The Ecology of Small Mammals in Urban Habitats. II. Demography and Dispersal

Abstract

(1) Demographic parameters were compared in two species of rodents, Apodemus sylvaticus and Clethrionomys glareolus, in three marginal (disturbed by humans) and three contrasting, good quality (undisturbed) habitat patches within the City of Oxford [Britain, UK] over a period of 13 months. (2) Population densities of both species, and survival and residency of A. sylvaticus, were greater in the undisturbed than in the disturbed patches. Most adults of both species achieved reproductive condition during summer, but a smaller percentage of sub-adults bred in the undisturbed than in the disturbed patches. (3) Long-distance movements between patches (100-500 m) were made principally by juveniles and sub-adults. For animals that moved between patches, minimum monthly rates of movement were 104.3 m for A. sylvaticus and 79.6 m for C. glareolus. (4) Both species re-established populations in experimentally cleared habitat patches within 6 months of removal. Re-establishment began earlier in patches that were close to source populatios, and was more rapid for A. sylvaticus than for C. glareolus. (5) Dispersal of A. sylvaticus occurred mostly during the breeding season from undisturbed habitat patches, and was probably a consequence of intensified spacing behaviour between the sexes and between juveniles and older individuals. Dispersal of C. glareolus occurred throughout the year from all populations. (6) Demographic flexibility is the major factor allowing both species of rodents to exploit urban habitat patches.