Environmental harshness, heat stress, and Marmota flaviventris

Abstract

Yellow-bellied marmots (Marmota flaviventris) were studied at three sites in central Oregon. Juveniles substantially reduced their foraging activity when equivalent black-body temperatures exceeded their upper critical temperature. Inclusion of heat stress into estimates of environmental harshness drastically reduced the differences in available foraging time between high elevation and low elevation sites.

Predicting seasonal diet in the yellow-bellied marmot: success and failure for the linear programming model

“…The values (mean SD) used in this study (monocot: 17.95 0.34 kJ á g-dry A1 ; dicot: 17.74 0.71 kJ á g-dry A1 ) were calculated from Golley's (1961) data for April±July. These values are similar to those found by Webb (1980) for plants eaten by yellow-bellied marmots in Oregon (dicots only: 16.8±18.2 kJ á g-dry A1 ).…”

“…But was it a true maximum? Webb (1980) showed that at sites about 1000 m in elevation, heat stress constrains foraging time in yellow-bellied marmots. My data support this ®nding.…”

“…The time that a herbivore spends active is governed largely by the thermal environment (Webb 1980;Belovsky 1986). During the summer, marmots exhibit a bimodal activity pattern with peaks of activity during early morning and late afternoon (Webb 1980;Belovsky and Slade 1986).…”

“…During the summer, marmots exhibit a bimodal activity pattern with peaks of activity during early morning and late afternoon (Webb 1980;Belovsky and Slade 1986). In hot weather, ground squirrels also adopt a strategy throughout the day of shuttling between the burrow and the surface to assist in thermoregulation (Vispo and Bakken 1993).…”

Individual variation in the ability of Columbian ground squirrels to select an optimal diet

“…Due to the difference in food abundance and thermal environment, the enclosure and field foraging environments are very different, although the enclosure conditions were within the range found at other ground squirrel colonies (Belovsky and Ritchie, 1989;Webb, 1980). Consequently, the impact of the immediate foraging environment can be determined by comparing an individual's foraging behavior in these two environments.…”