Vicuna antipredator diel movement drives spatial nutrient subsidies in a high Andean ecosystem

Large animals could be important drivers of spatial nutrient subsidies
when they ingest resources in some habitats and release them in others,
even moving nutrients against elevational gradients. In high Andean
deserts, vicuñas (Vicugna vicugna) move daily between nutrient-rich wet
meadows, where there is abundant water and forage but high risk of
predation by pumas (Puma concolor), and nutrient-poor open plains with
lower risk of predation. In all habitats, vicuñas defecate and urinate in
communal latrines. We investigated how 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 explore the source of fecal nutrients in latrines. Latrine soils had
higher concentrations of nitrogen, carbon, and other nutrients than did
non-latrine 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 that ~7%
of nutrients in plains latrines originated from vegetation in meadows,
which is disproportionately higher than the relative proportion of meadow
habitat (2.6%) in the study area. In contrast, ~68% of nutrients in meadow
latrines appear to originate from plains and canyon vegetation, though
these habitats made up nearly 98% of the study area. Vicuña diel movements
thus appear to concentrate nutrients in latrines within habitats and to
drive cross-habitat nutrient subsidies, with disproportionate transport
from low-lying, nutrient-rich meadows to more elevated, nutrient-poor
plains. Scaling these results up to the landscape scale, the amount of
nitrogen and phosphorus subsidized in soil at plains latrines was of the
same order of magnitude as estimates of annual atmospheric nitrogen and
phosphorus deposition for this region (albeit far more localized and
patchy). Thus, vicuña-mediated nutrient redistribution and deposition
appears to be an important process impacting ecosystem functioning in arid
Andean environments, on par with other major inputs of nutrients to the
system.