Population dynamics of the vicuña (Vicugna vicugna): Density-dependence, rainfall, and spatial distribution

The vicua (Vicugna vicugna) is a South American camelid that has been hunted to near extinction. Following the establishment of conservation programs, vicuas have successfully recovered to their current "Least Concern" International Union for Conservation of Nature and Natural Resources status. We analyze a 31-year vicua census data set from northern Chile in order to investigate the influence of various factors on vicua population dynamics. During the first 15 years, population dynamics are driven by strong growth as the population recovers from overhunting, and during the last 15 years dynamics are dominated by fluctuations around carrying capacity. We find that the best fit of the census data is a logistic growth model that takes into account how changes in rainfall and primary productivity lead to fluctuations in carrying capacity, suggesting that the resources limiting vicua population size are not constant but change over time. We also find that the spatial distribution of vicuas changes over time with respect to the nutrient-rich bofedales (Andean peatlands). Our study demonstrates the importance of collecting and analyzing long-term census data, and suggests that further insight could be gained if vicua location with respect to habitat type was recorded during the census.