Age and sex specific mortality of wild and captive populations of a monogamous primate (Aotus sp.)

Sam M. Larson, University of Pennsylvania
Fernando Colchero, University of Southern Denmark
Owen R. Jones, University of Southern Denmark
Lawrence Williams, Michael E. Keeling Center for Comparative Medicine and Research
Eduardo Fernandez-Duque, Yale University

Document Type Working Paper

Larson, Sam M., Fernando Cochero, Owen R, Jones, Lawrence Williams, and Eduardo Fernandez-Duque. 2014. "Age and sex specific mortality of wild and captive populations of a monogamous primate (Aotus sp.)." PARC Working Paper Series, WPS14-01.

Abstract

The age-specific mortality of polygynous primates exhibits accelerated mortality increases with age in males relative to females, but the patterns for monogamous primates are less clear. We analyzed the sex differences in mortality within wild and captive populations of owl monkeys (Aotus sp.), a monogamous primate exhibiting bi-parental care. We used Bayesian Survival Trajectory Analysis (BaSTA) to test age-dependent models of mortality conditioned on survival to two years. The wild population was best fit by the logistic-bathtub model and the captive one by the Weibull-bathtub model; both models imply a deceleration in the increase in mortality rate in the oldest ages. We found only moderately higher levels of mortality for females in captivity, but otherwise no differences between the sexes. Additionally, we calculated life expectancies and Keyfitz' entropies (a measure of the steepness of senescence and disparity in mortality) for both sexes in each population. In captivity, life expectancy is larger in males than in females, but these are the same in the wild. Additionally, there are no differences in disparity between sexes in both populations. These results indicate strong sexual monomorphism in mortality patterns for Aotus spp. in different environmental contexts. Comparing across populations, life expectancy is overall greater and disparity overall lower in the wild than in captivity. We argue that the greater disparity in the distribution of ages at death in captivity than in the wild is due to a selection effect where frail individuals die before reaching their second year in the wild, which translates into seemingly higher life-expectancy; this also implies higher disparity in the captive population since frail individuals are capable of surviving beyond the lowest age in our analysis, increasing the variance and therefore the disparity in the distribution of ages at death.