Date of Award
Master of Science
A socioecological study of the South American guanaco (Lama guanicoe) was conducted from July 1977 to June 1978 on Isla Grande, Tierra del Fuego, Chile. The study area was situated in an ecotone between open Patagonian plains and closed austral forest habitats. Observations of guanaco family groups were made from a 2 story observation hut and from a motor vehicle positioned on the road . Twelve vegetation types were defined and analyzed by the point frame method to determine plant species composition and percent cover. Sites of territorial defenses by family group males were plotted; maps for neighboring males were then compared and territorial boundaries for each season were drawn. Feeding territories were defended year-round by the family group adult male; neighboring groups overlapped very little in their use of space. Shapes of feeding territories were approximately rectangular; territories averaged 29.5 ha in size. Territory quality was estimated using mean primary production per unit area of territory, percentage surface area occupied by the 4 most preferred vegetation types, percentage surface area occupied by the 2 least preferred vegetation types, and mean escape distance from a highly preferred vegetation type to the forest. Two of the 12 vegetation types (VT-4 and VT-5) were highly preferred by adult female guanacos; VT-4 exhibited a statistically significant higher primary production than 8 of the other 11 vegetation types .. Feeding territories dominated by the 2 least preferred vegetation types (VT-11 and VT~14) were nearly twice the size of those territories with a low percentage surface area of those types. Guanaco family groups averaged 7 animals; however , the size of individual family groups fluctuated on a seasonal basis. There was no statistically significant difference in the number of adult females between groups. There also was no significant correlation between group size and total primary production per territory (r= -0.21, d.f.=6), but group size and production per ha of territory were close to the acceptable level of significance (r= 0.61). A negative correlation existed between summer and fall mean number of adult females and percentage surface area of the 2 least preferred vegetation types; no correlation existed between number of adult females and the percentage surface area of the 4 most preferred vegetation types. Territory size was positively correlated with the percentage surface area of the 2 least preferred vegetation types and also with mean distance from VT-4 to the forest edge. No statistically significant differences were found between territories using the territory quality variables for analysis. However, the differences that did exist may have caused females to select one territory over another. Explanations for female selection of territories and the benefits accrued to the female are discussed. Adult females did not appear to select territories on the basis of preferred forage availability; however, the amount of least preferred forage may have acted as a selective factor.
Robert Thomas Jefferson Jr.
Jefferson, Robert Thomas Jr., "Size and spacing of sedentary guanaco family groups" (1980). Graduate Theses and Dissertations. 16257.