Climate and small rodent dynamics in semi-arid Chile: the role of lateral and vertical perturbations and intra-specific processes

The study of the relative importance of the feedback structure (intrinsic processes) and exogenous (climatic or environmental) factors in determining population dynamics, in particular the interaction between density-dependence and climate, is a major question in population ecology. We sought to explain the numerical fluctuations of 2 sympatric rodent species at one well-studied site in semi-arid Chile using simple theoretically based population dynamics models and Royama's theoretical framework for analyzing the dynamics of populations influenced by exogenous climatic forces. We found that rainfall effects appear to operate in a different manner on the 2 rodent species. For one species (Phyllotis darwini), rainfall appeared to influence the carrying capacity of the environment, whereas for a second (Akodon olivaceus) the rainfall effect had a primarily additive influence on the maximum per capita growth rates.