Although all this is quite simplified, the first definition would pretty well fit a benign alien species, although some benign aliens do stick around without seemingly displacing natives -- possibly because they inhabit a human-modified landscape. An example might be the ringneck pheasant in agricultural landscapes.
The second would seem to define a small-scale or limited habitat invasive that is not noxious but still displaces some natives (or is that a contradiction in terms?). An example might be the adventive English daisy (Bellis perennis). The third would be a noxious invader and we can come up with many examples of this. See this U.S. Natural Resources Conservation Service website for a pretty good discussion of alien/invasive/noxious species definitions: http://www.pwrc.usgs.gov/WLI/wris1.htm Warren W. Aney Senior Wildlife Ecologist Tigard, OR 97223 -----Original Message----- From: Ecological Society of America: grants, jobs, news [mailto:[EMAIL PROTECTED] Behalf Of Lui Marinelli Sent: Thursday, January 10, 2008 9:50 AM To: [email protected] Subject: invasive I'm sure someone has already done this thinking and if so, please direct me towards it When is an invasive no longer an invasive? Presumably once the effect of an invasion is no longer "measurable" then one might say that the invader is no longer an invader but a resident. I can envision a variety of levels of invasion. 1. effect is minimal and the invasion is unsuccessful, the invader doesn't stick around 2. effect is measurable but not substantial, the invader nudges its way into the new ecosystem, everyone moves over and are effected (more competition for resources, carrying capacity may be reduced, etc.). The effect is measurable for a period of time, but then doesn't change...becomes stable. 3. effect is measurable and substantial, the invader bullies its way into the new ecosystem, everyone moves over, some get hit especially hard. The effect is measurable for a period of time, but then doesn't change...becomes stable. The 3 levels is a simplistic accounting for all that happens out there, but works as a general starting point, at least for me. Thoughts? Lui Lui Marinelli, PhD VP Contract Administration, SCFA Instructor, School of Renewable Resources Selkirk College 301 Frank Beinder Way Castlegar, BC V1N 3J1 CANADA (250) 365-1269 [EMAIL PROTECTED]
