Don't judge species on their origins

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Conservationists should assess organisms on environmental impact rather than on whether they are natives, argue Mark Davis and 18 other ecologists.


  1. Carroll, S. P. Evol. Appl. 4, 184199 (2011).
  2. Fleishman, E. et al. Bioscience 61, 290300 (2011).
  3. Chew, M. K. & Hamilton, A. L. in Fifty Years of Invasion Ecology (ed Richardson, D. M.) 3547 (Wiley-Blackwell, 2011).
  4. Wilcove, D. S., Rothstein, D., Dubow, J., Phillips, A. & Losos, E. BioScience 48, 607615 (1998).
  5. Davis, M. A. Invasion Biology (Oxford Univ. Press, 2009).
  6. Gardener, M. R., Cordell, S., Anderson, M. & Tunnicliffe, R. D. Rangeland J. 32, 407417 (2010).
  7. Chew, M. K. J. Hist. Biol. 42, 231266 (2009).
  8. Stromberg, J. C., Chew, M. K., Nagler, P. L. & Glenn, E. P. Rest. Ecol. 17, 177186 (2009).
  9. Aukema, J. E. et al. Bioscience 60, 886897 (2010).
  10. Gleditsch, J. M. & Carlo, T. J. Diversity Distrib. 17, 244253 (2010).

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Author information


  1. Mark A. Davis is DeWitt Wallace professor of biology at Macalester College, St Paul, Minnesota, USA.

  2. Matthew K. Chew is in the School of Life Sciences, Arizona State University, Tempe, Arizona 85287, USA.

  3. Richard J. Hobbs is in the School of Plant Biology, University of Western Australia, Crawley, Western Australia 6009, Australia.

  4. Ariel E. Lugo is in the International Institute of Tropical Forestry, USDA Forest Service, San Juan, Puerto Rico 00926, Puerto Rico.

  5. John J. Ewel is professor emeritus, Department of Ecology, University of Florida, Gainesville, Florida 32611, USA.

  6. Geerat J. Vermeij is in the Department of Geology, University of California, Davis, California 95616, USA.

  7. James H. Brown is in the Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.

  8. Michael L. Rosenzweig is in the Department of Ecology & Evolutionary Biology, University of Arizona, Tucson 85721 Arizona, USA.

  9. Mark R. Gardener is in the Restoration Group, Charles Darwin Foundation, Puerto Ayora, Galapagos, Ecuador.

  10. Scott P. Carroll is in the Department of Entomology University of California, Davis, California 95616, USA.

  11. Ken Thompson is in the Department. of Plant and Animal Sciences, University of Sheffield, Sheffield S10 2TN, UK.

  12. Steward T. A. Pickett is at the Cary Institute of Ecosystem Studies, Millbrook, New York 12545, USA.

  13. Juliet C. Stromberg is in the School of Life Sciences, Arizona State University, Tempe, Arizona 85287, USA.

  14. Peter Del Tredici is at the Arnold Arboretum, Jamaica Plain, Massachusetts 02130, USA.

  15. Katharine N. Suding is in the Department of Environmental Science, Policy, & Management, University of California, Berkeley, California 94720, USA.

  16. Joan G. Ehrenfeld is in the Department of Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, New Jersey 08901, USA.

  17. J. Philip Grime is professor emeritus, Department of Plant and Animal Sciences, University of Sheffield, Sheffield S10 2TN, UK.

  18. Joseph Mascaro is in the Department of Global Ecology, Stanford University, Stanford, California 94305, USA.

  19. John C. Briggs is professor emeritus, Department of Marine Science, University of South Florida, Tampa, Florida 33620, USA.

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  1. Report this comment #23872

    Jean SmilingCoyote said:

    The proposal to ditch the native-vs.-alien species distinction is, in my opinion, an insidious expression of biological imperialism. Yes, yes, I'm aware of the apparently beneficial adaptations some native species have made to some alien species. But none are as good as the ecosystem which didn't include any non-natives. And this article skips over some of the serious negatives related to alien species. Non-native peoples have long included other species from their homelands in their imperialistic activities. Even if the effects were neutral, non-native species diminish the distinct characters of each ecoststem. But you can't paint a pretty face on biological imperialism, for this is really what it's all about.

  2. Report this comment #23964

    Sarah Gibbs said:

    I am from New Zealand and am most familiar with island ecosystems.

    While the article briefly notes predators and pathogens on islands and lakes as an exception to their hypothesis, it then goes on to note that "In fact, the introduction of non-native species has almost always increased the number of species in a region5." This may be the case, but it may be at the expense of net global biodiversity. If, for example, 5 predator / competitor species reach an area and cause the extinction of 1 endemic native species, local biodiversity may have increased -but global biodiversity has decreased. This is particularly the case if the species is one of the last of a higher taxa, as the potential future ability for that taxa to speciate and re-diversify has also been lost.

    The importance of endemic species to global biodiversity is recognised in the International Convention on Biodiversity, which prioritises in situ conservation of species over ex situ measures. Islands are often biodiversity hotspots. The use of introduced species in ecological restoration needs to be approached with extreme caution. I would argue strongly that the distinction between native and exotic, and between native and endemic, remain useful scientific and management concepts.

  3. Report this comment #24084

    Sam Buchanan said:

    Coming from New Zealand, with an ecosystem highly vulnerable to disruption by introduced species, this argument is always worrying. There's a small but not insignificant political lobby here that favours introduced fauna (mostly hunters) and flora (fans of all things European, particularly gardens), and can frustrate efforts to protect native species and relatively unmodified environments.

    Advocates of the position taken in this article tend to be resident in highly modified or continental ecosystems, where the issue of native or non-native is much less clear cut, or largely irrelevant. It would be interesting to see an anthropological examination of attitudes to the debate – looking at the cultural and political backgrounds of those on both sides.

  4. Report this comment #24690

    Roseann Campbell said:

    I was first introduced to the idea of invasive species when I visited Australia and took part in several conservation projects. In my first project we hacked down non-native plants (Asparagus asparagoides or Bridal Creeper amongst others), in another we planted native grasses and in another we set up traps for Cane Toads (Bufo marinus). The Cane Toad is a particularly interesting story as it was purposely introduced to control the Cane Beetle and then became a bigger problem. And I have to say that the idea of controlling the Bridal Creeper and Cane Toads seemed an impossible one. Ten of us worked on an area of no bigger than 50 meters squared over the course of a week and didn't manage to clear it completely. The size of the total area that needed to be 'weeded' was huge and so our impact felt small (although part of a large conservation effort in this particular area).

    But what strikes me most about the concept of invasive species is the terminology used. As Jean says it sounds like justification for biological imperialism but we're just talking about plants and animals here right? So should emotive terms that hold a lot of historical significance like 'invasive' be applied to plants and animals?

  5. Report this comment #24743

    Mark Thompson said:

    I once shared the opinion of Jean SmilingCoyote, but after many years of thinking this through have had a change of heart. The human species is a predator and we like a good chase. Hardy invasives, weeds, or 'pests' as they are sometimes known in the derogatory sure pick up the human spirit to get out and do something about it. We've nearly hunted every organism to extinction over 45 kg through the Pleistocene to the present. We hold onto the fanciful or romanticized ideals of wild nature, I know I sure do.

    In my local community in behind my house little flags have been erected throughout a tiny forest remnant where my little boy and I play, collect and eat wild berries. The flags serve as markers stating that herbicide spot spraying has taken place to eradicate invasive pests. Conservationists on the flip side are working tirelessly to save the species within biodiversity hot spots of this planet. Both approaches are counter productive to our desired end of addressing the human affliction, our ecological dysfunction.

    Despite what many of us continue to believe, the human species is not separate from nature. We are very much part and product of nature – always have been. We are ecosystem engineers from the activities of indigenous peoples digging roots (bioturbators), collecting plants, and running controlled burns to stimulate the kind of niche that contains desired resources. The environments we ecologically engineer reciprocates back into our cultural and genetic evolution. Ecosystems have and will continue to evolve into the foreseeable future. What I find most troubling, however, is the biotic homogenization of our planet as Sarah Gibbs pointed out in her comment. The rise of the alpha lamenting the homogenization of beta diversity. Paradoxically, ecosystems on the edge with fewer species are more stable as recovery back to the same list of species that can tolerate the conditions is more parsimonious. Stability doesn't seem to be a desirable goal. An autopoesis of eco-cybernetic feedback negotiating a human ecology that engineers natural capital coupled to biodiverse ecosystems that supply a sustainable thread of services that contribute to the well being to our society is the goal. Does the eradication of invasive species further this goal?

    Our contemporary technoecosystems are filled with invasive and weedy species of technodiversity that enter into the nutrient cycles (e.g., mercury cycle or other plastic/nano 'recyclables') building a new global biogeochemistry afflicted with a warming climate. The good intentions of those doing the spraying to eradicate these pesky invasive plants are utilizing a little piece of technology we know little about. The secondary metabolites of the herbicide create residues in the soil and enter into the physiology of the planet. Herbicides at low concentrations turn into gender benders and persistent physiological predators that up regulate apoptotic genes disrupting out T-cell spleenic immune system. Do we really want to spend our time employing our technologically driven species and our economic energies toward a losing battle of killing invasive biodiversity? I think not. The idea of an invasive weed or 'pest' is a paradigm, a convenient way for us to organize our thoughts on the matter. However, we need to think past our prejudice and objectively consider the various roles we have in this. I agree with Sam Buchanan about hunters advocating for introduced fauna – fish stocking is common where I am from and it destroys native amphibian populations. But so do roads and the 'green' bioenergy plants that have been erected to service our community. Hate the hunters, love the grocery store trophism that is attached to agri-style sterile petroleum based Saran and Styrofoam base that hugs our meat. I think Paul Sears said it best in 1954: "When we as a profession learn to diagnose the total landscape, not only as the basis of our culture, but as an expression of it, and to share our special knowledge as widely as we can, we need not fear that our work will be ignored or that our efforts will be unappreciated." ( Sears, P. 1954. Human ecology: A problem in synthesis. Science 120 (3128): 959-963.)

    The human species is an invasive. More than this, we are culturally influenced with our preconceived cognitive notions that erect our ideas in mind before we execute them into nature; the so called noosphere of our species. In this noosphere the invasive weedy plant, the novel ecology destroying our idealized wild nature (the noosystem) must be stopped at all costs. Hunt and kill what we don't like, yet we don't understand. What about the bacteria, fungi, and invertebrates? What about the honey bee or the banana tree for that matter? Our ornamental gardens, our lawns, and the roads that permeate across this planet – what do we employ to halt these invasives? Biodiversity is not just about species, it is a hierarchical system of emergent resilience that fluctuates around a dynamic multi-dimensional stability. We have to get rid of this idea of trying to conserve endangered species and start to think about the services of nature. Population levels of biodiversity are the champions of biomass, the important currency in natural capital, and they create the trophic biostructure that services our communities. Yet it is the populations that we eradicate every day and here we are arguing about eradicating a few more species that we think and conceive as pesky. Our school grounds are wastelands segregated from the outer urban periphery where the natives live. The biodiversity that stimulated our species enough to drive the evolution of our brains is largely excluded from our early educational environments where we learn from others that it is best to kill and destroy these weeds. I agree with the authors of this article – we need to rethink the mindset on invasive species and the future evolution of novel ecosystems.

  6. Report this comment #25258

    Thomas Kirchhoff said:

    Do judge species on their origins – but only with regard to symbolic value

    Davis et al. (Nature 474, 153-154; 2011) present a long overdue counter-argument to the pervasive bias against alien species. Their conclusions require qualification, however. Rather than elaborating on existing ecological objections (Nature 475, 36-37; 2011), my comments are focused on nature's symbolic meanings.
    The argument presented by Davis et al. addresses rational, scientific and functionalist perspectives on nature, the latter pertaining specifically to direct and indirect use values. In applying their results, however, the authors refer to nature conservation and land management in their entirety. Yet these practices include non-rational, non-functionalist considerations that accord nature various aesthetic and symbolic values. My claim is that species' origins are an essential parameter in relation to some of these values.
    With regard to specific species, origin is relevant, for example, in the US Giant Sequoia National Monument and in the adoption of the Indian paintbrush as the state flower of Wyoming. Origin matters in relation to cultural landscapes whenever their unique visual character is highly valued as representing a region's particular cultural history: non-native species can alter a landscape's character in ways perceived as negative and may thus offend feelings of belonging and regional identity (cf. Bardsley and Edwards-Jones GeoJournal 65, 199-210; 2006). Finally, non-native species may compromise the basic connotation of wilderness as "nature untouched by human civilization" given that they are often introduced anthropogenically, thus symbolizing the omnipresence of human impacts on nature.
    In most Western countries nature conservation has arisen in response to the destruction of such aesthetic-symbolic qualities --- albeit by industrial land use, not by alien species. Preserving these qualities still constitutes its main non-rational, common-sense motivation, even if rational, so coalled ecological and functional arguments --- whose point of reference and rationale are inherently specific --- are often used nowadays to substantiate these non-rational goals.
    To disregard symbolic meanings that have historically shaped landscapes and their native species is equally to ignore powerful emotional motivations for disliking non-native species. In seeking to dismantle dubious so called ecological arguments against alien species, it may be helpful to concede that species' origins are in some cases relevant to nature's and landscapes' symbolic values.

    Dr. Thomas Kirchhoff,, Germany

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