Survival and reproduction
Both males and females produced fewer recruits in their first year of breeding (Table 3). Males produced, on average, fewer recruits in their first breeding year than females (first year fecundity rates: 0.27 for males and 0.33 for females). However, from their second year onwards, males produced more recruits than females per breeding attempt (fecundity rates: 0.57 for males and 0.47 for females). Males also had a higher survival probability than females on average (0.50 for females and 0.57 for males; Table 3). Thus, in total males had longer generation times, both because they lived longer and because they were more successful at reproducing when they were older (Figure S2). In addition, we found evidence for strong density regulation in recruit production, but not in adult survival (Table 3). In years when population size was relatively high compared to the average population size, recruitment was lower (Table 3). However, there was a trend suggesting that in populations where population sizes were on average higher individuals produced more recruits (Table 3). We further explored whether these density-dependent patterns were sex and age specific, but we did not find any evidence for this.
We found a positive correlation between survival and reproduction among individuals (0.25; CI 0.15- 0.34) and within individuals across years (0.20; CI 0.08- 0.33). This suggests that consistent variation in phenotypic “quality” and/or resources among individuals resulted in some individuals producing, on average, more recruits per year and at the same time being on average more likely to survive. In addition, in years when individuals produced more recruits they were also more likely to survive. These results seem to contradict the observed negative covariance between lifespan and reproductive rate. We therefore used simulations to address this issue (see Appendix S3), finding that the negative covariance between reproduction rate and lifespan, and between reproduction rate and generation time, was the result of the age-dependent patterns of survival and reproduction, and not necessarily caused by individual resource allocation trade-offs (see Discussion).