A project undertaken at The University of Western Australia, and supervised by Dr Nicola Mitchell.
Australia has the worst record of mammal extinction of any continent. Increasingly, in order to prevent further extinctions, we rely on predator-free havens; islands and fenced areas within which vulnerable fauna can persist. While this strategy has successfully secured many species, the predator-free conditions inside havens can cause rapid loss of antipredator behaviours. Once these behaviours are lost, havened mammals likely become easy prey for even their natural predators, and so may be unfit for release into unfenced habitats.
Figure 1. Predator-proof fence with a floppy top, buried skirt and electrified wires to keep out large invasive predators, like cats and foxes. Credit: Natasha Harrison
With only a small fraction of potentially habitable areas captured in havens, rapid loss of predator awareness may be jeopardising national conservation strategies for Australian mammals. Hence is it imperative that we monitor for, and manage against, loss of antipredator traits.
In this project we used proxy measures of anti-predator traits, including agitation behaviour, foraging and vigilance behaviours, and hindfoot length to compare havened and non-havened populations of woylies (a bettong species) and quenda (a bandicoot species). We provide clear evidence for the loss of anti-predator traits from havened woylies, and our results suggest that resource competition inside havens might accelerate the loss of these traits. Without predators to escape from, traits that are valuable for predator avoidance (like vigilance behaviour and longer feet) can be costly to maintain and may make individuals slower to gain resources. We also found that havened woylies had lower survival than non-havened woylies when released into a landscape with invasive predators, suggesting that there are important consequences if anti-predator traits are weakened.
Figure 2. A quenda being released following an assessment of its anti-predator traits. Credit: City of Joondalup.
We investigated mechanisms to prevent the loss of anti-predator traits from havened populations. A havened population of quenda that has maintained some exchange of juveniles through the fence with a non-havened population of quenda showed no evidence of lost anti-predator traits.
Figure 3. PhD candidate Natasha Harrison measures a woylies hindfoot (pes) length. Credit: Aiden Holmes
We also found that a havened population of woylies that has coexisted with chuditch, a native meso-predator, have the same level of anti-predator traits as their non-havened counterparts, and comparable survival rates when released into a novel environment with low densities of foxes and cats. While reducing resource competition and facilitating gene flow may help prevent the loss of anti-predator traits, we suggest that the most effective strategy is to expose havened populations to low, controlled, levels of predation pressure.
Figure 4. A woylie foraging in the evening. Credit: Natasha Harrison.
Predator exposure inside havens will require careful consideration of its suitability for each population and species but may prove to be an effective tool for conservation managers to preserve anti-predator traits in havened populations and improve the outcome of conservation translocations.
Our study has increased our conceptual and mechanistic understanding of the loss of anti-predator traits from havened populations and provides useful information to help conservation managers continue to preserve our unique biodiversity.