Differential effects of climate and densities on survival and recruitment of Daurian pikas

Background/Question/Methods

The relative importance of intrinsic and extrinsic forces has been a central theme of animal population ecology.  Densities and climate may have different effects on different demographic processes of animal populations.  Small mammal populations have substantial environmental variability, often exhibiting the boom-bust type of population dynamics.  It is plausible to hypothesize that survival and recruitment of small mammals, as income breeders, are susceptible to changes in climate (hereafter, climatically labile demography hypothesis).  Life history theory predicts that small mammal populations are more sensitive to changes in fecundity and recruitment than to those in other vital rates.  Additionally, delayed effects of densities on sexual maturity have been ascribed to the occurrence of delayed density dependence in northern small mammals.  Therefore, we hypothesize that density dependence would emerge first in recruitment or reproduction in small mammals (hereafter recruitment regulation hypothesis).  We live trapped a population of Daurian pikas (Ochotona dauurica) in north central Inner Mongolia, China biweekly during the plant growing seasons (April to November) from 2009 to 2012 using capture-recapture methods.  We fit Cormack-Jolly-Seber models to the trapping data with daily temperature and precipitation as well as minimum number of animals alive (MNA) as covariates to test our hypotheses.

Results/Conclusions

Our best approximating model with the lowest Akaike information criterion supports the climatically labile demography hypothesis.  Survival probabilities of Daurian pikas were inversely related to daily temperatures; however, recruitment was positively related to daily temperatures.  Additionally, survival was inversely related to daily precipitation.  Our results showed opposite effects of warning on survival and recruitment of the pikas.  On the contrary, increases in MNA only resulted in decreases in recruitment, supporting the recruitment regulation hypothesis.  Effects of densities and climate on the demography of small mammals appeared to be complex.  Therefore, studies of the demographic pathways of density dependence and climate effects are vital to understanding and forecasting the impacts of densities and climate on population dynamics.