Female reproductive suppression in an Australian arid zone rodent, the spinifex hopping mouse

The spinifex hopping mouse (Notomys alexis)is an Australian arid zone rodent that undergoes boom and bust population cycles in its natural environment. Most populations studied to date have been sympatric with exotic predators and introduced herbivores, likely affecting their population dynamics. Therefore, it is unclear whether high-density populations of hopping mice are regulated by purely extrinsic factors or whether intrinsic factors are also at play. We hypothesized that reproductive suppression of femaleN. alexismay occur in high-density populations as has been observed in some other rodent species. Reproductive condition of adult femaleN. alexiswas compared between a high-density population within the Arid Recovery reserve, where exotic predators and introduced herbivores are excluded, and a low-density population on adjacent pastoral properties (no exclusions). Trap success was 10 times higher inside the reserve than at pastoral sites, and no adult females were observed breeding in the reserve population, despite 26 % of females at pastoral sites recorded breeding. Our results indicate that adult femaleN. alexisin the high-density reserve population were reproductively suppressed, but the similar sex ratios in both populations and the high female body mass and body condition in the reserve indicated that this was not due to demographic differences between the two populations or food scarcity. Our study indicates that the 'busts' observed in arid zone rodent populations may be amplified due to the presence of exotic predators and/or grazing by introduced herbivores. We contend that prior to the introduction of exotic predators and introduced herbivores in Australia, the arid zone rodentN. alexiswould likely have been more abundant and intrinsic population regulation through female reproductive suppression may have played a larger role in population regulation.