The influence of differential early social experience upon spatial distribution within populations of prairie deermice

Summary This study measured the influence of different early social experience upon the spatial distribution of populations of prairie deermice in a semi-natural environment. Successive populations of deermice were raised in the laboratory from weaning age (21 days) in isolation or in groups. At 10 weeks of age, 4 bisexual pairs from each social treatment were systematically released into different ·44 acre “mouse proof” plots. There were 8 experimental periods between June 6th and November 21st, 1958, during which 8 successive populations of 4 bisexual pairs were living in each of the 2 plots. Following release into the plots, the daily occurrence of the mice in nest boxes was recorded. Seventeen days after release all mice were taken to the laboratory and isolated for 36 hours. Each was then reintroduced into its home plot at a point distant from its previously established home area. The location of each mouse for the next 3 days was recorded. In the last 3 experiments young alien mice were retained in one-half of the nest boxes during the first night after reintroduction of the residents. At the conclusion of each three-week experimental period, all field experimentals and their laboratory controls were killed, weighed, and adrenals removed and also weighed. The differential effects of the social treatments were as follows: (a) The mice raised in isolation combined with others less often than the mice raised in groups; were slower in combining; and generally maintained a greater distance from their fellows. (b) The mice raised in isolation homed significantly more often than those raised in groups during the experiments when homing was established as a phenomenon. The introduction of aliens into one-half of the nest boxes had a more adverse effect upon the homing performance of mice raised in isolation than of those raised in groups. (c) The mice raised in isolation appeared to be less sociable and more spatially orientated than those raised in groups. (d) The data suggest that spatial patterns of distribution existent in the plots were largely determined by social interaction and were of greater significance to mice raised in isolation than to those experiencing the group treatment. Mice raised in isolation adapted less easily to changes in the social and related spatial stimuli than the more sociable group raised mice and, thus, more frequently returned to the earlier established spatial patterns. The introduction of aliens disrupted the social-spatial equilibrium existent in the plots. This disruption had a more severe and longer lasting effect upon mice raised in isolation than upon group raised, due perhaps to the inability of the former to adapt quickly to the environmental changes. Differences in social behaviour have been shown to be important factors determining spatial patterns of distribution within local populations of prairie deermice. The hypothetical interrelationships between social behaviour, spatial distribution, and availability of requisites of the physical environment as factors operating via physiological mechanisms to cause cessation of population growth were discussed.