Habitat structure facilitates coexistence of native and invasive mesopredators in an Australian tropical savanna

Abstract

Context. The introduction of the cat (Felis catus) to Australia has been a key driver of the decline and extinction of the continent's endemic mammals. Currently, there is no clear long-term solution to controlling feral populations of cats at a landscape scale. As such, understanding how environmental conditions and habitat attributes can mediate the coexistence between introduced predators and native mammals can improve management outcomes for threatened species. Aim. We sought to compare the differences in habitat use by feral cats and a remnant population of the endangered northern quoll (Dasyurus hallucatus) to understand what environmental variables allow these two mesopredators to coexist in tropical savanna of Cape York Peninsula, Queensland. Methods. We deployed grids of motion-activated cameras three times per year over a 3-year period, across Eucalyptus tetrodonta-dominated plateaux known to be inhabited by feral cats and northern quolls. We modelled the spatial variation in the frequencies of detection of feral cats and northern quolls (referred to as 'habitat use'), as a function of biotic and abiotic environmental variables by using a generalised linear model for consistent variables and a generalised linear mixed-effect model for fluctuating variables. Key results. Habitat use by feral cats was most frequent in areas with high fire frequencies and low tree basal area, whereas habitat use by northern quolls was most frequent in areas of high basal area of E. tetrodonta (a commonly used den tree species), topographic ruggedness, and long-unburnt savanna. Conclusions. Frequent fires in tropical savanna promote habitat use by feral cats and can result in a reduction of critical habitat for northern quolls. Implications. We postulate that remnant populations of northern quolls on Cape York Peninsula occur in less frequently burnt refugia, primarily on top of plateaux that support high-biomass tropical savanna dominated by E. tetrodonta. Our findings highlighted that threatened mammals can persist alongside introduced predators in tropical savanna but are dependent on the maintenance of structurally complex habitat.

Where there’s smoke, there’s cats: long-unburnt habitat is crucial to mitigating the impacts of cats on the Ngarlgumirdi, greater bilby (Macrotis lagotis)

“…For example, previous studies conducted in the savannas of the Kimberley and Cape York Peninsula regions by McGregor et al (2014McGregor et al ( , 2015 demonstrated that feral cats exhibit improved hunting efficiency in grassland and recently burnt habitats. Similarly, Trewella et al (2023) found that habitat use by feral cats was most frequent in areas with high fire frequencies and low tree basal area. It is plausible, therefore, that mature Acacia shrubland and eucalypt woodland (>3 years post fire) limit the hunting efficiency of feral cats by providing complex vegetation cover for Ngarlgumirdi.…”

Midnight siesta: Bimodal temporal activity observed in an endangered marsupial predator

“…Camera‐trap models used included Reconyx HC550 (white flash), Reconyx HC600 (infrared flash), Reconyx PC900, Scoutguard 560DF (dual flash), and Scoutguard 565F (white flash). Cameras were mounted to a tree or post either 1 or 1.5 m above the ground and oriented vertically (facing downward), so as to capture unique spot patterning located on the dorsal surface of animals (see Diete et al., 2017; Indigo et al., 2023; Moore et al., 2020; Trewella et al., 2023). All cameras were baited (fish, peanut butter, or sesame oil) and left active for between 2 and 150 days at a time.…”