The mechanistic basis of the metabolic theory of ecology

We welcome the opportunity to respond to O’Connor et al. (2007). We hope that this exchange will help to clarify some of the strengths and weaknesses of the Metabolic theory of ecology (MTE), and will point towards fruitful areas for future research. The MTE has been formulated based on the premise that the structure and dynamics of ecological commu-nities are inextricably linked to individual metabolism. The individual metabolic rate is the rate at which an organism takes up energetic and material resources from the environment, transforms them into useable forms, and allocates them to the fitness-enhancing processes of survival, growth, and reproduction. Interactions be-tween organisms and their environment (including other organisms) are therefore constrained by metabolic rate. Physiologists have long known that there are three primary factors that control metabolic rate: body size, body temperature, and resource availability. MTE builds on this earlier work by providing a quantitative framework to better understand how these three variables combine to affect metabolic rate, and how metabolic rate, in turn, influences the ecology and evolution of populations, communities, and ecosystems (Brown et al. 2004). Gillooly et al. (2001) developed a model for the scaling of metabolic rate that combines the effects of body size and temperature (West et al. 1997, Gillooly