AbstractPopulation dynamics and habitat preferences of the dusky rat,Rattus colletti, were examined in the seasonal wetlands of the South Alligator River. Northern Territory, between late 1979 and 1982. Demographically, the species is characterized by short‐term seasonal shifts between habitats superimposed on a longer‐term irregular pattern of prolonged breeding and population irruption, followed by periods of relative rarity. These patterns are determined by the train of climatic events. The flexible life history strategy and movement patterns ofR. collettireflect fine‐scale adaptation to a climatic regimen which is markedly seasonal, but also highly variable between years in the amount and temporal patterning of rainfall.The distribution ofR. collettiamongst vegetation types is influenced by two sets of environmental factors, both reflecting a gradient in elevation, soil type and vegetation. The primary factors are vegetative cover and height, and the extent and duration of flooding; the secondary set comprises buffalo‐induced features such as the degree of pugging and grazing. These factors are interrelated, and their relative importance toR. collettivaries greatly between seasons.Feral buffalo appear to exacerbate the harsh effects of the wet and dry seasons. The removal of these animals may ameliorate environmental conditions considerably, both temporally and spatially, resulting m generally higher, more stable and spatially less variable populations ofR. c