In an opinion paper in Trends in Ecology and Evolution, James Russell and Tim Blackburn signal a rise in what they perceive as “invasive species denialism”. They state that more and more publications, including some in leading scientific and popular science media (e.g., Fred Pearce’s New Scientist article and the book Where Do Camels Belong? of Ken Thompson) “have challenged the existing scientific consensus” on invasive alien species (IAS). That scientific consensus, say Russell and Blackburn, is that invasive alien species cause serious damage by their global change of ecosystems. And, the authors argue, this rising trend of “IAS denialism” among scientists and science reporters is fuelled by political motives and employs selective use of research data. The parallel with denialism in global climate change is obvious, and alarming.
Russell and Blackburn then go on to show how to recognise and deal with IAS denialism. They first explain that legitimate scientific debate may exist over whether a species may classify as “invasive” and that there is the non-scientific assessment of value in deciding what is “damage”. Having said that, Russell and Blackburn then state that “[i]n some cases the rejection of scientific evidence of the negative impacts of IAS takes the form of a type of science denialism.” That is, “to manufacture uncertainty in the scientific consensus on an otherwise undisputed topic”. The political motives that lie behind this denialism are said to be those idealising free trade, the very enterprise that causes many of the harmful species introductions in the first place.
I have read Russell and Blackburn’s paper with increasing alarm. Because what do they really say? First, that species invade and that such invasives may be perceived as harmful. Second, that the assessment of “harm” can be subjective. And finally, that scientists should not cast undue doubt on undisputed scientific facts that invasive species cause harm and thus play in the hands of those grinding a political axe. However, the parallel with climate change, appealing though it may be, is not warranted. Denialism in climate change takes the form of casting aside scientific evidence that the global climate is changing. Similar denialism in the field of IAS would be a denial that more and more alien species are invading ecosystems, and nobody is denying this fact. What is debated is whether these invasions cause harm and, if so, on what time-scale. Since “harm” (unlike global temperature) cannot be objectively defined, the so-called “IAS denialism” lies outside of the realm of science and cannot be pinned on ecologists that happen to take a different view on invasive species than Russell and Blackburn.
What does lie within the realm of science are discussions on how energy flows within ecosystems are affected by species invasions, and how invasive species and the native species they interact with may evolve, and at what temporal scales. By casting such debates as “denialism”, Russell and Blackburn are not doing their colleagues a favour. By drawing an unjustified parallel with climate change denialism, their paper constitutes a pre-disapproval of ecologists who are trying to explore the concept of novel ecosystems, or take a long-term view of micro-evolutionary reconstitution of invaded ecosystems. I would take issue with labelling such ecological viewpoints as denialism. Rather, they are a legitimate way of dealing with the long-term effects of invasive species. Perhaps even more responsible than uncritically walking the conventional line of viewing IAS as one of the major challenges to biodiversity conservation of our time.
Russell and Blackburn end their paper by writing: “There should be a vibrant and robust dialogue on the negative, and potentially any positive, impacts of IAS and on the allocation of resources to remediate their diverse threats.” However, “such a discussion should be evidence based and not disrupted by appeals to values or denial of the magnitude of the threat. We believe it is imperative that invasion biologists engage constructively and lead on such discussions”. I could not agree more. But with this paper, the authors achieve the opposite. By drawing parallels with climate change denialism, they aid in creating an atmosphere in which any scientist exploring an unconventional long-term view on the issue of species invasions, may be labelled as politically incorrect.