Agricultural irrigation mediates climatic effects and density dependence in population dynamics of Chinese striped hamster in North China Plain

Summary1. Several studies show that climatic (extrinsic) factors can interact with density-dependent(intrinsic) factors to alter long-term population dynamics, yet there is a surprising lack ofinvestigations of how anthropogenic disturbance modifies such dynamics. Such interactionscould be especially important in agricultural systems subject to climate change.2. We investigated the effects of density dependence, climate, recurrent disturbance fromflood irrigation and their interactions on the population dynamics of an important rodentpest, the Chinese striped hamster (Cricetulus barabensis), over 27 years in the croplands ofthe North China Plain.3. Strong density-dependent feedbacks occurred at both annual and seasonal scales. Whilewarmer weather increased population sizes in nonbreeding seasons, this effect was counter-acted by the negative effect of flood irrigation in breeding seasons. Precipitation showedsignificant positive effects in nonbreeding seasons, but negative effects in breeding seasons.4. There were important interactions between intrinsic dynamics, extrinsic dynamics and dis-turbance. Low temperature significantly increased the strength of density dependence in non-breeding seasons, whereas intensification of flood irrigation area significantly increased thestrength of density dependence but reduced the effect of summer precipitation in breedingseasons.5. Overall climate change is expected to increase population levels, but anthropogenic distur-bance from flood irrigation will help prevent long-term population increases. The interactionsbetween anthropogenic disturbance and both intrinsic and extrinsic (weather-driven) popula-tion dynamics caution that we need to consider anthropogenic disturbance as an integralcomponent of population responses to climate change.Key-words: agricultural activity, global warming, human disturbance, small mammalIntroduction