Intensity of antibiotic inhibition (mean zone size) among all inhibitory isolate pairs from the same (sympatric, open bars) and different (allopatric, solid bars) locations. There were n=9 to 10 isolates from each location, and a total of n=72–90 sympatric interactions and 540–590 allopatric interactions for each location. Pairs of bars from the same location marked with an asterisk differ significantly (Welch two-sample t-test t=−6.5; P<0.05). MN1, MN3 and MN5 represent Minnesota 1, 3 and 5, respectively; KS, Konza Prairie; PVB, Panama Volcan Baru; PFS, Panama Fort Sherman and PSC, Panama Santa Clara.