How can we best support survival of threatened wildlife in a future facing invasive predators in our landscapes?
A new publication in Conservation Science and Practice by Evans et al. outlines a complementary approach to pivot current strategies into a long-term pursuit harnessing evolutionary tactics to ease the coexistence of threatened species with invasive predators in the wild – ‘co-existence conservation.’
This approach targets the ‘shifting baseline syndrome,’ a mindset involving the gradual decline in expectations that native species will be present in the wild. An entrenched mindset that at a societal level accepts native species will only be seen in areas such as sanctuaries and enclosures, and in conservation science hinders big picture thinking and innovative solutions.
Invasive predators have contributed to 58% of all bird, reptile and mammal extinctions. Across the globe there are momentous strategies to reduce or eradicate invasive species from unwanted areas. However due to increasing human impacts such as habitat destruction and climate change, complete eradication of invasive species on a continental scale is not feasible.
Successful removal of invasive predators is often only demonstrated in localised or fenced areas such as islands, sanctuaries and enclosures. These safe havens give predator-susceptible and often threatened species the chance to increase populations without the constant threat of predation.
Refuge strategies are of undisputed importance for protecting native species, but often are implemented for critical rescues or using a short-term mindset to stabilise populations. In these strategies, recent work has shown that without the threat of predators, populations are less likely to develop heritable behaviours that protect them against predators in the wild – known as “refuge naiveté.”
These are critical traits for survival in natural ecosystems, and without them establishment of populations “beyond the fence” of safe haven protection may be compromised. Current refuge strategies in safe havens may also not accommodate the changing environmental conditions that threatened species will need to adapt to in the future, and ongoing maintenance for such areas can be costly.
Co-existence conservation is defined as ‘the long-term, iterative, and adaptive process to enable the co-existence of threatened species and invasive predators.’ It is intended to harmonise with current strategies whilst pursuing innovations that drive adaptive changes to support species survival over the long-term.
Dr Andrew Weeks, Cesar Australia Director and ecological geneticist, was a co-author of this new framework. It holds a central point of difference from current management strategies, whereby predation is treated as the threat, rather than the predator. This means it is an outcome-focused approach (threat impact mitigation) instead of agent (threat control).
Under the umbrella of evolutionary genetics for conservation, it builds on the thesis of Urlich (2015) exploring the potential for selection pressures to manipulate natural selection to help support survival of native New Zealand birds in the presence of invasive predators.
Co-existence conservation, however, takes a universal approach for any situation where scientists and practitioners are addressing the challenge of recovering threatened species in the presence of invasive predators, assuming that total eradication of the invasive predator(s) is impractical or impossible.
Critical to this framework is a long-term vision. Harnessing evolutionary tactics requires a staged, multi-phase process of trials to be refined over time. Current short-term approaches, although undeniably important, will need a shift in mindset to consider how we increase survival of these species long-term in our landscapes.
Suite of tactics
The publication outlines a suite of 12 tactics that enables co-existence conservation to move from theory to practice, classified into environment, animal, and predator focused tactics. A common thread is consideration for adaptive processes for reintroduction and translocation of individuals with behavioural or physical traits beneficial for survival with invasive species.
This may be implemented by applying ‘targeted gene flow’ that deliberately aims to enhance beneficial traits such as disease resistance or size. For instance, a recent study has shown offspring of northern quolls (Dasyurus hallucatus) that avoided eating invasive and toxic cane toads were shown to be less likely to eat cane toads than offspring of ‘toad-naïve’ parents (Kelly & Phillips, 2019).
At an environmental level, a co-existence approach may alter habitat complexity to reduce predation impact. Research in Australia showed that feral cat and dingo occurrences declined as habitat complexity increased (Stobo- Wilson et al., 2020). Additionally, low structural complexity in non-native grasslands exposed locusts to increased predation by invasive hedgehogs in New Zealand (Norbury & Overmeire, 2019).
Whereas predator tactics framed appropriately as “bettering the devil” could impose directional, positive selection toward predators that have minimal impact on threatened species as prey. Another being conditioned taste aversion (CTA) that aims to create negative associations with taste for prey species. Using CTA, Gustavson et al. (1974) were able to suppress attacks by coyotes on lambs without affecting predation on other prey.
Additionally, this strategy argues consideration of differing levels of threats and tolerances experienced under prey and predator dynamics may be beneficial. For example, a tolerable level of predation could be viewed as a favourable outcome due to benefits such as improved population fitness and reduced naiveté́ in the prey species. The authors reiterate that it is important to remember that implementation is a long-term endeavour and will take repeated trials to achieve success.
Pathway to the wild
To reach the goal of coexistence, a ‘pathway to the wild’ step-by-step framework discusses how remnant populations can be used as founders to re-build threatened species populations in safe havens and may, where necessary, include the use of captive animals from zoos and breeding facilities. Therefore, safe havens form an integral part of co-existence conservation to ensure short term survival while building resilience within populations.
However, as with any conservation programs, there is commonly disagreement between stakeholders for environmental, economic, ethical and social factors. Notably, coexistence conservation will not be possible in every context. When the risk is too high, it should not be applied to threatened species where existence would be compromised by these applications.
Conservation practitioners need to embrace the role evolutionary adaptation can play in sustaining threatened species existence in the wild. At the current rate, we are at risk of losing many threatened species from natural environments and progress toward large-scale conservation, in the face of invasive predators, requires innovation, new ideas and a dramatic shift to long-term thinking.
We thank the authors: Maldwyn J. Evans, Andrew R. Weeks, Ben C. Scheele, Iain J. Gordon, Linda E. Neaves, Tim A. Andrewartha, Brittany Brockett, Shoshana Rapley, Kiarrah J. Smith, Belinda A. Wilson and Adrian D. Manning.
The article also draws on findings from:
Urlich, S. C. (2015). What’s the end-game for biodiversity: Is it time for conservation evolution? New Zealand Journal of Ecology, 39, 133– 142.
Kelly, E., & Phillips, B. L. (2019). Targeted gene flow and rapid adaptation in an endangered marsupial. Conservation Biology, 33, 112–121.
Stobo-Wilson, A. M., Stokeld, D., Einoder, L. D., Davies, H. F., Fisher, A., Hill, B. M., Mahney, T., Murphy, B. P., Stevens, A., Woinarski, J. C. Z., Rangers, B., Rangers, W., & Gillespie, G. R. (2020). Habitat structural complexity explains patterns of feral cat and dingo occurrence in monsoonal Australia. Diversity and Distributions, 26, 832–842.
Norbury, G., & Overmeire, W. (2019). Low structural complexity of nonnative grassland habitat exposes prey to higher predation. Ecological Applications, 29, e01830.
Gustavson, C. R., Garcia, J., Hankins, W. G., & Rusiniak, K. W. (1974). Coyote predation control by aversive conditioning. Science, 184, 581–583.