==================+==============+===========+=========================== Average lengths | Average | Average | in mm. at | length, | increment | Total, and beginning and | in days, | per day | number of each end of growth | of growth | in mm. | sex in sample period | periods | | ------------------+--------------+-----------+--------------------------- 97.0 to 126.6 | in 16.8 | 1.76 | 5 (1 [M], 4 [F] [F]) 103.3 to 127.3 | in 14.9 | 1.61 | 9 (3 [M] [M], 6 [F] [F]) 107.5 to 123.4 | in 11.0 | 1.44 | 8 (5 [M] [M], 3 [F] [F]) 114.0 to 132.3 | in 17.5 | 1.05 | 6 (5 [M] [M], 1 [F]) 118.5 to 136.0 | in 19.7 | .88 | 6 (3 [M] [M], 3 [F] [F]) 122.1 to 135.8 | in 16.2 | .85 | 15 (5 [M] [M], 10 [F] [F]) 129.3 to 145.5 | in 22.8 | .71 | 4 (all [M] [M]) 130.6 to 146.1 | in 19.8 | .78 | 12 (all [F] [F]) 139.8 to 147.5 | in 29.5 | .26 | 10 (all [M] [M]) 141.2 to 148.8 | in 26.2 | .29 | 23 (all [F] [F]) ------------------+--------------+-----------+--------------------------- [Illustration: FIG. 3. Changing numbers and composition (according to size of individual) in a population of voles on an area of approximately one half an acre that was intensively sampled with live-traps over periods of months. The population as a whole and the ratio of young to adults tended to be higher in spring and summer, but with little regularity from one year to the next. Weather was far more important than season in determining the population trend. Many of the voles recorded on the half-acre area ranged more or less beyond its boundaries.] [Illustration: FIG. 4. Weight in free-living prairie voles in a year-around sample from juveniles to large adults (grouped in length-classes of 6 mm. range, separate for each sex). In each sample mean, standard error, standard deviation, and extremes are shown. Note that mean weight is proportional to length, that in each size class females average heavier (because of pregnancy in some) and have a much wider range of variation in weight.]