Distance to Nearest Neighbor as a Measure of Spatial Relationships in Populations

but since logging operations and the burning and reburning that followed this logging, aspen and white birch have taken over the role as dominants. Thirty-two islands and 5 mainland areas were chosen for the study. Three species of hibernators, Eutamias minimum, Tamias striatus and Zapus hudsonias were taken on the mainland with only the Zapus being found on the islands. All six of the non-hibernating species taken were found on the islands. These include Microtus pennsylvanicus, Synaptomys cooper, Clethrionomys gapperi, Peromyscus rncaniculatus, Blarina brevicauda and Sorex cinereus. The degree of occupancy changed from 4 out of 21 islands in 1950 to 21 of 24 islands in 1952. Along with this increase in the proportion of islands occupied there was an increase in the number of species found on most of the islands although the average number of species found on each occupied island did not change appreciably. This increase in islands occupied was correlated with an increase in the density of the mainland populations. The water seemed to be an efficient barrier to travel during the summer but the ice of winter became a highway for dispersal of the various nonhibernating species in the winter. Considerable difference was found in the vulnerability of the several species to trapping. The Perornyscus were readily caught. The Clethrionomys were not as easy to capture as the former but were still readily taken. The Microtus, however, posed a different problem. They were difficult to capture and on two islands of about 2.2 and 4 acres respectively we were not able to elim-inate them after 16 days of trapping on a 15-foot grid. The populations of small mammals fluctuate quite widely and the several populations appear to be somewhat independent of each other. The islands appeared to lag behind the mainland in the development of their populations.