. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Systematics and evolution of Triodopsis • Vagvolgyi 239 R A N G E 0 F V A R I A T I 0 N 50 40 30 «. 8/« - £)•• • 0L08,'—!_ 10 15 20 NUMBER OF SPECIMENS 25 30 Figure 27. Scatter diagram of the range of variation in character index versus number of specimens in samples of 7r/o- dops/s fallax. Vertical scale in character index units. The hybrid samples have the widest range of variation, I. alaba- mensis, narrower, I. obso/e/o and f. fatlax, narrowest. Curves fitted by eye. dopsis which satisfy the above require- ments.
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Systematics and evolution of Triodopsis • Vagvolgyi 239 R A N G E 0 F V A R I A T I 0 N 50 40 30 «. 8/« - £)•• • 0L08,'—!_ 10 15 20 NUMBER OF SPECIMENS 25 30 Figure 27. Scatter diagram of the range of variation in character index versus number of specimens in samples of 7r/o- dops/s fallax. Vertical scale in character index units. The hybrid samples have the widest range of variation, I. alaba- mensis, narrower, I. obso/e/o and f. fatlax, narrowest. Curves fitted by eye. dopsis which satisfy the above require- ments. One is the strong armature in mountainous areas, the other, the smooth sculpture in valleys. Heavy armatures are observed in six spe- cies in Triodopsis. These are: T. triden- tata, grades C and D, rugosa, fraudulcnta, f. faUax, c. copei and m. midlani. Five of these fomis occur in mountainous habitats; thus, tridentota, ritgosa and fraudtdeyita in the Appalachians, /. falUix in the Blue Ridge Mountains, and m. midlani in the Cascade Range and the Rockies. The sixth form, c. copei, occurs however at low ele- vations, below 500 feet, in Texas (Fig. 20). The reason for its peculiar distribution is not known. Another anomaly is that T. /. fallax does not reach the peak region, but stops at about 1500 feet of elevation (Figs. 14,15). In spite of these two exceptions, it seems safe to conclude that the heavy armature is an adaptation to the mountainous habitat. This conclusion is supported by the case of T. tridentata, grades C and D, and fraiidu- lenta and /. fallax. These three forms occur strictly allopatrically in the Appalachian and Blue Ridge Mountains (Fig. 14). They do so probably because they are all moun- tain-adapted, and thus they would compete for habitats with each other if they oc- curred sympatrically. There is no explanation, however, of the significance of the heavy armature in moun-. Please note that these images are extracted from scanned page images
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