An optimum body size for mammals? Comparative evidence from bats

Abstract

1. The distribution of body sizes among mammalian species has been modelled by Brown, Marquet and Taper (1993), who suggest that reproductive power (the rate at which energy from the environment is channelled into offspring production) is maximized at a size of 100 g, and the observed size distribution among species reflects the way reproductive power depends on size. The model makes a testable prediction about life-history allometries: namely, that components of reproductive power should not scale linearly with body size but should change sign at the optimum size. 2. A large set of life-history data from a single clade of small mammals, the bats (Order: Chiroptera), was analysed to test this key prediction. The analyses in this study offer no support for the idea that allometries of reproductive power change sign in bats, either at 100 g or at any other size. Furthermore the life-history allometries of bats, which are mostly below the 100 g optimum, were broadly the same as in mammalian taxa larger than the optimum size. 3. These findings together contradict a key prediction of Brown et al.'s (1993) model to explain the skewed body size distribution across mammalian species.