TOP-DOWN VERSUS BOTTOM-UP AND THE RURITANIAN BEAN BUG

a recent article, Hunter uses the late George Varley and George Gradwe ll's long-term data on the winter moth (Operophtera brumata) and green tortrix (Tortrix viridana) populations to propose a method of quantif ying the relative importance of top-down effects (because of natural e nemies) and bottom-up effects (because of resource competition) in inf luencing population dynamics. We believe this approach is deeply flawe d. Using Varley and Gradwell's winter moth study, we show that the pro blems with Hunter's analysis lie in his misinterpretation of the popul ation dynamics and his inappropriate use of statistical techniques. We also emphasize the importance of distinguishing clearly between two q uite different things: firstly, top-down and bottom-up regulation of p opulations and secondly, the much simpler task of categorizing factors affecting changes in population density as either top-down or bottom up processes.