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Native plant advocates claim that native wildlife benefits from native plant restorations.  There is an intuitive logic that native animals require native plants.  After all, didn’t they “evolve together?”  In this post we will evaluate this claim, using our own eyes and what little scientific evidence is available about interactions between plants and animals.  The scientific literature informs us that wildlife does not necessarily benefit from native plant restorations and sometimes they are harmed by them.  The assumption that native animals are dependent upon native plants underestimates both the ability of animals to adapt to changing conditions and the harm caused by methods used to eradicate non-native vegetation.

Art Shapiro (UC Davis) has been studying California butterflies for over 35 years.  His observations as well as the work of other scientists have informed him that “…the extensive adoption of introduced host plants has clearly been beneficial for a significant segment of the California butterfly fauna, including most of the familiar species of urban, suburban and agricultural environments.  Some of these species are now almost completely dependent on exotics and would disappear were weed control more effective than it currently is.”  (1)

He explains that this is particularly true on the coast of California because this is where the highest concentration of introduced species of plants is naturalized and the butterfly population is less diverse because of the cool, foggy climate.  There are apparently few non-native plants in the desert and alpine regions of California and so butterflies in those regions have not had the opportunity or need to adapt to new plants.

Monachs in eucalyptus, Pacific Grove Museum

The most conspicuous example of a butterfly making use of an introduced plant is the migrating Monarch which overwinters in eucalypts in many locations on the coast of California.  A study of 180 of those locations found that 75% of the trees in which monarchs roost in the winter are eucalyptus.

Professor Shapiro also speculates that other insects have adapted to non-native plants as well:  “Introduced hosts, having a broader geographic range than native hosts, may permit the expansion of the insect population geographically.”

Bee in cotoneaster, Albany Bulb

Birds have also adapted to non-native plants and trees.  Researchers at UC Davis surveyed over 1,000 ornithologists in 4 states, including California, about their observations of native birds and non-native plants.  Responses from 173 ornithologists reported 1,143 “interactions” of birds with introduced plants considered invasive.  Forty-seven percent (47%) of those interactions were birds eating the fruit or seeds of those non-native plants and trees.  Other interactions were nesting, perching, gleaning (eating insects), etc.  (2)

Owl nesting in eucalyptus, courtesy urbanwildness.com

Interactions were frequently reported in non-native blackberry, which is found in most parks in San Francisco.  It is one of the most productive food sources for birds in San Francisco.  Unfortunately, it is being eradicated in many parks because it is non-native.  Since the birds eat it in one location and “deposit” its seeds in other locations, complete eradication of this important food source for wildlife seems unlikely.

The non-native blackberry also provides cover for wildlife.  It is an impenetrable bramble both physically and visually.  Birds and small mammals hide and make nests and dens in these thickets.  Coyotes are resident in San Francisco.  The thick undergrowth which has been removed in some parks by the Natural Areas Program now allows unleashed dogs to pursue them in areas where they were protected before.  If the safe havens of urban wildlife are destroyed, the animals may seek shelter elsewhere, a move that may be dangerous for them.  For more information about the rich family life of coyotes in San Francisco and what you can do to protect them, visit the CoyoteYipps blog.

Coyote chasing its tail, courtesy urbanwildness.com

Native plant restorations also require the use of herbicides to eradicate non-native trees and plants. Herbicides are sprayed on the blackberries that are a major food source for wildlife.  UCSF, when announcing its intention to destroy much of the forest and its understory on Mt. Sutro, has said that herbicides (Garlon and Roundup) must be used to implement their plans. (Update:  UCSF recently made a commitment to NOT using herbicides on Mount Sutro.)  Herbicides are used by most managers of public land to eradicate non-native plants, including by the Natural Areas Program in SF, the East Bay Regional Park District, and federal lands in the Bay Area such as GGNRA and Pt Reyes National Seashore.

We have described in other posts  the harmful effects of herbicides on the environment and the animals that occupy it so we won’t repeat that information here.  We will only add that one study performed by the US Forest Service for the EPA reported that exposure to Garlon significantly reduced the reproductive success of birds.  (3)

The Natural Areas Program in San Francisco is committed to the restoration of native plants to the city’s parks.  It is not designed to benefit the animals that most urban dwellers call “wildlife.”  Their management plan categorizes native raccoons and skunks as “subsidized predators,” along with a long list of non-native wildlife such as opossums.  They recommend “control” of all of these animals if they have an effect on native wildlife populations.  “Control” in this context should be interpreted as extermination.

Legally protected species such as Red-Legged Frog, San Francisco Garter Snake, Mission Blue Butterfly, and Western Pond Turtle are the only wildlife of interest to the Natural Areas Program.  Extensive efforts are made to reintroduce these legally protected species to the parks of San Francisco.  Why?  Because the legal protections for rare animals are much stronger than the legal protections for plants.  If a population of legally protected animals can be established, drastic measures are required to maintain them.  For example, toxic herbicides that are otherwise banned by the SF Department of the Environment are permitted on Twin Peaks because the Mission Blue Butterfly has been reintroduced there.  Prescribed burns are required on San Bruno Mountain because the Mission Blue exists there.  Trees are being destroyed on Hawk Hill in Marin County because habitat for the Mission Blue is being restored there.  The migrating raptors that use these trees do not have the legal status of the endangered butterfly, so their needs are secondary.

In other words, the native plant movement is selective about its interest in wildlife.  Their interest is primarily in rare, native animals.  Animal competitors of  legally protected animals are eradicated.  Animals that have adapted to non-native vegetation must move or die if their food source is destroyed by native plant “restorations.”

Micro-managing nature benefits few animals, least of all humans who watch their parks being torn apart by an ideology that is destructive at its core.

—————————————————————————— 

(1) SD Graves and AM Shapiro, “Exotics as host plants of the California butterfly fauna,” Biological Conservation, 110 (2003) 413-433

(2) CE Aslan and E Rejmanek, “Avian use of introduced plants:  Ornithologist records illustrate interspecific associations and research needs,” Ecological Applications, 20(4), 2010, 1005-1020

(3) Marin Municipal Water District, Herbicide Risk Assessment, page 4-24.

19 Comments leave one →
  1. entomologist permalink
    May 23, 2011 9:10 pm

    Adaptation to exotic species by specialist herbivores is unusual. Those butterflies that switch to exotics tend to be generalists already. This idea that exotic plants are as good for wildlife as natives is just plain pathetic, especially for anyone who knows about herbivory patterns on native and exotic plants. Insects eating plants are at the base of the food chain and native plants have more insect herbivores and support more native birds. Doug Tallamy’s work shows this in the eastern US conclusively. I certainly feel for the loss of trees, but the alternative is that we accept a homogenized set of urban-tolerant plants and wildlife. Maybe that’s ok if you don’t know the difference, but for those of us who actually pay attention it is profoundly sad.
    Webmaster: We have published a comprehensive response to this comment. Please see “Dialogue about insects and non-native plants.”

  2. May 6, 2013 9:57 pm

    This is brilliant! Thank you so much. Those people who want non-natives gone, should start with their own yards and then end with themselves.

  3. Clayton permalink
    January 13, 2017 9:56 am

    From GreenFacts (www.greenfacts.org)

    Biotic homogenization, defined as the process whereby species assemblages become increasingly dominated by a small number of widespread species, represents further losses in biodiversity that are often missed when only considering changes in absolute numbers of species. Human activities have both negative and positive impacts on species. The many species that are declining as a result of human activities tend to be replaced by a much smaller number of expanding species that thrive in human-altered environments. The outcome is a more homogenized biosphere with lower species diversity at a global scale. One effect is that in some regions where diversity has been low because of isolation, the species diversity may actually increase—a result of invasions of non-native forms (this is true in continental areas such as the Netherlands as well as on oceanic islands). Recent data also indicate that the many losers and few winners tend to be non-randomly distributed among higher taxa and ecological groups, enhancing homogenization (http://www.millenniumassessment.org/documents/document.273.aspx.pdf).

    McKinney, M.L. and J.L. Lockwood, 1999: Biotic homogenization: a few winners
    replacing many losers in the next mass extinction. Trends in Ecology &
    Evolution, 14, 450–453.

    • January 13, 2017 4:42 pm

      Homogenization is a popular myth about the loss of diversity. For example, many people believe that bird populations may not be in decline, but there are a few hardy species that dominate everywhere. John Marzluff’s studies of bird populations all over the world do not corroborate that belief. Five bird species are found in cities all over the world (house sparrows, starlings, Canadian geese, mallard ducks, and rock pigeons). However, these ubiquitous species are not the predominant bird species he found in cities. Of the 151 different bird species he found in the 10 cities he visited, 75% of them were unique to each of the cities. “Homogenization is barely perceptible.” (John M. Marzluff, Welcome to Subirdia,” Yale University Press, 2014)

      But there is a far stronger reason why the homogenization argument is not a scientifically valid argument. The fact that there are “winners” and “losers” in a changing environment is more accurately described as natural selection by evolutionary science. The “winners” don’t stop adapting and evolving when they arrive in new ranges. Within generations the winners develop new characteristics in response to their new surroundings and their new neighbors (genetic drift contributes to those changes). In the long term, they will be new species and that transition will not be observable in the short time span of humans. The monkeys that came to the New World from Africa are now distinct species of monkeys. Would you say that primates are now globally “homogenized?” If you understood the functioning of evolution, you would not say that.

  4. Clayton permalink
    January 17, 2017 10:32 am

    What Triggers Mass Extinctions? Study Shows How Invasive Species Stop New Life

    An influx of invasive species can stop the dominant natural process of new species formation and trigger mass extinction events, according to research results published today in the journal PLoS ONE.

    The study of the collapse of Earth’s marine life 378 to 375 million years ago suggests that the planet’s current ecosystems, which are struggling with biodiversity loss, could meet a similar fate.

    Although Earth has experienced five major mass extinction events, the environmental crash during the Late Devonian was unlike any other in the planet’s history.

    The actual number of extinctions wasn’t higher than the natural rate of species loss, but very few new species arose.

    “We refer to the Late Devonian as a mass extinction, but it was actually a biodiversity crisis,” said Alycia Stigall, a scientist at Ohio University and author of the PLoS ONE paper.

    “This research significantly contributes to our understanding of species invasions from a deep-time perspective,” said Lisa Boush, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which funded the research.

    “The knowledge is critical to determining the cause and extent of mass extinctions through time, especially the five biggest biodiversity crises in the history of life on Earth. It provides an important perspective on our current biodiversity crises.”

    The research suggests that the typical method by which new species originate–vicariance–was absent during this ancient phase of Earth’s history, and could be to blame for the mass extinction.

    Vicariance occurs when a population becomes geographically divided by a natural, long-term event, such as the formation of a mountain range or a new river channel, and evolves into different species.

    New species also can originate through dispersal, which occurs when a subset of a population moves to a new location.

    In a departure from previous studies, Stigall used phylogenetic analysis, which draws on an understanding of the tree of evolutionary relationships to examine how individual speciation events occurred.

    She focused on one bivalve, Leptodesma (Leiopteria), and two brachiopods, Floweria and Schizophoria (Schizophoria), as well as a predatory crustacean, Archaeostraca.

    These small, shelled marine animals were some of the most common inhabitants of the Late Devonian oceans, which had the most extensive reef system in Earth’s history.

    The seas teemed with huge predatory fish such as Dunkleosteus, and smaller life forms such as trilobites and crinoids (sea lilies).

    The first forests and terrestrial ecosystems appeared during this time; amphibians began to walk on land.

    As sea levels rose and the continents closed in to form connected land masses, however, some species gained access to environments they hadn’t inhabited before.

    The hardiest of these invasive species that could thrive on a variety of food sources and in new climates became dominant, wiping out more locally adapted species.

    The invasive species were so prolific at this time that it became difficult for many new species to arise.

    “The main mode of speciation that occurs in the geological record is shut down during the Devonian,” said Stigall. “It just stops in its tracks.”

    Of the species Stigall studied, most lost substantial diversity during the Late Devonian, and one, Floweria, became extinct.

    The entire marine ecosystem suffered a major collapse. Reef-forming corals were decimated and reefs did not appear on Earth again for 100 million years.

    The giant fishes, trilobites, sponges and brachiopods also declined dramatically, while organisms on land had much higher survival rates.

    The study is relevant for the current biodiversity crisis, Stigall said, as human activity has introduced a high number of invasive species into new ecosystems.

    In addition, the modern extinction rate exceeds the rate of ancient extinction events, including the event that wiped out the dinosaurs 65 million years ago.

    “Even if you can stop habitat loss, the fact that we’ve moved all these invasive species around the planet will take a long time to recover from because the high level of invasions has suppressed the speciation rate substantially,” Stigall said.

    Maintaining Earth’s ecosystems, she suggests, would be helped by focusing efforts and resources on protection of new species generation.

    “The more we know about this process,” Stigall said, “the more we will understand how to best preserve biodiversity.”

    • January 17, 2017 12:50 pm

      PLoS ONE is not a peer reviewed journal. It is a self-publishing platform. This article contains many absurd statements. Here is one example: “The invasive species were so prolific at this time that it became difficult for many new species to arise.”

      This is not a scientifically valid use of the word “invasive species.” That term is used exclusively to describe species introduced by humans outside the native ranges of the introduced species. This publication is reporting on the rise of new species during the Denovian Period, about 400 million years ago, long before humans—or primates for that matter—existed. To suggest that new species are “invasive” when they initially evolve is to deny the existence of evolution.

      I am publishing this in case you did not see this message on the last comment you posted on another article: “This is the last comment I will post for you. You are dumping studies without any indication of how those studies relate to the article on which you are commenting. This forces me to figure out what point you are trying to make. It also requires me to analyze the studies you are dumping on me. No work is required on your part. A lot of work is required on my part. This is a game of “rope-a-dope” that I am done playing.”

  5. Clayton permalink
    January 18, 2017 10:36 am

    Milliontrees,

    PLoS ONE is partly peer-reviewed. The point of citing this article is to point out that the present-day introduction of exotic species by humans in the Antropocene (the sixth great extinction) is similar in effect to the reconnecting of landmasses by tectonic forces. In a way, we are re-connecting Pangea. When North America and South America became connected through the rise of Isthmus of Panama, there was a mass extinction of the South American fauna.

    Webmaster: I understand the point of this article. The application of events in deep-time to present day circumstances is considered questionable by many academic ecologists. Major geological events, such as the break-up of Pangaea, are not comparable either in their impact or their relevance to the Anthropocene, in which most environmental impact is directly attributable to the activities of humans.

    Your citing of one study by John Marluff and over-generalizing to assert that homogenization is a myth does not stand up to scientific scrutiny. That is why I cited the two bird studies.

    Webmaster: John Marzluff’s book is not a single study. It is a book that is a compendium of studies done by many researchers, including his own studies. There are over 400 references to those studies in Professor Marzluff’s book.

    This comment has been edited as forewarned by the Webmaster.

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