Number And Size Of Offspring

Abstract

Abstract Two approaches dominate the analysis of the evolution of offspring number and size. The ornithologists have organized their understanding of offspring number around the Lack clutch, the clutch size that produces the most fledglings. In this tradition theory and experiment have aimed to understand what factors cause deviations, usually downward, from the Lack clutch. These include effects of clutch size on subsequent parental and offspring survival and reproductive performance and year-to-year variation in the optimal clutch size. An important theoretical tradition aims to optimize reproductive effort over the whole life history taking costs of reproduction into account. This approach is called either the General Life History Problem or the Reproductive Effort Mode/, and its predictions are well confirmed by experiments with poeciliid fish and with small, altricial, hole-nesting birds, but there are also substantial data on clutch sizes in sea birds, geese, ducks, and raptors and litter sizes in humans, rodents, deer, and other mammals. Recently the Lack tradition has been extended to parasitoid insects, where ‘clutch’ is taken to mean eggs laid per host.