High density and hurricanes early in life shorten the lifespan of a nonhuman primate population

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Stephanie J Gonzalez and Raisa Hernandez-Pacheco, Biological Sciences, California State University Long Beach, Long Beach, CA

Background/Question/Methods
Density dependence and environmental variability are major forces driving population dynamics. In nonhuman primates, both of these ecological factors influence individual performance and population fitness. Until now, we were unaware of the roles these ecological factors play as sources of early life adversities on a large population. Multiple sources of adversity early in life predict components of fitness by shortening lifespan, and thus reducing lifetime reproductive success. Here, we looked at individual life histories of Cayo Santiago rhesus macaques over the span of 47 years. Continuous and detailed life history records have been collected for this population since 1956, resulting in the world’s largest longitudinal demographic dataset of a nonhuman primate. During our study period, the population experienced different densities and three major hurricane events. To quantify the effects of density and major hurricanes early in life on lifespan, we carried out a survival analysis using a Cox proportional hazards regression model with density and hurricane events at birth as predictors.
Results/Conclusions
Based on data from 9,835 Cayo Santiago rhesus macaque individuals, we found that individuals experiencing high density and major hurricanes early in life showed a reduced lifespan. Specifically, increments in density by one individual increased the likelihood of dying by 0.2% at any age, and individuals who experienced a major hurricane early in life exhibited a 15% increase in the probability of dying at every age. We also observed differences in sex-specific survival with males dying sooner than females regardless of density experienced at birth and cohort membership. Besides regulating the population growth rate, our results showed that high population density at birth can also act as a source of adversity with consequences later in life. Our findings also revealed that extreme climatic events, although rare, can have long-term consequences in the demography of nonhuman primate populations. Our findings allow us to foreshadow possible consequences of predicted climate change in which extreme climatic events will become more frequent with significant long-term consequences on the viability of wild primate populations.