Abstract
Understanding the mechanisms that drive population dynamics is fundamental for management of wild populations. The guanaco (Lama guanicoe) is one of two wild camelid species in South America. We evaluated the effects of density dependence and weather variables on population regulation based on a time series of 36 years of population sampling of guanacos in Tierra del Fuego, Chile. The population density varied between 2.7 and 30.7 guanaco/km2, with an apparent monotonic growth during the first 25 years; however, in the last 10 years the population has shown large fluctuations, suggesting that it might have reached its carrying capacity. We used a Bayesian state-space framework and model selection to determine the effect of density and environmental variables on guanaco population dynamics. Our results show that the population is under density dependent regulation and that it is currently fluctuating around an average carrying capacity of 45,000 guanacos. We also found a significant positive effect of previous winter temperature while sheep density has a strong negative effect on the guanaco population growth. We conclude that there are significant density dependent processes and that climate as well as competition with domestic species have important effects determining the population size of guanacos, with important implications for management and conservation.
Highlights
To understand wildlife population dynamics it is important to identify how they are affected by environmental factors and density dependence (DD) processes; it is critical for conservation and wildlife management, in those species living in extreme environments
We evaluated the effects of density dependence and of environmental covariates on guanaco population dynamics; the environmental covariates considered were: annual precipitation and average winter temperature, and 25 years of data (1977–2002) were from the CRU TS 2.1 database, compiled by the Tyndall Centre, Climatic Research Unit, School of Environmental
The results of our Bayesian analysis show that the population of guanacos in Tierra del Fuego, Chile, is under strong density dependent regulation, and that it has already reached its carrying capacity (K546,563 individuals)
Summary
To understand wildlife population dynamics it is important to identify how they are affected by environmental factors and density dependence (DD) processes; it is critical for conservation and wildlife management, in those species living in extreme environments. Several studies have shed light on these issues for several species, e.g., wildebeest [1], white-tailed deer [2], and elands and impalas [3], still little is known about the mechanisms that regulate the populations of groups such as the wild South American camelids This is the case of the heavily exploited guanaco (Lama guanicoe) populations, that have diminished significantly during the last century because of grazing conflicts with a sheep-based society, and overhunting; in only three years between 1977 and 1980 around 140,000 guanacos were officially exported from Argentina mainly to eight countries in North America and Europe [4]. A sustainable management of guanacos requires understanding the processes that regulate their populations [8]
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