Invasion Ecology and Management Politics: Important Lessons From A Poorly Received Paper

Mark Davis and several of his colleagues wrote a comment in Nature this month which caught my eye, not because it is a new argument, but because it’s an old argument that drives ecologists and conservation biologists up the wall. The piece, titled “Don’t Judge Species On Their Origins,” argues that we should judge species on their impact, not on whether or not they are native to an area. Though it contains some nuggets of wisdom, this article appears to be more inflammatory than informative. The nuggets of wisdom, however, are valuable:

#1: There Is An Important Distinction Between Alien and Invasive Species

Davis et al. argue propose new rules for managers and governments that focus on species impacts instead of actively trying to remove non-native flora and fauna. This point is important: alien species arrive in new locations all the time, and from time to time our impulse to restore some ecosystems to what we have deemed the “natural” or “original” condition sometimes overcomes our ability to effectively prioritize potential invasive threats. The idea of something not belonging in an ecosystem is attractive to the human mind. So when ecologists prioritize species to target, it is essential to come up with a practical, impact-based reasoning for attempting to remove a species.

This new, impact-based definition, however, has been used by ecologists for a long time, and is included in the US Invasive Species Advisory Commission’s definition:

“An invasive species is defined as a species that is:

1) non-native (or alien) to the ecosystem under consideration and

2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health.”

Part (1) is alien vs. native. Part (2) is the impact of the species. It is apparent that the distinction Davis et al. make is neither new, nor necessarily controversial. This might be a big “Yawn” for the ecologists. But other people (most people) who have not immersed themselves in the world of ecological definitions will find this interesting, and it is a distinction worth making, re-evaluating, and constantly challenging.

#2: Engineer Species Are a Priority

Even if the rules the authors suggest are not new, the exceptions they offer are interesting. They identify a few types of organisms that can be eradicated without the rigorous impact evaluation they’re recommending: those are predators and pathogens in lakes and on islands, and organisms that “substantially change the fundamental character” of their environment, including those which alter nutrient cycling. Some of the organisms they cite as legitimate threats are also termed “invasive engineers” (e.g., zebra mussels, Cuddington & Hastings 2004) because they change the substrate and the water quality. Many invasive species in Hawaii do have these characteristics: invasive macroalgae like Gracilaria salicornia and Acanthophora spicifera change flow rates and pH, shrubs like Myrica faya change soil chemistry creating nitrogen-rich pockets for other invaders, and mangroves transform sediment chemistry and carbon cycling so dramatically that effects continue even 6 years after removal (see “A Big Rotten Loofah”). These species are high management priorities. This paper recommends what is already being done, and that is managing high-impact, ecosystem-tranforming species. The distinction, however, between a species that changes its new environment by co-opting a native niche or preying on a species of interest, and one that fundamentally changes the very habitat it invades is important, and may help to distinguish “high-impact” invaders.

#3: The Wrong Paper Can Provide Loopholes for Haters

Davis et al. recommend that we make management decisions for practical, “not emotive” reasons.  Of course we should. The sad truth is that critics of management programs seek out reasons to cut funding on the management of certain species, and grab hold of papers like this to characterize eradication efforts as emotional or reactive. Though there are certainly social implications to our ecological definitions (I, for one, was averse to the idea of an “invasion meltdown” before I knew the formal definition), the terms we use are carefully defined and reevaluated. Although the idea of an invader taking over resonates with people, ecologists mean something when they say “invader”- and it’s not just an alien species as the paper suggests (see #1). Publications like these remind us that for every research paper, there are political repercussions that can resonate in management, and a poorly reasoned paper is great evidence against the argument it makes. So, while the authors have had the privilege of publishing in a high-profile journal, they may actually have provided fodder for critics of all invasive species management, including the impact-oriented kind they promote.

What exactly is impacted may be the more important distinction to make: Is a species causing economic harm or ecological harm, including changing actual habitat availability? And most importantly, which of those things do we care about the most? History shows that the species that do all three get the most attention, but not all invasive species are nasty enough to do that. Deciding which of the three threats should be prioritized is truly the challenge at hand, and managers and scientists alike would benefit from discussing it in a public forum.

Davis MA, Chew MK, Hobbs RJ, Lugo AE, Ewel JJ, Vermeij GJ, Brown JH, Rosenzweig ML, Gardener MR, Carroll SP, Thompson K, Pickett ST, Stromberg JC, Tredici PD, Suding KN, Ehrenfeld JG, Philip Grime J, Mascaro J, & Briggs JC (2011). Don’t judge species on their origins. Nature, 474 (7350), 153-4 PMID: 21654782

Cuddington, K. (2004). Invasive engineers Ecological Modelling DOI: 10.1016/S0304-3800(04)00152-8

Vitousek, P., & Walker, L. (1989). Biological Invasion by Myrica Faya in Hawai’i: Plant Demography, Nitrogen Fixation, Ecosystem Effects Ecological Monographs, 59 (3) DOI: 10.2307/1942601


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  • Mahalo Nui Loa

    I recently graduated from the Donahue Lab at the University of Hawai'i at Manoa and am currently a graduate student at the University of Washington. This research is funded by a Graduate Research Fellowship from the National Science Foundation, as well a scholarship from the Seattle chapter of the Achievement Rewards for College Scientists (ARCS) Foundation.
  • “Where do ecological ideas come from? …Most do not spring deductively from the minds of ecologists, like Athena from the head of Zeus. Instead, they emerge when ecologists absorb the essential spirit of individual places– their genius loci.”

    ~Mary V. Price & Ian Billick, "The Ecology of Place"
  • “Aloha is the intelligence with which we meet life.”

    ~Olana A'i, Kumu Hula

  • “I no longer say ‘Hawaiian ways of knowing’ anymore. Because people relegate that to the margins. ‘Ways of knowing,’ as if it’s a quaint, anthropologic way of describing something outside us. No, it’s ‘epistemology,’ the philosophy of knowledge. Land educates. ‘Ike ‘aina. The land of your birth educates you. This land here educates you.”

    ~Manu Meyer

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