Exotic Species, Naturalization, and Biological Nativism

Environmental Values (2001)

Ned Hettinger


1.      Surprising antipathy toward exotics:

         a.      Former Montana Governor Marc Racicot: “I just hate them. They are genetically deviant miscreants that have no rightful place on this planet. We all have to be a part of this war on weeds.”

         b.      Nature lovers (the defenders of flora and fauna) poison fields covered with invasives like kudzu or shoot nonnative mountain goats from cliffs

         c.      Ned’s mimosa tree

2.      To understand this antagonism and see if it is justified

         a.      I propose a definition of exotic species

         b.      Explore naturalization (how exotic species become native)

         c.      Evaluate reasons for the opposition to exotics and explore the charge that this opposition is xenophobic


3.      Examples: Kudzu, Zebra mussels, Lake trout (& Mountain goats?) in Yellowstone

4.      Popular conception of exotics I reject: Species introduced by humans from some other geographical region & cause damage because upset natural balance

5.      My definition of exotics as “foreign species” = Species that have not significantly adapted to local biota/abiota and to whom resident species have not significantly adapted

         a.      “Adapted” does not mean “positively fit in” (aggressively competing is as much adapting as establishing symbiotic relationships)

         b.      Adapted does not mean suited to survive (historically adapted species can go extinct and species not historically adapted can be suited to survive–“pre adapted”)

         c.      Adapted means changed its behaviors, capacities, gene frequencies in response to new circumstances

         d.      Natives will have forged ecological/evolutionary links

6.      Distinction between native species migration/range expansion and exotics arrival

         a.      Geographical movement (in location) may or may not result in species becoming exotic

         b.      Depends on if arrive in ecological assemblage to which not previously adapted (Cattle egrets in S.A. yes, Bison outside Yellowstone no)

         c.      When species move geographically, they only become exotic if they arrive in a type of ecological assemblage to which they have not previously adapted (Cattle egrets yes, Bison no)

7.      Being exotic is a matter of degree: The greater the differences between species, their relationships, and abiota in old habitat and those in new, the more exotic the immigrant will be (Japanese Snow Monkey’s versus Mountain goats in Yellowstone)


8.      Exotics have caused massive amounts of damage

         a.      2nd leading cause of current mass extinction event (e.g., Brown tree snake)

         b.      15-20% of species in U.S. exotic and estimated to cause $138 billion in yearly damage: Human, animal, and plant diseases ($41 billion), weeds ($34 billion), European and Asiatic rats ($19 billion), insects that destroy crops and forests ($17 Billion), cats ($14 billion), and zebra mussels ($5 billion). Pigeons, fire ants, starlings, and feral pigs cost about $1 billion each ($17 Billion), cats ($14 billion), and zebra mussels ($5 billion). Pigeons, fire ants, starlings, and feral pigs cost about $1 billion each

9.      But we should not identify exotics as damaging species

         a.      Some natives are damaging (“Native pests” Asian longhorn beatles, barnacles that proliferate wildly)

         b.      Many exotics can’t even survive in their new habitat and those that do, need not be weedy, aggressive, or pests

10.    Tens rule: 10 percent of introduced exotics succeed in establishing a breeding population, and 10 percent of those become highly invasive, thus only 1% of exotics typically cause serious problems

11.    Exotics can even be beneficial in their new habitats

         a.      Native monarch butterflies rely on an introduced species of Eucalyptus tree in California

         b.      The common apple tree came from Europe and West Asia: It’s hard to imagine that these apple trees have not benefitted the North American landscape

         c.      Quote Michael Pollan: “It’s hard to imagine a New England roadside without its tawny day lilies and Queen Anne’s lace, yet both these species are aliens marked for elimination. . . . Could it be these plants have actually improved the New England landscape, adding to its diversity and beauty? Shouldn’t there be a statute of limitations on their alien status?”

12.    Some even argue that exotics introduced into the U.S. have been beneficial on balance

         a.      98% of crops and animals produced in U.S. were exotic to North America: Including corn, wheat, rice, soybeans, cattle, poultry, and honey bees

         b.      Provide $800 billion in annual economic benefits and this exceeds the estimated $130 billion of economic damage caused by exotics

         c.      Humans have had some success in introducing, controlling, and benefitting from some exotic species

13.    Assumption that exotics are invariably harmful results from either unfair stereotyping or accepting false idea of an idyllic balance of nature

         a.      Pollan : "The current attack on alien species usually cites a few notorious examples of imported plants that have behaved badly, such as kudzu, Japanese honeysuckle, multiflora rose and purple loosestrife. These demon species are then used to tar the entire class of aliens with guilt by association"

         b.      Many native assemblages don’t form stable communities exotics could disrupt

14.    It is a mistake to assume exotics invariably destabilize native ecosystems

15.    Nonetheless there are good reasons for being suspicious of the disruptive potential of exotics

         a.      As its native predators, parasites, diseases and competitors are not likely present to limit proliferation

         b.      And local prey, hosts, competitors have not had a change to evolve defensive strategies


16.    Many–very probably most--exotics are now introduced by humans

         a.      Humans transport exotics distances, speeds, and between assemblages that are infrequent or impossible with naturally-dispersing exotics

         b.      Exotics hitch-hike in ship ballast water, pallet wood, airplane wheel-wells

17.    But some species get to new ecosystems (and become exotic) without human help (Cattle egrets, First finches on Galapagos Islands)

18.    And some human-introduced species are not exotic: E.g., the restored Yellowstone wolves

19.    One might think this last example is cheating, because returning a species to a place it previously existed guarantees the species is not exotic

20.    But not all human-caused return of species is native restoration: E.g., returning camels to North America would be exotic introduction, because those species have not adapted with present day ecological assemblages on the continent

21.    Even human introduction of species to places they have never been need not be exotic introduction, if the introduced species has adapted with the local assemblage (which has moved en mass except for one straggler)


22.    When an exotic is human introduced, we have a reason for negatively evaluating it

23.    Antagonism toward human-assisted immigrant species is justified by the value of wild nature as independent other

         a.      Massive humanization of earth is ongoing and increasing, resulting in a radical diminution in the sphere of wild nature

         b.      Perhaps ½ planet’s surface is significantly disturbed by humans and ½ of that is human-dominated

         c.      As un-dominated nature becomes more rare it markedly increases in value

         d.      Also, human life becomes radically impoverished as we increasingly live in a totally humanized, artifactual world of our own making.

24.    The presence of human-introduced exotics significantly contributes to the loss of wild nature as independent other and thus provides a reason for opposing such species



25.    Why believe in naturalization? (To avoid most species in ecosystems being exotic)

         a.      Because many (perhaps most?) species are have moved into foreign habitats and are not in the ecological assemblage in which they 1st evolved, if they couldn’t naturalize most species would be exotics

         b.      To avoid this we need a “statute of limitations on their alien status” (Pollan)

26.    Naturalization involves both ecological naturalization and evaluative naturalization

27.    Ecological naturalization is when an exotic significantly adapts to the resident species and the local abiota, and the residents significantly adapt to it

         a.      This is a matter of degree and typically increases over time

         b.      I don’t think this ecological naturalization guarantees that the one-time exotic is now native

28.    Many immigrant species have been in their new habitats long enough to ecologically naturalize (i.e., significantly adapt) and yet we justifiably hesitate to consider them natives

         a.      Kudzu not native species even though: Been here for over 125 years and is likely to have significantly adapted with locals in some habitats

         b.      Hawaiian feral pigs introduce by Polynesians (1500 years) still not native, though undoubtedly significantly adapted

29.    Becoming native involves evaluative naturalization in addition to ecological naturalization

30.    Natives are ones we judge to be “natural” members of ecosystems: Their presence must not represent significant ongoing human influence

         a.      To become a native, an exotic must not only significantly adapt (ecologically naturalized) but the human influence (if any) represented by its presence in the ecosystem must no longer be evaluatively significant

31.    Because human influence over natural systems WASHES OUT over time, like bootprints in the spring snow, human-introduced exotics can evaluatively naturalize

         a.      Natural processes can once again take control (as when old mining roads erode and vegetation overgrows them)

32.    Washout of human influence (and the resulting evaluative naturalization) depends on the amount of human influence, its temporal distance, and other factors

         a.      The greater the extent of human influence, the more difficult it is to wash away

                   i.       Feral Pigs on Hawaii: One reason to think that feral pigs on Hawaii have not evaluatively naturalized is because the only way pigs could get to the Hawaiian Islands is with human assistance: Hawaiian nature would have remained without pigs virtually forever, but for human intervention: This is a significant human influence over Hawaiian nature

         b.      Sufficient temporal distance can wash away almost any degree/type of humanization:

                   i.       Suppose wolves were descendants of the dogs Pleistocene humans brought with them as they crossed the bearing straight (13,000 ago)

                   ii.      Historically wolves would be human-introduced exotics, but they would have long ago naturalized evaluatively (as well as ecologically)

                   iii.     Any human influence over landscapes by Pleistocene peoples is likely to have long since washed away

33.    Evaluative naturalization should not be defined as occurring when human-introduced exotics cease causing damage


34.    Biological nativists (who favor native species and oppose exotics) have been charged with xenophobic prejudice (like hostility to human immigrants)

35.    Some claim that biological nativism embodies a purist ideology like that of the Nazis (their native plant movement purifying the biology of their country as they purified their culture of Jews)

36.    Rutgers’ ecologist David Ehrenfeld thinks these claims “deserve ridicule

         a.      Quote Ehrenfeld: “Comparing the antagonism toward exotics with real biases such as racial profiling of African-Americans and Hispanics “deserves ridicule. The . . . analogy between stereotyping alien species and stigmatizing human races is . . . far fetched. While pejorative generalizations about human races are demonstrably untrue, it is a simple matter to show that gypsy moths, Kudzu vines, and Argentine ants are destructive precisely because they are alien species in new environments. . . .There are more than enough cases in which exotic species have been extremely harmful to justify using the stereotype.”

         b.      But assuming that only 1/100 exotics cause serious problems, stereotypes about exotics are probably no better statistically grounded than are the morally-obnoxious, racial and sexual stereotypes about humans.

37.    Opposition to exotics as foreign species–unlike other definitions of exotics (as damaging or human introduced)--is clearly open to the charge that it is xenophobic and supports racial purity

         a.      Why isn’t this a morally troubling desire to keep locals pure from foreign biological pollution

         b.      Seems similar to the morally obnoxious attitude that blacks and whites should not marry and have offspring.

38.    But some versions of both cultural and biological nativism/purism are rational and praiseworthy; others, based on fear, hatred, or feelings of superiority, are morally repugnant

         a.      Examples of rational and praiseworthy cultural nativism

                   i.       Preservation of indigenous peoples/cultures is desirable

                   ii.      When Jewish parents lobby their children to marry other Jews

                   iii.     Or when people who live in the south send their kids to southern colleges

                   iv.     The attempt is to preserve diverse cultural practices of great value, not to reinforce or perpetuate prejudices, fear or hatred of those who are different

39.    Biological nativism is laudatory insofar as it aims to preserve a valuable kind of biodiversity that is increasingly disappearing

         a.      But doesn’t adding an alien species increase, not decrease biodiversity?

40.    Although adding an exotic to an assemblage increases the species count (and thus adds to biodiversity in that sense), the widespread presence of exotics impoverishes the diversity between types of ecosystems by making them more like each other

         a.      Adding a dandelion to a wilderness area where it previously was absent diminishes the biodiversity of the planet by making this place more like everyplace else

         b.      Adding a mimosa tree to Sullivan’s Island, makes the Lowcountry of South Carolina mor like some Asian assemblages.

         c.      When this is done repeatedly and at an every increasing rate–as is now occurring–we get a trend toward the globalization of flora and fauna

41.    This wanton human mixing of species from around the globe threatens to homogenize the world’s ecological assemblages into one giant mongrel ecology

42.    This is a conceptual diminution of diversity, distinct from the causal diminishment that occurs when an exotic extirpates native species

         a.      The mere presence of great numbers of exotics diminishes the diversity between ecological assemblages

43.    Some suggest we accept the increasing cosmopolitanization of the planet’s biota

         a.      Quote Dale Jamieson: “It is not implausible to suppose that we may come to see our preference for isolated, indigenous ecosystems as anachronistic; and instead come to favor ecosystems that are more cosmopolitan, in much the same way in which many people now prefer multicultural experiences to those which are provincial. A celebration of alien plants and surprising biological juxtapositions may be more in tune with the postmodern world than attempts to protect native species”

44.    Such a view ignores the great value lost as the ever-rising flood of exotics diminishes the diversity between ecosystems

45.    The logical endpoint of the spread of exotics is that ecological assemblages in similar climatic and abiotic regions around the world will be composed of the same species–a clear case of biotic impoverishment

46.    Globalization of flora and fauna also exacerbates the human loss of a sense of place

         a.      Quote Mark Sagoff: Native species “share a long and fascinating natural history with neighboring human communities. . . . Many of us feel bound to particular places because of their unique characteristics, especially their flora and fauna. By coming to appreciate, care about, and conserve flora and fauna, we, too, become native to a place”

         b.      Using knowledge and love for local native species to help ground a sense of place will no longer make sense in a world where most species are cosmopolitan

47.    Just as the spread of exotics threatens to homogenize the biosphere and intensify the loss of a human sense of place, so too economic globalization and cosmopolitanization of humans threaten to impoverish the diversity of earth’s human cultures and to undermine people’s sense of community

         a.      Keeping a dandelion out of Yellowstone is much like keeping Wal-Mart out of a small New England town or McDonalds out of India

         b.      Kudzu in the American South is like T.V. in Nepal, a threat to the diversity of the planet’s communities and ways of life

         c.      Cosmopolitan humans–though likely more accepting of diverse cultural practices–are also not likely to preserve local cultural practices or biotic communities

48.    Conclusion: Biological nativists’ opposition to exotic species--even non-damaging and naturally-occurring ones--can be justified as a way of preserving the diversity of ecological assemblages from the homogenizing forces of globalization