DISTRIBUTION AND MOVEMENTS OF COLUMBIAN GROUND-SQUIRRELS (SPERMOPHILUS-COLUMBIANUS (ORD) - ARE HABITAT PATCHES LIKE ISLANDS

Habitat patches have been compared to oceanic islands, land-bridge islands, or continental land masses on the basis of inferences about interpatch movements drawn from distribution patterns. This study presents data on movements of Columbian ground squirrels (Spermophilus columbianus (Ord)) within and between patches of uncultivated habitat. Although squirrels moved between habitat patches, colonization of new habitats did not occur, because emigrants settled near other squirrels rather than in vacant patches. Patch occupancy was related to distance from a source of squirrels but not to area. Because of low colonization rates, ground squirrels may decline dramatically in agricultural regions where they are confined to patchy habitats if patches lose populations through extinction.