Comparison of Adaptive Units
Dimensionless numbers for each of the four variables used in calculating composite scores were derived as follows. Ratios of measured to predicted values were used for basal metabolism (Hbr) and minimum wet thermal conductance (Cmwr). Thermoregulatory ability at low temperatures is closely related to the ratio Hbr/Cmwr (McNab, 1966). This ratio was used, therefore, to gauge each species' cold tolerance. For Dd we used the ratio of food categories actually used by a species to the total number of food categories taken by all species tested (Ddr). The ratio of calculated to expected intrinsic rates of natural increase was used to derive rmaxr. Composite scores were calculated as
| Composite score = [(Hbr/Cmwr) + Ddr + rmaxr]/3 | Eq. 3 |
The correlation between number of climates these species occupy and their composite scores was tested by linear regression.
Results
Body Mass