Hi all =20 I think the issue of extinctions is always a tricky one. Complete extinctio= n seems to be rare, particularly for plants, but has been found in many isl= and situations (e.g. Guam, offshore islands in NZ). In the case of plants t= here always seem to be a few individuals "hanging in there somewhere". In t= he long term (VERY long-term) the fossil record is right (in as much as it = indicates true species richness) - the invaders do speciate but the new com= munity is very different from what there was there before. Do we really wan= t to bequeath our children (and at least 100 more generations) drastically = impoverished natural environments? Spotted knapweed from horizon to horizon= ? Every island in the Everglades covered only in Old World climbing fern? T= his debate has led to some serious flaming once before.... =20 I also think that focusing on species is not necessarily very convincing fo= r the lay public or amateur interest groups. I think we can really make a m= uch stronger case by showing whether (or not) invasions alter ecosystem fun= ction and the delivery of ecosystem services (as described in general terms= in the Millennium Ecosystem Assessment). For example, is a marsh dominated= by Purple Loose-strife providing the same quality and quantity of water to= downstream users as the diverse native species community? At what level of= dominance is there a change (if any?) =20 My 2c worth =20 David
>>> "Kathleen S. Knight" <[EMAIL PROTECTED]> 11-Apr-2006 8:43:10 PM >>> I've been reading "Species Invasions: Insights into ecology, evolution, and biogeography" (2005) edited by Dov Sax, John Stachowicz, and Steven Gaines.= =20 Several of the chapters touch on this subject. In chapter 1, Bruno et al. = do a meta-analysis of invasion studies to look at the prevalence of competition vs. other interactions, and find that other interactions like predation and facilitation are just as important. They say that while competition reductions in abundance or size of natives, there is little evidence for extinction. In chapter 12, Vermej discusses historical invasions from the fossil record and what we can learn from them. One of his conclusions is that while invasions do cause extinctions in islands, in the long term they're not very destructive. Anyway, I think it's good reading and I'd recommend it to anyone interested in this subject. If anyone else out there has read it and has thoughts on it, I'd be really interested in hearing the= m! --Kathleen _______________________________ Kathleen S. Knight Dept. of Ecology, Evolution, and Behavior Dept. of Forest Resources University of Minnesota --=20 This message is subject to the CSIR's copyright, terms and conditions and e-mail legal notice. Views expressed herein do not necessarily represent the views of the CSIR. =20 CSIR E-mail Legal Notice http://mail.csir.co.za/CSIR_eMail_Legal_Notice.html=20 =20 CSIR Copyright, Terms and Conditions http://mail.csir.co.za/CSIR_Copyright.html=20 =20 For electronic copies of the CSIR Copyright, Terms and Conditions and the C= SIR Legal Notice send a blank message with REQUEST LEGAL in the subject line to [EMAIL PROTECTED] This message has been scanned for viruses and dangerous content by MailScan= ner,=20 and is believed to be clean.
