The spacing of rhesus monkey troops changes when a few group members receive delta 9THC or D-amphetamine

Free ranging troops of 18--25 rhesus macaques were housed in large enclosures where a few higher-ranking monkeys were given psychotropic agents (delta 9THC: 4 mg/kg or d-amphetamine: 2 mg/kg). Measures of group spacing were (1) mean distance between all animals. (2) daily variance in mean distance, (3) nearest neighbor distance, (4) daily variance in nearest neighbor distance, (5) index of clumping (S2/mean ratio), (6) % touching, and (7) % movement/2 sec. When 3--4 animals were drugged, the entire group moved closer together and distances were more variable. Acute changes after the first week of delta 9THC and effects after delta 9THC withdrawal were seen in two experiments. Chronic behavioral changes were found for d-amphetamine and in one delta 9THC experiment.