LAUSR

Abstract Context. Boom and bust population cycles are characteristic of many arid-zone rodents, but it is unknown to what extent these dynamics might be influenced by the presence of invasive rodents, such as the house mouse (Mus musculus) in Australia. Aim. To determine whether the presence of M. musculus can have negative consequences on the population abundance and reproduction of two old Australian endemic rodents (the spinifex hopping mouse, Notomys alexis, and sandy inland mouse, Pseudomys hermannsburgensis). Methods. The study took place on the sand dunes of a cattle station in central Australia. Population abundance was estimated as the number of individuals caught in small mammal traps, and female reproductive condition by external examination and, in a few cases, euthanasia and inspection of the reproductive tract. Key results. Two synchronous periods of high abundance of N. alexis and M. musculus occurred several months after significant rainfall events, whereas the abundance of P. hermannsburgensis was consistently low. No reproduction took place in N. alexis or M. musculus when populations had reached high abundance. During low-rainfall periods, M. musculus was not detected on the sand dunes, and the two endemic species were sparsely distributed, with reproduction occasionally being evident. Conclusions. During dry periods, M. musculus contracted back to refuges around the homestead and, after significant rainfall, it expanded onto the sand dunes and became abundant at the same time as did N. alexis. In contrast, and unlike in areas where M. musculus was generally rare, P. hermannsburgensis always remained at a low abundance. These patterns suggest that in areas of the natural environment close to human-modified sites, populations of at least one species of an old endemic rodent are supressed by the presence of M. musculus. Reproduction did not occur in the old endemics at times of high M. musculus abundance, but did take place in spring/early summer, even in some dry years. Implications. The spread of M. musculus into the Australian arid zone may have had negative impacts on the population dynamics of P. hermannsburgensis. These findings suggest that the presence of human settlements has resulted in refuges for house mice, which periodically spread out into the natural environment during ‘boom’ times and adversely affect the natural population cycle of ecologically similar species such as P. hermannsburgensis.