Under the terminology and definitions promoted by leading invasion
biologists including David Richardson and Petr Pyšek, 'alien' species and
their subset 'invasive' species are not routinely identified by their
ecological characteristics. Aliens are identified by subtracting historical
local biotas (meaning species lists) from recent local biotas, then deciding
which positive bits of the difference can plausibly be attributed to
dispersal via human agency. Invasive species are a subset of aliens: those
with the capacity to spread, identified simply by having done so,
somewhere.
Native species are literally those for which we have no record or
'suspicion' of a history of human dispersal. The sole criterion of
nativeness is therefore absence of evidence. Nativeness has nothing to do
with relative fitness, complexity of interactions, diversity yielding
stability, stability yielding diversity or anything else ecological. It has
only to do with reifying a particular view of humans and 'nature'.
On that basis, numerous studies have concluded that 'natives' and 'aliens'
are ecologically different (or not). At best they have shown some ways that
two different species or populations are ecologically different (or not) in
a specific context. That context is often barely defined in ways that
mainly reiterate the labels 'native' and 'alien'.
Comparing 'invading' species with established ones ('native' or 'alien')
confirms that a population new to some context is measurably growing and
spreading, while one less new isn't. The new one is exhibiting fitness under
prevailing conditions. That might (or might not) affect the fitness of
longer established species in in a discretely measurable way. There's no
reason they should be similar.
If we manage to demonstrate a strong effect, we still have to compare it to
a stipulated preference before declaring it desirable (or not). Even claims
about changing rates of change require stipulations. Departure from an
inferred previous rate carries no message in itself. Deciding change is
happening too fast for comfort is more about comfort than ecology.
Consensus on that score is still consensus about comfort.
Endorsing the general claim "alien invasive species threaten [something]"
stipulates a preference. Such endorsements routinely appear in the
introductions of peer-reviewed papers. Anthropologists or sociologists of
science might call the phrase a disciplinary talisman or password meaning
something besides the sum of its parts. Unfortunately, it also indicates
that the authors and reviewers of such articles share a significant
confirmation bias.
It isn't my place to dictate how anyone should feel about the current (or
any historic) array of human influences on biogeography - but those
influences are prevailing facts of life on this planet. Nor is it mine to
dictate whether anyone should promote fear and loathing of 'aliens' or
'invasives' with inflammatory caricatures. But it is my place to warn that
the bulk of modern peer-reviewed literature regarding the outcomes of
human-mediated dispersal is 'tragically flawed'– by the fact that invasion
biology's currency is vehement, almost competitive antipathy to its objects
of study. The defining "anti" stance makes invasion biology intuitively and
emotionally (thus politically and bureaucratically) appealing. But it also
makes it scientifically unsustainable.
The situation is becoming so obviously silly and overblown that
environmental journalists have begun contacting me to discuss their
misgivings and explore the issues, rather than asking for quotable quotes.
Think about it.
Matthew K Chew
Assistant Research Professor
Arizona State University School of Life Sciences
ASU Center for Biology & Society
PO Box 873301
Tempe, AZ 85287-3301 USA
Tel 480.965.8422
Fax 480.965.8330
mc...@asu.edu or anek...@gmail.com
http://cbs.asu.edu/people/profiles/chew.php
http://asu.academia.edu/MattChew
