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How long is something an "invasive" species?

Tim Smith

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Just curious how long does a fish have to be established before it loses it's "invasive" status.


This one's from Mark K on jim_b's carp thread. I think it's a pretty cool question.


Here's an opinion...


The two things that matter most about ecosystems are their ecosystem functions and services (clean water, fisheries, lumber, aesthetics...things we use), and biodiversity (different kinds of species, genotypes, ecosystems, habitats). As long as a new species modifies an ecosystem to the point that it is a threat to ecosystem function or biodiversity (i.e. it might cause extinction or cause the loss of a natural resource), then it's invasive. As the native biota adapt or die off and the system is "stable" again, then a species begins to deserve the term "native".


Carp have been here less than 200 years. That's still a new arrival compared to how long it takes for new species to evolve. There are still some species like blue sucker and river redhorse plus some minnow species that are hanging on by their fingernails and might be suffering from their presence. I'd say that one's still invasive.

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What's the present consensus on the zebra mussel, in particular their effect on the Great Lakes?


Still invasive. By far.


I would guess that the people having to buy new water intakes still consider them invasive, and it's probably true too that we haven't seen all the effects of zebra mussels yet.


Remember too that the Great Lakes are connected to the Illinois River which is connected to the Mississippi River valley. Billions of veligers enter the Illinois River from the Great Lakes (sometimes that many every day). The Lake Michigan zebra mussel population is considered a source population for the entire Mississippi basin. That makes them a threat to biota from the Rocky Mountains to Appalacians (although there are many stable sub-populations that have taken over that role). Malacologists expect there will eventually be numerous extinctions of native mussels due to the presence of zebra mussels.


...BUT...over time the way the biota around them are responding to them has changed a bit. Numerous fish species eat them now (ironcially including round goby, but also many natives). The changes in water clarity associated with zebra mussels seem to be a somewhat of a beneficial by-product, although the long term effects of that are still playing themselves out.

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