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Demography and dispersal in island and mainland populations of the deer mouse, Peromyscus maniculatus Sullivan, Thomas Priestlay

Abstract

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 ha were periodically cleared of mice on Samuel Island (206 ha) and Saturna Island (3102 ha) in the Gulf Islands of southwestern British Columbia., A similar experiment was conducted on the mainland at Maple Ridge, B.C., The average density of mice per hectare on Saturna (43.5) was twice that on Samuel Island (22.0) and nearly two and one-half times 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 than 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 five times faster than mainland animals, and Saturna growth rates were double those on the mainland. Island adult males showed very few aggressive tendencies in laboratory behaviour tests compared with the seasonal changes in aggression reported in the literature for mainland deer mice. Dispersal (or colonization) rate was reduced on the two islands compared with that on the mainland. Eecruitment of young animals occurred throughout the breeding season on the islands but was delayed until the end of breeding on the mainland. There was little difference in the demographic attributes of control populations when compared with those of colonist populations on either the mainland or the two islands. These results indicate that seasonal changes in aggressiveness of the adult population may be sufficient but not necessary to determine breeding density and seasonal changes in survival of juvenile deer mice., A more intensive study is reguired, but regulatory processes in populations of Peromy_scus oa&iculatus may be different on islands and perhaps should not be generalized over different geographic areas.

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