Wild guanacos as scapegoat for continued overgrazing by livestock across southern Patagonia

Abstract

1. In a recently published paper, Oliva et al. concluded that domestic grazing pressure across Patagonian rangelands approached carrying capacity due to decades of stock adjustment, but that guanaco overpopulation may have altered that balance. The authors argued that unless guanaco numbers are controlled, they will reduce forage available for domestic stock and will negatively affect rangelands. We consider that the herbivore-stock analysis presented is inaccurate and deserves revision, and that the stated conclusions lack empirical support. 2. When the spatial distribution of herbivores is accounted for in the Oliva et al. analysis, domestic stock is far above carrying capacity, indicating that domestic overgrazing continues. 3. Theoretical and empirical evidence on bottom-up regulation and competitive exclusion challenges the supposed guanaco overpopulation and the hypothetical reduction of forage available for livestock. 4. Even if guanaco numbers are reduced, grassland degradation and production losses will continue because their main drivers, domestic overstock and heterogeneous grazing, are still operating. 5. Synthesis and applications. Oversimplified models with poor ecological insight can lead to erroneous conclusions and misguide management decisions. The incorrect inference that Patagonian domestic stock is adjusted to carrying capacity could help to consolidate current domestic overgrazing by reducing incentives to improve livestock management practices. Regarding guanacos, a controversial species in an unfavourable context, control-oriented harvest without a clear justification threatens populations' viability and genuine attempts of productive diversification. Addressing relevant ecological processes, such as niche partitioning, competitive exclusion and population regulation, is essential to correctly assess joint carrying capacity in multi-herbivore systems, as well as to identify the true factors driving degradation processes and to optimize rangeland use on a sustainable basis.

Are Patagonia grasslands being overgrazed? A response to Marino et al. (2020)

“…On the contrary, references (Baldi, Albon, & Elston, 2001; Pedrana, Bustamante, Travaini, & Rodríguez, 2010) used by Marino et al. (2020) leave open alternative explanations to competitive exclusion, including a direct influence of human presence, as guanacos tend to occur where human pressure is lower because of poaching and general productive activity. Marino et al.…”

“…Marino et al. (2020) also claim that guanacos can only occupy areas where they are able to exploit forage that is out of reach of livestock, and cite as an example the southern grasslands of Peninsula Valdés. We believe that this case cannot be generalised; guanaco populations are found in productive areas of Patagonia with sheep (Hernández et al., 2017; Karesh et al., 1998) suggesting that they can coexist.…”

“…We believe that the subject of guanaco conservation and management as framed by Marino et al. (2020) only reflects the nature preservation sector of the stakeholders around the guanaco–domestic stock conflict. That perspective underpins their claim that ‘Massive economic and political efforts are underway by the Santa Cruz Provincial and National governments to change current legislation and allow the reduction of guanaco numbers, instead of fostering the improvement of livestock management schemes’.…”

“…Faced with a sharp increase in grazing pressure from guanacos and livestock, we are currently forced to manage the Patagonian land to preserve it, including an improvement of livestock management schemes, as Marino et al. (2020) request, but also through the sustainable management of native herbivores such as the guanaco. To postpone management of native herbivores based on weak institutional and technical expertise at this stage would only induce poaching and illegal culling, and block the early commercial development of guanaco products that can transform an apparent competitor into a valuable natural resource, complementary to sheep raising.…”

“…Marino et al (2020) claim that regional carrying capacity estimations of theOliva et al (2019) analysis are unrealistic because they provide estimates for different species based on the assumption of 'each herbivore having exclusive use of the land'. We suggest that this is based on a misinterpretation of our approach, as it is clear that different domestic and native herbivore species share the land.…”