We investigated relationships between Pseudomys pilligaensis and other small mammal species in terms of their population fluctuations and habitat selection during a population irruption of P. pilligaensis. Antechinus flavipes showed only seasonal fluctuations in numbers, suggesting that it did not respond to the same environmental factors as P. pilligaensis. A. flavipes consistently selected areas with less sand in all phases of the irruption of P. pilligaensis, resulting in a clear separation from P. pilligaensis except in the Peak phase of the latter’s irruption. Numbers of Mus domesticus fluctuated similarly to P. pilligaensis until the latter’s irruption peak in April 2000. However, M. domesticus disappeared after July 2000 from our sites. M. domesticus seemed to occupy the area only temporarily when seeds were abundant. In the Increase and Peak phases of the irruption of P. pilligaensis, M. domesticus occupied core habitats characterised by more sand and shrub, and less litter, while in the Low phase P. pilligaensis occupied the core habitats that M. domesticus used to occupy. This may suggest that M. domesticus was excluded from core habitats through competition with P. pilligaensis in the Low phase of the latter’s irruption. However, since increased anthropogenic disturbance might create conditions that M. domesticus prefers, it is important to assess carefully any impacts of such disturbance on P. pilligaensis.