Figure 1.

Frequency distributions of correlation coefficients calculated from species' abundances across study sites. A distribution shifted to the left of the solid line at zero would indicate density compensation. Observed distributions are shifted to the right of zero, indicating mostly positive correlations among bee species. (a) All pairwise values of Pearson's r for the 11 bee species in the New Jersey/Pennsylvania dataset. (b) All pairwise values of Pearson's r for the nine bee species groups in the California dataset. (c) Values of Pearson's r calculated between the abundance of each bee species and the summed abundances of all other species, for the New Jersey/Pennsylvania dataset. (d) Values of Pearson's r calculated between the abundance of each bee species group and the summed abundances of all other species groups, for the California dataset.