Invasive species, the unbelievably villainous enemy of biodiversity

Are invasive species that bad? Image By Edans [CC-BY-2.0 (], via Wikimedia Commons

Are invasive species that bad? Image By Edans [CC-BY-2.0 ( by/2.0)], via Wikimedia Commons

There is very little black and white in nature; when it comes to environmental ethics, many management actions are a compromise between different valid perspectives, incorporating something that’s a little good and a little bad, no matter how you look at it. The concept of invasive species (even the tone of the term) is one that immediately points the finger at certain unwitting species, calling them out as “bad guys.” But categorizing species into the bins “native,” “nonnative,” and “invasive” is a human construct that nature does not necessarily follow in any clean way. So, I was intrigued when I read Gabriel Popkin’s recent profile of Ariel Lugo of the U.S. Forest Service’s International Institute of Tropical Forestry, who advocates that introduced species can have a neutral or positive effect on an ecosystem. Popkin then points out that in the face of rapid species losses and climate change, “What difference does it make if something is native to a place where it can no longer survive?”

Lugo has stirred the ecological community with his contentious position that “it’s good news that nature reacts to us by remixing and reforming and reshaping and restructuring. Novel systems that are a reflection of our activities—I love those. They’re saving our ass.” Direct opposition has come from community ecologists, led by Dan Simberloff (notoriously vocal, opinionated and prominent ecologist that he is). Popkin relates one particularly provocative presentation by Lugo at the 1986 National Forum on BioDiversity organized by E. O. Wilson, at which Lugo reported his unexpected finding that invasive species in Puerto Rico had not caused native species extinctions. The idea that there is a finite number of ecological niches and that invasive species take over niches at the expense of native species is part of invasive biology theory. Lugo contends that this is not always true.

But, sometimes it is true. Extinction is really difficult to study (see this article for examples). There are very few studies out there that causally link a native species’s extinction with an invasive species introduction–in fact, there are very few studies that even show that long-term population declines have been caused by an invasive species introduction (although numerous studies have demonstrated the exclusion of a native species because an invasive species outcompetes it. Here is an example with more citations therein.) But that by all means does not mean that such extinctions don’t happen. It’s just really difficult to monitor these dynamics from beginning to end. Understanding any cause and effect is complicated by the fact that something that starts off being “bad” (from whatever species or system perspective you choose) may not continue to be so as long-term ecological responses play out and as all organisms within an ecosystem, new and established, begin to coevolve (discussed by UC Berkeley’s Robert Holt here).

Improving managers’ ability to predict where introductions may happen and what outcomes are predicted could be the best strategy for dealing with the inevitability of nonnative introductions. Monitoring each nonnative introduction that manifests invasive characteristics is important for understanding how each system is responding and what managerial concerns need to be considered. Lugo’s question–“What difference does it make whether something is native to place where it can no longer survive?”–is ultimately a question about management goals. Are we managing to save biodiversity? Ecosystem services? An endangered species? These are the difficult questions, but once such goals are established, it sure would be nice to actually be able to make some predictions to inform management. Quibbling over how bad a broad human-constructed term is seems moot when we still lack a great deal of predictive and theoretical power (To be fair, I also understand that a word conveys a meaning that we have to agree upon to communicate well.) Let’s do more field biology and ecological modeling, y’all.

A correction was made on August 6, 2013: The quote “What difference does it make if something is native to a place where it can no longer survive?” in the first paragraph was unclear in who was quoted, Popkin or Lugo. The sentence structure made it sound like it was Lugo when in fact it was Popkin’s idea–the edited version is clearer. 

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