Demographic dynamics of a neotropical small rodent (Phyllotis darwini): feedback structure, predation and climatic factors

1. The leaf-eared mouse (Phyllotis darwini) exhibits large numerical fluctu ations associated with high- and low-rainfall years in semi-arid Chile. Usi ng capture-mark-recapture (CMR) statistical modelling.. we provide a detail ed description of the demographic variation in this species. We studied bet ween-year and seasonal variation of demography, and tested for the relative importance of endogenous and exogenous factors as covariates of survival, recruitment, maturation and reproduction over a 12-year period. 2. The demographic variables studied show larger between-year than within-y ear (seasonal) variation, emphasizing the importance of this source of exte rnal variability. We found that both feedback structure and exogenous facto rs operate together on different demographic processes of this species. 3. We found positive direct feedback effects on survival rate and negative feedback on recruitment, fraction of reproductive individuals and female ma turation rates. The ratio between barn and magellanic homed owls showed an important effect on most of the demographic variables of leaf-eared mice, i n particular by influencing negatively survival rates and the fraction of r eproductive individuals, thus suggesting the importance of non-lethal preda tion. 4. Hence, feedback intrinsic mechanisms (density-dependence), owls and clim ate (rainfall and Southern Oscillation Index (SOI)) operate simultaneously in determining the demography of leaf-eared mice. We hypothesize that troph ic interactions with owls (and perhaps other predators) may cause second-or der feedback responses in demography and population dynamics of this small rodent species.