Monday, May 11, 2009

Imbalance, or In Balance?

Walk along any Idaho stream or river this spring, and you may catch a glimpse of the creature above: the American mink. Mink are common in Idaho, but never occur at very high densities.

They roam along streams, feasting on frogs, muskrats, crayfish and fish. They're a small predator, but quite efficient. Their sleek form allows quick movements and rapid attacks. But whether it's frogs or crayfish, stream creatures have evolved to better escape the mink's attacks.

Such is not the case in England, where mink are not native. Enough American mink have escaped from fur farms to establish substantial wild populations.

Which is bad news for England's stream creatures, particularly the water vole (pictured above).

On a recent trip to England, I saw one of these little mammals, which my brother described as a swimming guinea pig. They are, however, becoming an increasingly rare sight--the water vole is England's most rapidly declining animal.

Water voles are not adapted for the mink's hunting tactics, thus even a small number of mink can completely wipe out water voles from whole streams.

Removed from their native North American habitat, a mink becomes a pest.

Of course, European imports can have similar effects here. On the same England trip, I visited Cholderton Estate, a remarkable organic farm and wildlife conservation project owned by Henry Edmunds. (More on his extensive conservation efforts in an upcoming post).

Henry knows his plants, and showed me some of his favorite wildflowers in various meadows. I did a double take, though, when he described the spotted knapweed as "quite a nice plant." I've heard knapweed called many things, but "nice" is not one of them.

Of course, in England, it is a nice plant, because native insects keep it in check. In Idaho, it out-competes native plants and turns whole hillsides into knapweed monocultures.

Research often demonstrates that a "balance in nature" is a human construct. Natural systems ebb and flow, and are in constant states of change. Non-native species will likely prove to become more in balance with their habitats over time--although it may be in time frames much longer than humans are accustomed to thinking.

That said, the deliberate introduction of non-native species is avoidable and usually unnecessary. The imbalance caused by these introductions is not worth losing water voles, or native Idaho wildflowers. --Matt Miller

The spotted knapweed photo is by Kirt L. Onthank, licensed by the Creative Commons Attribution ShareAlike 3.0 License. Other photos are courtesy Wikimedia Commons.

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