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

Abstract

Summary1. We examined the eects of food and predators on population limitation in the arctic ground squirrel (Spermophilus parryii plesius Richardson) in the 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 areas (one predator exclosure treatment, two food addition treatments, and one predator exclosure plus food addition treatment). 3. Predator exclusion increased body condition, percentage lactating, percentage weaning litters, litter size, and doubled population density relative to controls, but had no eect on juvenile growth rate, overwinter survival, or juvenile emergence date. 4. Food addition advanced juvenile emergence date and increased adult body condition, percentage lactating, percentage weaning litters, litter size, population density relative to controls (4±7 fold), but had no eect on juvenile growth rate or overwinter survival. 5. Predator exclusion combined with food addition increased adult body condition, percentage lactating, percentage weaning litters, and population density relative to controls (19-fold). 6. We conclude that arctic ground squirrels in the boreal forest are limited by an interaction between food and predation, acting primarily through changes in reproduction, and that their impact on density was multiplicative.

Mass-Balance Analyses of Boreal Forest Population Cycles: Merging Demographic and Ecosystem Approaches

“…For prey species, densities were sampled from sites throughout the valley (Folkard and Smith 1995;Karels and were assessed in a 100 km 2 intensive study area, and these densities were extrapolated to the entire area Smith 1994, 2001;Rohner 1996;Rohner and others 2001). For the mammalian predators, density estimates were made on a valleywide basis-that is, 400 km 2 (O'Donoghue andothers 1997, 2001).…”

Experimental manipulation of predation and food supply of arctic ground squirrels in the boreal forest

“…Spring population estimates were used to calculate rates of change. We then used a multiple regression to evaluate the importance of various demographic parameters (per capita reproductive output and overwinter survival, both from Karels et al (2000), and adult and juvenile survival during the active season) on rates of population change during our study. Changes in avian-and mammalian-predator numbers (calculated in autumn of each year) and snowshoe hare autumn population densities were also monitored from 1990 to 1995.…”

“…Hubbs and Boonstra (1997) examined the effects of predation and food on arctic ground squirrel populations during the early decline phase of the snowshoe hare cycle; among-treatment effects indicated that food was the major factor limiting ground squirrel populations, whereas among-year effects clearly indicated that predation must have accounted for major differences in adult survival during this time. Karels et al (2000) found that food supplementation increased adult and juvenile growth rates, body condition, and reproduction, and possibly interacted with predation to affect population densities of arctic ground squirrels in the low phase of the snowshoe hare cycle.…”

“…Ground squirrel populations have also responded to food supplementation (e.g., Columbian ground squirrels (Spermophilus columbianus), Dobson andKjelgaard 1985a, 1985b;Dobson 1995;arctic ground squirrels, Green 1977;Hubbs and Boonstra 1997). However, rarely have the interactive effects of food and predation on arctic ground squirrel populations been examined (Karels et al 2000). In this paper, we focus on the effects of predation and food supply on population density, adult and juvenile survival, and population growth rates of arctic ground squirrels from 1990 to 1995.…”

Long-day photoperiod interacts with vasopressin and food restriction to modulate reproductive status, and vasopressin receptor expression of male Golden spiny mice

“…However, in desert ecosystems, relying solely on photoperiod to anticipate habitat and ecological changes can certainly endanger reproduction and offspring success, as these harsh environments are generally characterized by unpredictable climatic conditions and food and water availability (Noy-Meir, 1973;Bronson, 1985;Bronson, 2009). Several environmental cues have been suggested to interact with photoperiod to form a more reliable network to prime the timing of reproduction in unpredictable environments, including precipitation, food availability and temperature (Bronson and Heideman, 1994;El-Bakry et al, 1998;Karels et al, 2000;Shanas and Haim, 2004).…”