The interactive effects of food and predators on reproduction and overwinter survival of arctic ground squirrels

1. We examined the effects of food and predators on population limitation i n the arctic ground squirrel (Spermophilus parryii plesius Richardson) in t he boreal forest of the south-western Yukon. We focused on ground squirrel reproduction and overwinter survival. 2. Squirrel populations were monitored by live-trapping and radio-telemetry from 1993 to the spring of 1996 on four control and four experimental area s (one predator exclosure treatment, two food addition treatments, and one predator exclosure plus food addition treatment). 3. Predator exclusion increased body condition, percentage lactating, perce ntage weaning litters, litter size, and doubled population density relative to controls, but had no effect on juvenile growth rate, overwinter surviva l, or juvenile emergence date. 4. Food addition advanced juvenile emergence date and increased adult body condition, percentage lactating, percentage weaning litters, litter size, p opulation density relative to controls (4-7 fold), but had no effect on juv enile growth rate or overwinter survival. 5. Predator exclusion combined with food addition increased adult body cond ition, percentage lactating, percentage weaning litters, and population den sity relative to controls (19-fold). 6. We conclude that arctic ground squirrels in the boreal forest are limite d by an interaction between food and predation, acting primarily through ch anges in reproduction, and that their impact on density was multiplicative.