A demographic analysis of a southern snowshoe hare population in a fragmented habitat: evaluating the refugium model

摘要

The allegedly noncyclic dynamics of southern snowshoe hare (Lepus americanus) populations may be explained by a model invoking habitat fragmentation and facultative predation (the refugium model) under which animals dispersing from patches of preferred habitat fail to establish themselves because of predation by facultative carnivores. We compared the refugium model with a revised model invoking heavy on-site predation in preferred habitat as the proximal mechanism responsible for the stability of southern snowshoe hare populations. The survival and movements of hares in a fragmented habitat in central Idaho were monitored via radiotelemetry on 6 sites differing in habitat quality (indexed by understory cover) from 1998 to 2000. In support of the revised model, predation rates were high irrespective of cover availability or hare density, and predators did not kill dispersing animals disproportionately. Furthermore, predation was focused on small hares, suggesting that poor recruitment of juveniles may be the mechanism ultimately responsible for the damped dynamics of southern snowshoe hare populations. The low survival rates we measured suggest that the population under study was undergoing a marked decline. However, the observed decline, determined by comparing study-site population estimates, was less severe, implying that the persistence of local snowshoe hare populations in some areas of the species' southern range may be influenced by metapopulation dynamics. Specifically, southern snowshoe hare populations in small patches of usable habitat may be prevented from going extinct by the arrival of immigrants from similar nearby patches.