Effects of predation risk on behavior, hormone levels, and reproductive success of plateau pikas

Abstract Predation is a strong selective force that affects animal population dynamics either through direct killing or predation risk effects. Although recent empirical research has shown that the non‐consumptive effect of predator risk on prey dynamics can be as large (or even larger) as direct effects, little is known about the strength of predation risk effects in wild populations or the physiological mechanisms that mediate them. Here, we test both the predator‐sensitive food hypothesis and predation‐stress hypothesis in a single system by investigating activity budgets, stress/sex hormone levels, and demography of plateau pikas ( Ochotona curzoniae ) and their predators in Haibei Alpine Meadow Ecosystem Research Station of the Chinese Academy of Science. During the study period (2009 and 2010), plateau pikas experienced various predation pressures due to many predators being poisoned in 2010. In the year of high predator numbers, pikas spent more time on vigilant duty and less time foraging and they also showed higher plasma corticosterone levels and lower plasma estradiol and testosterone levels. Reproductive success and male with developed testes also reduced in the year of higher predation risk. In general, our results support both the predator‐sensitive food and predation‐stress hypothesis. Predator‐induced risk affects prey reproduction by changes in feeding patterns and stress physiology.