Demography and Dispersal in Island and Mainland Populations of the Deer Mouse, Peromyscus Maniculatus

If dispersal is reduced on islands, then the demography of island populations of deer mice should be different from that of mainland populations. Areas of 1.1 hectare were periodically cleared of mice on Samuel Island (206 ha) and Saturna Island (3, 102 ha) in the Gulf Islands of southwestern British Columbia. A similar experiment was conducted on the mainland at Maple Ridge, British Columbia. The average density of mice per hectare on Saturna (43.5) was 2° that on Samuel Island (22.0) and nearly 2.5° higher than that on the mainland (18.7). The reproductive rate, as measured by length of breeding season, number of successful pregnancies, proportion of breeding animals, and number of recruits surviving to breed, was much higher on Samuel Island that on either Saturna or the mainland. Survival was lowest on Samuel Island, with little difference between the mainland and Saturna Island. Mice on Samuel Island grew more than 5° faster than mainland animals, and Saturna growth rates were double those on the mainland. Dispersal (or colonization) rate was reduced on the two islands compared with that on the mainland. Recruitment of young animals occurred throughout the breeding season on the islands but was delayed until the end of breeding on the mainland. Seasonal changes in aggressiveness of the adult population may be sufficient but are not necessary to determine breeding density in deer mice. Regulatory processes in populations of Peromyscus maniculatus may be different on islands.