Competitive exclusion and herbivore management in a context of livestock-wildlife conflict

Abstract

Understanding competitive interactions is essential to properly inform management strategies, in particular in the context of livestock-wildlife conflict across a degraded land, such as the case of wild guanacos in Patagonia. Guanacos are historically perceived by ranchers as livestock’s main competitors, and there is a growing demand for reducing their numbers. However, both competition theory and available evidence suggest a more complex interaction than the one assumed by the current management approach. This study aimed to test the occurrence of competitive exclusion of guanacos by domestic sheep at intra-ranch scale. We assessed the spatial segregation of guanacos and sheep and compared guanaco occupancy patterns within a sheep ranch with those recorded within an adjacent protected area free from livestock. The probability of a group of herbivores being sheep instead of guanacos increased in bottom valleys and smaller paddocks and decreased as the distance to water increased. These results agree with the expected patterns of sheep habitat use resulting from physiological restrictions and grazing behaviour. Occupancy patterns within the ranch showed a higher proportion of guanacos in ridges, away from water sources and in larger paddocks, opposing those observed in the sheep-free area where guanacos occupied mostly bottom valleys, irrespective of the distance to water. Areas used consistently by guanacos showed a higher per cent cover of preferred forage and basal-plant cover, indicating a better range condition than those used predominately by sheep. Our results add to the solid body of evidence on spatial segregation of these species at coarser spatial scales, support the competitive exclusion of guanacos by sheep and suggest that intra-ranch coexistence is possible because guanacos occupy areas underused or inaccessible to sheep. Under these conditions, it is unlikely that guanaco culling will improve sheep production and the empirical verification of the assumptions underlying current management initiatives becomes crucial.