Unit pricing: Economics and the evolution of litter size

Variability in litter size and the concept of optimality are central to our current understanding of parental investment patterns and life histories. A fundamental component of most models of optimum litter size is an apparently inescapable trade-off between litter size and size of offspring. Most previous models of litter size have focused on the evolution of an optimum litter size rather than variability in litter size. Because variability provides the raw material from which numerous optimal litter sizes are fashioned to meet prevailing conditions, approaches that specifically address adaptive patterns of variability might provide new insights into the evolution of litter size. A model based on a non-linear relationship between total parental effort and litter size reduces trade-offs between offspring size and offspring number to simple reproductive economics, and illustrates how litter size variability might be predictable under certain environmental conditions.