Demography and climate influence sex‐specific survival costs of reproduction over 60 years in a free ranging primate population

Abstract

The life‐history tradeoff between reproduction and survival often results in a discordant timing of peak mortality risk for males and females in seasonally reproducing species. Understanding how this seasonal association between reproductive investment and survival is impacted by individual age, demography, and climate is increasingly important as anthropogenic influence is driving rapid global climate and population structure changes. We investigate how tradeoffs between seasonal reproductive investment and survival have fluctuated in response to observed changes in demography and climate using 60 years of demographic records collected from a free‐ranging population of rhesus macaques Macaca mulatta (n = 1919 males, 1609 females). Seasonal mortality rates fluctuated significantly over the 60‐year period for both males and females. In males, but not females, age‐specific survival was different during periods of low and high reproductive investment, indicating that tradeoffs between reproduction and survival are particularly age‐dependent in males. There was no little to no evidence for an effect of sex ratio on survival in either sex. In both sexes, higher population density was associated with lower survival, and this negative effect of density was particularly strong during each sex's period of low reproductive investment. While there was no evidence for an effect of temperature on female survival during periods of low reproductive investment, during periods of high reproductive investment there was a positive association between average daily temperature maximum and female survival. Female survival was higher overall when rainfall was greater, and this positive effect of rainfall on survival was particularly strong for females during periods of low reproductive investment. Conversely, there were no effects of temperature or rainfall on male survival. The results of this study illustrate the considerable ways that climatic and demographic factors can influence sex‐specific mortality during each sex's distinct periods of reproductive investment.