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Baldi, R., Pelliza-Sbriller, A., Elston, D., & Albon, S. (2004). High Potential For Competition Between Guanacos And Sheep In Patagonia. Journal of Wildlife Management, 68(4), 924–938.
Abstract: Guanacos (Lama guanicoe) are the largest native Artiodactyl in South America and the most widely distributed. In arid Patagonia, densities are low and negatively related to domestic sheep numbers in space and time consistent with interspecific competition theory. Although guanacos and domestic sheep have been described as intermediate feeders sharing food resources, no studies have been conducted to compare their diets in sympatric conditions and explore whether the potential exists for direct interspecific competition. We assessed the diet of both species across 9 different sites and 2 seasons by microhistological analysis of fecal samples. We found that (1) guanacos and sheep are generalist herbivores feeding on a wide range of plant species; (2) both are intermediate feeders able to include both monocotyledoneous and dicotyledoneous plants in their diet; (3) both are able to change their diets seasonally; and (4) food niche overlap is high, particularly in summer when food resources are more scarce than in spring. We conclude that the potential for competition between guanacos and sheep is high and could have played a major role in the demise of guanacos. Consequently, current management practices focused on maximizing sheep numbers are not compatible with the recovery of guanaco populations.
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Sibbald, A. M., Elston, D. A., Smith, D. J. F., & Erhard, H. W. (2005). A method for assessing the relative sociability of individuals within groups: an example with grazing sheep. Appl. Anim. Behav. Sci., 91(1-2), 57–73.
Abstract: We describe a method for quantifying relative sociability within a group of animals, which is defined as the tendency to be close to others within the group and based on the identification of nearest neighbours. The method is suitable for groups of animals in which all individuals are visible and identifiable and has application as a tool in other areas of behavioural research. A sociability index (SI) is calculated, which is equivalent to the relative proportion of time that an individual spends as the nearest neighbour of other animals in the group and is scaled to have an expectation of 1.0 under the null hypothesis of random mixing. Associated pairs, which are animals seen as nearest neighbours more often than would be expected by chance, are also identified. The method tests for consistency across a number of independent observation periods, by comparison with values obtained from simulations in which animal identities are randomised between observation periods. An experiment is described in which 8 groups of 7 grazing sheep were each observed for a total of 10, one-hour periods and the identities and distances away of the 3 nearest neighbours of each focal animal recorded at 5-min intervals. Significant within-group differences in SIs were found in four of the groups (P < 0.001). SIs calculated using the nearest neighbour, two nearest neighbours or three nearest neighbours, were generally highly correlated within all groups, with little change in the ranking of animals. There were significant negative correlations between SIs and nearest neighbour distances in five of the groups. It was concluded that there was no advantage in recording more than one neighbour to calculate the SI. Advantages of the SI over other methods for measuring sociability and pair-wise associations are discussed.
Keywords: Association; Grazing; Nearest neighbour; Sheep; Sociability; Social behaviour
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