Niche partitioning in a guild of invasive mammalian predators

Abstract

Predators compete aggressively for resources, establishing trophic hierarchies that influence ecosystem structure. Competitive interactions are particularly important in invaded ecosystems where introduced predators can suppress native prey species. We investigated whether niche partitioning exists within a guild of invasive mammalian predators and determined the consequences for native species. Over 4405 camera-trap days, we assessed interactions among three invasive predators: two apex predators (feral cats Felis catus and ferrets Mustela furo) and a mesopredator (stoats Mustela erminea), in relation to their primary prey (lagomorphs, rodents and birds) and habitat use. Further, we tested for mesopredator release by selectively removing cats and ferrets in a pulse perturbation experiment. We found compelling evidence of niche partitioning; spatiotemporal activity of apex predators maximized access to abundant invasive prey, with ferrets targeting lagomorphs and cats targeting rodents. Mesopredators adjusted their behavior to reduce the risk of interference competition, thereby restricting access to abundant prey but increasing predation pressure on diurnal native birds. Stoats were only recorded at the treatment site after both larger predators were removed, becoming the most frequently detected predator at 6 months post-perturbation. We suggest there is spatial and resource partitioning within the invasive predator guild, but that this is incomplete, and avoidance is achieved by temporal partitioning within overlapping areas. Niche partitioning among invasive predators facilitates coexistence, but simultaneously intensifies predation pressure on vulnerable native species.

Keywords: Carnivora; community ecology; food web; interference competition; invasive species; mustelid; niche differentiation; wildlife management.

FIGURE 1

Trail camera grid at the non‐treatment (gray dots) and treatment (red dots) sites at Hawke's Bay, on the North Island of New Zealand. Eighty cameras were deployed at monitoring stations (40 at each site), with 500‐m spacing between cameras

FIGURE 2

Pairwise comparison (from top: cat vs. ferret, cat vs. stoat, ferret vs. stoat) of the daily activity of three invasive predators. The larger predator in the pairing (left symbol) is represented by a solid line and the smaller predator (right symbol) by a dashed line. Overlapping periods of activity are shaded as gray. Species' activity patterns are displayed over the 24 h dial period, which we re‐scaled to equal periods of daylight (6:00 ‐ 18:00) and night (18:00 ‐ 6:00)

FIGURE 3

Predator (cat, ferret, or stoat; solid lines) overlap in activity with the activity of primary prey species (rabbits, rodents, or birds; dashed line). Overlapping periods of activity are shaded as gray

FIGURE 4

Site use estimates (±95% CI) and naïve site use (no error bars) for cats (●), ferrets (▲), and stoats (■) at non‐treatment and treatment (predator removal) sites