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Index of Subjects Hi Paul, This is a very interesting question. I know David Webster has commented on invasives before as has Fred Schueler so I look forward to their input on the subject. Personally, I don't think there is a definitive answer. For example, should we limit our view to Nova Scotia, expand it to Canada or remove the political boundaries from the equation and look at North America. What time frame should we look at when evaluating a species? The last century, since Europeans arrived, since the last ice age or longer? Many species would have crossed into North America on the land bridge from Asia after the last ice age and even today there are at least some bird species that are 'colonizing' Canada from elsewhere. One provincial government that shall remain nameless but is composed of Toronto Maple Leaf fans, defines invasive species as "... coming from other countries or regions and moving outside their native habitat". Depending on how restrictive a definition is placed on "native habitat" this would seem to rule out a number of species that are often considered invasive. House Sparrows for instance. For the most part, they are certainly occupying the same habitat (broad definition) as they are in Europe. Perhaps a human assistance component must be added in for something to be considered 'invasive' but this isn't in their definition. Perhaps some things we consider invasive aren't really invasive in the truest sense of the word. Or perhaps a measure of negative impact to the existing, established species should be taken into account. If that were the case, House Sparrows would fall under the invasive category. To get back to your original question Paul, I think the time frame of consideration has been artificially restricted to within the past 100 years or so and the area of consideration is again artificially set by whichever group or agency is looking at it. Anything which has arrived within this time frame and in the area under consideration via some form of human assistance is popularly considered invasive. Having defined these parameters, personally I don't think there is a time limit after which the invasive becomes native. Once an organism has been labeled as invasive it stays as invasive. If it has escaped this scrutiny (e.g. earthworms through most of North America are of European settler origin I believe) they are thought of as at worst, non-native rather than invasive. All the best, Lance From: naturens-owner@chebucto.ns.ca [mailto:naturens-owner@chebucto.ns.ca] On Behalf Of Paul MacDonald Sent: Wednesday, March 21, 2012 10:29 AM To: Nature NS Subject: EXTERNAL: [NatureNS] Invasives Hi All We see a lot about invasives nowaday, birds, fish and so on. My question is how long does a species have to be in the province before it changes from an invasive to become a native? Seems to me the word has become similar to d*mn or other words the Maple Leaf fans will be using today LOL At some point the DNA of these new species can be differanted from DNA of other populations. Lake whitefish are a good example. Nobody can be sure if the ones we have in our midst are native or if they are descendants of stocked fish about 100 years ago. Have a nice day Paul
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