Insectivore life histories: further evidence against an optimum body size for mammals

1. This study tests a model of the relationship of body mass to reproductive power (the rate of conversion of energy from the environment to an organism’s offspring). Specifically tested is the prediction that the regression of life-history variables on body size will change slope and sign about an ‘optimum’ body mass of 100 g.2. Life-history data from the mammalian order Insectivora have been collated and analysed using a phylogenetic comparative method to test this prediction. 3. The analyses showed little evidence for significant changes in slope or sign around 100 g body mass, or other possible optimal body masses, contradicting the predictions of the model. These findings agree with those of similar analyses on life-history variables of bats.