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Understanding differential and integrated effects of weather and population density on vital rates (birth,death rates) helps elucidate the ecological and demographic mechanisms underlying animal population dynamics.Nonlinear responses of the vital rates to changes in weather conditions are critical to predicting the effects of climate changes on small herbivorous mammals in arid and semi-arid environments.We aimed to test the hypotheses: 1) that increased precipitation would exert quadratic effects on the survival probability of the Daurian pika (Ochotona dauurica) ,a small herbivorous mammal in semi-arid grassland; and 2) that density dependence would result in stronger effects on recruitment than on survival of O.dauurica as a regulatory mechanism of population dynamics.We live trapped a population of O.dauurica in north central Inner Mongolia,China biweekly between May 2010 and November 2012,and estimated the effects of temperature,precipitation,and density on the survival probabilities and recruitment rates of O.dauurica using mark-recapture methods.Increases in temperature improved the recruitment but reduced the survival of O.dauurica,resulting in positive net effects on population growth rates.Increased precipitation resulted in quadratic effects on population growth rates primarily through nonlinear effects on survival probabilities,supporting the optimum precipitation hypothesis.Our results also support the hypothesis that population densities exert stronger effects on recruitment than on survival of small mammals.Our findings shed light on the demographic mechanisms underlying the complex effects of weather and density on small mammal populations.