Matt has important points.
1. Alien is from somewhere else (that is, it's recent evolutionary
history does not include its current location) and natives are from the
place where they reside. AFTER that definition, we come to think that
aliens are different than residents, and we often find they are (not
surprisingly) and are not. Many marine species have unknown historical
ranges, so we have no idea where thare are from, and we call those
cryptogenic (hidden origins).
2. Whether organisms are bad for being alien is a judgement call, and
subjective. Sure, we can say that they cost money, but that only means
that they inconvenience us in some way - still subjective. Sure we can
say that they change community dynamics, but does the community care? If
evolution were allowed to run its course, I am sure that we would all
agree than in another million years or so, all the current aliens will
have become natives (adapted for where they are, and fitting - in some
way - in the community at that time). Thus, the VALUE statements about
aliens and invasives are invariably subjective.
3. Politics is about appealing to emotion to justify getting money (and
science is often politics). The trend that this breeds is to inflate the
value of whatever it is that we want money for. So, how do we justify
spending billions on invasive species control? Economically, not
scientifically.
My objective, scientific reasons for justifying the removal of invasives
and alien species are, in fact, subjective. After all, even Elton said
it well, although subectively - and I paraphrase - the continued
introductions of species will have the net effect of reducing
biodiversity, simplifying interactions in nature, and making the world a
less interesting place. I can see a future where ecologists study how
introduced species have adapted to their adopted homes, how new
interactions evolve in communities dominated by introduced species, how
biodiversity changes over time with introductions and extinctions. We
will have a whole new science of biogeography - rather than Hubbell's
"Unified Neutral Theory of Biodiversity and Biogeography" we will have
someone's "Unified Neutral Theory if Biodiversity due to Introductions
and Extinctions."
I can't help but (subjectively) think that such a place will be much
poorer than our natural world of today (and I recognize how much poorer
our natural world of today is compared to that of Darwin, for example).
Cheers,
Jim
Matt Chew wrote on 13-May-10 11:59:
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.
