Long-term fluctuations in distribution and populations of a threatened rodent (Pseudomys novaehollandiae) in coastal woodlands of the Otway Ranges, Victoria: a regional decline or extinction?

Abstract

Abstract. Since European settlement Australian native rodents have experienced dramatic extinctions and declines. We investigated long-term population and distribution changes during 1981-2003, and known or potential causal factors of decline in the vulnerable New Holland mouse (Pseudomys novaehollandiae). We found that populations (n = 8) were extant for 1-6 years and were predominantly small, localised and extinction prone. High-density populations occurred after above-average rainfall but declined precipitously during drought. Wildfire resulted in the extirpation of some populations, while others survived in unburnt refugia. We propose that post-fire vegetation (3-7 years) contemporaneous with aboveaverage rainfall delivered productive habitat resulting in both a population irruption, and recovery after wildfire. Population declines occurred in drought periods. Recent trapping at 42 sites (2013-17) failed to record any New Holland mice. The species has not been recorded since 2003. Recovery is unlikely without intensive management, focussed on remnant or reintroduced populations, including protection from habitat fragmentation and inappropriate fire regimes. Prevention of extinction of the species throughout its southern range will require similar management strategies.

Accounting for detectability and abundance in survey design for a declining species

“…Like many native Australian rodents, P. novaehollandiae is readily lured by standard mammal bait (rolled oats, peanut butter and golden syrup) and easily trapped when at high local abundance (McCall, Reside, & Collyer, ), thus its poor early detection history is likely due to lack of effort, rather than it being an innately cryptic species. Resurvey efforts since these initial discoveries indicate that many populations have declined, potentially to local extinction (Lazenby, Bell, Driesen, Pemberton, & Dickman, ; Wilson, ; Wilson, Lock, & Garkaklis, ). Historically, the standard survey effort for P. novaehollandiae was three consecutive nights of live trapping using 30 Elliott traps, with abundance indices drawn from trap success or capture–mark–recapture data (Atkin & Quin, ; Lock & Wilson, ; Quin, ; Wilson, White, Hanley, & Tidey, ).…”

“…As the species declines in abundance, this effort may no longer be sufficient for detection, and low‐abundance populations may be mistakenly considered extinct. Further, abundance estimates may be clouded by seasonal fluctuations in detectability, due both to true shifts in abundance and to behavioural changes across the year; dispersal of young occurs in March–May following the November–March breeding season (Fox, ; Kemper, ; Wilson, ; Wilson et al, ).With purported local extinctions at seven of 12 historically occupied regions in Victoria (Quin, ; Wilson et al, ), there is an acute need to delineate the species' current distribution to guide management efforts and test causes of decline.…”

Habitat selection and genetic diversity of a reintroduced ‘refugee species’

“…The species has been extinct from the ACT for probably over 130 years (ACT ESDD, ). Sub‐fossil distributions indicate a range contraction occurred around the time of European settlement, probably due to the impacts of exotic predators, changes in fire regimes and habitat clearing (Breed & Ford, ; Lock & Wilson, ; Wilson, Lock & Garkaklis, ). Genetic evidence suggests the species may have occurred as a continuous population across mainland Australia.…”

“…Current populations are heavily fragmented and exist only along the east coast, concentrated to the central coast and northern New South Wales (NSW), and have experienced relatively recent genetic divergence (Myroniuk, ; Breed & Ford, ). Recent severe population declines in Victoria and Tasmania suggest that the species has become extinct at more locations and is more threatened than previously considered (Lazenby et al , ; Wilson et al , ).…”

“…Preferred habitat type is consistently documented to be floristically rich open coastal heathland, woodland of low vegetation cover or vegetated sand dunes (Fox & Fox, ; Hocking, ; Cockburn, Braithwaite & Lee, ; Fox & McKay, ; Fox & Fox, ; Wilson, 1991 b ; Wilson et al , ; Lazenby et al , ), with soft, deeper topsoils and sandy substrate, which is preferred for burrowing (Wilson & Laidlaw, ; Lazenby et al , ). Regular fire disturbance is commonly identified as a key habitat requirement, with populations peaking in abundance 3‐7 years post‐fire and after periods of above average rainfall (Fox & McKay, ; Fox, ; Wilson, 1991 b ; Wilson et al , ). However, these strict habitat conditions are linked to extreme population fluctuations and localized extinctions (Wilson et al , ; Wilson et al , ), and did not exist across much of the species historical distribution (Breed & Ford, ).…”