The individual optimization of fitness: variation in reproductive output, including clutch size, mean nestling mass and offspring recruitment, in manipulated broods of great tits Parus major

摘要: 1 The functional prediction of the Individual Optimization Hypothesis (Pettifor et al. 1988) is explicitly tested, namely that ‘the optimal clutch size n for birds choose to lay eggs, regardless actual value n’ (Hogstedt 1980). 2 Over a 10-year period, we examine recruitment from 1392 nests great tits, 575 which had their brood experimentally manipulated. We defined final manipulation as difference between number young ringed and original size. 3 Mean nestling mass declined with manipulation: those broods were removed significantly higher mean fledging than control broods, in turn fledged at been added. There was significant strength this effect years. 4 Addition (final ≥ 2 young) more offspring (x = 10·96, SE = ± 0·16, n = 167) =−1, 0 or +1 young; x = 8·68, SE = ± 0·07, n = 646), removal ≤ 2 x = 5·68, SE = ± 0·09, n = 579). 5 Recruitment per nest (the key measure upon selection would act since parental survival independent study) greatest parents rearing equal own size. Averaged over 10 years, Poisson model recruited showed maximal occur 0·42 extra added This not different zero (i.e. when rear same size). 6 Using restricted data set, where there no loss through egg-hatch failure and/or very small young, examining respect experimental manipulation, indicated an additional 0·44 young. The broods). 7 The laid by female indicative ‘condition’ parents. Manipulation naturally laying larger clutches ‘fitter’ smaller that, comparing all made size, parents, nests. 8 There differences years shape relative extent both and, separately, but year did addition recruit broods. 9 All these results are consistent – individual optimization via phenotypic plasticity most parsimonious explanation observed variation range individuals.