PIKAS (OCHOTONA PRINCEPS, LAGOMORPHA) AS ALLOGENIC ENGINEERS IN AN ALPINE ECOSYSTEM

Pikas (Ochotona princeps: Lagomorpha) build caches of vegetation (''ha ypiles''), which serve as a food source during winter in alpine and su balpine habitats. Haypiles appear to degrade over time and fc,rm patch es of nutrient-rich soils in barren talus and scree areas. We sampled soils underneath and next to haypiles, and plants growing on and near haypiles in an alpine cirque in northwestern Wyoming, USA, to determin e the effects of pika food caches on N, C, and C/N ratios in soils and plants. We found that (1) haypile soils had significantly higher carb on and nitrogen levels and lower C/N ratios than both adjacent soils a nd soils in the general study area, (2) two of three plant species tes ted (Polemonium viscosum and Oxyria digyna) had significantly higher l evels of tissue percent N when growing on haypile soils, and (3) total standing plant biomass at the study site increased with soil percent N suggesting that vegetation was nitrogen limited. Pikas may therefore function as allogenic ecosystem engineers by modulating nutrient avai lability to plants.