Age-specific survival and reproductive probabilities: evidence for senescence in male fallow deer (Dama dama)

Abstract

Survival and reproduction are key features in the evolution of life–history strategies. In this study, we use capture–mark–resighting and multi–state models to examine survival senescence and reproductive senescence in six successive cohorts of fallow bucks that were studied for 16 years. We found that the overall age-specific survival probabilities of males were highly variable and the best–fitting model revealed that fallow bucks have four life–history stages: yearling, pre–reproductive, prime–age and senescent. Pre–reproductive males (2 and 3 years old) had the highest survival. Survival declined sharply after the age of 9 years, indicating that senescence had begun. When we considered reproducing and non-reproducing males separately, there was no evidence of senescence in the former, and steadily decreasing survival after the onset of social maturity in the latter. Reproduction probability also declined in older males, and thus we provide very strong evidence of senescence. Reproducers had a greater chance of reproducing again in the following year than non–reproducers. Furthermore, there were differences in the survival probabilities, with reproducers consistently surviving better than non–reproducers. In our study population, reproducers allocate more to the effort to reproduce than non–reproducers. Therefore our results indicate the generally higher phenotypic quality of reproducing males. These results, along with earlier studies on the same population, could indicate positive relationships between fitness correlates.