In Table 11, procyonid species are arranged in descending order with
respect to the number of major climates that are included in their
geographic distributions (Hall and Kelson, 1959:878-897;
Poglayen-Neuwall, 1975; Kortlucke and Ramirez-Pulido, 1982; Nowak and
Paradiso, 1983:977-985). Composite scores ranged from a high of 1.47
for _Procyon lotor_ to a low of 0.39 for _Potos flavus_, whereas
_Nasua nasua_, _Nasua narica_, _Procyon cancrivorus_, and _Bassariscus
astutus_ had intermediate values ranging from 0.64 to 0.79 (Table 12).
Figure 8 demonstrates that there is a direct relationship between the
number of climates these species occupy and their composite scores.
Regression analysis (Y = 2.68.X + 0.24; where Y is number of climates,
and X is composite score) demonstrates a high degree of correlation
between these variables (R = 0.94) and indicates that 89% of the
variance in distribution can be explained by composite scores. The
various combinations of adaptations expressed by these species do,
therefore, play a role in delimiting their climatic (latitudinal)
distributions.
_Procyon lotor's_ normalized scores were higher in all categories than
those of other procyonids. _Procyon lotor_, therefore, possesses those
traits that have allowed it to become the premier climate generalist
of the procyonid family. As an adaptive unit, these traits provide
_Procyon lotor_ with the physiological and behavioral flexibility
required to take full advantage of a wide range of climates and
habitats, and its distribution verifies that it has done so. Even so,
it is probably not fair to assume that this species represents a
perfect physiological match with climate over its entire distribution.
_Procyon lotor_ is, in many respects, still a forest-dwelling species,
and its ability to expand its distribution into other habitats such as
prairie and desert may well be due, in part, to its use of behavior to
take advantage of favorable microclimates in otherwise hostile
environments (Bartholomew, 1958, 1987). This feature of _Procyon
lotor's_ biology needs to be further examined.
TABLE 12.--Normalized and composite scores for selected procyonids.
(H_{br} = ratio of measured to predicted basal metabolism (Table 7),
C_{mwr} = ratio of measured to predicted minimum thermal conductance
(Table 7), D_{dr} = ratio of food categories actually utilized by
each species to total food categories eaten by all six species
(calculated from Table 9), r_{maxr} = ratio of calculated to
expected r_{max} (Table 10).)
----------------------+----------------------------------------------
| Normalized scores
Species |---------------------------- Composite[a]
|H_{br}/C_{mwr} D_{dr} r_{maxr} score
----------------------+----------------------------------------------
_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[b] 0.64
_Nasua nasua_ | 0.48 0.33 1.11[b] 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 = [(H_{br}/C_{mwr}) + D_{dr} + r_{maxr}]/3.
[b] 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 [.H]_{b}'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
H_{br}/C_{mwr} 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 T_{lc}, 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 D_{dr}
and r_{maxr} values than on differences in their H_{br}/C_{mwr}
ratios. This is supported by the fact that _Potos flavus_, which has
the lowest D_{dr} and r_{maxr} values, is confined to a single
climate, whereas _Nasua nasua_, _Nasua narica_, and _Procyon
cancrivorus_ each possess larger D_{dr} and r_{maxr} 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.
[Illustration: 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 [.H]_{b}, is found
in three climates, which indicates that it has greater ecological
flexibility than _Nasua nasua_, _Nasua narica_, or _Procyon
cancrivorus_. D_{dr} and r_{maxr} 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 (C_{mwr} = 0.85; Table 7), so its
H_{br}/C_{mwr} 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
H_{br}/C_{mwr} 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 H_{br}/C_{mwr} 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 [.H]_{b}, _Bassariscus astutus_ represents the pinnacle of
adaptation for climate generalization.