Habitat structural complexity explains patterns of feral cat and dingo occurrence in monsoonal Australia

Abstract

AimAn interaction between reduced habitat structural complexity and predation by feral cats (Felis catus) has been hypothesized as the primary driver of mammal decline in northern Australia. However, we have a limited understanding of the drivers of the distribution and abundance of feral cats at a landscape scale, including whether the occurrence of a top predator, the dingo (Canis familiaris [dingo]), limits feral cat populations. We modelled feral cat and dingo site occurrence, to provide the first broad‐scale assessment of their distributional patterns and co‐occurrence within monsoonal Australia.LocationAbout 370,000 km2 of monsoonal area in the Northern Territory.MethodsWe surveyed 376 sites using camera traps. We used single‐ and two‐species occupancy models to investigate feral cat and dingo site occurrence and the influence of dingoes on feral cat occupancy. We included predictor variables that relate to hypotheses of predator occurrence, including both environmental and disturbance‐related variables.ResultsFeral cat occurrence and dingo occurrence were best predicted by indices of habitat structural complexity; feral cat occurrence declined with increasing productivity, except in areas of relatively high fire activity (fire frequency and extent), and dingo occurrence declined with terrain ruggedness. We found no evidence that dingoes are spatially limiting feral cat occurrence.Main conclusionsOur findings suggest the protection and enhancement of habitat structural complexity at both the local and landscape scale could enable conservation managers to reduce the exposure of small‐ and medium‐sized mammals to feral cats and dingoes. This can most likely be achieved through improved fire and feral herbivore management, which is a more feasible management option than lethal predator control.

Cat ecology, impacts and management in Australia

“…In this special issue, Davies et al (2020) extend the generality of these observations yet further, by showing that the abundance of feral cats on Melville Island, Northern Territory, is positively related to increased disturbance from high frequencies of intense fire and heavy grazing by feral stock. This corroborates another recent study from northern Australia that found that feral cats were less likely to be present in productive habitats unless those habitats experienced high fire activity (Stobo-Wilson et al 2020a).…”

Variation in feral cat density between two large adjacent islands in Australia’s monsoon tropics

“…Unfortunately, we do not have ground-based data with which to compare the density of understorey vegetation across our four grids. However, a remote-sensed measured response of habitat productivity, that correlates with the density of green vegetation (Pickett-Heaps et al 2014;Stobo-Wilson et al 2020), does not support this. Instead, it suggests that the average vegetation density across the Ranku grid is more comparable with that of the Pickertaramoor grid, while the vegetation density at Cache Point is comparable to that of the Cape Fourcroy grid (H. Davies, unpubl.…”

“…In northern Australian savannas, feral cat site-occupancy is higher in areas with lower understorey vegetation density (Stobo-Wilson et al 2020). As such, productivity-driven variation in vegetation density across the islands could have contributed to the observed variation in cat density.…”

“…However, we note that the Ranku grid was similarly placed near habitat with an open understorey, including plantations of Acacia mangium and treeless plain. Although vegetation density influences feral cat movement, activity and occupancy in northern Australian savannas (McGregor et al 2014;Stobo-Wilson et al 2020), the extent to which natural variation in vegetation density (due to productivity and/or between habitat types) influences feral cat density warrants further investigation.…”

“…Given the similarities with previous mammal extinctions (Murphy and Davies 2014;Woinarski et al 2015), it seems likely that if these declines continue unabated, more species will be lost forever. Although predation by feral cats has been implicated in these declines (Ziembicki et al 2015), the movement, activity and impact of feral cats in northern Australian savannas is strongly influenced by fire and grazing by feral herbivores (Leahy et al 2016;McGregor et al 2015aMcGregor et al , 2016b, and there is growing evidence that such processes are important drivers of spatial variation in feral cat occupancy (Stobo-Wilson et al 2020) and density (Heiniger et al 2020). This is thought to reflect the heightened predation efficiency afforded to predators by processes that reduce the density of understorey vegetation.…”