SIBLING COMPETITION, PARENT OFFSPRING CONFLICT AND CLUTCH SIZE

Population genetic models have shown that exploitation competition for resources between siblings can often lead to severe reductions in offspring fitness. As the parental optimum is normally the absence of competition, the presence of sibling competition is an aspect of parent-offspring conflict. Phenotypic techniques are developed for modelling sibling competition in broods where all members have equal competitive ability. Two forms of sibling competition are modelled, one suggested by competition between nestling birds, and the second suggested by competition between the larvae of gregarious insects. The phenotypic models confirm the genetic analysis and allow the study of the relationship between sibling competition and clutch size (the genetic models assumed infinite clutch size). Conflict may either increase or decrease with clutch size depending on how the costs of competition are spread among the members of the brood. It is also shown that in the presence of sibling competition, parents may be selected to produce smaller clutches than those that would be optimum in the absence of sibling competition. © 1992 The Association for the Study of Animal Behaviour.