How density-dependence and climate affect guanaco population dynamics

Abstract

The guanaco (Lama guanicoe) is one of the two South American native wild camelid species, and despite its important ecological role and economic value conservationists are in a permanent conflict with sheep ranchers. Currently, management programs are being developed in Argentina and Chile to guarantee guanaco and grassland conservation. We developed a non-linear simulation, three stages-structured matrix model of guanaco population dynamics, with climatic and density-dependence effects, that can be used as a tool to devise optimal management interventions. We estimated population parameters using a 41-year time-series data from a guanaco population in Tierra del Fuego (Chile). We conducted a multivariate multiple regression analysis between matrix demographic parameters (survival at each stage and fertility) as dependent variables, and climatic variables and population density as independent variables. Guanaco density was significantly correlated with female newborn and adult annual survival while annual precipitation correlated significantly with the fertility (females born per female per year), in contrast to population regulation mechanisms commonly seen in other ungulate species. This guanaco model allows the evaluation of the effects of different events (e.g. offtake, particular dry or wet years, poaching) on specific sexes and life stages which is the field information commonly available.