We monitored European ground squirrels (Spermophilus citellus) in a recreation area near Vienna, Austria, over a 7-year period to follow their population dynamics. Data were obtained by mark–recapture and daily checklists in an attempt to track the fates of individuals present in a defined area. Abundance of nonjuveniles present in spring decreased from 56.0 individuals/ha in 1992 to 6.3 individuals/ha in 1998. Litter size and yearling-male reproduction were inversely related to density, whereas immigration, juvenile survival, and proportions of nonjuvenile males exhibited a positive relationship. We conclude that the study population had been a dispersal sink and that ceasing immigration combined with poor local survival caused the population to crash. The temporal coincidence of these 2 effects indicates an extrinsic factor acting both on residents and potential immigrants.
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