Abstract

A trapping study from 1994 to 1996 examined the population structure and dynamics of two sympatric populations of rodent, Mus domesticus and Leggadina lakedownensis, inhabiting an island off the coast of Western Australia. Population abundance fluctuated dramatically within and between years for both species, and those of M. domesticuswere influenced by cyclones that passed close to the island. Population densities for M. domesticus reached 13.4 mice ha^–1 in November 1995, and were always twice those of L. lakedownensis. M. domesticus bred throughout the year. In contrast, the breeding season for L. lakedownensis was strictly seasonal, and was restricted to the mid-year months. Numbers of M. domesticus were correlated with rainfall that fell 3–6 months previously. Similarly, numbers of L. lakedownensis were correlated with rain that fell 3 months previously. Although no significant relationship was detected between total invertebrate and mouse abundance, numbers of M. domesticus were correlated with those of lepidopteran larvae collected in pitfall traps. These data suggest that species coexistence on the island may be mediated by extreme rainfall events, and a lack of competition during low population densities.