Hank49:
But where do you draw the line? There is a huge gray area in which it would be hard to determine an "unatural" exotic introduction, vs natural.
Hence, it's more effective to not draw a line at all. If it's a newcomer, it needs to go. Natural or unnaturally-derived, it doesn't make much difference in the grand scheme. Only on evolutionary time scales may it conceivably matter, and even then, it probably
still won't matter if the vector is natural or unnatural. Resource managers have concerns on much more immediate time scales.
Toying with the natural trends in nature that would happen even if man were not on the planet in order to "preserve nature"?????
Yes. That is exactly it. We are safeguarding our remaining ecosystems by helping to retain their present community structure. Invasive species can tamper with community structure. That's a no-no.
Natural immigration processes of the "true" invasive sort (biome or gamma-scale level, vs. beta-scale) are quite rare. The cost/benefit tradeoff of spending the time to figure out what is natural vs. unnatural intrusion is simply not worth it, when one considers just how thin on the ground our funding and personnel are. There are also cases where ecologies are so damaged already, that ANY outside perturbation (natural or unnatural) is quite bad. I volunteer my services at one such "critical habitat" in Texas. We're trying to restore a habitat to what we *think* it once looked like. Contemporary wildlife managers for land-based systems are fully aware of this need to keep the
status quo, as evidenced by their much more advanced management techniques. Marine-based resource management is pitifully embryonic in comparison.
The very best technique known for habitat management is to leave the area alone. Sometimes in order to make this happen, we have to help with "border security". If it were possible to easily filter out natural vs. unnatural immigrants, we could be more flexible. But there
is no such easy way, and unnatural immigration is altering ecosystems across the planet at a nightmare pace. Taking this last factor alone into consideration, the solution is clear. Allow no invasive species. Pull thumbs out of butts.
Kill the lionfish!