Anthropogenic influence can be the direct agent of "invasiveness" (as in actively introducing a species into a new area, willingly or not) or the indirect agent (as in changing the climate and land use patterns so that conditions change and new environments become available for species). In addition, as WT pointed out, there are also changes that are not anthropogenic and that can create conditions for the "invading" organism to thrive. If there's one thing we can count on is the fact that, given the right conditions, species WILL disperse and reproduce. So, I would argue that where humans are indirect agents or other events create conditions for "invasives" to thrive, it may be very hard to control or avoid invasiveness/dispersal, since species are only doing what they are supposed to do. Unless we can change the climate back or turn land uses to previous states, or change those events that led to the right conditions in a certain system, species will move, and some will cause damage to the native system and some won't. Those that cause damage are invasives, those that don't are just, well, dispersing, even though both are just doing their thing - and sometimes things just are out of our control (pun intended). I mean, is it really possible to stop a species from naturally dispersing? How about 100 species? For how long and at what cost?
Astrid Caldas, Ph.D. Climate Change and Wildlife Science Fellow Defenders of Wildlife 1130 17th Street N.W. Washington D.C. 20036-4604 Tel: 202-772-0229 | Fax: 202-682-1331 acal...@defenders.org | www.defenders.org http://experts.defendersblog.org/author/acaldas -----Original Message----- From: Ecological Society of America: grants, jobs, news [mailto:ECOLOG-L@LISTSERV.UMD.EDU] On Behalf Of Wayne Tyson Sent: Sunday, April 22, 2012 4:39 PM To: ECOLOG-L@LISTSERV.UMD.EDU Subject: [ECOLOG-L] Ecosystem function Re: [ECOLOG-L] Invasion, or progression? Josh et y'all: Note: There once was a teacher who would grant an "A" to any student who asked one intelligent question, regardless of whether the question implied knowledge or ignorance. (Sigh . . .) "Invasion" means that the dimensions of the habitat (temperature, radiation, Ph, nutrients, water, etc.) favor the "invading" organism. This requires the presence of a propagule or other reproductive unit (e.g. a male and a female in the case of sexual reproduction) and conditions favorable to the "invading" organism's survival, reproduction, and persistence as breeding population. Such conditions may exist at the time the propagule is introduced, or they may be created by various forms of disturbance, which may or may not be anthropogenic. All this occurs within the energy/nutrient cycle. The rub comes in with culture. Culture may take certain advantage of the energy/nutrient cycle, but cultivation radically alters the habitat. Irrigation and fertilization bring elements of habitat into one system from another--robbing "Peter" to pay "Paul." This alters the "donor" system too, with consequent changes "there" too. WT PS: Josh, what do YOU mean by "progression" and "ecosystem evolution?" ----- Original Message ----- From: "Joshua Wilson" <joshua.m.wils...@gmail.com> To: <ECOLOG-L@LISTSERV.UMD.EDU> Sent: Sunday, April 22, 2012 7:01 AM Subject: [ECOLOG-L] Invasion, or progression? > Good morning, > > I know that invasive and non-native species have been getting a great deal > of attention lately, and justly. I understand the basic ecological > impacts > and concerns invasive species cause, and the disruption of the native > system. My main question is: > > Why are invasive species considered a nuisance, instead of adaptation, > progression, or perhaps ecosystem evolution? > > Yes, human beings have been a main cause of the large majority of these > invasions. But even so, I feel we are part of the natural system. If an > invasive species exhibits more plasticity or is more competitive and > adaptive than the present species in an ecosystem, does that necessarily > imply catastrophic impacts? There are multiple arguments against this, I > know, many of them strong and verified. I am not an advocate of invasive > species dominated ecosystems, but am just curious why this change and > shift > is considered so extremely detrimental. I feel that stable and > progressive > change and adaptation is the basis of a strong ecological system. > > I would welcome any thoughts on this, or perhaps to start a discussion. I > am still an undergrad, so my question may seem farfetched and ridiculous > to > some. Even so, just something to ponder on a lovely Sunday morning. > > Have a good day all, > > Josh Wilson > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 10.0.1424 / Virus Database: 2411/4950 - Release Date: 04/21/12 >
