An examination of interspecific competition using observations in behaviour and physiology: A case study of Guanaco (Lama guanicoe) and domestic sheep (Ovis aries) in Chilean Patagonia

Abstract

The introduction of a new species to ecosystems can result in competition between native species and the introduced, with adaptations that may allow coexistence, through resource facilitation or partitioning, unable to evolve, given the short co-evolutionary time period. Consequently, in cases where livestock species have been introduced to a new system, competitive interactions between native and domestic species have been directly instigated, with interspecific competition between sympatric, free living ungulates and domestic livestock becoming an increasing concern for conservationists. Understanding the specific ways and mechanisms in which this competition manifests is critical for informing conservation management, both of wild species, and domestic livestock. Throughout this thesis, I examine the case study of wild guanaco (Lama guanicoe) and domestic sheep (Ovis aries), in the Patagonian Steppe ecosystem of Southern Chile, a system in which competition has been demonstrated as highly probable. Two key elements in guanaco-sheep competition were investigated, to determine whether competitive effects manifest in (1) foraging behaviour, by examining the effects of sheep presence on the behavioural changes in guanaco, and (2) physiology, by examining the effects of sheep presence on guanaco separately for cortisol and testosterone. (1) Guanaco bite rates generally increased with vegetation biomass availability. However, when sheep were present in high densities, the pattern reversed, with guanaco bite rates decreasing with vegetation abundance. Additionally, the probability of guanaco feeding occurring at any one time was shown to be higher in areas shared with domestic sheep than in national parks, where sheep are absent. Both results suggest guanaco prioritise feeding behaviours at the expense of other behaviours, where sheep are present. (2) Sheep presence did not predict either the cortisol or testosterone profiles of guanaco. Instead, cortisol concentrations were influenced by the group number and composition (number of adults and juveniles). Conversely, testosterone content was influenced mainly by the specific Age-Sex Class (social group) of the individual.