Search

The alternative-prey hypothesis predicts that predation on goose eggs will be most severe the year following a lemming peak. We tested this by investigating how predators of goose eggs responded to lemming abundance on the Kent Peninsula, Nunavut, Canada, where nest success of white-fronted geese (Anser albifrons frontalis) and Canada geese (Branta canadensis hutchinsii) fluctuates widely. The main predators of both goose eggs and lemmings are arctic foxes (Alopex lagopus), glaucous gulls (Larus hyperboreus), and parasitic jaegers (Stercorarius parasiticus). Foxes responded functionally to lemming density: in prime goose-nesting areas they spent less time foraging during the peak lemming year than during the increase, and were seen foraging in prime nesting areas less often during the peak than during the decline. However, numbers of fox sightings in the study area during the nesting period did not differ significantly among years. The total response (functional × numerical) of gulls was lowest at the lemming peak and highest during the increase. The total response of parasitic jaegers did not vary significantly among years. Hence, we predicted that the number of nests lost to all predators combined should be lowest at the peak and possibly highest during the increase. During the 3 years of this study, loss of Canada goose nests was lowest at the peak but highest during the decline, and annual losses of white-fronted goose nests varied little. In cycles prior to this study, nest loss was high in declines but not particularly low during peaks. Several factors may alter the functional and numerical responses of predators, obscuring the simple pattern of nest loss predicted by the alternative-prey hypothesis.

We tested whether dispersal of juvenile lemmings occurs at high population densities and whether predation risk affects movements of juveniles. The study was conducted in July and August 1996 on the Kent Peninsula, Northwest Territories, during a peak in the lemming cycle. We fitted 43 juvenile collared lemmings (Dicrostonyx groenlandicus) of the summer generations on a control plot and a predator-exclosure plot with radio transmitters and examined their home ranges and movement patterns. We tested the following hypotheses: (i) extensive juvenile dispersal will occur at high population densities, (ii) male juveniles will move greater distances than females, and (iii) juveniles will move greater distances in the absence of predators. We rejected all these hypotheses. All juvenile collared lemmings remained in the vicinity of their original home ranges. Home-range sizes of all juveniles were similar, the mean size being 100 m2. Mean and maximum distances moved were similar among all juveniles. However, juveniles moved less frequently on the control plot than on the exclosure plot. Juvenile collared lemmings do not disperse at high densities. The lack of dispersal may have been the result of avoidance of confrontations with other lemmings, and may also have been related to delayed breeding, since most juveniles and subadults did not mature in late summer. Differential predation risk or predation mortality may have had no effect on the distances moved by juveniles or may have been masked by strong density effects on both plots.