Choosing what is left: the spatial structure of a wild herbivore population within a livestock-dominated landscape

Abstract

Shrublands and grasslands comprise over 30% of the land surface and are among the most exploited ecosystems for livestock production. Across natural landscapes, the distribution and abundance of wild herbivores are affected by interspecific competition for foraging resources, hunting and the development of infrastructure among other factors. In Argentine Patagonia, the abundance of domestic sheep grazing on native vegetation outnumbers the widely distributed guanaco (Lama guanicoe) and sheep ranching monopolizes the most productive lands. In this work, we aimed to assess the spatial variation in the abundance of guanacos in Península Valdés, a representative landscape of Patagonia, investigating the incidence of natural and human-related factors. We conducted ground surveys during the austral autumn in 2017 totaling 383.4 km along areas with and without sheep ranching. We built density surface models to account for the variation in guanaco abundance and obtained a map of guanaco density at a resolution of 4 km2. We estimated an overall density of 11.71 guanacos.km−2 for a prediction area of 3,196 km2, although the density of guanacos tripled in areas where sheep ranching was terminated (in around 20% of the surface of Península Valdés) compared to areas with sheep. Guanacos were more abundant at lower values of primary productivity and sheep stocking rates and further from inhabited ranch buildings, suggesting competition with sheep and conflict with humans. Although guanacos selected open, grass-dominated habitats across sheep-free sites, fences dividing properties and paddocks played a significant role in the spatial structure of their population in Península Valdés affecting negatively the abundance of guanacos. Our results indicate that actions to improve habitat connectivity for guanacos, favor the coexistence among guanacos and sheep ranching, and promote responsible human activities and attitudes towards wildlife are needed.

South American Camelids: their values and contributions to people

“…These direct actions targeting guanacos due to their perceived role as competitors for sheep has resulted in a dramatic drop in the guanaco population, from over 10 million specimens to approximately 1.5 million in Patagonia, a trend that continues today (Franklin 2011 ). In the Valdes Peninsula, guanacos have concentrated in the few low stock or sheep-free areas, in a pattern that has been described as “choosing from what is left” (Antún and Baldi 2020 ). Successful capture and shearing projects have emerged as a conservation strategy through sustainable use of guanacos (Carmanchahi et al 2015 ; Lichtenstein and Carmanchahi 2012 ).…”

Past and Recent Effects of Livestock Activity on the Genetic Diversity and Population Structure of Native Guanaco Populations of Arid Patagonia

“…Despite the availability of relatively few water sources, there was a rapid increase in the numbers and densities of sheep that led to a reduction in the forage available for guanacos. As a result, guanacos were displaced to less productive areas, such as Loma Blanca and Bajada del Diablo [ 61 , 62 ], well removed from the open grassland habitats that they had commonly used in the past [ 63 ].…”

“…However, prolonged drought, overgrazing by livestock, declining productivity, and demand for wool have caused ranches to reduce activity or close [ 59 , 67 ], which has increased habitat availability for guanacos [ 68 ]. Concurrently, increased habitat protection on private ranches and the reduction of sheep numbers and poaching [ 63 , 69 ], which facilitates the movement and increases the survival of migrants, has had positive impacts [ 70 , 71 ]. The absence of heterozygosity excess in Bajada del Diablo–Las Plumas–Ameghino is consistent with a rapid increase in population sizes and the appearance of novel genetic variation.…”

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

“…2015; Traba et al . 2017; Antún & Baldi 2020; Flores et al . 2020), with guanacos often restricted to poorer habitat or livestock‐free areas, such as wildlife reserves.…”