David I. Theodoropoulos, Las Sombras Biological
Preserve, Box 337, La Honda, CA 94020-0337 USA
(408) 236-3728
dt@dtheo.org
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.
(Title Slide)
"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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FOOTNOTES
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.