Employing Native Predators in Dealing with Invasive Species

Humans have been killing larger native predators and other species that they have competed with or feared throughout evolution. This process was especially successful in Ireland and the United Kingdom, where lynx and wolves that people once shared their lives with are no longer present.

Humans have also transported valued species outside of their natural ranges, inadvertently creating invasive species by introducing plants, animals, and microorganisms into ecosystems where they did not evolve. This caused native species to become extinct by competing with, eating, and exposing them to new diseases. Over the last century, studies have shown that invasive species have been the primary cause of vertebrate extinction.

More and more evidence shows that those once-despised native predators are now critical for controlling invasive prey.

Love for Native Predators

According to new research, the eradication of native predators contributed to the current invasive species crisis. However, the researchers in Ireland conducted a series of surveys between 2007 and 2019. It included public sightings of grey squirrels and pine martens to see how the return of a native predator can cause the rapid decline of a long-established invasive species, the grey squirrel, across entire landscapes.

Joshua Twining, a Cornell University Population Ecology research scientist who is also a postdoctoral researcher at Queen's University Belfast, collaborated on the study with Xavier Lambin and five other researchers.

Twining's team looked at both species' populations to see what factors influence a native predator's ability to control an invasive species after restoration. These factors include the invasive prey's failure to recognize or respond to the threat of a newly recovered predator, the predator's ability to switch prey, and the availability of hiding places for the prey to flee.

Predator-Prey Relationship

Native predators preferentially hunt invasive prey by a factor of two or even three, from wolves hunting non-native Corsican moufflon in the Mercantour mountains of southeastern France to red-banded snakes predating invasive bullfrogs in China.

Understanding why this is the case can help determine when and where native predators can help control invasive species.

For example, Lynx has a proven ability to suppress deer populations by changing the species of deer they hunt. There are no areas accessible to deer that are restricted to lynx. The combination of these factors suggests that restoring lynx populations will benefit ecosystems where sika deer are a problem. Where alternate prey, such as roe deer, is scarce or absent, such as in Ireland and Britain, lynx are likely to have a greater impact on these invasive populations.

Welcoming Native Predators

The natural recovery of some large predators in mainland Europe, such as bears, lynx, and wolves, is well underway. This challenges long-held beliefs about the need for carnivores for a pristine habitat. Despite intensive urban sprawl and farming, the only requirement was for people to stop killing the predator species to recolonize their former range. Extinct predators will not naturally recover in Britain because it is surrounded by the sea. Any attempts to reintroduce them would require societal agreement, which does not currently exist.

The ecological justification for restoring native predators is to help control and limit the spread of invasive species, according to our findings. However, living near large carnivores has its drawbacks, including the loss of livestock and sometimes, even pets. This is unavoidable, but it can be mitigated through proactive management.

Twining points out that if people are to accept the restoration of any native predator, the benefits, such as reducing the damage caused by invasive species, must be balanced against plans to mitigate the costs.