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

Abstract

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 female N. alexis may occur in high‐density populations as has been observed in some other rodent species. Reproductive condition of adult female N. alexis was 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 female N. alexis in 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 rodent N. alexis would likely have been more abundant and intrinsic population regulation through female reproductive suppression may have played a larger role in population regulation.

High survivorship and rapid population growth of the greater bilby (Macrotis lagotis) reintroduced to a feral predator exclosure

“…The potential for high densities to supress reproduction in bilbies could have important implications for future management of fenced bilby populations and warrants further research (e.g. Berris et al 2020b). We suggest that the population at CNP is now in a 'regulation phase', where recruitment and/or survival rates decrease due to increased population density (IUCN/SSC 2013).…”

“…Density-dependent reproduction has been recorded in another arid-dwelling mammal, the spinifex hopping mouse (Notomys alexis) (Breed and Leigh 2011;Breed et al 2017;Berris et al 2020b). At high population densities, adult female hopping mice were reproductively suppressed, despite having higher mean body mass than mice from lower density sites, which were reproductively active (Berris et al 2020b). Further, Berris et al (2020a) also observed reductions in reproductive output in a reintroduced population of bilbies on Thistle Island, where the population was assumed to be close to its maximum size.…”

“…It is possible that in 2022, the population at CNP was nearing its maximum size/density, and that we observed a suppressive effect on reproduction at the higher population density estimate. Density-dependent reproduction has been recorded in another arid-dwelling mammal, the spinifex hopping mouse (Notomys alexis) (Breed and Leigh 2011;Breed et al 2017;Berris et al 2020b). At high population densities, adult female hopping mice were reproductively suppressed, despite having higher mean body mass than mice from lower density sites, which were reproductively active (Berris et al 2020b).…”

Influence of interactive effects on long‐term population trajectories in multispecies reintroductions

“…The cumulative rainfall period affecting track counts was higher for bettongs and likely is related to this species’ longer generation time and dependence on herbivory, but track density in all 3 paddocks increased with increasing rainfall up until approximately average annual rainfall. After this point, the relationship became difficult to interpret due to low sample size, but density dependence could cause suppression of breeding in bilbies and bandicoots at high densities in a confined area, as has been found in hopping mice ( Notomys alexis ) at the site (Berris et al., 2020) and for other native mammals globally (Wolff, 1997). The negative relationship between the IOD and track density observed in stick‐nest rats is also likely related to rainfall; the IOD has been negatively correlated with winter rainfall in central Australia (Ashok et al., 2003) and extreme rainfall events in southwest Western Australia (England et al., 2006).…”