Data from: Reproductive performance of a tropical apex predator in an unpredictable habitat

Variation in life history traits is directly linked to individual fitness.
This interplay is complicated by environmental perturbations in an
unpredictable habitat. To maximise fitness, individuals react to
environmental changes by reallocating resources between maintenance,
growth and reproduction. Disentangling these factors is complicated as
traits are interlinked by trade-offs between current reproduction and
future survival and reproduction. This study provides first estimates of
life history traits and trade-offs of a tropical apex predator, the
Galapagos sea lion (Zalophus wollebaeki), in an unpredictable habitat, the
Galapagos archipelago. Thirteen years of individual data on birth mass,
early growth and offspring, and environmental data allowed the examination
of factors influencing reproductive performance of adult females and
calculation of pupping rates. Females became primiparous between ages 4
and 9. Neither oceanographic nor body condition in the females’ first year
of life influenced age at primiparity. Age at primiparity had no effect on
a female’s birth rate, on average one pup every 2 years. Sex of a pup did
not influence the subsequent inter-birth interval, but first-year pup
survival lengthened it. Until age 6, females showed lower birth rate
(< 0.40). Fecundity was higher between age 6 and 14 (birth rate
0.40–0.48). We could not detect an influence of inter-annually differing
oceanographic conditions on pupping rates. Female Galapagos sea lions
appear to deal with variation in early-life history traits and
environmental unpredictability by a low but stable reproductive output
modified only by the trade-off between current and future reproduction.