Abstract
Invasive predators, land clearing and altered fire regimes have been implicated in species decline and extinction worldwide. Enhanced knowledge of how these factors interact and influence medium-sized mammals is warranted. We tested three hypotheses using occupancy data for a diverse mammal assemblage including three threatened species, five common species, two introduced mesopredators and an apex predator in eastern Australia. We hypothesised that occupancy of mammal species within the assemblage would be influenced by (i) the physical environment (rainfall, vegetation type and elevation), (ii) habitat disturbance (number of fires and habitat fragmentation) and (iii) mesopredator release, whereby occupancy and/or detection of medium-sized mammals are influenced by mesopredators, the feral cat (Felis catus) and the red fox (Vulpes vulpes), which are influenced by an apex predator, the dingo (Canis familiaris). We utilised camera-trapping data from 173 sites (692 camera locations) across a north–south gradient spanning ~ 1500 km in eastern Australia. Although hypotheses i (physical environment) and ii (habitat disturbance) are not mutually exclusive, we show that the variables considered in each were only weakly correlated. We conducted occupancy modelling to investigate the physical environment and habitat disturbance hypotheses. We conducted co-occurrence modelling to investigate interactions between species. The physical environment hypothesis best supported occupancy models for six mammal species: red-necked pademelon (Thylogale thetis), bandicoots (Isoodon macrourus and Perameles nasuta), swamp wallaby (Wallabia bicolor), red-necked wallaby (Macropus rufogriseus), eastern grey kangaroo (Macropus giganteus) and feral cat. The disturbance hypothesis best supported occupancy models for four mammal species: long-nosed potoroo (Potorous tridactylus), red-necked pademelon and both mesopredators. Support for the mesopredator release hypothesis was equivocal. Large macropods showed site avoidance towards the red fox. Four species showed higher detection at sites where mesopredators were not detected. The fox showed a negative detection interaction to the dingo and the cat did not. Our study highlights how factors such as rainfall, land clearing, elevation and number of fires influence the occupancy of species within a diverse mammal assemblage at the macroecological scale. Our findings have implications for the conservation of threatened species in managed landscapes and suggestions for further research following the recent 2019–2020 wildfires.
Highlights
IntroductionThe world is facing a biodiversity crisis with the continuing extinction and decline of species globally (Johnson et al 2017; Rosenberg et al 2019)
Thirty-four of Australia’s 273 endemic mammal species have become extinct in the past 200 years (Woinarski et al 2019) and at present, there are 30 species listed as endangered under Federal legislation with a further 46 listed as vulnerable (Environment Protection and Biodiversity Conservation Act 1999)
The physical environment hypothesis had support for most generalist species whereas the habitat disturbance hypothesis was supported for sensitive habitat specialists and introduced mesopredators
Summary
The world is facing a biodiversity crisis with the continuing extinction and decline of species globally (Johnson et al 2017; Rosenberg et al 2019). While human activities have increased the rate of species extinctions to more than 1000 times the natural background rate (Pimm et al 1995), managed conservation areas are experiencing secondary legacy effects from human activities long after initial threats have subsided Threats such as habitat disturbance, introduced predators and altered fire regimes impact biodiversity within protected areas and these factors are likely to be exacerbated outside of conservation lands. Thirty-four of Australia’s 273 endemic mammal species have become extinct in the past 200 years (Woinarski et al 2019) and at present, there are 30 species listed as endangered under Federal legislation with a further 46 listed as vulnerable (Environment Protection and Biodiversity Conservation Act 1999) Among those affected are medium-sized terrestrial mammals (Burbidge and McKenzie 1989; Cardillo and Bromham 2001). The broad factors that drive global extinctions are well known (Gibbons et al 2000; Stuart et al 2004; Skerrat et al 2007; Szabo et al 2012; Sánchez-Bayo and Wyckhuys 2019), further investigation of factors causing declines in managed landscapes are paramount to inform conservation and management and arrest further declines
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