David I. Theodoropoulos, Las Sombras Biological
Preserve, Box 337, La Honda, CA 94020-0337 USA
INVASION of the ALIENS!
Science or Pseudoscience?
Version presented at the meeting of the American Association of Botanic Gardens and Arboreta, June
2003. I am grateful to the Association for inviting me to speak. Material in [brackets] did not
appear in the original talk, but is added for clarification. Citations were not given in the
original talk. They appear at the end of the paper. Slides and footnotes are linked - click to read
or view, then click back.
"Alien invaders" are a hot topic. In his book "Alien Invasion" (Photo Slide) Robert Devine vilifies botanic gardens- Quote:
"Kanapaha, like almost all botanic gardens, is loaded with invasive exotics…By helping fuel the alien invasion, botanical gardens give legitimacy to the dangerous status quo… most botanic gardens are oblivious to the issue of invasive species…"
He claims that you have "a reluctance to discontinue sales of exotic plants that have been big moneymakers" for botanic gardens (Devine 1998:206-208).
Unfortunately, invasion biology, with its irrational fear of the movement of species, is a century out of step with ecological science.
Natural dispersal has been frequent, long-distance, and beneficial (Section Title Slide) (Axelrod 1959; Clark 1988; Clark et al. 1989; Crow et al. 1988; Darlington 1957; Darwin 1948; Davis 1983; Davis 1988; Elias 1994; Elliott-Fisk 1988; Gleason & Cronquist 1964; Kuc 1995; Menard 1974; Munz & Keck 1959; Neill 1969; Orban 1995; Paus 1995; Peglar et al. 1989; Simpson 1942; Thornton 1971). Dispersal is essential to maintaining biodiversity, and has been a powerful driving force of evolution (1).
(Text Slide) Contrary to the antiquated and discredited ecology on which invasion biology rests, natural biota are not coevolved, tightly-integrated, perfectly balanced systems. (Text Slide) All evidence from modern ecology and paleobiology indicates that current species assemblages are recent, non-coevolved aggregations, that species disperse independently, and species interactions form and dissolve readily (Davis 1983; Kellman 1980; Lawton 1998). (Text Slide) All extant species assemblages are resilient and are accustomed to integrating new members (Vermeij 1991). The fossil record is clear (Text Slide) - invasion increases biodiversity (2), and the experimental record indicates that the greater the rate of invasion, the higher the diversity of the resulting assemblages (Robinson & Edgemon 1988). As Turner (1996) stated, "life evolves at the edge of chaos, the area of maximum vitality and change."
(Text Slide) Invasion is identical to entirely natural processes - note this dense, invading monoculture (Photo Slide) - this is our native bracken fern [Pteridium aquilinum] (3). No scientific model can distinguish this from an "alien" invasion. (Text Slide) Again and again, we find "invaders" to be disturbance indicators only, symptoms of industrial abuse of the land (4), integrating ecologically, and with many beneficial effects that are carefully ignored by those promoting a "crisis" (Colwell & Dodd 1995; Essink & Dekker 2000; Francour et al. 1995; Holland et al. 1995; Kuuispalo et al. 1995; Marshall 1991; Peles et al. 1995; Sagoff 1999; Stewart & Samways 1998).
(Text Slide) The data indicate that in all cases, including even the oceanic islands, anthropogenic dispersal has increased biological diversity (Baskin et al. 1995; Harrison 1999; Harty 1993; Hickman 1993; Klick et al. 1989; Moulton & Pimm 1986; Simberloff 1986) (5). The alpha diversity of species counts has risen, beta and gamma diversity have increased, and phylogenetic omega diversity has risen. Novel assemblages have formed, new functional and structural elements have been added to landscapes, and entirely new ecological interactions have arisen.
Anthropogenic dispersal is an essential conservation strategy - at-risk clades need to be naturalized in new regions to prevent extinction, and hyperdiverse preserves established (Theodoropoulos 1993, 1999). There are no theoretical limits to diversity (Cornell & Lawton 1992).
(Section Title Slide) Given the current level of hysteria on this subject, it's time for a reality check.
Purple loosestrife [Lythrum salicaria], the poster weed of invasion hysteria, is said to be aggressive, forming dense, monotypic stands, displacing native vegetation and destroying waterfowl habitat, quote "reducing its wildlife value to roughly that of a parking lot" (Bright 1998). The NISC [National Invasive Species Council] places it in their top ten invaders. Bright calls the plant a "monster." Not one of these claims is true. Whitt and coworkers (1999) studied 258 plots and found higher avian densities in loosestrife stands than other vegetation types, including ten breeding species. Treberg and Husband (1999) studied 41 plots and found no significant difference in vascular plant species richness, regardless of the percentage of loosestrife cover. A number of native species were found more likely to grow in plots containing purple loosestrife. Hager and McCoy (1998) traced the history of purple loosestrife and found little scientific evidence that it has deleterious effects, and state that, quote "there is currently no scientific justification for the control of loosestrife."
Saltcedar [Tamarix spp.] is said to be a disastrous ecological menace, one of the nation's worst weeds, changing river hydrology, increasing flooding, sedimentation, and salinization, crowding out cottonwood [Populus deltoides] and willow [Salix spp.], and driving native species "to the edge" (Malakoff 1999; U.S. Congress Office of Technology Assessment 1993). Yet, studies have demonstrated that native seedlings are competitively superior to saltcedar (Sher et al. 2000), and that it establishes in soils too saline for natives to germinate (Anderson 1996). Stromberg (1998) found that saltcedar actually enhances floristic diversity - herbaceous species richness and cover is significantly greater in saltcedar than cottonwood, and stem densities of native woody successional species are equivalent. Anderson (1998) has found that avian species richness and density in saltcedar is equivalent to native vegetation, and "biomass and diversity of insects in saltcedar stands is comparable to those in cottonwood and willow." In fact, 90% of the endangered willow flycatcher [Empidonax traillii extimus] nest in saltcedar (Malakoff 1999). Over 20 years ago Everitt (1980) pointed out that saltcedar is only a symptom of abuse of riparian areas, and he has recently stated that quote "There is no evidence that it actively displaced native species nor that it played an active role in changing the hydraulic or morphological properties of the river" (Everitt 1998). These are not biased people - all have killed saltcedar during riparian restorations.
Eucalyptus [Eucalyptus spp.] is said to invade and destroy native ecosystems, killing plants and birds - quote:
"Their silent beauty masks a quiet destructiveness, for they are among the most monstrous organisms on earth. Outside of their native Australia, their leaves and bark are so toxic that they kill all plants around them and ensure that there will be no competition" (Ward 1994).
Note the dense native shrubs at the base of this eucalyptus (Photo Slide). Studies have shown that 47 species of native birds use the tree in California, including species not found in surrounding native vegetation, and the understorey included 36 species, which were correlated with site characteristics, not tree density (Stein & Moxley 1992). Three centimeters of eucalyptus mulch did not inhibit germination of native species (Yamada & Sandoval 2000), and eucalyptus stands are preferred sites for overwintering monarch butterfly [Danaus plexippus] congregations (Marriott 1997). In Brazil, eucalyptus buffer zones are protecting the endangered black lion tamarin [Leontopithecus chrysopygus], and aid native forest regeneration (Cullen et al. 2001).
This is a transect leading up to a eucalyptus trunk - note the dense introduced grasses (Photo Slide), and as we approach the tree (Photo Slide), note that the native plants increase (Photo Slide), leading up to 100% natives (Photo Slide) when we reach the base (Photo Slide) (Photo Slide). A dense native understorey in a eucalyptus grove (Photo Slide). Compare this to the complete suppression of understorey by this invader (Photo Slide), the California redwood [Sequoia sempervirens], which invaded from the north during the Tertiary. A monarch overwintering cluster in eucalyptus (Slide not available - copyrighted). And this is what the nativists do to our groves (Photo Slide).
Star thistle [Centaurea solstitialis] - said to be devastating invader of no use to wildlife - this native bumblebee [Bombus vosnesenskii] doesn't agree (Photo Slide), this native hunting spider finds it good camouflage (Photo Slide) - a native skipper [Hesperiinae] (Photo Slide) - a native butterfly (Photo Slide). I observed 23 native species utilizing the plant in a single half-hour. Note the sharp ecotone (Photo Slide), demonstrating that the thistle is a symptom of past land abuse, as the barbed-wire fence cannot stop the thistle seed. Poison hemlock (Conium maculatum) also a "useless invader" (Photo Slide) - these are a few of the native organisms that utilize the plant - a native fly, a spider web, aphids (Photo Slide), a ladybird (Photo Slide), a beetle (Photo Slide). Birds are attracted to this rich invertebrate fauna (Photo Slide), and return later in the season to eat the seeds.
Caulerpa, the so-called "killer algae" (Photo Slide) - is claimed to be an "aquatic astroturf," devastating the Mediterranean (Bright 1998; Meinesz 1999). Yet, studies have shown that it has no effect on composition or richness of the ichthyofauna (Francour et al. 1995) (6). It removes pollution from the water (Jaubert et al. 1999) (7), and species richness and diversity of epiphytic fauna are greater than in native Cymodocea nodosa seagrass beds (Frakes 2001).
Similarly, Hydrilla is called one of Florida's "most aggressive alien plant species" (Schmitz et al. 1993). Yet it supports the highest avian species diversity in Florida, and has the highest fish density and biomass, with 6.3 times the density and five times the biomass as the native Potamogeton (Chick & McIvor 1994).
The cost of invaders was placed by Pimentel and coworkers (2000) at $137 billion annually in the US, and this figure has become one of the most widely quoted "facts" on invasion. Yet this figure is entirely fictitious - damage from cats, fully 12% of the total was fabricated out of thin air, and has no factual or economic basis whatsoever. They claim that St. Johnswort [Hypericum perforatum] is a quote "newly introduced non-native plant" when 5 minutes in a library would show that it has been present here for probably two centuries, nearly complete bio-control achieved 50 years ago, and the plant is a multi-million-dollar medicinal crop with compounds showing activity against HIV. Pimentel's paper has zero credibility.
The second-most quoted "fact" about invasion - that invaders are the "second greatest threat to biodiversity", or "the second greatest cause of endangerment" is equally vacuous. Matt Chew (2002) has investigated the origin of this claim and found that there is zero hard data to back it up - it is based entirely on anecdote and supposition.
I repeat, there is no credible evidence that this is true.
(Text Slide) Invasion biology has been deeply influenced by the herbicide and regulatory industries. Every Exotic Pest Plant Council has had herbicide industry representatives involved from the beginning (Photo Slide) (8), and anti-invader publications (Photo Slide) which call plants pollution and chemicals the cure, are supported by herbicide industry advertising (Photo Slide) (9). A Monsanto booth at a CalEPPC [California Exotic Pest Plant Council] meeting (Photo Slide). How can we tolerate this corruption of science by industry?
By every definition of legitimate science, invasion biology is pseudoscientific, whether by Popper's criterion of falsification (10), [Imre] Lakatos' test of a progressive, strengthening research program vs. a degenerating, hedging, side-stepping program, or Jerry Ravetz' criterion of the suppression of uncertainty of inputs in quantitative methods (11).
Invasion biology is nonsense, a pseudoscience (Text Slide). To anyone who claims otherwise, a challenge - operationally-define the essential terms of your field - "invasion" "native" "alien" "harm" (Text Slide) (12). Articulate even a single falsifiable hypothesis, and then test it. Cease repeating discredited anecdotes. Identify measurable criteria that will allow the identification of non-natives under double-blind conditions. And if any of my criticisms of invasion biology are in error, I invite you to refute them - that's how science works (13).
The NISC is promoting a "clean-list" or "white-list" approach to the entire biosphere, in which all species are prohibited except those that are explicitly permitted by government bureaucrats (Theodoropoulos 2000). This will be implemented through "risk assessment" an alleged ability to predict which species will "invade." This is scientifically indefensible. Such prediction is impossible due to complexity, chaos, and emergent properties. All models developed to date rely on entirely non-operational constructs, undefined terms, an anecdotal data-pool, and have a high level of false positives. Garbage in, garbage out. Williamson (1999) cites ten reasons why prediction may fail: target not precise enough, significance statistical but not useful, extrapolation fails, statistical shrinkage, base rate effect (14), new variables, lack of phylogenetic correlation (15), time lags, non-linearity and chaos, and complexity and situation-specific detail. These are substantial obstacles to risk assessment.
Ecosystems often are attracted to disequilibrium and are intrinsically unpredictable. Modern ecological theory indicates that many ecosystems self-organize towards critical states that are susceptible to catastrophic events which in turn are essential to the maintenance of biodiversity (see Turner 1996 for a non-technical overview). In their current status, models predicting "invasiveness" are naïve at best, and at worst will be an expensive bureaucratic disaster.
The greatly increased regulation of all species through risk assessment and vastly expanded quarantines will place enormous burdens on those who are actively preserving biodiversity - scientific researchers, zoos, botanic gardens, and grassroots preservation efforts (Theodoropoulos 2000). In South Africa anti-invasion extremists are promoting laws requiring that, in addition to risk assessment, insurance policies must be purchased for each species imported, and they explicitly state that this is intended to make the movement of species too expensive to engage in except where large industrial profits will result, calling anything less a "frivolous introduction."
To use their own rhetoric against them, this is leukemia of the body-politic - the former protector cells have multiplied out of control and have turned against the body, attacking it and diverting important resources towards their own cancerous growth.
Biological diversity has been likened to a great library - these are the book-burners in our libraries of diversity (Text Slide). Appeasement does not work. We must stand up and call this nonsense the pseudoscience it is. Government agencies tried three times during the 1970s to impose "clean-list" regulations, and each time they failed because concerned scientists had the courage to speak out (U.S. Congress Office of Technology Assessment 1993:22-24). Now, it's our turn.
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1. Vermeij (1996) points out "the potentially crucial role that invasions and
invaders have played in stimulating evolution." Back.
2. "Not only total faunal richness, but local richness in comparable communities has risen steadily for at least 100 million years" (Cornell & Lawton 1992). Back.
3. Bracken may change soil properties, preventing regeneration of certain forest trees, and may persist for centuries (Johnson-Maynard et al. 1997). These phenomena are identical to the ecological effects of certain invaders, and which are described as "catastrophic." Back.
4. True causes of 'invasion' include pre-extinctions (Collins 1988; Fender & McKey-Fender 1990; Moyle 1986; Myers 1986; Vermeij 1993), hydrological changes and water pollution (David 1999; Vaughn & Taylor 1999; Wakeman 1989; Williams 1964), fire regime changes (Christensen & Burrows 1986; Edelbrock 1991; Smeins & Merrill 1988), and many others (see Theodoropoulos 2003). Back.
5. It has been mathematically demonstrated that invasion increases diversity. See Rosenzweig (2001). Back.
6. And it is favorable for recruitment of some fish species (Francour et al. 1995). Back.
7. This 8-year study also found that it helped the recovery of native Posidonia seagrass beds (Jaubert et al. 1999). Back.
8. Monsanto employee Dr. Nelroy Jackson was a founding board member of CalEPPC, is on the National Invasive Species Advisory Committee, and "is Product Development Manager for Monsanto Company, with responsibility for the development of Industrial, Turf and Ornamental Markets in California, Arizona, Nevada and Hawaii. [He] has been instrumental in the development of Roundup® and Rodeo® herbicides for vegetation control in the west." (quote from CalEPPC publication, photocopy available on request) Back.
9. Wildland Weeds, published by the Florida EPPC, for example. Back.
10. Philosopher of science Sir Karl Popper (1902-1994) developed the criterion of falsification - "A theory which is not refutable by any conceivable event is non-scientific." If no test can be devised that will demonstrate the theory false, it is 'non-falsifiable' (Popper 1935, 1963). Invasion biology rests on non-operational definitions, and is far too incoherent to be falsifiable. The sole testable claim of invasion biology, that anthropogenic dispersal decreases biological diversity, is already entirely falsified by available data. Back.
11. That is, uncertainties must be suppressed in mathematical models or the output will become indeterminate. Back.
12. See Peters (1988), for example, for a brief discussion of the problems of non-operational definitions in ecological research. Back.
13. See Theodoropoulos (2003) for an outline of these criticisms. Back.
14. That is, disproportionate false positives. See Reichard's (1997) model, for example. Back.
15. That is, related species do not behave in the same manner. The differing abilities of carp (Cyprinus carpio) varieties to spread, for example (Arthington & Mitchell 1986). Back.