Factors influencing guanaco distribution in southern Argentine Patagonia and implications for its sustainable use

Abstract

The Guanaco (Lama guanicoe) has suffered a progressive decline in numbers because of unregulated hunting and poaching by an assumed competition with sheep. Inadequate livestock management, including keeping sheep numbers above carrying capacity, has led to a degradation of the Patagonian steppe. Recently, interest has grown towards a reduction in sheep density and diversification of extractive activities. Guanaco populations could be potentially amenable to a number of sustainable uses. Our aim was to investigate the factors that determine guanaco distribution in southern Argentine Patagonia and to generate a predictive cartography at the regional scale. We hypothesized that guanaco distribution could be determined by primary productivity, terrain ruggedness, human disturbance and poaching, and competition with livestock. Guanaco surveys were performed from vehicles using a road survey method. To analyze the relationship between guanaco occurrence and potential predictors we built Generalized Additive Models (GAMs) using a binomial error and a logistic link. We found that guanaco occurrence increased in the less productive and remote areas, far from cities and oil camps, and decreased in regions with high sheep density. These results suggest that guanacos tend to occur where human pressure is lower. One way to promote guanaco conservation would be to highlight the economic value of guanacos under the regulations imposed by a sustainable exploitation of their populations. The predictive models developed here could be a useful tool for the implementation of conservation and management programs at the regional scale.

Guanaco abundance and monitoring in Southern Patagonia: distance sampling reveals substantially greater numbers than previously reported

“…Within the modal class, mean (±SD) perpendicular distance to contacts was 24 ± 12 m. We estimated a mean density of 4.79 ind/km 2 with a coefficient of variation of 20% ( Table 2). As expected, density estimates increased with the predicted probability of guanaco occurrence defined by Pedrana et al (2010) as classes of expected relative abundance. Overall mean density greatly varied from areas with expected low relative abundance (1.12 ind/km 2 ) to areas with expected high relative abundance (7.74 ind/km 2 ; Table 2).…”

“…We divided the study area into 12 geographical regions or strata, based on the combination of two environmental variables (Normalized Difference Vegetation Index, or NDVI, and mean slope) that we expected could influence the frequency of contacts with guanaco. Indeed, both variables accounted for guanaco distribution in Santa Cruz (Pedrana et al 2010). NDVI was used because vegetation productivity could be an important driver of guanaco abundance, and mean slope because guanacos could prefer plains to rugged areas and their detectability could be affected by terrain irregularity.…”

“…This further suggests that major environmental variation across Santa Cruz was adequately captured by our road transects. Pedrana et al (2010) modeled guanaco distribution in Santa Cruz using environmental predictors. Predicted probabilities of guanaco occurrence were divided in three classes and were plotted on a map (Figure 2).…”

“…Abundance estimates were calculated for each observable social unit, and for all guanaco contacts pooled together, within each area of expected relative abundance of guanacos and then for the whole study area. As predictions of guanaco occurrence were not made for water bodies, forests, areas above the treeline, and other habitats unsuitable for guanaco (Pedrana et al 2010), the area for which abundance was estimated (222,545 km 2 ; Table 1) was 91% of the surface of Santa Cruz province.…”

“…As classes of relative abundance were built with distribution models based on environmental predictors (Pedrana et al 2010), assuming that guanaco densities fall within the confidence intervals shown in Table 2 in similar environments, we estimated a total guanaco population of 1,066,600 individuals in Santa Cruz (95% CI 727,800 to 1,563,200). Half of the estimated population size would appear in the form of breeding groups (Table 2).…”