Costs and Tactics in the Evolution of Reproductive Effort

Abstract: This study focuses on various aspects of costs of reproduction and the evolution of energetic breeding tactics. It emphasizes the distinction between demographic costs of reproduction expressed already before current offspring have reached independence (prebreeding costs), and costs expressed only after offspring independence (postbreeding costs). Prebreeding costs have only rarely been appreciated in earlier studies on life history evolution. A constrained optimization model that evaluates the effect of pre- and postbreeding costs on the evolution of reproductive effort tactics is presented. The results show that effort tactics which imply prebreeding costs are at a relative disadvantage compared to tactics that imply postbreeding costs, and that tactics with postbreeding costs should be favoured as the prospects of future fitness decline. In a conceptual paper, two general tactics of resource use in reproduction, capital and income breeding, are discussed from energetic and demographic perspectives. This thesis also includes two empirical studies on a population of the Eurasian kestrel (Falco tinnunculus) breeding in Finland. The first examines the relationship between daily energy expenditure (DEE), using the doubly labeled water technique, and variables of flight activity, food delivery, and body mass in breeding kestrels. No relationships between DEE and flight activity, food delivery, or daily mass change were found in female kestrels, but DEE was strongly negatively associated with the time an individual was in sight. This suggests that activities when the bird was out of sight contributed importantly to individual variation in DEE. DEE increased surprisingly steeply with body mass in both male and female kestrels. Several possible explanations for this result are discussed. In the second kestrel study, patterns of body mass during breeding were analysed. Finnish kestrels breed under highly variable food and thermal conditions, which may affect the opportunity and benefit of collecting reserve energy prior to egg laying in the female. Mean body mass in female kestrels during both incubation and mid-nestling was lower than reported for populations breeding in central and western Europe. Also male kestrels had lower body masses during mid-nestling. Although female kestrels would potentially benefit from higher reserve levels, particularly in the early nestling period, the migratory habit, short breeding season and harsh thermal environment at the time when reserves should be formed may make it unfavourable to collect more reserves. This is because the delay in date of egg laying that would result from additional reserve formation could have negative effects on parental and offspring survival.