Mr. Mowbray, I would disagree with your claim that "we" ecologists (smile) agree that early succession natives are "invasive species" in the sense of the Ms. Faber's question. I was out of town during that last discussion (still trying to find the time to go thru it and comment), but my knee-jerk response to your statement is: lumping natives and exotics lumps different issues together and would be a mistake.
Ms. Faber, I have worked with the issue of invasive species often over the last 5 years in the field of restoration ecology. Obviously this is in the applied sense, and much of the conceptual work preceded my own. But I have also had to accept, reject or adapt the concepts I have learned. This has led me to develop an opinion on the subject... Of course what's needed is consensus, not more opinions; fortunately there are examples of majority consensus. One I am familiar with: in California State, the problematic species are called "noxious weeds". That term traditionally relates to plants that invade agricultural crops but the definition has widened as the State learned that plants can be significant negative impacts in other sectors of the economy. You can get more info on that program here: http://www.cdfa.ca.gov/phpps/ipc/noxweedinfo/noxweedinfo_hp.htm And here are several definitions of "weeds": http://www.blm.gov/ca/pa/weeds/weed_definitions.html It has been my experience that the term "invasive" is singularly subjective, and I can appreciate many (but not all) of those, ah, let me just say it - value judgment. Just as you pointed out, "bad" is a value judgment; so too is "invasive". Therefore, you will have to determine what your criteria are for making that judgment, preferably a priori. In your pursuit of a working definition of "invasive" I suggest you start by defining what is "native". The components of 'nativity' will guide your definition of what is not, and how that difference relates to the ecology of your system. And from that point you can look at an exotic species' impacts and determine your value judgment of what is "invasive". Components of nativity: the temporal component is important. Are you going to rely upon historical accounts or work with the paleoecologists on what was present in, say, the pollen record. For example: http://links.jstor.org/sici?sici=0002-9122%28197811%2F12%2965%3A10%3C111 7%3ATOOCSV%3E2.0.CO%3B2-6&size=LARGE Your question, "does how long ago it was introduced matter?" is a good one. Perhaps rather than set a "naturalization" time period rule, consider ranking other factors higher. If a species (or a direct ancestor...) is known by paleobiologists to have occurred onsite prior to human influence then you are safe in assuming it is a native. If not, then you may have to consider other factors in determining what "matters". Other factors... there is a good group in my State that deals with invasive plants: http://www.cal-ipc.org/ if you look at their invasive plant inventory it will state a short blurb for each category that I think is very helpful. Sorry I am not much help with the other Kingdoms but perhaps these concepts will be applicable in yours or at least wrap your brain around the concepts? All that and I didn't even get to use my favorite label: "Cosmopolitan Species"... (eucalyptus trees in California) but it is Friday! I'd be happy to discuss this more if you wish. David Thomson M.S. Restoration Ecologist/Wetlands Scientist Schaaf & Wheeler 100 N. Winchester Blvd., Suite 200 Santa Clara, CA 95050-6566 (408) 246-4848 x119 (408) 246-5624 (fax) [EMAIL PROTECTED] -----Original Message----- From: Ecological Society of America: grants, jobs, news [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Thursday, April 20, 2006 2:31 PM To: [email protected] Subject: Re: Definition of invasive species... Betty - We had a long discussion on this topic right here about a week or so ago. The discussion went on for about 10 days. I assume that this listserve has an archive which members can access. If so, you might want to take a look at the archives for the month of April (perhaps even the last couple of days of March, but if you look at the first week or so of April that should tell you whether you need to expand your search on either end). The discussion started when someone asked for suggestions for textbooks to use in teaching ecology to landscape architecture students. I think that we agreed that an invasive does not have to be introduced - that many early successionary species are invasives. Invasive exotics are introduced, and, I don't think it should make any difference how long ago they have been introduced although perhaps it shoujld be limited to the time period during which man has had the capability to spread invasive exotics to new environments. I would classify domestic animals which have the ability to escape and outcompete native plants and animals as invasives - feral cats perhaps. Certainly goats in places like the Galapagos. Bob Mowbray Tropical Forest Ecologist -----Original Message----- From: Ecological Society of America: grants, jobs, news [mailto:[EMAIL PROTECTED] On Behalf Of Betty Faber Sent: Thursday, April 20, 2006 1:19 PM To: [email protected] Subject: Definition of invasive species... I am working up some programs on the Asian long-horned beetle and more general aspects of invasive organisms. >From a cursory glance at the internet, and various publications, there seems to be many different definitions for "invasive species." Are there accepted views on this term? I would guess that an invasive is always introduced but does "how long go it was introduced" matter? Are invasives always "bad" and does bad have real meaning? Are domestic animals that are not indigenous considered invasives? Thank you for any discussion. Betty Faber, PhD Science Consultant Liberty Science Center
