Island populations and gene flow in the deer mouse, Peromyscus leucopus

Lake Opinicon in southeastern Ontario contains 57 islands.In 1963 deer mice were found on 20 of these, in populations of one to 50. Fewer islands had mice in 1964,but two of these had much higher populations than in 1963. Mice were found primarily on the larger islands;degree of isolation seemed to be of little importance.Some islands with suitable habitat shad few or no mice, while others with apparently unsuitable habitats had relatively dense populations. Mice were introduced to 26 uninhabited islands, to help determine whether these islands could support populations.There was a high rate of loss, largely by emigration,but this was compensated for by breeding that apparently was stimulated by the colonization. Many colonists bred at a season when there was little breeding in natural populations. The rate of emigration was greatly reduced when an artificial food supply was put on the islands.