. The Ecology of arboreal folivores : a symposium held at the Conservation and Research Center, National Zoological Park, Smithsonian Institution, May 29-31, 1975 . ENVIRONWIENTAL TEMPERATURE (°C) Figure 1. Body temperature and rate of oxygen consumption in 10 three-toed sloths, Bradypus griseus, as a function of ambient temperature. tance. The best estimate probably is that the lower limit equals 18°C and that thermal conductance is cc02/g hr°C, which is 75 percent of the value expected for a temperate mammal of kg. The low conductance is due to a dense wool undercoat and a long, c
. The Ecology of arboreal folivores : a symposium held at the Conservation and Research Center, National Zoological Park, Smithsonian Institution, May 29-31, 1975 . ENVIRONWIENTAL TEMPERATURE (°C) Figure 1. Body temperature and rate of oxygen consumption in 10 three-toed sloths, Bradypus griseus, as a function of ambient temperature. tance. The best estimate probably is that the lower limit equals 18°C and that thermal conductance is cc02/g hr°C, which is 75 percent of the value expected for a temperate mammal of kg. The low conductance is due to a dense wool undercoat and a long, coarse overcoat. Rates of metabolism equal to basal are found as low as 7°C in Bradypus; these values correspond to a lower limit of thermoneutrality equal to 11°C and a conductance of cc02/g hr°C, which is only 56 percent of the value expected from body weight. This low conductance, however, may simply reflect a reduced peripheral circulation associated with a low body temperature. Bradypus almost appears to regulate its rate of metabolism by varying body tem- perature, whereas most endotherms regulate Tb by varying the rate of metabolism. Choloepus hoffmanni, the two-toed sloth, regulates body temperature and the rate of metabolism in a manner similar to Bradypus (Figure 2). Its basal rate is equal to 45 percent of the value expected from weight (Table 1), which is similar to the 37 percent re- ported by Scholander et al (1950). Again, the lower limit of thermoneutrality is difficult to determine, as "basal" values can be found at ambient temperatures as low as 7 °C, although most of these values are associ- ated with low body temperatures. If the lower limit of thermoneutrality is equal to 24°C, thermal conduc- tance is ccOVg hr°C, which is 117 percent of the value expected from temperate mammals. How- ever, if the lower limit is equal to 12°C, thermal conductance of CCO</g hr°C, or 65 per- cent of the value expected. Choloepus appear
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