Key to Genera (continued 2)

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.

Rennell and Ontong Java are relatively isolated from other islands in the Solomons (see Fig. 17). Only one kind of bat (Pteropus howensis) is known from Ontong Java and apparently is endemic to that atoll. Pteropus tonganus geddiei, one of the megachiropterans that occurs on Rennell (Table 5), also is found in the New Hebrides and on New Caledonia (Table 4). This makes P. t. geddiei the only megachiropteran bat in the Solomons that is more closely related to bats on islands to the southeast of the Solomons than to bats on other islands of the Solomons, the Bismarcks, or New Guinea, to the north and west. The other species of megachiropterans (Dobsonia inermis and Pteropus rayneri) on Rennell are found also on other islands in the Solomons. It is to be noted that Mayr (1931) regarded the avifauna of Rennell as most nearly like that of the New Hebrides and New Caledonia. He suggested that the prevailing winds from the southeast have been important for birds that have reached Rennell. The New Hebrides and New Caledonia are four and a half times farther from Rennell than are San Cristobal and Guadalcanal. On first consideration a person might doubt that the winds would be favorable enough to compensate for the great distance between Rennell and the New Hebrides and New Caledonia. Darlington (1938) has used the formula X n/m to obtain a comparison of barriers of different widths. [X = the probability of an individual crossing a barrier of width m; the probability of an individual crossing a similar barrier of width n is the ratio n/m.] If this formula is applied here, one finds that winds from the southeast (that is, from the New Hebrides and New Caledonia) would have to be more than 100 times more favorable than winds from the northeast (from Guadalcanal and San Cristobal) in order to compensate for the distance of Rennell from the New Hebrides and New Caledonia. Even so, tropical storms with unusually strong winds, frequent during some parts of the year, possibly account for the present distributional pattern of bats and birds that live on Rennell.

Whatever the means by which bats of the species P. tonganus reached Rennell, the fact remains that specimens from Rennell cannot be distinguished from specimens of P. tonganus geddiei from the New Hebrides and New Caledonia, more than 500 miles to the southeast.

Note: An important and interesting paper on zoogeography of bats, which was published too late to be included here, is: Krzanowski, A., 1967, The magnitude of islands and the size of bats (Chiroptera), Acta Zool. Cracoviensia, 12:281-348.

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Transcriber's Notes

Obvious typographical and punctuation errors repaired. The "Key to Pteropus in the Solomon Islands" was moved above the beginning of the listing for Pteropus Brisson. Where figures or tables split paragraphs, they were moved above or below the split.

Typographical Corrections

Page Correction

797 Liuinuwu → Liuniuwu

809 intermis → inermis

824 adbiventer → albiventer

832 Gaudalcanal → Guadalcanal