Doug Tallamy speaks…Art Shapiro responds…Million Trees fills in the gaps

Smithsonian Magazine published an interview with Professor Doug Tallamy, the entomologist who is committed to the eradication of non-native plants and most influential with native plant advocates in the United States.  The Smithsonian article gives Professor Art Shapiro an inadequate opportunity to respond to Tallamy’s assertions about the superiority of native plants.  Million Trees steps up to fill in the gaps in response to Tallamy.

  • The Smithsonian article says, “As a scientist, Tallamy realized his initial obligation was to prove his insight empirically. He began with the essential first step of any scientific undertaking, by applying for research grants, the first of which took until 2005 to materialize. Then followed five years of work by relays of students.”

The first study that Tallamy conducted is not mentioned in this article because it disproved his hypothesis:  “Erin [Reed] compared the amount of damage sucking and chewing insects made on the ornamental plants at six suburban properties landscaped primarily with species native to the area and six properties landscaped traditionally.  After two years of measurements Erin found that only a tiny percentage of leaves were damaged on either set of properties at the end of the season….Erin’s most important result, however, was that there was no statistical difference in the amount of damage on either landscape type.” (1)

  • The Smithsonian article says, “… insects tend to be specialists, feeding on and pollinating a narrow spectrum of plant life, sometimes just a single species. ‘Ninety percent of the insects that eat plants can develop and reproduce only on the plants with which they share an evolutionary history’…:”
Anise Swallowtail butterfly in non-native fennel. Courtesy urbanwildness.org

A “specialist” insect is rarely confined to using a single plant species.  Mutually exclusive relationships in nature are very rare because they are usually evolutionary dead-ends.  The study in which this claim about “specialization” originated, actually concluded:  “More than 90 percent of all insects sampled associate with just one or two plant families.”* There are over 600 plant families and thousands of plant species within those families.  Most plant families include both native and non-native plant species.  An insect that uses one or two plant families, is therefore capable of using both native and non-native plant species.  For example, there are 20,000 plant members of the Asteraceae family, including native sagebrush (Artemisia) and non-native African daisy.  In other words, the insect that confines its diet to one family of plants is not very specialized.

  • The Smithsonian article says, But he [Tallamy] thinks this [transition of insects to non-native plants] is likely to take thousands of generations to have an impact on the food web. Shapiro maintains he has seen it occur within his own lifetime.”

There are many empirical studies that document the transition that insects make from native to non-native plants within generations.  Professor Tallamy provides a few examples of such rapid transitions in his first book, Bringing Nature Home:  wooly adelgids from Asia have had a devastating effect on native hemlock forests in the eastern United States; Japanese beetles introduced to the United States are eating the foliage of over 400 plant species (according to Professor Tallamy), some of which are native (according to the USDA invasive species website).

Soapberry bug on balloon vine. Scott Carroll, UC Davis

The soapberry bug made a transition from a native plant in the soapberry family in less than 100 generations over a period of 20 to 50 years. The soapberry bug-balloon vine story is especially instructive because it entailed very rapid morphological as well as behavioral change; the beak length was quickly (a few years) selected for the dimensions of the fruit of the new host. (2)

  • Doug Tallamy claims that Art Shapiro’s findings are “anecdotal.” They are not.  Art Shapiro’s published study is based on nearly 40 years of data. (3)
Monachs in eucalyptus, Pacific Grove Museum

In a recent NY Times article about declining populations of monarch butterflies on the West Coast, an academic scientist explains how he used Professor Shapiro’s data set to study the decline:  “The monarch’s decline is part of a larger trend among dozens of butterfly species in the West, including creatures with names like field crescents, large marbles and Nevada skippers, said Matt Forister, an insect ecologist at the University of Nevada, Reno, whose conclusions are based on a nearly 50-year set of data compiled by Art Shapiro, a researcher at the University of California, Davis. “The monarch is very clearly part of a larger decline of butterflies in the West.”  Clearly, other academic entomologists do not consider Professor Shapiro’s data “anecdotal.”

The Burghardt/Tallamy study (4) does not contradict the findings of Professor Art Shapiro because Professor Shapiro is studying butterflies (not moths) in “natural areas” that have not been artificially created by choosing a limited number of plant species, as Tallamy’s study did.  In other words, the adult and larvae stages of butterflies that Professor Shapiro studies have more options, and when they do they are as likely to choose a non-native plant as a native plant for both host plant and food plant.  You might say, Professor Shapiro’s study occurs in the “real world” and the Burghardt/Tallamy study occurs in an artificially created world.

Dismissing observations as anecdotal is a well-worn rhetorical device.  Creationists often claim that evolution cannot be proven because the theory is based on millions of observations, rather than empirically tested by experiments. Yet, virtually all scientists are firm believers in the validity of evolutionary principles.

  • Tallamy dismisses climate change as a factor in plant and animal extinctions, preferring to place the blame solely on the mere existence of non-native plants.

This claim is contradicted by a multitude of studies, such as a collection of studies recently reported by Yale E360 that concludes:  “A growing number of studies show that warming temperatures are increasing mortality in creatures ranging from birds in the Mojave Desert, to mammals in Australia, to bumblebees in North America. Researchers warn that heat stress could become a major factor in future extinctions.”

Climate change is the environmental issue of our time.  When the climate changes, the vegetation changes.  When the vegetation changes, wildlife adapts or dies.  Non-native plants are one of the consequences, not the cause of climate change or plant and animal extinctions.

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*Professor Shapiro has provided a caveat to this definition of specialization of insects in a private communication, published with his permission:  A couple of observations: Hardly any insects feed on entire plant families. Rather, they feed on specific lineages within those families, typically defined by secondary chemistry (which is the necessary releaser for oviposition and/or feeding behavior). The relationship was summed up symbolically by A.J.Thorsteinson half a century ago: feeding=presence of nutrients+presence of required secondary chemicals-deterrents-antifeedants-toxins. Thus the Anise Swallowtail species-group feeds on the carrot family, Apiaceae, but NOT on Apiaceae lacking the proper chemistry.But they DO feed on some Rutaceae (including Citrus) that, though unrelated, are chemically similar. That was worked out by Vincent Dethier in the 1940s and further developed by John Thompson at UC Santa Cruz. A whole slew of things require iridoid glycosides as oviposition and feeding stimulants. Most plants containing these were in the family Scrophulariaceae before DNA systematics led to its dismemberment, but one whole branch of Scrophs is chemically unsuitable. Milkweed bugs eat milkweed, but they also eat the Brassicaceous genera Erysimum and Cheiranthus, which are chemically similar to milkweeds but not to other Brassicaceae…and so on. Native vs. non-native has nothing to do with it.”  (emphasis added)

  1. Tallamy, Doug, “Flipping the Paradigm:  Landscapes that Welcome Wildlife,” chapter in Christopher, Thomas, The New American Landscape, Timber Press, 2011
  2. Carroll, Scott P., et. al., “Genetic architecture of adaptive differentiation in evolving host races of the soapberry bug, Jadera haematoloma,” Genetica, 112-113: 257-272, 2001
  3. SD Graves and AM Shapiro, “Exotics as host plants of the California butterfly fauna,” Biological Conservation, 110 (2003) 413-433
  4. Karin Burghardt, Doug Tallamy, et. al., “Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities,” Ecosphere,November 2010

Stephen Jay Gould examines the concept of “native plants”

The native plant ideology is inconsistent with the basic principles of evolutionary theory and has dangerous political implications which have been applied in the past.  In his article (“An Evolutionary Perspective on Strengths, Fallacies, and Confusions in the Concept of Native Plants”), published by Arnoldia, the journal of Harvard University’s arboretum, Stephen Jay Gould describes the concept of “native plants” as “a notion [which] encompasses a remarkable mixture of sound biology, invalid ideas, false extensions, ethical implications and political usages both intended and unanticipated.”(1)

First, who is Stephen Jay Gould and why should we care what he thinks about the ideological construct of “native plants?”  Professor Gould taught geology and paleontology at Harvard University and biology and evolution at New York University, while also working at the American Natural History Museum in New York.  His most significant achievements as a scientist were in the field of evolutionary theory.  He is one of the most frequently cited scientists in the field of evolutionary theory.  But he is best known as a writer of essays and best-selling books on natural history for the general public.  Incidentally, he had a life long interest in civil rights and he brought that interest to his scientific inquiries with his abiding opposition to the use of pseudoscience to promote racism or sexism.(2) It is that interest that led him to his analysis of the concept of “native plants.”

Native plant advocates believe in the inherent superiority of native plants.  This belief is based on an assumption that native plants “belong” in a particular place and that their presence in the proper location represents an “optimal” landscape for that place.  This belief is based on a lack of understanding of the concept of natural selection. 

As Gould explains, “Natural selection does not preferentially lead to plants that humans happen to regard as attractive.  Nor do natural systems always yield rich associations of numerous, well-balanced species.  Plants that we label ‘weeds’ will dominate in many circumstances…weeds often form virtual monocultures, choking out more diverse assemblages than human intervention could maintain.”   The mechanism of natural selection does not produce the optimal adaptation, but only the adaptation that is better than its competitors at any particular point in time, which is why introduced plants are frequently more competitive than their predecessors deemed “native.” 

The argument that native plants “belong” in a particular place is equally fallacious because it assumes that the plants are there because they are best suited to conditions in that location.  In fact, plants are “products of a history laced with chaos, contingency, and genuine randomness.”  Plants have been moved—and continue to be moved—about the planet by weather, by birds and animals, including humans.  “’Natives’, in short, are the species that happened to find their way…not the best conceivable for a spot.”  (see video, “The Fallacy of Native Plants“)

A closely related argument used by native plant advocates to justify their crusade against non-native plants and trees is that the natives have “co-evolved” with other species of plants and animals and that they therefore fit together like some magic puzzle, implying that if the native plants disappear, native animals will also disappear because they are dependent upon the plants.  Gould says, “this notion, however, popular among ‘new agers,’ must be dismissed as romantic drivel.” 

Gould credits the native plant movement for efforts to preserve biodiversity, a goal that is defeated if other plants are simultaneously eradicated by their efforts.  He counsels native plant advocates to balance their efforts to achieve an inclusive biodiversity and we share that view.  We encourage native plant advocates to preserve the plants they prefer and plant more if they wish, but to quit destroying the plants they do not prefer.

But Gould does not come to this topic solely from his knowledge of the principles of evolution and his desire for the public to correctly understand its mechanisms.  He is also concerned about the “slippery slope” of nativist ideology from application to plants to application to humans.  This is not a theoretical anxiety on his part.  It is based on historical precedents. 

Wikimedia Commons

In Nazi Germany and in the United States around the same time, horticultural theories abounded about the superiority of native landscapes and those theories were inextricably linked to the belief that non-native humans were also inferior.  For example, “In 1942 a team of German botanists made the analogy explicit in calling for the extirpation of Impatiens parviflora, a supposed interloper:  ‘As with the fight against Bolshevism, our entire Occidental culture is at stake, so with the fight against this Mongolian invader, an essential element of this culture, namely, the beauty of our home forest, is as at stake.’”   And similar sentiments from an American horticulturalist, Jens Jensen, “’The gardens that I created myself shall…be in harmony with their landscape environment and the racial characteristics of its inhabitants.  They shall express the spirit of America and therefore shall be free of foreign character as far as possible…Latin spirit has spoiled a lot and still spoils things every day.”

Having debated many times with native plant advocates about their plans to eradicate non-natives, and listened to their justifications for those plans, we know that no counter argument inflames them more than the suggestion that their plans are reminiscent of similar efforts to eradicate human non-natives.  However, for the vast majority of the public who have not engaged in this debate, we provide the scientific evidence that the native plant movement is an ideology not based on scientific principles which has been associated in the past with horrific discrimination against non-native humans. 

"The New Case Against Immigration: Both Legal and Illegal" Book cover in the public domain

 We cannot dismiss these historical precedents as irrelevant at a time when anti-immigration sentiments are rampant in our society.

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(1) All quotes are from “An Evolutionary Perspective….”