Elsewhere we have developed a speculative model of the early human colonisation of Sahul (Pleistocene Australia-New Guinea). Here we elaborate it, using theory from behavioural ecology, and data from palaeoclimatology and modern hunter-gatherer ethnography. We argue that colonisers focused mainly on coastal ecotones while crossing Wallacea, but spread more widely across favourable habitats after landing on Sahul. Movement was archaeologically instantaneous, driven primarily by serial depletion of high-ranked prey. Human populations subsequently remained far smaller than sometimes imagined, probably because of difficult climatic and environmental conditions. Archaeological data are generally consistent with these expectations. These findings challenge the frequent assertion that human colonisation alone led to significant changes in Sahul ecology, and may help explain the simplicity of its Pleistocene lithic technology.