Friday, March 09, 2007

Can an Endemic Species be Invasive?

In a recent post I referred to Red Cedar as an invasive species saying:
"So what we have in red cedar is a species, that has at least some of the characteristics of more traditional invasive species: adaptability to many habitats, suitability as an early successional species, rapid dispersal, ability to crowd out other species by direct competition for resources by altering microclimate and indirectly by allelopathy."
Today I received an interesting response from another Kansas Blogger, Gaia Gardener, who took issue with my characterization of Red Cedar as an invasive. Gaia argues:
"I think that labeling this plant as invasive is just an excuse by certain elements of the agricultural community to 1)justify attacking the species with herbicides and 2) to try to shift blame for groundwater and surface water shortages away from human overappropriation and overuse, often by those same agricultural interests.

"I know that redcedars are a nuisance, and I've pulled and cut out many a cedar seedling or sapling myself. In fact, we've just bought a new home, complete with a 5 acre pasture that has redcedars speckled liberally throughout it. And we've started cutting them out. But a weed is just a plant out of place, and I love redcedars in their proper place. Let's not put a negative label on a plant that encourages us to "throw out the baby with the bathwater," metaphorically speaking."
I have lots of sympathy for Gaia's point of view here. But successful weeds are a bit more than plants out of place. Successful weeds often have high reproduction rates, good methods of dispersal, rapid growth rate, often some attribute such as allelopathy that gives them an advantage of other species-exactly the sort of characteristics that we attribute to invasive species. Gaia and I think agree that the root cause of Red Cedar's invasive tendencies is poor land management, especially failure to understand the role of fire in prairie maintenance.

The fact is though that human activities are altering the ecosystems of our planet providing opportunities for endemic species with invasive (OK use weedy if you want) tendencies to spread and these species may prove to be less benign than Red Cedar.

For instance consider the diatom, Didymosphenia geminata recently discussed in a Christian Science Monitor report. The report notes that even where the species is endemic and usually a minor component of the flora of cold streams the diatom has become a major problem, prone to major blooms even in warm water streams.

Now outbreaks of this diatom historically occur from time to time, but appears that it's characteristics lend themselves to invasiveness in ecosystems that are excessively disturbed. Perhaps there is normally some keystone species or grazer that keeps this species down. This diatom also has recently invaded parts of the world such as New Zealand where the species is not endemic, as shown to the left.

Image from showing a young colony of "Didymo".

The United States' EPA has additional background information on this diatom at

So it seems to me that regardless of whether you call them invasive or weedy or tramp species, the fact is species with characteristics similar to classic invasive species are going to become a greater and greater issue for us as human mismanagement of formerly natural systems gets more intense.

By the way the individual organism is quite beautiful; it is the mats that are the problem. Here is an individual Didymosphenia from the EPA site. Could we have predicted that this individually beautiful diatom would respond to human disturbance as an invasive?

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