Now, for the first time, a University of Georgia ecologist has been able to assign numerical estimates to the two approaches.
"It has been difficult to attach numerical values to the relative importance of predation and plant quality for a number of reasons," said Dr. Mark Hunter. "Although this kind of study has been done in lakes, we believe it is the first for any terrestrial species."
The research was published today in the Proceedings of the National Academy of Sciences.
Hunter's work has been an inventive combination of experimental analysis and detective work. It began with a re-examination of data collected by two British scientists, George Varley and George Gradwell. They collected data for some 16 years on the interactions of two insect species, the winter moth and the green oak leaf roller moth, that feed on English oaks in Wytham Woods near Oxford, England.
The research published by Varley and Gradwell has long been considered a classic of population ecology. And yet they left some tantalizing puzzle-parts with their long-term study. First, although they collected information on five different trees, they published their information as averages for all the trees and didn't consider each tree as an individual. Second, and most interestingly, they also collected information on the green oak leaf roller moth for some 18 years but never published their results.
Hunter speculates that one reason for the latter may be that
the data was extremely difficult to analyze, because it showed a
Contact: Mark Hunter
University of Georgia