LAUSR

Organisms use energy to grow and reproduce, so the processes of energy metabolism and biological production should be tightly bound. On the basis of this tenet, we developed and tested a new theory that predicts the relationships among three fundamental aspects of life: metabolic rate, growth, and reproduction. We show that the optimization of these processes yields the observed allometries of metazoan life, particularly metabolic scaling. We conclude that metabolism, growth, and reproduction are inextricably linked; that together they determine fitness; and, in contrast to longstanding dogma, that no single component drives another. Our model predicts that anthropogenic change will cause animals to evolve decreased scaling exponents of metabolism, increased growth rates, and reduced lifetime reproductive outputs, with worrying consequences for the replenishment of future populations. Description Optimized strategies for life Metabolic theory posits that physical constraints on energy uptake and allocation drive biological processes. This theory predicts broad ecological patterns such as the observed allometric scaling relationship between animals’ metabolic rate and body size. White et al. developed a new theory showing that such patterns can also be explained by evolution acting concurrently on organisms’ metabolism, growth, and reproduction. Using data from over 10,000 species from 12 animal phyla, they found support for the prediction that species’ lifetime reproduction is optimized, with growth and reproduction both increasing with metabolic level. This work proposes a bridge between metabolic and life history theory, two basic ways of understanding ecological patterns. —BEL Evolution acting on metabolism, growth, and reproduction can optimize lifetime reproduction and create allometric scaling patterns.