Is it Time to Change How We Feel About Non-Native Species?

While non-native species are often targeted by eradication campaigns, this course of action may be based more on values than science.

Alien species are animals not native to a specific geographical region where they have instead been introduced by people, either deliberately or accidentally, at some point in history. Generally, if you have studied or are familiar with ecology and conservation, you frown at alien or non-native species because you assume they have negative impacts on local ecosystems and biodiversity. Nonetheless, there are ongoing nuanced debates among scientists and conservationists on the extent to which introduced species are actually harmful to host ecosystems. In a new paper1 published in Biological Reviews, Dr Marcelo Cassini of the Istituto de Biología y Medicina Experimental in Argentina, goes on to deconstruct such debates.

His review suggests that at the conceptual level it is unclear whether there are specific traits that make some species more or less likely to establish themselves in a host ecosystem, which makes it hard for conservationists to predict the impacts an introduced animal may have. He also finds that it is ambiguous whether how long ago a species was introduced should inform its labelling as native or non-native. For instance, one would tend to expect local wildlife to develop some kind of adaptations to cope with the presence of a new species, or to possibly go extinct by failing to do so. Following this logic, species introduced thousands of years ago, such as dingoes in Australia, should by now be coexisting with the local wildlife. If that’s so, should they still be considered non-native? Should their eradication still be pursued?

The field of invasion biology is anchored on the assumptions that ecosystems are at balance and they should not be influenced or disturbed by human activity. Nonetheless, these concepts have been heavily criticised, especially by social scientists who emphasise the active role that our species has always played in shaping the functioning of ecosystems. In fact, the concepts of pristine habitats and a nature at balance would appear to be largely flawed and attributable to western ideology and cultural constructs.

From a methodological perspective, Dr Cassini highlights that many studies appear to confound correlation with causation, thus bolstering the impacts of invasive species. “Although it is well known that correlation does not mean causality, numerous studies conclude that expansion of a non-native species caused the decline of native species when these two phenomena occurred simultaneously in the same locations”, he says. “Another frequent source of bias in impact reviews is the unclear distinction between economic impacts and ecological impacts. Wild species of plants and animals can become pests that threaten agricultural production, damage infrastructure, and even transmit diseases to humans and domestic animals. While these costs are important and relevant, they must be clearly differentiated from costs linked to the risks of species extinction or the functioning of natural ecosystems, as they represent two different problems”.

Moreover, while many papers in invasion biology present introduced species as the second greatest threat to biodiversity conservation, Dr Cassini stresses that “recent studies have questioned the validity of this claim because it relies on data that were skewed by the inclusion of ecosystems or regions with a high prevalence of invasive species and the exclusion of those where invasive species are less threatening”. Meanwhile, the eradication of introduced species is hardly feasible, with a success rate of less than 3% when island ecosystems are not considered.

At the societal level, the management of alien species often outbursts into heated conflicts between people and groups, especially since the introduced animals are often killed, which raises all sorts of ethical and moral concerns. The field of invasion biology also tends to adopt a militaristic language with terms such as “invasion, enemy, battle, combat, attacks, defence, casualties, and victims [which can] motivate overly strong actions or cause unforeseen collateral damage, such as the stigmatization of non-native species”, Dr Cassini explains.

Ultimately, he concludes, the debate on the management of non-native species seems to be largely influenced by values. “Investigating the values that underlie our attitudes towards non-native species could be the first step to reconciling currently confrontational situations”.

Dr Cassini also explains that there are other discourses present in the scientific community other than the traditional one advanced by invasion biologists. For instance, an alternative to the eradication of non-native species is encapsulated in the concept of “novel ecosystems”, whereby management is not focussed on restoring ecological conditions of the past, but rather on maximising aspects such as ecosystem productivity and biodiversity outcomes through fostering the production of hybrid landscapes composed of both native and introduced animals.

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  1. Cassini, M.H., 2020. A review of the critics of invasion biology. Biological Reviews.

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