“Invasive Species Denialism” Increases Exponentially


Anthony Ricciardi and Rachael Ryan have analyzed 77 articles published from 1994 to 2016 in scholarly journals and the mainstream media that express some level of “invasive species denialism”. Denialist articles appearing in these publications have increased exponentially over the past three decades, most notably in the mainstream popular press – and they have the graph, fitted to a curve, to prove it.

The authors cite Diethelm and McKee (2009) in defining “science denialism” as “the use of rhetorical arguments to give the appearance of legitimate debate where there is none, with the ultimate goal of casting doubt on scientific consensus.” Similar strategies have appeared in disputes over the dangers of tobacco smoking and climate change.

Ricciardi and Ryan say that “[u]nlike normal scientific debates, which are evidence based, this discourse typically uses rhetorical arguments to disregard, misrepresent or reject evidence in attempt to cast doubt on the scientific consensus that species introductions pose significant risks to biological diversity and ecosystems….” In their view, the “denialist” articles assert an absence of damage from bioinvasion “despite peer-reviewed research that shows otherwise ….”  One example of evidence ignored by the contrarians are several analyses of the causes of endangerment or extinction of vertebrate species listed on the Red List maintained by the IUCN [as reported in my blog from May 2016 link]

Furthermore, these claims are almost always made in the absence of peer review – either in popular media or as opinion articles in scholarly journals. Many of the writers are social scientists and philosophers, not natural scientists. Only five of the 77 articles, or 6%, were published in natural science journals.

Ricciardi and Ryan say that unlike genuine scientific debate, “denialists” reject scientific evidence while repeating claims that have already been refuted in the scientific arena. Often, “contrarians” link invasion biology to xenophobia and latent racism, or otherwise impugn the motives of those engaged in the invasion biology field.

Ricciardi and Ryan consider possible reasons for the rise in “denialist” articles. Possible reasons include anti-regulatory ideologies, distrust of scientific institutions, conflicting values and perceptions of nature, even individuals’ desire for attention. They note that despite the absence of a true scientific controversy, the “denialists’” assertions gain credibility because science reporters think they need to present “both sides” of the argument.

Unlike the situation in the contrived controversies over climate change and risks from tobacco, we at CISP have not found a powerful industry backing the contrarians.

Ricciardi and Ryan express concern that the growing number of articles rejecting decades of research on invasive species might undermine policy initiatives at a time when invasion biology’s relevance to biosecurity, conservation, and ecosystem management is increasing. Gaining public support is critical to the success of such policies.

This concern is especially well-founded given that the authors’ results underestimate the extent of invasive species denialism. That is, they omitted from their analysis articles from internet blogs – known to be major platforms for promoting “science denialisms” – and websites that specifically attack invasion biology.

While Ricciardi and Ryan published this as a “note,” it is packed with information, e.g., references on science denialism, in general; and, in supplementary information, a table citing the 77 denialist articles.



INVASION NOTE. Ricciardi, A. & R. Ryan The exponential growth of invasive species denialism. Biological Invasions. Published online 12 September 2017


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