Cohort variation in male survival and lifetime breeding success in red deer

1. We investigated cohort differences in the lifetime breeding success and survival of male red deer Cervus elaphus L. in an increasing population on the Isle of Rum, Scotland. 2. There were significant differences in survival through different stages of the life span between 15 cohorts of males, ranging between: 0.26 1.00, c alf survival through first winter; 0.56 1.00, yearling survival; 0.44-0.94, adult survival. This variation in survival was related to environmental co nditions in the cohorts' year of birth, whilst controlling for annual effec ts. 3. For 10 cohorts of males with complete lifetime data, mean breeding succe ss also varied significantly, between 0.83 and 3.86. This variation, too, w as associated with environmental conditions in the cohorts' year of birth. 4. Since in many sexually dimorphic mammals, the growth and survival of mal es is more strongly affected by adverse environmental conditions than that of females, we expected that cohort variation would be more extreme amongst males than females. This was true, for both cohort survival and reproducti on. 5. We expected to observe selection on cohort adult body size, related to s urvival or reproduction. However, there was no evidence of variation in adu lt body size between cohorts, nor for relationships between differences in body size between cohorts and measures of survival or breeding success. Coh orts which underwent high initial mortality subsequently experienced higher adult survival than cohorts not subjected to high density-related selectio n early in life.