Modelling effects of pika and livestock herbivory on pastureland of the Tibetan Plateau

Background/Question/Methods The plateau pika (Lagomorpha: Ochotona curzoniae) is endemic the Tibetan Plateau, where it digs extensive burrow systems housing large social family units. In spite of mounting evidence pointing to their role as keystone species and ecosystem engineer, plateau pikas are extensively poisoned throughout their range. Pikas are commonly regarded as "rodent pests" because they are thought to cause soil erosion and compete with livestock for forage. However, little research has been done regarding the extent and nature of pika-livestock interactions. We develop a simple mathematical model to investigate the effects of pika and livestock grazing on alpine meadow habitat. The model is structured as a competitive interaction between components of the resource base (graminoids and forbs), while the effects of resource users (pika and livestock) are treated as parameters.

Results/Conclusions Analysis of the model reveals that stability is primarily controlled by competitive abilities of forage components, rather than pika or livestock herbivory. However, high rates of herbivory by either user can push the rangeland to forb dominance. A diverse resource base, defined as a stable system of both graminoids and forbs, can only occur under light to moderate grazing by both resource users.