MTE has profound implications for the interpretation of population growth and community diversity. Classically, species are thought of as being either "r" selected (where populations tend to grow exponentially, and are ultimately limited by extrinsic factors) or "K" selected (where population size is limited by density-dependence and carrying capacity). MTE explains this diversity of reproductive strategies as a consequence of the metabolic constraints of organisms. Small organisms and organisms that exist at high body temperatures tend to be "r" selected, which fits with the prediction that "r" selection is a consequence of metabolic rate. Conversely, larger and cooler bodied animals tend to be "K" selected. The relationship between body size and rate of population growth has been demonstrated empirically, and in fact has been shown to scale to "M"−1/4 across taxonomic groups. The optimal population growth rate for a species is therefore thought to be determined by the allometric constraints outlined by the MTE, rather than strictly as a life history trait that is selected for based on environmental conditions.