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Determining Whether the Impacts of Introduced Species Are Negative Cannot Be Based Solely on Science: A Response to Russell and Blackburn
TREE 2214 No. of Pages 2
Letter
Determining Whether the Impacts of Introduced Species Are Negative Cannot Be Based Solely on Science: A Response to Russell and Blackburn Jacques Tassin,1 Ken Thompson,2 Scott P. Carroll,3,4 and Chris D. Thomas5,* In a recent article in TREE, Russell and Blackburn [1] consider that challenging the negative impacts of invasive alien species (IAS) is akin to science denialism and, by citing and referring to our work, implicitly denounce us as science or IAS denialists. Furthermore, they draw strong parallels between IAS denialists and those who deny the ‘risks of tobacco smoking or immunisation, the causes of AIDS or climate change’. We find this allusion to be poorly considered and indefensible. IAS are defined as ‘generating a negative impact’ [1]. Once any particular person or society has decided how to define ‘alien’ and ‘negative impact’, it then becomes a matter for scientific evidence to determine [24_TD$IF]if the organism in question is an IAS in a particular part of the world, whether that be on economic, social (including medical), or biological grounds. In this sense, Russell and Blackburn are correct to assert that there is an undisputed scientific consensus on the negative impacts of IAS. However, the consensus breaks down when it comes to the definition of
‘negative impact’, which is influenced by social values, as Russell and Blackburn acknowledge. In other words, perfectly legitimate alternative social values will determine whether few or many introduced species are designated IAS, even if the scientific data are undisputed. More broadly, society’s spectrum of diverse perspectives, aspirations, and personal trade-offs, which effectively constitute what Russell and Blackburn impugn as ‘vested interests’, could and should influence society’s debates rather than be discredited. It is up to invasion biologists who share Russell and Blackburn’s views to advocate them to greater society, not decry those who hold alternative values as deniers. We are not disagreeing with (sic ‘denying’) the excellent science being carried out on species that have been transported around the world; neither are we advocating ‘laissez-faire regulation’. In fact, we and Russell and Blackburn share the same orthodox social values that global-scale, species-level extinctions can generally be regarded as a negative impact. Such events are concentrated in endemic-rich islands and freshwaters, although not exclusively so (e.g., chytrid-infected amphibian extinctions). However, it is less easy to reach unanimity in many other situations. Incoming species may increase the total number of species that are present in a given region (more arrive than die out), but potentially reduce the average abundance per species (if the same total abundance is now divided between more species). Depending on our relative valuation of diversity versus abundance, and human-oriented preference for some species over others (whether intrinsic or because of explicit goods or services they provide), such events could either be judged to be positive or negative. We can describe these changes objectively, in scientific language, but we can only make a
subjective judgement whether we prefer the earlier or later state. Given that biological change is inevitable and essential to the survival of species and [25_TD$IF]to the maintenance of ecosystem services during periods of rapid environmental change, we must be careful not to regard deviation from some historic baseline (in terms of species distributions, abundances, and community composition) as necessarily negative. There can be a positive side to recent arrivals and planned introductions, for example in saving a species that is threatened elsewhere, or replacing or enhancing an ecosystem service. In this context, what can easily come across as zero-tolerance invasion biology is outmoded and fails to address the reality that is faced by environmental managers, who must make critical and tactical judgements about how best to apply limited resources to large-scale dynamic challenges. A broader remit will help identify sustainable management options that would be closed to zero-tolerance thinking (e.g., being open to novel ecological and evolutionary interactions and biological controls). We should take advantage of whatever opportunities are available to develop effective, long-term approaches to an issue that will forever be more out of our control than within it. Given that there are honest and reasonable grounds to take different perspectives, we entreat Russell and Blackburn to reconsider their approach, which seems to be aimed at shutting-down discussion. Their tactical use of unpleasant comparators to suppress dissenting voices is shortsighted and, ultimately, likely to discredit the science community. We hope that increased, rather than decreased, discussion will improve understanding of the biological causes and consequences of the dispersal of organisms, and provide a growing appreciation of the
Trends in Ecology & Evolution, Month Year, Vol. xx, No. yy
1
TREE 2214 No. of Pages 2
circumstances under which we can and wish to intervene deliberately to influence such events. 1
Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), UPR Forêts & Sociétés, 34398 Montpellier, France
2
2
Department of Animal and Plant Sciences, Western Bank, University of Sheffield, Sheffield S10 2TN, UK 3 Institute for Contemporary Evolution, 711 Oak Avenue, Davis, CA 95616, USA 4 Department of Entomology & Nematology, University of California Davis, Davis, CA 95616,USA 5 Department of Biology, University of York, Wentworth Way, York, YO10 5DD, UK
Trends in Ecology & Evolution, Month Year, Vol. xx, No. yy
*Correspondence: [email protected] (C.D. Thomas). http://dx.doi.org/10.1016/j.tree.2017.02.001 Reference 1. Russell, J.C. and Blackburn, T.M. (2016) The rise of invasive species denialism. Trends [26_TD$IF]7Ecol. Evol. 32, 3–6
Letter
Determining Whether the Impacts of Introduced Species Are Negative Cannot Be Based Solely on Science: A Response to Russell and Blackburn Jacques Tassin,1 Ken Thompson,2 Scott P. Carroll,3,4 and Chris D. Thomas5,* In a recent article in TREE, Russell and Blackburn [1] consider that challenging the negative impacts of invasive alien species (IAS) is akin to science denialism and, by citing and referring to our work, implicitly denounce us as science or IAS denialists. Furthermore, they draw strong parallels between IAS denialists and those who deny the ‘risks of tobacco smoking or immunisation, the causes of AIDS or climate change’. We find this allusion to be poorly considered and indefensible. IAS are defined as ‘generating a negative impact’ [1]. Once any particular person or society has decided how to define ‘alien’ and ‘negative impact’, it then becomes a matter for scientific evidence to determine [24_TD$IF]if the organism in question is an IAS in a particular part of the world, whether that be on economic, social (including medical), or biological grounds. In this sense, Russell and Blackburn are correct to assert that there is an undisputed scientific consensus on the negative impacts of IAS. However, the consensus breaks down when it comes to the definition of
‘negative impact’, which is influenced by social values, as Russell and Blackburn acknowledge. In other words, perfectly legitimate alternative social values will determine whether few or many introduced species are designated IAS, even if the scientific data are undisputed. More broadly, society’s spectrum of diverse perspectives, aspirations, and personal trade-offs, which effectively constitute what Russell and Blackburn impugn as ‘vested interests’, could and should influence society’s debates rather than be discredited. It is up to invasion biologists who share Russell and Blackburn’s views to advocate them to greater society, not decry those who hold alternative values as deniers. We are not disagreeing with (sic ‘denying’) the excellent science being carried out on species that have been transported around the world; neither are we advocating ‘laissez-faire regulation’. In fact, we and Russell and Blackburn share the same orthodox social values that global-scale, species-level extinctions can generally be regarded as a negative impact. Such events are concentrated in endemic-rich islands and freshwaters, although not exclusively so (e.g., chytrid-infected amphibian extinctions). However, it is less easy to reach unanimity in many other situations. Incoming species may increase the total number of species that are present in a given region (more arrive than die out), but potentially reduce the average abundance per species (if the same total abundance is now divided between more species). Depending on our relative valuation of diversity versus abundance, and human-oriented preference for some species over others (whether intrinsic or because of explicit goods or services they provide), such events could either be judged to be positive or negative. We can describe these changes objectively, in scientific language, but we can only make a
subjective judgement whether we prefer the earlier or later state. Given that biological change is inevitable and essential to the survival of species and [25_TD$IF]to the maintenance of ecosystem services during periods of rapid environmental change, we must be careful not to regard deviation from some historic baseline (in terms of species distributions, abundances, and community composition) as necessarily negative. There can be a positive side to recent arrivals and planned introductions, for example in saving a species that is threatened elsewhere, or replacing or enhancing an ecosystem service. In this context, what can easily come across as zero-tolerance invasion biology is outmoded and fails to address the reality that is faced by environmental managers, who must make critical and tactical judgements about how best to apply limited resources to large-scale dynamic challenges. A broader remit will help identify sustainable management options that would be closed to zero-tolerance thinking (e.g., being open to novel ecological and evolutionary interactions and biological controls). We should take advantage of whatever opportunities are available to develop effective, long-term approaches to an issue that will forever be more out of our control than within it. Given that there are honest and reasonable grounds to take different perspectives, we entreat Russell and Blackburn to reconsider their approach, which seems to be aimed at shutting-down discussion. Their tactical use of unpleasant comparators to suppress dissenting voices is shortsighted and, ultimately, likely to discredit the science community. We hope that increased, rather than decreased, discussion will improve understanding of the biological causes and consequences of the dispersal of organisms, and provide a growing appreciation of the
Trends in Ecology & Evolution, Month Year, Vol. xx, No. yy
1
TREE 2214 No. of Pages 2
circumstances under which we can and wish to intervene deliberately to influence such events. 1
Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), UPR Forêts & Sociétés, 34398 Montpellier, France
2
2
Department of Animal and Plant Sciences, Western Bank, University of Sheffield, Sheffield S10 2TN, UK 3 Institute for Contemporary Evolution, 711 Oak Avenue, Davis, CA 95616, USA 4 Department of Entomology & Nematology, University of California Davis, Davis, CA 95616,USA 5 Department of Biology, University of York, Wentworth Way, York, YO10 5DD, UK
Trends in Ecology & Evolution, Month Year, Vol. xx, No. yy
*Correspondence: [email protected] (C.D. Thomas). http://dx.doi.org/10.1016/j.tree.2017.02.001 Reference 1. Russell, J.C. and Blackburn, T.M. (2016) The rise of invasive species denialism. Trends [26_TD$IF]7Ecol. Evol. 32, 3–6