A Population Study of House-Mice Temporarily Inhabiting a South Australian Wheatfield

shelter. When the study first began it was assumed that mice lived all year round in the wheatfields. But after a few months I began to suspect that the fields might be temporarily inhabited only and invaded each year. Trapping in a nearby reed-bed indicated that it might hold permanent populations that could provide the wheatfield's colonists; so another intensive population study began there. Though related, these two studies have been presented separately (see Newsome (1969) for the study in the reed-bed) because the ways mice lived in the two habitats were so different. In the wheatfield, population control was extrinsic whereas in the reed-bed intrinsic factors played a part in it. As MacArthur & Connell (1966) have suggested, the kind of population control depended on the harshness of the environment. Descriptions of climate, soils, and vegetation of the study-area, which is the area dominated by red-brown earths shown in Fig. 1, follow.