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).