Jim Roper,
There's a difference between saying that two species are not
ecologically equivalent and saying that two categories of species are not
ecologically equivalent. If exotic species (as a category) were
ecologically equivalent to native ones, you would still find that every
species would differ from every other species by at least a few measures.
I'm saying that, as a category, exotic species are ecologically different
from native ones.
I am deliberately leaving this difference vague because the term
"ecologically different" can serve as an umbrella for all kinds of
differences that are relevant to interactions among organisms and between
organisms and their environment. Specific differences I would expect to
find include: (1) exotic plants have fewer insect herbivore species and
lose a smaller percentage of their biomass to insect herbivores than native
plants, and (2) exotic species have fewer pathogens than native species.
Similarly, I am using vague terms like "behave" and "matters" because I want
to include a wide array of phenomena, though I suppose you could reasonably
argue against the idea of species "behaving" on the grounds that behavior is
something individual organisms or closely connected groups of individuals
do.
I think most of the "confusion" in this conversation comes from the fact
that Matthew Chew and I just don't agree on whether there's any ecological
difference between exotic species and native ones. If they aren't, then
what's the point in investing time, money, and energy in controlling exotic
species or propagating natives?
William Silvert,
I didn't really mean to disagree with your fuzzy definitions. In fact, I
like them, and I think you could get some ecological insights by using those
definitions that you could miss with artificially clear distinctions. Also,
I've said more than once that, if we have to throw out any term with
indistinct boundaries, we won't find we have much at all left to discuss in
the field of ecology. We would not be able to talk about forests,
pollinators, the Mediterranean Sea, etc. I just wanted to emphasize, in
anticipation of certain "everything's the same as everything else" arguments
that have come up before, that there's a difference between categories with
fuzzy boundaries and categories that are totally indistinct and therefore
meaningless.
One of the keys to arguing against controlling invasive exotic species is
destroying the moral arguments that motivate people to bother in the first
place. To do this, it helps to use clever language to blur the lines
between categories to the point where it's hard to see that "native,"
"exotic," "invasive," and "non-invasive" have any meaning at all, except as
inflammatory terms used by people who want to manipulate your emotions. The
same basic approach is used to stop people doing anything about global
warming (e.g., the globe warms and cools all the time; without global
warming, earth would be frozen and hostile to life; why do we get excited
about human CO2 emissions and not volcanic ones?), species extinctions
(repeat the above, modifying appropriately), deforestation (repeat), and so
on. For that matter, blurring the lines between humans and everything else
("humans are part of nature") is very effective. For one thing, humans ARE
a part of nature, and we do cause some harm by saying we're not. For
another, it's easy to reduce this down to "humans are just another animal,"
thus ignoring our truly exceptional intellectual abilities and capacity for
empathy and moral thought. Anyway, I wanted to head off these sorts of
defitions-so-fuzzy-they-mean-nothing, not to disagree with the definitions
you gave.
As for oceans merging, I can't see a big ecological distinction between the
Mediterranean joining the Alantic without human intervention and humans
building the Suez and Panama Canals. If anything, I bet the
Mediterranean-Atlantic merger was more ecologically dramatic than the
canals, in that it probably changed the sea level and salinity of the
Mediterranean quite a bit, and the migration of species into the
Mediterranean was probably more rapid. Also, it can hardly be argued that
two oceanic mergers via human-made canal within a century is a rapidly
greater rate of mergers than one merger without human intervention in the
same amount of time. All my arguments about humans bringing more species in
greater numbers than other dispersal agents, and tending them more carefully
after dispersal, do not apply to these cases, as far as I know.
Jim Crants
