| Species | Normalized scores | Composite[a] score | |||
|---|---|---|---|---|---|
| Hbr/Cmwr | Ddr | rmaxr | |||
| Procyon lotor | 0.95 | 0.95 | 2.52 | 1.47 | |
| Bassariscus astutus | 0.80 | 0.33 | 1.24 | 0.79 | |
| Nasua nasua | 0.48 | 0.33 | 1.11[] | 0.64 | |
| Nasua nasua | 0.48 | 0.33 | 1.11[] | 0.64 | |
| Nasua narica | 0.40 | 0.53 | 1.11 | 0.68 | |
| Procyon cancrivorus | 0.55 | 0.33 | 1.32 | 0.73 | |
| Potos flavus | 0.60 | 0.11 | 0.48 | 0.39 | |
[a] Composite score = [(Hbr/Cmwr) + Ddr + rmaxr]/3.
[] Value calculated for Nasua narica ([Table 10]) and used with the assumption that it must be similar to the value for Nasua nasua.
All five species with low Ḣb's have composite scores less than 1.0 ([Table 12]; [Figure 8]). Four of these five, Nasua nasua, Nasua narica, Procyon cancrivorus, and Potos flavus, have Hbr/Cmwr ratios that are 0.6 or less, which indicates they are the least cold-tolerant procyonids (McNab, 1966). These four species also are confined to either tropic, or tropic and subtropic climates ([Table 11]). This suggests that these species share a common thermoregulatory adaptation that represents a specialization to these climates. Attendant with this adaptation, however, is a high cost of thermoregulation at temperatures below their Tlc, and this must be an important factor in limiting their distributions to tropic and subtropic climates. Differences in their distributions within these climates, therefore, must hinge more on differences in their Ddr and rmaxr values than on differences in their Hbr/Cmwr ratios. This is supported by the fact that Potos flavus, which has the lowest Ddr and rmaxr values, is confined to a single climate, whereas Nasua nasua, Nasua narica, and Procyon cancrivorus each possess larger Ddr and rmaxr values and are found in two climates. Thus, Potos flavus, with its highly specialized diet and low reproductive potential, is the most ecologically specialized of these procyonids, and its distribution is limited to the single climate that can provide its requirements. Nasua nasua, Nasua narica, and Procyon cancrivorus are less specialized and thus show more ecological flexibility in their distributions.
Figure 8.—Relationship between number of climates in which a species is found and its composite score. Symbols for Nasua nasua overlap at coordinates (0.64, 2). Solid line represents linear regression of climates (Y) on composite scores (X): Y = 2.68·X + 0.24; R = 0.94.
Bassariscus astutus, the other species with low Ḣb, is found in three climates, which indicates that it has greater ecological flexibility than Nasua nasua, Nasua narica, or Procyon cancrivorus. Ddr and rmaxr are comparable for these four species ([Table 12]). This suggests that the greater ecological flexibility of Bassariscus astutus is derived largely from its greater cold tolerance. Bassariscus astutus has a more insulative pelt than these other procyonids (Cmwr = 0.85; [Table 7]), so its Hbr/Cmwr ratio is higher (0.80; [Table 12]). This, and its greater capacity for evaporative cooling (Chevalier, 1985), allows Bassariscus astutus to take advantage of a wider range of thermal environments than these other species. However, even with its higher Hbr/Cmwr ratio, the composite score for Bassariscus astutus is not much different than those for Nasua nasua, Nasua narica, and Procyon cancrivorus ([Table 12]). Consequently, Bassariscus astutus is found in more climates than would be predicted for it on the basis of its composite score ([Figure 8]). This suggests that either the Hbr/Cmwr ratio carries greater weight in determining distribution than is reflected in this analysis, or as has been described for some other species (Bartholomew, 1958, 1987), Bassariscus astutus may extend its distribution farther than expected via use of its behavior. In either case, for procyonids with low Ḣb, Bassariscus astutus represents the pinnacle of adaptation for climate generalization.