the populations of constituent meio-invertebrate fauna scaled positively with body mass in the rock pool system as a whole. Both the population- and ecosystem-level results indicate that the "energetic equivalence rule," the idea that the amount of energy used by a population per unit area per unit time is independent of body mass, does not hold in these systems. Furthermore, results from computer simulations suggest that the energetic equivalence rule is unlikely to hold consistently at smaller scales of observation in general. Since the energetic equivalence rule is a central tenet in the scaling of the mass- and temperature-dependence of organism metabolism to derive patterns at higher-levels of biological organisation, the evidence presented here suggests that the metabolic theory of ecology may be unable to consistently predict higher-level patterns at smaller scales of observation. |
