Size and survival in a stochastic environment.

Spatial and temporal variability in environmental conditions can significantly influence fluctuations in body size if the environmental heterogeneity gives rise to variable size dependent mortality rates, or dispersal between sites incurs a reproductive cost. Temporal variability has a greater effect than spatial variability. These conclusions are derived from a model based on the assumption that the innate capacity for increase, r m , is a suitable fitness measure. The limitations of this model are discussed and an alternative approach using the parent-offspring regression presented. It is suggested that models based upon the latter approach are more appropriate for investigations of the evolution of traits (showing continuous variation) in variable environments because it does not require the assumption that some fitness measure is being optimized and because it may give more insight into the rates of change of the character.