Earlier breeding shortens life in female greater horseshoe bats

Life history theory predicts that an individual may gain in fitness by postponing reproduction if, by doing so, future reproductive capacity or longevity is enhanced. To test this theory I studied the survival and fecundity of earlier (start age 2 years) and later (start age 3 years or later) breeding female bats. Mature females produce one young annually, may miss breeding in some years and can still breed at age 29 years. Earlier breeders (e b) have similar mean skeletal size and birth date to later breeders (l b), but they have higher fat reserves late in their first winter and in their second autumn, when follicular development starts, and are probably superior foragers. eb averaged 5.6 and lb 8.1 years at death. Higher mortality in the former group was associated with parturition later in July during early breeding attempts. Lifetime reproductive success (lrs) of both groups was highly variable and strongly correlated with lifespan, which explained 99 and 96% of observed variation respectively. Differences in mean lifespan had no significant effect upon the mean lrs of eb and lb (4.4 and 5.1 births per female respectively). Although earlier breeding reduces lifespan, because it starts a year earlier and breeding rates are higher in eb than in lb (96% cf. 85% per year), overall there appear to be equal fitness benefits. During rapid population recovery after a climate-induced crash, earlier breeding was enhanced and may be advantageous until the population stabilizes. Hence studies testing life history theory should take account of population trends and climate. These seem to be crucially interconnected via food availability, the growth of individuals, and fat storage.