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 reproductiv e power (the rate of conversion of energy from the environment to an organi sm'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 collate d and analysed using a phylogenetic comparative method to test this predict ion. 3, The analyses showed little evidence for significant changes in slope or sign around 100 g body mass, or other possible optimal body masses, contrad icting the predictions of the model. These findings agree with those of sim ilar analyses on life-history variables of bats.