Environmental factors influencing guanaco distribution and abundance in central Patagonia Argentina

JULIETA PEDRANA; ALEJANDRO TRAVAINI; JUAN IGNACIO ZANÓN; SONIA CRISTINA ZAPATA; ALEJANDRO RODRIGUEZ; JAVIER BUSTAMANTE

WILDLIFE RESEARCH

CSIRO PUBLISHING

Lugar: Collingwood; Año: 2019

1035-3712

Context. The guanaco is the largest wild herbivore inhabiting Patagonian steppes. Since the end of the 19th century it has suffered a progressive decline in numbers, because of poaching and by unregulated hunting based on an assumed competition with sheep. Unfortunately, there has never been a management program for guanaco populations in the Argentine Patagonia. Consequently, guanaco is still considered a pest species by ranchers and has never been considered profitable in the range management model implemented in Patagonia. Aims. We update the distribution limits of guanaco, and estimate its abundance, across Chubut, a large province of Patagonia, Argentina. We also assess the relative effects of several environmental and anthropogenic factors on guanaco distribution. Methods. We used road surveys (7010 km) and species distribution modelling to build a habitat suitability model and a distribution map. Distance sampling method was used to estimate guanaco population densities and size. We also calculated the survey effort required to monitor population trends in this region. Key results. According to the best habitat suitability model, guanaco distribution decreased with altitude and primary productivity, as measured by NDVI, and increased with the distance to the nearest urban center and oil field. Guanaco distribution showed a clear geographical pattern in Chubut, with low to medium occurrence probability towards the west and higher values towards the east. Guanaco population size was estimated as 657 304 individuals (95% CI 457 437 to 944 059), with a mean density of 2.97 guanacos/km2. Finally, through simulations of guanaco monitoring we estimated that an annual survey effort of 10 to 30-km road transects is needed to detect with confidence a significant population decrease or increase over the next six or ten years Conclusions. Our habitat suitability map highlights areas with high guanaco densities in Chubut, where it would be possible to identify ranches suitable for performing profitable herding and shearing experiences. Implications. Our maps of guanaco distribution and density, the survey effort required to monitor population trends may be used to inform decisions concerning the sustainable use of this species.