the effects of variable interval (vi) schedules of reinforcement on the dispersion patterns and aggregate densities of a small population of rats was studied. eight male rats were permanently housed in an arena in which food pellets were delivered to eight food troughs when a bar press response followed a scheduled period of time. once every minute for each 30 minute session the dispersion and density of the rats in the arena was recorded. there were 20 sessions in which the rats were exposed to each of the following vi values; 5, 10, 20, *40 and 80. gradual changes in dispersion and density over ascending vi values were observed and formed curvilinear u-shaped relationships. this supports the contention that vi schedules of reinforcement influence the spatial and temporal dispersion and density of rat colony members. it is suggested that ecological data can be studied in terms of operant behavioural principles.