Kill Those Invaders or Welcome Them? Scientists Split Over Invasive Species

Several critical voices have been calling for a re-evaluation of the role of these animal and plant migrants and even urge compassion toward these invaders

A nutria at Israel's Lake Hula.
Gil Eliahu

Do you wage an all-out war against invaders — or do you treat them with compassion?

The question is a burning one — at least among environmentalists, scientists and government agencies in Israel trying to develop a strategy for handling invasive species. Until recently the approach was clear: War. The means employed include shooting to kill invasive animals and using herbicides to destroy invasive plants.

In a similar spirit, the Society for Protection of Nature in Israel filed a petition last month demanding that the state present a plan to fight invasive species (after the Environmental Protection Ministry pledged to do so). While the Supreme Court rejected the petition Justice Noam Sohlberg called invasive species “a threat to nature, water sources and humans,” and said that “no one disputes that invasive species that have made inroads in nature do indeed cause damage to habitats and natural assets, including protected natural assets.”

According to scientists and nature protection groups, these species push out local species, spread disease and broadly change ecosystems. In their petition to the Supreme Court, the SPNI wrote that in 54 percent of endangered species of flora and fauna worldwide, invasive species are the main threat.

But there are scientists who say that these creatures actually enrich the ecosystem to which they migrated. These critical voices have been calling for a re-evaluation of the role of these animal and plant migrants and even urge compassion toward these invaders. They are behind a new school of research called “compassionate nature conservation,” which now has its Israeli defenders as well. They are centered at Tel Aviv University, where a research group in this field has been established, led by Dr. Dror Ben-Ami.

A recent issue of the Israel Journal of Ecology and Evolution, edited by Ben-Ami and devoted to compassionate nature conservation, included an article by Dr. Arian Wallach of the University of Technology Sydney, dealing with migrant plants and animals in Israel. These are the species that came here not necessarily “on purpose.” Some were animals raised as pets and released to the wild by their owners and multiplied. Nutrias, which were brought to Israel to be raised for their fur, escaped their fate and reproduced in nature.

Other species, mainly plants, came with cargo aboard ship. Some were brought intentionally, like the acacia, planted to stabilize sand dunes but over-proliferated.

All of these species are discussed in the article by Wallach, an Israeli scientist who has been in Australia for some years and monitors policy on invasive species there. Wallach has found 122 migrating species in Israel, two thirds of which are plants and invertebrates.

It turns out that the migrants have increased Israel’s biodiversity by 104 species (after subtracting now extinct species). To date, there has been no evidence of any migrating species causing the extinction of local species, Wallach states in her article.

Wallach writes that one concern of the field of “invasive biology” was that migrant species endanger local species because they had not evolved together. But observations show that native species adapt to the newcomers. For example an invasive plant in Australia initially went wild because no local species fed on it, but gradually, local bacteria developed the ability to reach the roots of the plant and consume it.

The illusion of back to the past

Wallach agrees that in some cases local populations are negatively impacted by migrant species, but says that killing off the migrants is not the only answer, and in many cases is impractical. One way to deal with the problem is to make sure there are natural spaces where a wide variety of species can exist. According to Wallach the desire to get rid of migrant species is the illusion that nature can be returned to some stage in the past.

However, “In contrast to invasion biology that was adopted relatively late, compassionate conservation established in Israel almost immediately.” This, Wallach says in the article, “provides an opportunity for reflection before entrenching policies that are harmful, divisive and difficult to reverse.”

The concept Wallach represents is centered on ethical considerations. Two of the main principles of compassionate conservation are that all wildlife has value and animals should be treated as individuals that can experience pain. Another principle is “do no harm” which is also a basic precept of medicine. For example, sometimes it’s best to do nothing rather than interfere in the functioning of an ecosystem.

These principles hold, according to Wallach, even in cases of species considered problematic by nature protection authorities, such as biting fire ants, which came to Israel from South America, or white sallow, a species of acacia from Australia that has taken over wide swaths of dunes and changed the ecosystem.

“Humans have acted violently toward different organisms throughout history, from ants to elephants,” Wallach told Haaretz. Wallach says that species like the white sallow “contradict opinions about the way nature should look. These opinions are based on an arbitrary and half-religious definition of nature as maintaining certain conditions in a narrow time frame. But from the perspective of compassionate nature conservation, ecosystems with or without the white sallow have an intrinsic value.”

Such arguments will not persuade those who see nature in Israel changing due to migrant species, for example, the myna, which came from East Asia and often pushes out other birds, or ambrosia, from the United States, which has taken over natural and cultivated areas.

“We don’t need to reach the point of complete extinction to know that action must be taken against invasive species,” counters Dr. Yehoshua Shkedy, science chief at the Israel Nature and Parks Authority. “These species do push out local speciesthere’s enough experience in the world to see this. It’s happened with us where there are acacias, and eucalyptus as well,” he says, warning that if action is not taken “we’ll lose biodiversity throughout the world.”