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Hi Lance & All, March 21, 2012
This is a swamp of questions that will predictably generate much heat
and little light. But interesting all the same.
I have come to believe, by lessons often learned the hard way, that if
you comprehend a system well enough to ask meaningful objective questions
then you know it as fully as it can be known.
And, in that same vein, if the questions posed are not entirely free of
prejudice then the conclusions will be nothing more than prejudice dressed
up in a suit and tie.
It was fashionable e.g. in the 50's to 'prove' that animals were simply
machines that processed stimuli and from these generated responses. And if
the experimenter tabulates every change in environment as a stimulus and
tabulates everything the animal subsequently does as a response then he/she
'proves the model to be true'.
After that preamble one can think about invasive species. To objectively
evaluate a suspect species one must get rid of the invasive or even alien
label (because both labels bristle with prejudice) and simply ask how does
this species behave and interact with soil, biota etc.
Some of these species, such as Rhamnus frangula, are weedy but if their
vigorous 'invasions' conserve nutrients and enrich a future forest soil the
overall effects may be positive even if use of the fruit as a favoured fall
bird food is discounted.
Many so called invasives, such as Polygonum cuspidatum (Japanese
Knotweed) and Lythrum salicaria (Purple Loosestrife) simply move onto
disturbed soil generated by that truly invasive species; Homo sapiens or are
moved by that species as highway fill etc.
Yt, Dave Webster Kentville
----- Original Message -----
From: "Laviolette, Lance (EXP)" <lance.laviolette@lmco.com>
To: <naturens@chebucto.ns.ca>
Sent: Wednesday, March 21, 2012 1:43 PM
Subject: RE:[NatureNS] Invasives
> 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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