Differing effects of productivity on home-range size and population density of a native and an invasive mammalian carnivore

Context Home-range size and population density characteristics are crucial information in the design of effective wildlife management, whether for conservation or control, but can vary widely among populations of the same species. Aims We investigate the influence of site productivity on home-range size and population density for Australian populations of the native, threatened spotted-tailed quoll (Dasyurus maculatus) and the alien and highly successful feral cat (Felis catus). Methods We use live trapping and fine-scale GPS tracking to determine the home-range size and population density for both species across five sites in Tasmania. Using these data, as well as published estimates for both species from across Australia, we model how these parameters change in response to productivity gradients. We also use the telemetry data to examine the energetic costs of increasing home-range size for both species. Key results For both species, decreasing site productivity correlates with lower population density, and in spotted-tailed quolls and female feral cats, it also correlates with larger home-range sizes. However, the relative magnitude of these changes is different. Feral cats show smaller increases in home-range size but larger decreases in population density relative to spotted-tailed quolls. Our results suggest that these differences may be because increases in home-range size are more costly for feral cats, demonstrated by larger increases in nightly movement for the same increase in home-range area. Conclusions We suggest that knowledge of both home-range size and population density is needed to accurately determine how species respond to habitat productivity, and inform effective management across their geographic range. Implications These results have clear management implications; for example, in our low-rainfall sites, an adult female spotted-tailed quoll requires up to five times the amount of habitat expected on the basis of previous studies, thus dramatically increasing the costs of conservation programs for this threatened native species. Conversely, productivity-driven differences of up to four-fold in feral cat population density would influence the resources required for successful control programs of this invasive species.