Data from: Trade-offs between age-related breeding improvement and survival senescence in highly polygynous elephant seals: dominant males always do better

Life history trade-off theory predicts that current reproduction can
negatively affect survival and future reproduction. Few studies have
assessed breeding costs for males of polygynous species compared to
females, despite substantial variation in breeding success among
individual males (e.g. subordinate cf. dominant breeders). Specifically,
differentiating between the cost of attending breeding seasons, and the
additional cost of successfully securing and mating females is lacking. We
investigated whether trade-offs are present in the highly polygynous male
southern elephant seal (Mirounga leonina) using 34-years of
individual-level data. We compare age-specific survival, recruitment and
future breeding success probabilities of pre-breeders (males yet to
recruit) and breeders (subordinate and dominant social ranks) using
multievent models. Pre-breeders and breeders of overlapping ages had
similar survival probabilities, suggesting that there was no attendance
cost for early recruits. In addition, the probability of recruiting as a
dominant breeder never exceeded recruitment probability as a subordinate
breeder of the same age. Therefore, older pre-breeders that delayed
attendance costs generally did not improve their breeding success
(probability of being dominant) at recruitment more than younger recruits.
Rather, recruitment age may be a function of individual quality, with
lower quality individuals requiring more time to socially mature. When
comparing subordinate and dominant breeders, we found clear evidence for
survival senescence, with subordinate breeders having a higher baseline
mortality. In contrast, age-specific future breeding success (probability
of being dominant at t+1) increased with age, with dominant breeders
maintaining higher subsequent breeding success than subordinate breeders.
The opposite trends in survival and future breeding success for both
subordinate and dominant breeders may indicate a lifetime,
population-level trade-off. However, we found no evidence to suggest that
being a dominant breeder consecutively (and having a higher accumulated
breeding cost) accelerated the rate of senescence when compared to
individuals that were previously subordinate. Thus, males experienced
actuarial senescence regardless of social rank, with dominant (and
possibly high quality) breeders showing a reduced trade-off between
survival and future breeding success. We make several novel contributions
to understanding polygynous male life histories and southern elephant seal
demography.