Figure 3

Coefficients of direct density dependence (solid circles) and direct climatic influence of the North Atlantic Oscillation (open circles) on the dynamics at individual trophic levels on Isle Royale, USA (1958–88). Bars indicate ± 1 SE. Note that the coefficient of direct density dependence at each trophic level includes a constant that reflects the predicted dimension of the time series at that level (see equations [4] and, e.g., ref. [[26]]); these constants were subtracted for the purpose of comparing the strength of statistical direct density dependence among levels. Results for Welch's approximation of the t-test for coefficients with heterogeneous variances [40] were, for direct density dependence: wolf vs. moose t_0.05,48 = 0.87, P > 0.50; moose vs. fir t_0.05,52 = 1.02, P = 0.30; wolf vs. fir t_0.05,52 = 0.07, P > 0.50; and, for direct climatic influence: wolf vs. moose t_0.05,48 = 1.67, P = 0.05; moose vs. fir t_0.05,52 = 1.97, P = 0.02; and wolf vs. fir t_0.05,52 = 0.15, P > 0.50.