Browsing by Author "Stenseth, NC"

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    Demographic dynamics of a neotropical small rodent (Phyllotis darwini)
    (2001) Lima, M; Julliard, R; Stenseth, NC; Jaksic, FM
    1. The leaf-eared mouse (Phyllotis darwini) exhibits large numerical fluctuations associated with high- and low-rainfall years in semi-arid Chile. Using capture-mark-recapture (CMR) statistical modelling.. we provide a detailed description of the demographic variation in this species. We studied between-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.
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    Demography and population dynamics of the mouse opossum (Thylamys elegans) in semi-arid Chile
    (2001) Lima, M; Stenseth, NC; Yoccoz, NG; Jaksic, FM
    Here, we present, to the authors' knowledge for the very first time for a small marsupial, a thorough analysis of the demography and population dynamics of the mouse opossum (Thylamys elegans) in western South America. We test the relative importance of feedback structure and climatic factors (rainfall and the Southern Oscillation Index) in explaining the temporal variation in the demography of the mouse opossum. The demographic information was incorporated into a stage-structured population dynamics model and the model's predictions were compared with observed patterns. The mouse opossum's capture rates showed seasonal (within-year) and between-year variability, with individuals having higher capture rates during late summer and autumn and lower capture rates during winter and spring. There was also a strong between-year effect on capture probabilities. The reproductive (the fraction of reproductively active individuals) and recruitment rates showed a clear seasonal and a between-year pattern of variation with the peak of reproductive activity occuring during winter and early spring. In addition, the fraction of reproductive individuals was positively related to annual rainfall, while population density and annual rainfall positively influenced the recruitment rate. The survival rates were negatively related to annual rainfall. The average finite population growth rate during the study period was estimated to be 1.011 +/- 0.0019 from capture-recapture estimates. While the annual growth rate estimated from the seasonal linear matrix models was 1.026, the subadult and adult survival and maturation rates represent between 54% (winter) and 81% (summer) of the impact on the annual growth rate.
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    Food web structure and climate effects on the dynamics of small mammals and owls in semi-arid Chile
    (2002) Lima, M; Stenseth, NC; Jaksic, FM
    Population dynamics of small mammals and predators in semi-arid Chile is positively correlated with rainfall associated with incursions of El Nino (El Nino Southern Oscillation: ENSO). However, the causal relationships between small mammal fluctuations, predator oscillations, and climatic disturbances are poorly understood. Here, we report time series models for three species of small mammal prey and two species of owl predators. The large differences in population fluctuations between the three small mammal species are related to differences in their respective feedback structures. The analyses reveal that per capita growth rate of the leaf-cared mouse is a decreasing function of log density and of log barn owl abundance together with a positive rainfall effect. In turn, per capita population growth rate (R-function) of the barn owl is a negative function of log barn owl abundance and a positive function leaf-eared mouse abundance, suggesting a predator-prey interaction. The dramatic population fluctuations exhibited by leaf-cared mouse (Phyllotis darwini) are caused by climate effects coupled with a complex food web architecture.