Allocating grassland resources to wildlife: A simulation approach to balance sheep production with guanaco (Lama guanicoe) conservation in semi-arid Patagonia

Livestock managers at the interface between the natural world and society are faced with the question of how to allocate grassland resources between wild and domesticated grazers. We developed an interactive decision tool for resource managers in the Santa Cruz province of Argentina to explore how various levels of grassland allocation can maximize grass consumption by domestic grazers while controlling local extirpation risk to wild guanacos ( Lama guanicoe ). We used population viability analysis in conjunction with climate and grassland productivity data from Santa Cruz, and four decades of guanaco demographic data from a similar environment in Chile, to parameterize a stochastic model depicting guanaco population dynamics. We projected dynamics using simulation across 100 years to understand the likelihood of subpopulation (local herd) extirpation under a variety of constrained grassland resources set aside for consumption by guanaco. The resulting interactive software application allows managers to compare the number of wild guanacos that need to remain on the landscape under different grassland allocations and ranch sizes to ensure wildlife viability while maximizing consumable grass for domestic grazers. We found that at least 22 female guanacos (or 44 total guanacos) must exist in a localized herd to ensure the population overcomes the Allee effect. Years with severe winters were more likely to cause extirpation than years of drought. The interactive tool may be downloaded and modified to investigate countless variations to the simulation and can serve as a framework to investigate management outcomes in other systems. The tool is at https://doi.org/10.7298/sxad-f115 .