While strong predation on mussels had a consistent effect under all the conditions examined, the effects of weak predation were highly variable. In individual situations, weak predation actually had important effects on mussel abundance, but these effects varied from place to place and time to time.

"The effects were visually dramatic," Berlow said. "Some weak predation plots were dominated by mussels while others had none. So even though the effects of weak predation by whelks 'averaged out' to about zero, it would be a serious mistake to treat the effects as minor or insignificant.

"Sometimes what we consider to be noise is in fact an important part of the signal," Berlow said. "We just weren't listening right, we haven't always measured the right things."

In a management context, Berlow said, the experiment makes a case for managing whole ecosystems, since ecosystem health is likely to depend on the interactions of many species, the abundant ones as well as the rare ones, the keystones and the "not-so-keystones."

And in efforts to better understand ecosystem function, he said, researchers will have to begin paying far closer attention to seemingly unimportant plant or animal species.

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Contact: Eric Sanford
sanforde@ava.bcc.orst.edu
541-737-5359
Oregon State University
25-Mar-1999