Abstract

We report on a long-term population study (started in 1969) of three sympatric rodent species in a tropical Queensland (Australia) rainforest. Populations were censused annually using live-trapping and individual marking on two grids in different habitat types. Two of the species, Melomys cervinipes and Uromys caudimaculatus, are ‘old endemics’ and have slower life-histories than the third species, Rattus fuscipes, which invaded Australia more recently. The numbers of all three species fluctuated markedly over the study period. Rattus numbers started low, peaked in the early 1980s, and then crashed to zero by 1993. In contrast, Melomys climbed gradually throughout the study period but crashed to zero by 1996. Melomys numbers increased in drier years whereas Uromys numbers decreased, but these results were confounded by autocorrelation over time. When the effects of time (year of study) were removed statistically, the correlations with rainfall disappeared, but the number of Rattus remained negatively correlated with the number of Melomys on one grid. We discuss the possibility that numbers of these two species are determined by a combination of climate and interspecific competition.