Stages of earthworm invasion

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Joe

Re: Stages of earthworm invasion

Post by Joe » Tue Jun 21, 2011 3:05 pm

Amazing--- this is all a shock to me--- I've always thought well of earthworms because gardners seem to love them- I always thought they were beneficial to soil because they keep turning it over. Since I always saw them in my family's garden in the Berkshires- I just assumed they were in the forests too, though maybe not- I never look for them so it was a dumb assumption.

As bad as they may be- the ants are worse- where I am now, as I mentioned earlier, the ground is loaded with them. They're in the garden and everywhere in the lawn. I have no idea what they eat- the roots of the grass and garden vegetables? The lawn is terrible, barely alive. The soil is very sandy loam and it's disturbed because the entire area was ripped up for gravel and not property restored. I wonder if any creature eats ants? Or if there is any "natural" way to discourage them.
Joe

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KoutaR
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Re: Stages of earthworm invasion

Post by KoutaR » Tue Jun 21, 2011 4:35 pm

Joe and Lee,

Why the European earthworms have succeeded to re-colonize northern glaciated areas and the American earthworms not? It is hard to believe there would be so much differences between European and American members of such an primitive and ancient animal group as there were land bridges between Eurasia and North America up to 5 Ma. I have understood it so, that the advancing speed of earthworms to re-colonize new regions is very slow, but in Europe the ancient agriculture and direct human transport have aided the worms to re-colonize the northern areas. At least this paper seems to support this view:

http://www.uni-kassel.de/upress/online/ ... t.frei.pdf

See the beginning of the page 9.

Lee, have I understood the topic correctly?

Kouta

Joe

Re: Stages of earthworm invasion

Post by Joe » Tue Jun 21, 2011 6:03 pm

Kouta, then you are suggesting that in fact the earthworms had lived in northern areas of North America before the glacial period? If that's the case, then why are they considered "invasive" if all they're doing is returning to where they once lived? Of course some species came from outside North America.

The same can be said for some North American flora such as black locust which is often considered invasive in New England- once they are planted, they "escape" quickly to surrounding properties. But if they spread so quickly then they must have been here before the last glaciation- so why are they considered invasive? I don't get it.
Joe

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edfrank
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Re: Stages of earthworm invasion

Post by edfrank » Tue Jun 21, 2011 6:27 pm

If you assume there were earthworms in northern US and Canada prior to the glaciations, these were eliminated by the continental ice sheets and adjacent permafrost in these areas. Since that time native earthworm populations have migrated northward, but at relatively slow rate. The European and oriental earthworms were introduced at locations often hundreds of miles farther north than the current northward extent of the native earthworm populations. In some maps you can see the alien earthworms spreading from lakes where they were dumped by fishermen at the end of the day. This human mediated introduction has allowed these alien earthworms to colonize areas that might otherwise have not been reached by native earthworm populations for thousands of years.

With climate change and warming population boundaries are shifting northward. I don't know what the answer is to your specific example Joe. Extending your range northward as climate conditions change isn't the same thing, IN MY OPINION, as is a species from thousands of miles away suddenly making an appearance in the local forest as an escapee from a planting.

Ed
"I love science and it pains me to think that so many are terrified of the subject or feel that choosing science means you cannot also choose compassion, or the arts, or be awe by nature. Science is not meant to cure us of mystery, but to reinvent and revigorate it." by Robert M. Sapolsky

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James Parton
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Re: Stages of earthworm invasion

Post by James Parton » Tue Jun 21, 2011 11:22 pm

If only people who fish do what I do. Throw your unused worms in the lake after your day of fishing is through. You feed the fish and the invasive worms don't spread into the landscape.
James E Parton
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http://www.druidcircle.org/nod/index.ph ... Itemid=145

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KoutaR
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Re: Stages of earthworm invasion

Post by KoutaR » Wed Jun 22, 2011 9:51 am

I go further... Why are the European earthworms more cold tolerant and capable to invade boreal regions? In Europe, the earthworms probably re-colonized northern regions after glaciations with the aid of human transport. Were they initially more cold tolerant or did they develop the cold tolerance during the northward migration? I think such simple animals with short generations could well adapt themselves to new climate through evolution during a few thousand years. Of course, this is only my speculation.

Kouta

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Lee Frelich
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Re: Stages of earthworm invasion

Post by Lee Frelich » Thu Jun 23, 2011 10:14 am

Kouta, Joe, Ed, James:

Interesting discussion. The European earthworm species are generally more aggressive and less specialized in habitat and climate than the North American native species. There have been studies that show European species displacing North American species over time, although there seems to be a long period of coexistence in some cases (such as Konza Prairie in Kansas, and some old-growth forests).

The hypothesis that earthworms from Europe are more cold resistant because they were introduced throughout the continent by people is reasonable, but not proven. The distribution of Lumbricus in particular, is extremely closely tied to human activity in North America, and it is certainly reasonable to hypothesize the same for ancient times Europe.

Also, it has not been proven that earthworms in North America existed throughout the northern forests prior to glaciation. So, I try not to mention the hypothesis that forests across the northern U.S. were earthworm free because of the glaciers, but it has been a persistent hypothesis and I am frequently asked about it. If they didn't make it to the northern U.S. during this interglacial, they probably wouldn't have made it there in previous interglacials either, unless those were either longer or warmer (which the one 400,000 ybp might have been). I think that during the periods of peak of glaciation, which lasted tens of thousands of years for each glacial maximum over the last two million years, the North American earthworm species had plenty of chance to adapt to colder climates, since the boreal forest was as far south as Tennessee, and the entire temperate zone was packed into a small area between the boreal forest and Gulf of Mexico, and yet they don't seem to have done so. There must be some fundamental difference in the North American and European families of earthworms. Perhaps Lumbricus is like the dandelion of the earthworm world.

In any case, earthworm are ecosystem engineers on a vast scale and invasive earthworms are a major agent of change in forests throughout the world, whether native earthworms are present or not, since invasive species reach higher densities than natives, and are often in different functional groups that do different things to the soil than native species.

Joe--we don't know much about interactions between earthworms and ants, but I do notice that ant communities are much different and reduced after worms invade (I need to get an ant expert involved, but no luck so far). Of course, this won't help you since earthworms are not going to become abundant on your sandy soils. From a human perspective, ants may be more bothersome, but from an ecosystem perspective, I think the earthworms will have bigger impacts.

PS--the tornado Tuesday was a minor one, winds were only 70-80 mph and it only had a path 5 miles long, and didn't hit my building. So, it was pretty minor compared to the tornado that plowed through Minneapolis a month ago with 120 mph winds and a path 0.5 miles wide and 25 miles long (also missing both my apartment and office). That tornado destroyed a great blue heron rookery, but the herons have already moved to a new stand of cottonwood trees along the Mississippi, and established a new rookery.

Lee

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KoutaR
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Re: Stages of earthworm invasion

Post by KoutaR » Thu Jun 23, 2011 4:08 pm

Lee & others,

Probably earthworms did not exist throughout the northern US prior to the last glaciation or even prior to the Pleistocene, as they also in Europe do not exist or are very scarce in many forest types like in beech forests and boreal coniferous forests. It is a very good argument that probably they did not make it to the north during other interglacials because they did not make it during the Holocene. I was thinking the time before all the glaciations, i.e. the Tertiary.

It is also a good argument that the American earthworms had plenty of time to adapt to colder climates, when their environment became colder. But what if earthworms are capable to live in cold climates only in habitats created by man? I do not know if it is so, but then the American earthworms would have not been able to live in cold climates but the Europeans worms would have been able to do that in human created habitats and brought by humans. Again, this is only my speculation. Maybe there was a fundamental difference between the European and the American earthworms already before man, but somehow I have difficulties to buy the theory as our habitats are otherwise so similar but the human history so dissimilar.

Kouta

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Lee Frelich
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Re: Stages of earthworm invasion

Post by Lee Frelich » Fri Jun 24, 2011 10:49 am

Kouta:

I agree that during the Tertiary earthworms were likely present much further north. At that time they had much milder climates (perhaps as mild as the climates we will experience due to global warming in the next few centuries) and probably a few million years to move as far north as they were able.

Regarding the hypothesis about living in environments created by humans, the evidence is against this for North American species, which tend to do poorly in human disturbed areas, and the evidence is mixed for European species, which are very highly associated with humans and do well in human dominated ecosystems. However, they also do well in the Porcupine Mountains, and in areas of the Canadian boreal forest with almost no human influence other than introducing them. In these wild areas the entire landscape is not inhabited by earthworms mostly because they have not had time, and although some boreal forests also have unpalatable leaf litter, there does not appear to be a climate limitation for European earthworms in Canadian boreal birch and aspen forests other than the presence of permafrost.

Lee

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KoutaR
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Re: Stages of earthworm invasion

Post by KoutaR » Sat Jun 25, 2011 11:00 am

Lee,

Perhaps the American earthworms have not adapted to human disturbed areas because there is not such a long history of intensive agriculture in America?

Earthworms also live in northern Scandinavia in birch and aspen forests and some species, at least Dendrobaena octaedra, also in coniferous forests. But could the acidophobic taxa, like Lumbricus, live continuously in boreal forest without humans? Broadleaf forests in the boreal zone are naturally early seral forests after wildfires etc. Could Lumbricus live "semi-nomadic" life: persist is small birch stands and alluvial willow - alder bushes, and colonize more extensive areas after a large-scale disturbance?

Kouta

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