Figure 1.
Stress triangle: Non-consumptive costs of introduced predators on native predators and prey, and the potential pathways of these costs.
The ‘predator stress hypothesis’ predicts that fear will drive a chronic glucocorticoid (GC) response that leads to immunosuppression and consequent increases in parasite load. The ‘predator sensitive foraging hypothesis’ predicts that animals will reduce their foraging efficiency and hence lose body condition. This may lead directly to immunosuppression and an increase in parasite load, or indirectly by stimulating a GC response. These pathways can be set in train by an introduced predator via competition or the risk of predation on native predators and prey, respectively, forming the base of the triangle. Arrows show direction of pathway, with symbols representing an increase (+) or decrease (−) in an individual’s response.
Figure 2.
Map of the Cape Conran Coastal Park and Murrungowar state forest study region, situated in Far East Gippsland, Victoria (37°48′S 148°52′E).
Dots indicate the locations of the 76 transect lines used for trap and sand pads to sample the lace monitor (Varanus varius). Colour of dots indicates treatment area; black represents fox (Vulpes vulpes) suppression areas (baited with 1080 poison) with low densities of V. vulpes, white represents control areas (baited with non-toxic baits) with high densities of V. vulpes.
Figure 3.
Percentage of common ringtail possums (Pseudocheirus peregrinus) that adopted low, medium or high vigilance behaviours in response to capture in areas of fox suppression (with low densities of foxes) and control (high densities of foxes).
Capture responses were categorized into 3 vigilance levels; low (successful capture, no escape attempt), medium (delayed escape behaviour), and high (immediate escape behaviour).
Figure 4.
Foraging choice (%) of lace monitors (Varanus varius) in areas of fox suppression (with low densities of foxes) and control (high densities of foxes).
Choice of foraging behaviour was between high risk-high reward sites (represented by traps) vs. low risk-low reward sites (represented by sand pads).