Fig. 5.

Evidence supporting the ecological drift hypothesis in the experiment. (A) Frequency distribution of the number of species per container in the first and last years of the experiment. Vertical dashed lines indicate mean values. Inset shows the distribution of the differences in richness between the last and first years of the experiment (note that the data are based on the species found in the whole container and may, therefore, involve some edge effects). (B) Effect of habitat heterogeneity on compositional dissimilarity among metacommunities quantified using the Jaccard index of dissimilarity (in black; P = 0.043, one-tailed randomization test for differences in means) and on the relative frequency of H. spontaneum (in red; P = 0.0037, one-tailed χ² test). (C) Effect of the presence of H. spontaneum on the number of other species in local communities representing control and fertilized deep soils in heterogeneous metacommunities (P = 0.044, one-tailed t test). (D) Effect of increasing the effective area of local communities on species richness under the three treatments for which data were available (control, clipping, and NPK fertilization). Error bars indicate two SEs.