Fig. 17. The number of subspecies of megachiropterans known from individual islands (number within a circle) is compared with the number of subspecies common to different islands (number without a circle). For names of islands see [Fig. 2].
Distributions of subspecies of polytypic species are summarized in [Table 6] and [Figure 17]. Generally, more subspecies are known from the larger islands than from the smaller islands (Guadalcanal with 5, Bougainville, Choiseul, and Santa Ysabel with 4, Fauro with 2.) The distributions of some subspecies can be used to judge the differential effectiveness of water gaps between islands. The distribution of Pteropus rayneri lavellanus and P. rayneri rubianus is an example.
Choiseul and Santa Ysabel are separated by about 50 miles of water (see [Fig. 17]) but have three subspecies in common (Pteropus rayneri grandis, Dobsonia inermis minimus, and Nyctimene albiventer minor.) Choiseul is about 50 miles from Kolombangara and about 35 miles from Vella Lavella, but shares no subspecies with these smaller islands although some species are shared (Tables [5] and [6]). From these data one can conclude that exchange of genes between populations on Choiseul and populations on Santa Ysabel is frequent but for some reason exchange of genes between populations on Vella Lavella and Choiseul and Kolombangara and Choiseul is infrequent. A series of small islands (Rob Roy, Wagina, and the Arnavon Islands, not named on the maps) connect Choiseul and Santa Ysabel in stepping-stone fashion (see [Fig. 17]). Possibly these small islands enhance movement of megachiropterans between Choiseul and Santa Ysabel.
Table 6. A Summary of Distribution of Polytypic Species of Megachiropteran Bats in the Solomon Islands. Only Islands Well Known Faunistically Are Listed.
| Subspecies | ||||||||||||||||
| P. atrata atrata | X | X | ||||||||||||||
| P. atrata anceps | X | X | ||||||||||||||
| Pt. a. solomonis | X | X | X | |||||||||||||
| Pt. a. colonus | X | |||||||||||||||
| Pt. a. grandis | X | |||||||||||||||
| Pt. r. rayneri | X | X | ||||||||||||||
| Pt. r. grandis | X | X | X | |||||||||||||
| Pt. r. rubianus | X | |||||||||||||||
| Pt. r. lavellanus | X | |||||||||||||||
| Pt. r. monoensis | X | |||||||||||||||
| Pt. r. cognatus | X | X | ||||||||||||||
| Pt. r. rennelli | X | |||||||||||||||
| D. i. inermis | X | X | X | X | X | X | X | X | X | X | ||||||
| D. i. minimus | X | X | ||||||||||||||
| N. a. bougainville | X | X | X | |||||||||||||
| N. a. minor | X | X | X | |||||||||||||
| Totals | 4 | 4 | 4 | 1 | 2 | 1 | 2 | 2 | 3 | 2 | 1 | 5 | 2 | 2 | 2 | 1 |
Florida, of the Nggela Group, is approximately halfway between Santa Ysabel and Guadalcanal. Pteralopex atrata anceps occurs on Santa Ysabel and on Guadalcanal but is unknown from Florida. Fauro lies between Bougainville and Choiseul. Pteralopex atrata atrata and Pteropus rayneri grandis occur on Choiseul and on Bougainville but are unknown from Fauro. As suggested earlier, small islands like Fauro and Florida possibly cannot support large fruit bats, although they probably would utilize these small islands when in transit between larger islands.
Fauro apparently is important to the distribution of the two subspecies of Dobsonia inermis and Nyctimene albiventer in the Solomons (see Figs. [9] and [13]). In both species, one subspecies is found in the eastern chain of islands and one subspecies is found in the western chain. Specimens of Dobsonia inermis from Fauro and Bougainville can be identified as the subspecies inermis whereas those from Choiseul are assignable to the subspecies minimus. Nyctimene albiventer bougainville occurs on Bougainville but specimens of N. albiventer from Fauro and Choiseul can be identified as the subspecies minor. Although interchange of genes occurs between populations on Bougainville and Fauro in the case of D. inermis, the population of N. albiventer on Fauro is at least partially isolated from the population on Bougainville.