Are exotics good or bad? They are neither. They just are. But some exotics cause harm and impede certain priorities, and debates about exotics often ignore reality.
Book review: Fred Pearce. 2015. The New Wild:
Why Invasive Species Will Be Nature’s Salvation. Beacon Press
There has been much soul-searching in invasion biology, with
attacks, and subsequent rebuttals, on the very nature of why we study, manage
and attempt prevent the spread of exotic species (Davis et al. 2011) (Alyokhin 2011, Lockwood et al. 2011, Simberloff 2011).
What is needed at this juncture is a thoughtful and balanced perspective on the
nature of the discipline of biological invasion. Unfortunately, the book “The
New Wild” authored by Fred Pearce, is not that balanced treatment. What is
presented in this book is a very one-sided view, where counter-evidence to the
thesis that exotics will save nature is most often overlooked, straw men are
erected to aid in this goal, and the positions of working ecologists and
conservation biologists are represented as simplistic, anachronistic or just
plain incorrect.
What Pearce has written is a book-long argument about why
exotics shouldn’t be feared, but rather embraced as a partial solution to
anthropogenic land use change. I do not wish to undermine the reality that
exotics can play important roles in urban landscapes, or that some ecologists
and conservation biologists do indeed harbour suspicions of exotics and subscribe
to unrealistic notions of purely native landscapes. Exotic policy is at the
confluence of culture, science, economics and politics, and this is why the
science is so valuable (Sandiford et al. 2014). For Pearce, the truth of
what most ecologists do and think seems like an inconvenient reality. There are a number of pervasive, frustrating
problems with Pearce’s book, where bad arguments, logical flaws and empirical
slight-of-hand obfuscate issues that desperately need honest and reflective
treatment.
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A monoculture of the exotic plant Vincetoxicum rossicum that spans open
and understory habitats near Toronto, Canada (photo by M. Cadotte). This is a
species that interferes with other management goals and needs to be actively
managed.
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There are major problems with ‘The New Wild’ and these
include:
1) A premise
built on a non sequitur and wishful thinking. The general premise of the
book, that exotics represent a way out of our environmental doldrums, is
myopic. Pearce’s reasoning seems to be that he has conflated “the world is not
pristine and restoration is difficult…” with the alternative being that exotics
are positive and “we should bring them on”. Certainly we can question exotic
control efficacy, costs and conservation goals, but that does not mean that
exotics are necessarily the solution.
2)
Underrepresenting
the observed effects of some invasive non-indigenous species. Pearce’s book
is not balanced. The perceived benefits of exotics in this ‘New Wild’ are extolled while dismissing
some of the problems that invasive ones might cause. He says that exotics
typically “die out or settle down and become model eco-citizens” (p. xii). But
there is a third outcome that Pearce ignores –they move in and become unruly
neighbours. When he must acknowledge extinctions, he minimizes their
importance. For example when discussing Hawaiian bird extinctions: “The are only 71 known extinctions” (p. 12
–italics mine), or with California: “But only
30 native species are known to have become extinct as a result [of exotics]”
(p. 64 –italics mine).
He also implies throughout the
book that exotics increase diversity because “Aliens may find new jobs to do or
share jobs with natives.” (p. 113). The available evidence strongly suggests
that the numbers of species inhabiting communities has not increased over time (Vellend et al. 2013, Dornelas et al. 2014).
Which on the surface seems like a good thing, except that many communities are
now comprised of 20-35% exotics. This means that there have been losers.
Vellend and colleagues (2013) show that the largest impact on native species
diversity has been the presence of exotics. So, they do not necessarily find
new jobs, but rather outcompete some natives.
3)
Conservation
biologists and ecologists in the crosshairs. Pearce continually lauds those
like-minded, outspoken advocates of exotics while belittling ecologists and
conservation biologists who don’t agree with him. His disrespect for the
process of science comes in two forms. First, he seldom considers evidence or
presents opinions counter to his thesis. He gives a partial reason about this
bias; he says that ecologists (except for those few brave pioneering souls)
ignore novel ecosystems and the functional contributions of exotics (for
example on p. 13). This is demonstrably false (see next section). Pearce has
little affection for conservation biologists and mainstream ecologists. Both
groups are disparaged and dismissed throughout the book. Conservation
biologists get a particularly rough ride, and he never acknowledges the
difficulty of their task of balancing multiple priorities: extinction vs.
ecosystem function, habitat preservation vs. socioeconomic wellbeing, etc. For
example, Pearce states: “Conservation scientists are mostly blind to nature
outside of what they think of as pristine habitats and routinely ignore its
value” –again a demonstrably false assertion.
In a particularly galling
example, Pearce resorts to ‘guilt by association’ as an ad hominem attack to undermine the validity of opposing views. He
links conservation with eugenics: “Many conservationists of the first half of
the twentieth century were prominent proponents of eugenics” (p. 141). It would
be equally valid to state that most journalists were proponents of eugenics in
the first half of the twentieth century. Pearce, being a journalist, should see
this as a specious argument at best.
Ecologists share in this odd and
unfair derision. “Ecologists are tying themselves in knots because they refuse
to recognize that these novel, hybrid ecosystems are desirable habitats for
anything.” (p. 156). Unfortunately for Pearce, there are more than 4000 papers
on ‘novel ecosystems’.
4)
Misrepresenting
modern ecology and conservation.
Pearce attacks ecological science throughout the book and as an example Pearce
makes observations about the role of disturbance and refusal to acknowledge this
by ecologists “intent on preserving their own vision of balanced nature” (p.
144). However, disturbance has been a central component of community ecology
for the past five decades. Because of this balance-of-nature view, Pearce says
ecologists are not studying degraded, disturbed or recovering systems. For
example, with secondary forests, he says: “Yet the blinkered thinking persists.
Degraded forests and forests in recovery are almost everywhere under-researched
and undervalued.” (p. 157). Yet there are almost 9,500 papers on secondary
forests –highlighting the ecological interest in these widespread systems.
There are numerous such examples.
5)
A
black and white, either-or dichotomy. What
Pearce provides is a series of stark dichotomies with little room for subtle
distinction. He ties resilience and ecosystem wellbeing to the arrival of exotics,
without adequately assessing the drawbacks: “Nature’s resilience is
increasingly expressed in the strength and colonizing abilities of alien
species …we need to stand back and applaud” (p. xii).
Invariably in ecology, debates over ‘either/or’
dichotomies end up with the realization that these dichotomies are endpoints of
a continuum. This is exactly the case with exotics. Are they bad or good? The
answer is neither. They just are. Some exotics species provide economic
opportunity, ecosystem services and help meet other management goals. Some
exotics cause harm and impede certain priorities. Modern management needs to
be, and in many cases is, cognizant of these realities.
References
Alyokhin, A. 2011. Non-natives: put biodiversity at
risk. Nature 475:36-36.
Davis, M. A., M. K. Chew, R. J. Hobbs, A.
E. Lugo, J. J. Ewel, G. J. Vermeij, J. H. Brown, M. L. Rosenzweig, M. R.
Gardener, and S. P. Carroll. 2011. Don't judge species on their origins. Nature
474:153-154.
Dornelas, M., N. J. Gotelli, B. McGill, H.
Shimadzu, F. Moyes, C. Sievers, and A. E. Magurran. 2014. Assemblage Time
Series Reveal Biodiversity Change but Not Systematic Loss. Science 344:296-299.
Lockwood, J. L., M. F. Hoopes, and M. P.
Marchetti. 2011. Non-natives: plusses of invasion ecology. Nature 475:36-36.
Sandiford, G., R. P. Keller, and M.
Cadotte. 2014. Final Thoughts: Nature and Human Nature. Invasive Species in a
Globalized World: Ecological, Social, and Legal Perspectives on Policy:381.
Simberloff, D. 2011. Non-natives: 141
scientists object. Nature 475:36-36.
Vellend, M., L. Baeten, I. H. Myers-Smith,
S. C. Elmendorf, R. Beauséjour, C. D. Brown, P. De Frenne, K. Verheyen, and S.
Wipf. 2013. Global meta-analysis reveals no net change in local-scale plant
biodiversity over time. Proceedings of the National Academy of Sciences 110:19456-19459.
