Population variability among three small mammal species in the semiarid Neotropics: the role of density‐dependent and density‐independent factors

We addressed the role of density‐dependent (direct and delayed) and density‐independent (precipitation) factors in shaping the dynamics of fluctuating populations of three small mammal species. Using a stepwise regression procedure, we tested the effects of nonlagged population density (log 10 N t‐1 ), lagged population density (log 10 N t‐2 ), and annual precipitation on the per capita rate of population change of Phyllotis darwini, Akodon olivaceus , and Thylamys elegans in two habitat types of a semiarid region of Chile. The most irruptive species ( P. darwini ) showed direct and delayed density‐dependent effects in equatorial subpopulation, and only direct density‐dependence in polar subpopulation. The per capita rates of population change of A. olivaceus showed direct density‐dependent and precipitation effects in both habitats types, while T. elegans showed direct density‐dependence and precipitation effects in the equatorial subpopulation but only a marginal effect of direct density‐dependence in the polar subpopulation. The presence of delayed density‐dependent strongly suggests the importance of biological interactions in shaping the dramatic irruptions exhibited by P. darwini.