Stemming the tide: progress towards resolving the causes of decline and implementing management responses for the disappearing mammal fauna of northern Australia

Abstract

Introduction: Recent studies at sites in northern Australia have reported severe and rapid decline of several native mammal species, notwithstanding an environmental context (small human population size, limited habitat loss, substantial reservation extent) that should provide relative conservation security. All of the more speciose taxonomic groups of mammals in northern Australia have some species for which their conservation status has been assessed as threatened, with 53 % of dasyurid, 47 % of macropod and potoroid, 33 % of bandicoot and bilby, 33 % of possum, 30 % of rodent, and 24 % of bat species being assessed as extinct, threatened or near threatened. However, the geographical extent and timing of declines, and their causes, remain poorly resolved, limiting the application of remedial management actions. Material and methods:Focusing on the tropical savannas of northern Australia, this paper reviews disparate recent and ongoing studies that provide information on population trends across a broader geographic scope than the previously reported sites, and examines the conservation status and trends for mammal groups (bats, macropods) not well sampled in previous monitoring studies. It describes some diverse approaches of studies seeking to document conservation status and trends, and of the factors that may be contributing to observed patterns of decline.170 THERYA Vol.6(1):169-225 DECLINING MAMMALS OF NORTHERN AUSTRALIA Results and Discussion: Current trends and potential causal factors for declines. The studies reported demonstrate that the extent and timing of impacts and threats have been variable across the region, although there is a general gradational pattern of earlier and more severe decline from inland lower rainfall areas to higher rainfall coastal regions. Some small isolated areas appear to have retained their mammal species, as have many islands which remain critical refuges. There is now some compelling evidence that predation by feral cats is implicated in the observed decline, with those impacts likely to be exacerbated by prevailing fire regimes (frequent, extensive and intense fire), by reduction in ground vegetation cover due to livestock and, in some areas, by 'control' of dingoes. However the impacts of dingoes may be complex, and are not yet well resolved in this area. The relative impacts of these individual factors vary spatially (with most severe impacts in higher rainfall and more rugged areas) and between different mammal species, with some species responding idiosyncratically: the most notable example is the rapid decline of the northern quoll (Dasyurus hallucatus) due to poisoning by the introduced cane toad (Rhinella marina), which continues to spread extensively across northern Australia. The impact of disease, if any, remains unresolved. Conservation Management Responses.Recovery of the native mammal fauna may be impossible in some areas. However, there are now examples of rapid recovery following threat management. Priority conservation actions include: enhanced biosecur...

High mortality and small population size prevent population recovery of a reintroduced mesopredator

“…The impending extinction crisis reinforces the need to explore all factors responsible for mammal declines; in this respect, increased predation by subsidized apex predators has so far been overlooked (Ziembicki et al, 2015). The impending extinction crisis reinforces the need to explore all factors responsible for mammal declines; in this respect, increased predation by subsidized apex predators has so far been overlooked (Ziembicki et al, 2015).…”

“…Fire influences the structure and species composition of vegetation assemblages (Russell-Smith, Ryan & Cheal, 2002;Woinarski et al, 2004), and frequent, intense fires reduces shelter and refugia for prey species (Vigilante & Bowman, 2004), exacerbating the effects of predation. Dingoes Canis dingo (Crowther et al, 2014) also show increased activity after fire (Leahy et al, 2016), however, the role of dingoes and other free-living canids in the current small mammal decline in Northern Australia is less clear (Woinarski et al, 2011;Ziembicki et al, 2015). Dingoes Canis dingo (Crowther et al, 2014) also show increased activity after fire (Leahy et al, 2016), however, the role of dingoes and other free-living canids in the current small mammal decline in Northern Australia is less clear (Woinarski et al, 2011;Ziembicki et al, 2015).…”

Fauna and vegetation responses to fire and invasion by toxic cane toads (Rhinella marina) in an obligate seeder-dominated tropical savanna in the Kimberley, northern Australia

“…One of the key groups identified in northern Australia as having predominantly negative responses to fire is the group of small and mediumsized mammals including rodents and marsupial species up to 5 kg in size (Andersen et al 2005;Woinarski et al 2010Woinarski et al , 2011Ziembicki et al 2015). However, small mammals made up only a small component of pindan survey captures, reflecting generally low abundance and diversity of mammals in this rainfall zone (<1000 mm) across the Western Australian Kimberley region (Radford et al 2014).…”

“…Another significant threat to savanna biodiversity in northern Australia is invasion by the toxic anuran Rhinella marina (the cane toad; Shine 2010; Woinarski et al 2011;Ziembicki et al 2015). This species has several documented impacts among savanna ecosystems (Shine 2010).…”

Fire-Driven Decline of Endemic Allosyncarpia Monsoon Rainforests in Northern Australia

“…A substantial body of evidence indicates that contemporary anthropogenic fire regimes are causing significant impacts on a wide range of fire-vulnerable biodiversity elements in north Australia's relatively unmodified savannas, including: avifauna [17,18]; small mammals [19,20], and obligate seeding flora [21][22][23]. In large part, these recent fire regime impacts can be attributed to widespread Aboriginal societal collapse from the end of the nineteenth century, and associated breakdown of former systematic fire management approaches focusing on imposing fine-scale spatial patchiness over the annual burning season [24][25][26].…”