The islands of the tropical Pacific as the homes of new genera and new species.—The significance of a large endemic element.—Synopsis of the eras.—The era of endemic genera.—The endemic genera of Compositæ.—Their affinities and mode of dispersal.—The mystery of the suspension of the dispersing agencies.—Mr. Bentham’s views.—The remnant of an ancient Composite flora in the tropical Pacific.—The dispersion of the Compositæ antedates the emergence of the island-groups of the Fijian region at the close of the Tertiary period.—Summary.
The Endemism of the Pacific Island Floras.
As far as the production of new species is concerned, the Hawaiian group presents the same contrast with the Fijian and Tahitian groups in respect of the flowering plants that it does as regards the ferns and lycopods. The proportion of endemic species, after excluding all introduced plants, is in Hawaii 80 per cent., in Fiji about 50 per cent., and in Tahiti 35 per cent. (see Table A). The same contrast is also displayed in the number of peculiar genera. In Hawaii there are, according to Dr. Hillebrand, 37 or 38, and in Fiji Dr. Seemann discovered 16; whilst, as we learn from Drake del Castillo, there are only 3 or 4 in the Tahitian Islands. (As will be pointed out later on, these numbers for Fiji and Hawaii have to be reduced, but the general inference to be drawn from them is not materially affected; see Table B.)
But if we look at the accompanying table (Table B) we notice that the flora of Hawaii is sharply contrasted with those of Fiji and Tahiti not only in the large proportion of endemic genera, but also in the large number of non-endemic genera with peculiar species, and in the small proportion of genera possessing no peculiar species. There is an endemic element of greater or less degree in about 70 per cent. of the Hawaiian genera, whilst in Fiji only about 53 per cent. and in Tahiti as few as 34 per cent. of the genera contain to a varying extent peculiar species. Another feature brought out in this table is the relative poverty of genera in the Hawaiian Islands. Fiji, though about the same size as Hawaii, contains nearly half as many genera again, whilst the islands of the Tahitian region, which in the aggregate amount to only one-third or one-fourth of the area of the islands of Hawaii, possess nearly as many genera.
Table A (Flowering Plants).
Proportions of Endemic Species in the Hawaiian, Fijian, and Tahitian floras, with those
for Samoa, Tonga, and Rarotonga added.
| Groups. | Number of species. | Number of endemic species. | Percentage of endemic species. | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Hawaii | 686 | 546 | 80 | ||||||
| Fiji | S. 617 | 288 | 47 | ||||||
| H.1086 | 620 | 57 | |||||||
| Tahiti | 315 | 112 | 35 | ||||||
| Samoa | 326 | 110 | 34 | ||||||
| Tonga | 285 | 17 | 6 | ||||||
| Rarotonga Island | 140 | 17 | 12 | ||||||
Remarks.—The materials for this table have been obtained from the works of Hillebrand for Hawaii, Seemann and Horne for Fiji, Drake del Castillo for Tahiti, Reinecke for Samoa, Hemsley and Burkill for Tonga, and Cheeseman for Rarotonga. The two estimates for Fiji are marked S. for Seemann and H. for Horne, the last being a rough preliminary computation made by Horne himself.
The results given are only to be considered as approximations liable to emendation, but as regards the proportion of endemic species in the several groups they no doubt illustrate fairly well the relative degree of endemism in the various archipelagoes. The results for Samoa, Tonga, and Rarotonga are merely added in order to enable a comparison to be made with sub-groups of a region and with solitary islands, the Hawaiian, Fijian, and Tahitian groups being regarded as the three principal centres of plant-life in the open Pacific.