Julia D. Monk , Emiliano Donadio, Pablo F. Gregorio, Oswald J. Schmitz

Spatial subsidies of nutrients within and among ecosystems have profound effects on ecosystem structure and functioning. Large animals can be important drivers of nutrient cycling and transport as they ingest resources in some habitats and release them in others, even moving nutrients against elevational gradients. In high Andean deserts, vicuñas (Vicugna vicugna) navigate a landscape of fear by migrating daily between productive wet meadows, where there is abundant water and forage but high risk of predation by pumas (Puma concolor), and open plains, where soils are nutrient-poor and forage is less abundant but the risk of predation is low. As they move, vicuñas also defecate and urinate in communal latrines to maintain the cohesion of their family groups. We investigated whether these latrines impacted soil and plant nutrient concentrations across three habitats in the Andean ecosystem (meadows, plains, and canyons), and used stable isotope analysis to determine the source of fecal nutrients in latrines. We found that latrines increased the concentrations of nitrogen, carbon, and other nutrients in soils across all habitats. These inputs corresponded with an increase in plant quality (lower C:N) at latrine sites in plains and canyons, but not in meadows. Stable isotope mixing models suggest ~7% of nutrients in latrines in plains originated from vegetation in meadows, even though meadows accounted for only 2.6% of the study area; in contrast, ~68% of nutrients in latrines in meadows originated from plains and canyon vegetation, though these habitats made up nearly 98% of the study area. Thus, vicuña diel migrations, motivated by predator avoidance, appear to drive reciprocal nutrient subsidies between low-lying, nutrient-rich meadows and more elevated, nutrient-poor plains, and latrines also recycle and concentrate nutrients within habitats. Scaling these results up to the landscape scale, we found that the amount of additional nitrogen and phosphorus in soil at plains latrines were of the same order of magnitude as estimates of annual atmospheric nitrogen and phosphorus deposition for this region (albeit far more localized and patchy). These results suggest that vicuña-mediated nutrient cycling and deposition is an important process impacting ecosystem functioning in arid Andean environments, on par with other major inputs of nutrients to the system.