Mark Davis, “A Friend to Aliens”

Mark Davis, Professor of Biology at Macalester College is interviewed in the February issue of Scientific American.  He tells us that invasion biology must distinguish between change and harm when labeling non-native species as “invasive,” a term which he believes should be used only in those rare cases when the non-native species pose “health threats” or economic harm.  With the exception of isolated places, such as islands, Mr. Davis tells us that non-natives have not been the cause of extinctions of native species.

 He believes it is irresponsible to label non-native species as “invaders” if they do not cause such harm because attempts to eradicate them are wasteful of scarce resources and often harm the environment more than the mere existence of non-natives.   He advises us to learn to live with those species that are not harmful. 

 He also points out that the eradication of non-natives is often futile and is likely to become even more futile in the future as global travel and commerce increase and the climate continues to change.  All species are going to move, both natives and non-natives and in fact, natives are as likely to cause problems in their expanded range as the non-natives in those regions.  He offers the example of the mountain pine beetle in Western coniferous forests, which is killing half the timber forest in British Columbia as it expands its range, probably in response to increasing temperatures.

Mr. Davis was also interviewed by Environment 360, a publication of Yale University, in November 2009.  In that interview, he is joined by Dov Sax, assistant professor of biology at Brown University, one of the growing number of biologists who are questioning the assumptions of invasion biology.  He provides a local example  of exaggerated claims of invasiveness:  “Dr. Sax says he began to question exotic species orthodoxy as an undergraduate at the University of California, Berkeley.  A professor leading a field trip described the Bay Area’s abandoned plantations of Australian eucalyptus trees as a “biological desert.”  Says, Sax, ‘There was all kinds of stuff growing in there.  I found there were really a similar number of species in both [native oak and eucalyptus] woodland types.  Exotics weren’t always doing the awful things people seemed to think they were doing.’” 

Owlets in eucalyptus, Claremont Canyon, Oakland

We attended a few lectures of an undergraduate course at UC Berkeley that fit with Dr. Sax’s experience.  Students in this undergraduate course were required to “volunteer” in a variety of different “restoration” projects in the Bay Area.  One of the projects on the property of UC Berkeley focused on the eradication of eucalypts.  The leader of this project and supervisor of the students who chose his project had an undergraduate degree in “natural resources” and an MBA in “operations management.”  He made a number of unsubstantiated claims to justify the eradication of eucalypts, but the most flagrantly stupid statement was this:  “The carbon sequestered in non-natives doesn’t count.  Only the carbon sequestered in natives counts.”  This statement has no scientific meaning.  We assume it is intended as a philosophical statement.  In any case, students aren’t learning any science from such a statement. 

Critics of native plant ideology are accustomed to criticism from true believers and Mark Davis is no exception.  In an interview available on the Macalester College website, Mr. Davis says he,  “…received rebuttals that, he felt, veered toward ad hominem attacks on his inexperience in the field.”  But he has not backed down and has come to view this debate as an example of the “values and age-old religious attitudes toward nature [that] frame scientific study and debates more than most scientists would acknowledge.”  He concludes that interview with this observation:  “People can get addicted to paradigms.  Then paradigms become an ideology.  Belief and conviction are very difficult adversaries since they are little affected by data and evidence.”   

9 thoughts on “Mark Davis, “A Friend to Aliens””


  2. Mark Davis says, “…paradigms become an ideology. Belief and conviction are very difficult adversaries since they are little affected by data and evidence.”

    He is so right. One of the leaders in the Bay Area native plant movement responded to the Davis Scientific American interview in his “Nature News” newsletter. Dr. Davis’s ideas are called “claptrap” without a single one of those ideas challenged on fact or logic. And so the “debate” on “invasion biology” continues: ideology vs. data and evidence, and never the twain shall meet. “Nature News” and other native plant enthusiasts are simply unable to distinguish between introduced species that are harmful and those that are not. They are all invasive aliens.

    “Nature News” says, “I can’t understand most of what I read [in Scientific American].” In the case of Dr. Davis’s interview, it’s not that complicated. Some introduced species cause great harm, including extinctions; most do not. If “invasion biologists” want to be considered scientists, they will have to learn to distinguish between those two cases. There should be less focus on where a species is from and more on how it actually functions in its environment. As Dr. Davis points out, without knowing its history, “invasion biologists” can’t tell just by examining a plant in its environment whether it is native or exotic; it’s just a plant.

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