Exotic does not equal invasive!!! Exotic species are introductions (generally by humans [anthropochore]) that did not previously occur in the area.
Invasive species are those species that can readily take over a habitat when conditions are right. Classic exotic invasive species: fire ants in North America, European house finch, European starling. Classic native invasive species: sweet gum in the SE US cypress-tupelo forest, bullfrogs, sugar maples in oak hickory forests. Classic exotic noninvasive species: This is harder to come up with, but you could argue Mediterranean Geckos or cattle egrets. However, invasiveness is condition dependent and one could argue that any species can become invasive when the conditions are right. Malcolm McCallum On Sat, Jun 11, 2011 at 11:21 PM, Warren W. Aney <[email protected]> wrote: > Empirical evidence is not needed when observational evidence shows severe > and widespread adverse effects of invasive species on local systems. > Examples I know of include: > Reed Canary Grass (Phalaris arundinacea) monocultures replacing diverse > native sedge and forb wetland species mixes and reducing wildlife habitat > productivity. > Himalyan (Armenian) Blackberry (Rubus discolor) monocultures taking over > meadows, pastures and field edges and reducing native wildlife use. > Feral Horse (Equus cabalus) overuse of steppe grasslands and damage to > streambanks, increasing soil erosion and stream degradation. > Feral Pig (Suus scrufa) soil disturbance, vegetation removal and disease > transmission. > Knapweeds (Centaurea and Acroptilon spp.) taking over both disturbed and > undisturbed rangelands, replacing native grasses and forbs, and reducing > herbivory; some species also supress native grasses and forbs through > allelopathy. > Garlic mustard (Alliaria petiolata) takeover of forest floor systems by > outcompeting native species and effective allelopathy. > English and Irish Ivy (Hedera spp.) monocultural takeover of forest floor > and shrub systems, excluding native forbs and shrubs, adversely affecting > tree survival and severely reducing native wildlife use. > Cheatgrass (Bromus tectorum) invasion of rangelands outcompeting native > grasses by usurping soil water and promoting early wildfire (after which it > quickly reseeds). > > As is the case with many ecological concepts, "invasive" is a subjective and > relative term and not an absolute categorization. Some may consider > dandelions to be invasive and others may say they're just a weed (another > subjective term) adding diversity to lawn monocultures -- they are seldom a > "takeover" species causing localized extirpation of native species as is the > case with too many other prolific exotics. And not all "invasives" are > non-native to a particular continent or region -- but they are usually and > typically non-native to a particular adversely affected ecosystem. > > My conclusion: There have been successes in invasive control (e.g., tansy > ragwort), and there are numerous cases where lack of control efforts will > seriously deplete natural system diversity and value (both ecological and > economic). All of the species I've listed above, and many more, are worth > controlling or eliminating, and not all of this effort will make Monsanto > richer. > > Warren W. Aney > Senior Wildlife Ecologist > Tigard, Oregon > > -----Original Message----- > From: Ecological Society of America: grants, jobs, news > [mailto:[email protected]] On Behalf Of Jeff Houlahan > Sent: Saturday, 11 June, 2011 16:19 > To: [email protected] > Subject: Re: [ECOLOG-L] EcoTone: Speaking of species and their origins > > 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 > -- Malcolm L. McCallum Managing Editor, Herpetological Conservation and Biology "Peer pressure is designed to contain anyone with a sense of drive" - Allan Nation 1880's: "There's lots of good fish in the sea" W.S. Gilbert 1990's: Many fish stocks depleted due to overfishing, habitat loss, and pollution. 2000: Marine reserves, ecosystem restoration, and pollution reduction MAY help restore populations. 2022: Soylent Green is People! The Seven Blunders of the World (Mohandas Gandhi) Wealth w/o work Pleasure w/o conscience Knowledge w/o character Commerce w/o morality Science w/o humanity Worship w/o sacrifice Politics w/o principle Confidentiality Notice: This e-mail message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message.
