OOS 3-5 - Vicuña diel migration drives nutrient subsidies from wetlands to plains

Spatial subsidies of nutrients within and among ecosystems have profound effects on ecosystem structure and functioning. Large animals can be important drivers of nutrient 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 habitats in the arid Andean ecosystem, and used stable isotope analysis to determine the source of fecal nutrients in latrines. We found that latrines significantly and substantially increased the concentrations of nitrogen, carbon, phosphorus, and other nutrients in soils across all habitats; vicuña-mediated nitrogen inputs in particular occurred at roughly the same order of magnitude as estimated annual atmospheric nitrogen deposition in the region. These inputs also corresponded with an increase in plant quality (lower C:N) at latrine sites in arid plains, but not in wet meadows, where plants appear not to have been nitrogen limited. As we predicted, a substantial proportion (>30%) of nutrients in plains latrines originated from vegetation in meadows, even though meadows accounted for only 2.6% of the landscape. Thus, vicuña diel migrations, motivated by predator avoidance, drive nutrient subsidies from low-lying, productive meadows to more elevated, nutrient-poor plains. These subsidies increase soil and plant nutrient availability in arid habitats, altering ecosystem functioning across the landscape at latrine sites.