Experimental tests of trophic dynamics: taking a closer look

The relative importance of bottom-up versus top-down forces, and the effect of productivity on community dynamics continue to be of much interest to e cologists, Trophic dynamic theories are difficult to test, as they require explicit knowledge of the many organisms involved, as well as the nature of the interactions between them. The Oksanen-Fretwell (OF) theory, which sug gests that the relative roles of top-down and bottom-up factors vary with p rimary productivity, is well known in the literature, but is difficult to t est rigorously. Recently, two experimental studies have tried to test OF th eory. In this paper we discuss methodological problems associated with thes e studies that may weaken the conclusions drawn by the authors.