Primary selection of mass specific metabolism explains differences between endotherms and ectotherms
Evidence on the scaling of the intercepts of traditional Kleiber allometries is not as clear as for the mass-rescaling exponents. But with ectotherms having field metabolic rates that are 12 to 20 times smaller than in similar sized endotherms (Nagy, 2005), we expect ectotherms to have longer lifespans and to be more abundant than similar sized endotherms, and this is generally the case (Peters, 1983; Currie and Fritz, 1993; de Magalhaes et al., 2007). The predicted inverse relationship between lifetime reproduction and the mass-rescaling intercept for mass specific metabolism is also in agreement with fecundity estimates that are about ten times higher in reptiles than in mammals (Peters, 1983) reflecting, as predicted, a higher probability to survive to reproduce in mammals.
Other evidence on the metabolic-rescaling of the life history is related to the transitions in the overall exponent for mass specific metabolism across the tree of life (see next section on final body mass allometries).
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