The role of so-called pest species in alternatively causing, or responding to, changing rangeland conditions remains contentious. Most scientists have concluded that high densities of plateau pikas (Ochotona curzoniae) on the Qinghai-Tibet Plateau, China, are a response to sparsely vegetation conditions, but demographic studies to support this hypothesis are lacking. During February–July 2009 we captured, weighed, and released plateau pikas monthly on 16 plots arrayed along a continuum of vegetation cover and pika density, both of which reflected differing land use for livestock management. We estimated apparent survival of adults using the Cormack–Jolly–Seber approach and recruitment of juveniles using the Pradel approach (in program MARK), modeling both as functions of habitat conditions, including vegetation cover. The probability of an adult pika captured in February being alive and present where initially captured in late July was ∼0.04; male and female survival rates were similar. Best-supported models of survival included vegetation cover and an index of late winter pika density; survival was negatively related to percent vegetation cover. Pika body condition varied monthly, and was negatively associated with percent vegetation cover during February–May, but positively associated in June. Pikas living where yaks had reduced vegetation cover displayed no lower recruitment, and higher survival, than where vegetation cover was higher. Thus, our results support the hypothesis that high pika density is a response to, rather than a cause of, “rangeland degradation.” Reducing undesired high pika densities will require addressing root causes of undesirable rangeland conditions.
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Vol. 94 • No. 5