Living Habits of Reptiles (Part 4)

In the study of the geographical distribution of animals, the inhabitants of islands are of special interest. The kinds of animals that live on an island are a clue to its past, to its possible connections with land areas in past geologic times. The record of sedimentary rocks is often hidden under water or under other deposits. Geologists, doubtful about the character and scheduling of connections among islands, turn to the distribution of plants, and especially of animals, for guidance. The evidence provided is indirect and often ambiguous or muddled, but it is frequently the best available. To get trustworthy data from island animals, one has to be able to recognize cases of introduction by man. Geckos, for instance, are inveterate stowaways, and some of them have worked their way all over the tropics by just being on hand when man's cargoes were being shipped around the globe.

To some extent the same qualities that makes an animals a good stowaway may qualify it for more natural kinds of overseas dispersal, especially for traveling on rafts. Although there can be little doubt that many of the lizards that are widespread members of island faunae got there across water barriers, the exact method of their transportation is not known. Although this is probably quite true, it seems that the anole lizards, which are slim, light, arboreal and characteristic of island fauna, might be an exception. But for most island reptiles, raft transportation is surely a more important factor. It is a shame that the distribution of animals by natural rafts has been so little studied. There are various places in the world where much could be learned by direct observation. The south shore of Trinidad, where flood water from the Orinoco brings in all kinds of raft-borne waifs, would be a good place to undertake such a project.

To be continued...

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