| Summary: | Invasive rats on oceanic islands impact a large number of native species. Control programs, and in cases complete eradication, are used to alleviate these impacts. Basic biological data on rodent biology facilitates the design of management plans, and are particularly required for programmes on tropical islands where they are lacking. Here, we test complex environmental effects and their interactions on two tropical islands (Iles Eparses) that may alter black rat demography, space use dynamics, and inform rodent management. Five years of summer and winter trapping data were analysed using spatially explicit capture-recapture to determine rat population dynamics and calculate rat range size, coupled with spool and line experiments. Variation in demography and individual rat space use is primarily driven by bottom-up effects of seasonal rainfall pulses on habitat, but is altered by island-specific contexts. In the absence of other introduced mammals, rats tend to have stable range overlap throughout the year but seasonal home range size fluctuations associated with rat density. The presence of other introduced mammals causes a more variable response in home range size, although predictable, which we hypothesise to be a behavioural adjustment to fluctuating levels of predation pressure on rats in relation to seasonal influxes of breeding seabirds. We eventually discuss relevance of data for eradication strategies.
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