[APWG] Plants Alien Definition

[Wayne Tyson]

Quite. Note that I took care not to claim that "other" organisms did not exploit niches that meet their life requirements; all organisms are opportunists. Indigenous plants are, by definition, matched in their life requirements with the conditions under which they have developed adaptations (these niches are not always broad regions, but niche layers within them). Healthy ecosystems tend to resist invasion. Invasions may require "disturbances" to reproduce and persist. Just killing invaders, while satisfying to the practitioner, is not likely to prevent reinvasions unless the disturbed conditions which tipped the balance toward invasion also are corrected. One test of a true ecosystem restoration is its resistance to invasion. 

WT
  ----- Original Message ----- 
  From: Bill Stringer 
  To: Wayne Tyson ; apwg at lists.plantconservation.org 
  Sent: Monday, August 02, 2010 6:47 AM
  Subject: Re: [APWG] Plants Alien Definition


  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

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