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Diurnal Torpor and Its Relation to Food Consumption and Weight Changes in the California Pocket Mouse Perognathus Californicus

Vance A. Tucker
Ecology
Vol. 47, No. 2 (Mar., 1966), pp. 245-252
Published by: Wiley
DOI: 10.2307/1933771
Stable URL: http://www.jstor.org/stable/1933771
Page Count: 8
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Diurnal Torpor and Its Relation to Food Consumption and Weight Changes in the California Pocket Mouse Perognathus Californicus
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Abstract

Perognathus californicus is a nocturnal, burrowing rodent and in the mountains of southern California is locally distributed in association with the edge of grasslands. The thermal environment of P. Californicus is moderate. Temperatures on the surface of the ground at night range from 0 to 25@?C in summer. P. Californicus undergoes a daily period of torpor if its food supply is reduced below its ad libitum consumption. At an ambient temperature of 15@?C, 17 g of bird seed per 100 g body weight is required each day to maintain weight in the absence of torpor. If this food ration is reduced, mice on a 12-hr photoperiod with lights on from 0600 to 1800 hr enter torpor between 2000 and 0500 hr and allow their body temperatures to drop to about 16@?C. The earlier times of entry into torpor are associated with smaller food rations. Since the mean time of arousal is between 1100 and 1330 hr on all food rations, the duration of the torpor period increases as the food ration decreases. The torpor period in the laboratory may encroach on the nightly activity period and decrease the total activity of mice on rationed food. A linear relation exists between daily food ration, time in torpor, and weight loss. This relation can be explained theoretically and measures the food requirement for weight maintenance in the absence of torpor, the food savings associated with torpor, and the influence of food ration on the rate of weight loss. This information, together with data on population dynamics, could be used to estimate the population energetics of P. californicus.

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