Alien mollusk

Posted February 9th, 2010 by kcorliss. Comment (0).

Invasive species have a long and ignominious history of wreaking havoc on native ones once introduced into the landscape. It’s been going on forever and continues even today (think zebra mussel or leafy spurge).

Most invasive stories in this country come from the southern edges of the country where tropical species thrive in the warm moist climates of Florida and the Gulf Coast. Here’s another one: A recent U of Florida study is looking at the effects of an invader (island apple snail from South America) on a species highly dependent upon snails in its diet–the aptly named snail kite.

I’ve been lucky enough to see this Florida specialty on more than one occassion. It’s a raptor with a unique life history, so tied to the native apple snail that it is scarce outside the Everglades. Some might suggest this is a dead-end strategy for long term survival, it being so narrowly focused in its food choice. Perhaps.

The story is here from the U of Fla. News.

The problem, according to the study, is the invaders are huge–about the size of a tennis ball–and the kites have a difficult time holding them to eat.

Adult kites had trouble handling island apple snails but got enough to eat. Juvenile kites had more difficulty, possibly because they’re less experienced at holding and devouring prey.

The younger birds dropped invasive snails eight to 10 times more often than native snails, and it took them four times longer to attempt to eat the invasives, Cattau said.

The study suggests juvenile kites on a steady diet of invasive snails might burn more calories than they consume because they expend so much effort trying to eat the snails, said Chris Cattau, one of Kitchens’ graduate students.

“In some cases this could impact survival,” said Cattau, who co-wrote the paper.

It sounds alarming. And it might be. So far, however, the two snail species appear to coexist and not wage in a winner-take-all struggle for survival. That could be good news.

Here’s an interesting quote:

“There’s an 80 percent probability that in the next 30 years, snail kites will be extinct in the U.S., for all practical purposes,” Kitchens said.

Um, how did he arrive at that I wonder? In any case, this shows the tremendous upheaval such seemingly innocuous events can cause. Unintended consequences to be sure.

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