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> Well if 'system in equilibrium' includes the regime of checks and balances
> that the resident must deal with you may need to rethink the above. What if
> a native or resident species has homegrown predators and parasites to deal
> with and the invader species comes in on a ship sans parasites from homeland
> and enters the resident species' turf sans the invader species normal array
> of predators? What will hold the invader in check as it competes within the
> niche that it shares to whatver degree with the resident? What if the
> invader carries a parasite or pathogen that it has become immune to over the
> course of many generations in its homeland and this parasite/pathogen can
> spread to the resident species or population without immunity or any means
> of defense? If a resident species has a tenuous grip on its niche and is
> just scaping by and an invader has the means to outcompete "hitting the
> ground running" with more efficient strategies and an explosive reproductive
> potential it could wipe out or seriously displace the resident species.
> I do not have much for actual evidence to support the above hypothetical
> situations, but the logic alone is possibly damaging to the resident always
> wins argument.
Absolutely - we have to bear in mind here that the principle is just
that, and adding factors to the scenario will indeed make it breakdown.
If as you say, the invader is unburdened by parasites or specialised
predators, because it is an alien species to the ecosystem, it may well
displace members of another species from their preferred habitat. Really
though this principle applies best within a species, when members of
that species are competing for resources. Also, to put the opposite case
for the sake of it, if the invader was not prepared for some aspect of
the resident's environment (say some generalist predator that the
invader had no experience of) then the ressie would have the jump on the
An example of the (entirely valid) scenario you describe might be the
demise of the marsupial wolf (Aussie), displaced I think by the dingo.
I'm not sure whether Dingos are just better all round (big fast etc.)
whether they came to Australasia unburdened by parasites/predators, or
were perhaps better at coexisting with humans, but something meant they
became the new residents in that niche.
Chris Taylor (firstname.lastname@example.org)
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