Finally, Catania compared the vibrations produced by worm grunting and those of a mole burrowing. "The moles are quite noisy. Often you can hear the sounds of a mole digging in the wild from a few feet away," he says. Analyzing the geophone recordings of the two types of sound, he found that the worm grunting vibrations were more uniform and concentrated near 80 Hz whereas the moles produce a wider range of vibrations that peak at around 200 Hz. Nevertheless, there is a considerable overlap between the two.
According to Catania, one of the most interesting aspects of his results is the fact that the worm grunters, like the foot-paddling gulls and stomping turtles, appear to be benefiting from what evolutionary biologist Richard Dawkins has termed the "rare enemy effect." The moles, which can eat up to their own weight in worms each day, are one of the worm's most serious predators. It seems that human collections have a much lower impact on the worm population. So the worms have not changed their behavior as a result of the earth grunters' activity. There are so many moles in Apalachicola that a worm's best strategy is still to flee to the surface whenever there is a strong vibration. Usually it means there is a mole around, and it's the unlucky ones that meet the rarer human predators, and end up on a fishing line.
|Contact: David F. Salisbury|