Ecomorphological variations in the guanaco population of Patagonia (Argentina)

Abstract

This paper studies the body sizes of modern, continental and insular Patagonian (Argentina) Lama guanicoe populations based on the osteometric analysis of four forelimb bones (humerus, radio-ulnae, metacarpus and first phalanx). A sample of more than 100 individuals from the Provinces of Río Negro (40°S), Santa Cruz (48-52°S) and Tierra del Fuego (53-54.5°S) were analyzed. The morphological size variations were evaluated considering the eco-environmental variables of temperature (maximum/ minimum), precipitation (summer, winter and annual), aerial net primary productivity (ANPP) and normalized difference vegetation index (NDVI). The data was analyzed using a number of uni and multivariate statistical models. The results show that, at a macro-regional scale, there was a clinal variation in the body sizes of guanaco populations (with individuals from Tierra del Fuego being significantly bigger than those from Santa Cruz, with the latter in turn being larger than those from Río Negro). All eco-environmental factors strongly associated with bone sizes (maximum temperature, ANPP, NDVI) co-vary, in the study region depending on latitude. The clinal pattern observed was, in principle, consistent with the expectations of Bergmann’s Rule. Also different environmental and biogeographic variables influenced the size patterns of modern Patagonian guanacos, thereby underscoring that the relationship between body size and environment is of a complex nature - and cannot be explained simply and directly by a single factor.