Re: [ECOLOG-L] EcoTone: Speaking of species and their origins

[Jeff Houlahan]

Hi all, not that Esat needs me to defend him but the list of species  
that can be 'googled' and identified as invasive scourges is, I  
suspect, longer than the list that actually are scourges.  One of the  
species that was identified in Amyarta's list, purple loosestrife, is  
a classic example.  You can go to hundreds of websites that will  
identify it as a species that competitively excludes native plant  
species and causes local extirpations.  The empirical evidence to  
support this claim is almost non-existent (or was a couple of years  
ago when I checked last).  There have been several reviews done on the  
topic and most conclude that there is little evidence that loosestrife  
causes extinctions at almost any scale.  This isn't to suggest that  
invasives are never a problem but my understanding of the literature  
is that there is lots of evidence of extinctions caused by invasive  
predators and relatively little evidence of extinctions caused by  
competitive exclusion (zebra mussels are probably an exception to that  
general statement).  I don't think it's a bad idea to actually step  
back and see if the investment in controlling invasive species is  
warranted.

Jeff Houlahan