[APWG] Plants Alien Definition

[John Barr]

Wayne,

Your definition for Alien appears to be workable.

Your definition for Invasive is, in my opinion, uselessly broad.   
Using this definition, please name an organism that is not invasive?    
All organisms attempt to "exploit niches that meet requirement for  
life", otherwise they die.

Adding to what Bill said, alien invasive species can be problematic  
not only because they have "very effective fitness traits", but  
because they can arrive without their coevolved biologic controls.   
Citing one local example, fire ants arrived without phorid flies.    
The non native fire ants are not necessarily more fit than native fire  
ant species.  The natives are held in check by coevloved controls.  http://www.sbs.utexas.edu/fireant/Research%20Program.html 
   Given enough time (and damage to native ecosystems) some controls  
for the fire ant will be expected to evolve locally.    (For the  
record, introducing one species to control another is something that I  
greatly fear.  The track record for these introductions is extremely  
poor.  In my opinion, much harm has been done.)

Native invasives on the other hand would much more likely arrive with  
their coevolved natural controls.  Using Robert Layton Beyfuss's  
example of native plants expanding up hillsides with climate change,  
the coevolved natural controls would be expected to move with the  
native invaders.  An entire ecosystem would likely move upslope.  This  
does not change the likelihood that the higher elevation species will  
be displaced, possibly to extinction, but we would not likely see the  
monocultures that the most problematic alien invaders are capable of  
producing.

So, we need to narrow the definition of invasive. This is guaranteed  
to ruffle feathers.  I

n my opinion, the concepts of "alien" and "invasive" are creations of  
people and not creations of nature.  I believe that most of us would  
not consider the species that arrived on the Galapagos islands before  
man to be alien invaders, but certainly we would consider those  
species man brought to the islands to be alien invaders.

As a second pass, I would propose: An alien invasive species is one  
that arrives in a new ecosystem, as a result of human intervention, to  
the detriment of the native ecosystem.  An alien invader can benefit  
one or more native species, but it must be understood in the context  
of the entire ecosystem.

By my definition, brown tree snakes on pacific islands invade with the  
direct intervention of humans (planes and boats), the native  
ecosystems climbing elevation as a result of human caused climate  
change is an indirect intervention, but an alien invasion none-the  
less.  If the climate change is not human caused, they are not alien  
invaders.  Our beloved armadillos in Texas are not alien invaders  
because they, apparently, arrived without human intervention.

Yikes,

John

On Aug 2, 2010, at 8:47 AM, Bill Stringer wrote:

> Wayne, all organisms exploit niches that meet their life requirements.
>
> Invasive organisms invade, ie. they move in and aggressively  
> displace indigenous organisms and communities, thus decreasing the  
> species diversity.  They are successful because they have 1 or more  
> very effective fitness traits that allow them to exploit a wide  
> range of niche conditions, and deny/ reduce resource availability  
> for indigenous plants.
>
> Indigenous plants, because they have evolved in an ecosystem to be  
> compatible with many other species in that ecosystem, are not by  
> nature aggressive exploiters of resources in that "home" ecosystem.
>
> Ramble, ramble..........
>
> Bill Stringer
>
> At 05:35 PM 7/30/2010, Wayne Tyson wrote:
>> APWG:
>>
>> Definitions, to be useful in moving a discussion forward as opposed  
>> to spinning its wheels in polarizing dialectics, must be understood  
>> equally well and agreed upon by all participants. While it would  
>> seem unnecessary to engage in such a discussion with respect to  
>> "alien" and "invasive," I find that different posts seem to define  
>> these key terms differently. Therefore, I will propose some  
>> definitions (particularly as they relate to plants, but they should  
>> hold true for any organism). I ask that responses be confined to  
>> corrections to the definitions in the form of alternative  
>> definitions to keep the discussion from wandering off into the  
>> intellectual weeds. Separate footnote discussions about the  
>> reasoning that supports the definitions will be welcome, of course,  
>> but I respectfully request that we keep it simple and stick to the  
>> subject. It is not my intention to preserve these definitions, nor  
>> to start arguments; my hope is that definitions will evolve that  
>> will serve to communicate these concepts clearly. If no unanimity  
>> can be found or resolved, clarity in communication can still be  
>> served by using modifiers to define the kind of "alien" or  
>> "invasive" is intended. Anyone can define anything any way one  
>> wants, but only one person may understand that definition in the  
>> same way as the originator.
>>
>> 1. Alien (plant or other organism). An organism that did not evolve  
>> with other organisms in a given habitat.
>>
>> 2. Invasive (plant or other organism). An organism that exploits  
>> niches that meet its requirements for life.
>>
>>
>> Relevant comments:
>>
>> 1. All plants and animals reconcile their requirements for life  
>> with environments that meet them. Invasions may occur, but the  
>> invading organisms must "find" or create environments that are  
>> suitable for their requirements in order to establish and maintain  
>> populations that are able to reproduce.
>>
>> 2. Environmental change is the rule, and there are no exceptions.  
>> Change may be very fast or very slow, but nothing stays the same.
>>
>> 3. Organisms "track" changes within their sphere of influence/ 
>> capacity.
>>
>> 4. Analogously, human cultures acquire places to live in which they  
>> exclude others (aliens). In that process, other species exploit the  
>> effects of human cultural differences. Some species of rats, for  
>> example, have become almost entirely dependent upon human cultures  
>> for their existence and would be restricted to non-cultivated or  
>> undeveloped habitats and might not survive, at least in large  
>> populations, outside the boundaries of human cultures. Certain  
>> plants have become highly dependent upon human cultures for their  
>> existence ("crops" and "weeds"), and may have evolved as a result,  
>> perhaps to such an extent that they could not otherwise exist (or  
>> could be highly restricted to certain habitats) in its absence.
>>
>> I look forward to alternative definitions and supportive reasoning  
>> and discussion.
>>
>> WT
>>
>> _______________________________________________
>> PCA's Alien Plant Working Group mailing list
>> APWG at lists.plantconservation.org
>> http://lists.plantconservation.org/mailman/listinfo/apwg_lists.plantconservation.org
>>
>> Disclaimer
>> Any requests, advice or opinions posted to this list reflect ONLY  
>> the opinion of the individual posting the message.
>
> _______________________________________________
> PCA's Alien Plant Working Group mailing list
> APWG at lists.plantconservation.org
> http://lists.plantconservation.org/mailman/listinfo/apwg_lists.plantconservation.org
>
> Disclaimer
> Any requests, advice or opinions posted to this list reflect ONLY  
> the opinion of the individual posting the message.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.plantconservation.org/pipermail/apwg_lists.plantconservation.org/attachments/20100802/326e7cf3/attachment.html>