Living Habits of Reptiles

Reptiles are found almost throughout the world. This does not mean that any reptile is likely to turn up in just any place, or that any particular kind of reptile lives everywhere. It does mean that almost every part of the world is inhabited by reptiles of one kind or another and has something to offer them that they have made use of, be it in the water, the air, on the land or even under the land. Whether you are swimming or walking or climbing trees or digging in the ground, you are liable to encounter some sort of reptile, and you come upon them in every major region of the globe except Antarctica. More than anywhere else, reptiles prosper and abound in the tropics. That is where most of the reptile families are represented. Some of these tropical families have representatives in the Temperate Zones too, but only two families are peculiar to the cooler regions of earth--a minor group of worm lizards in California and the tuatara on its chill New Zealand islands. Reptiles are not very good at withstanding cold. Only three species reach the Arctic. They seem to be even less able to put up with conditions at high altitudes, and there are almost none of them in the highest mountain zones.

The distribution of a plant or an animal through the world is known as its range. Range simply means geographic territory occupied. The ranges of reptiles, like those of any creature, are molded by several kinds of factors. Some of these are historical, reflecting the age of the species or group and the geologic events that have occurred in the region occupied. Others are ecological, involving the tolerances and preferences of the creature in question. A close look at the ranges of number of reptiles—or of animals or plants of any kind—soon reveals that none of them, neither the young new species nor the old complex groups, appear to be occupying all the territory they should be capable of inhabiting. The reasons for this are diverse. Some are obscure, some clearly evident; all are worth thinking about.

Although complicated influences shape the ranges of animals the fundamental fact is that patterns of distribution have been built, over a period of time, by animals spreading into suitable and accessible territory. Thus, other things being equal, the older a form of life is, the bigger its range will be. But other things are hardly ever equal, and while this principle is a necessary one to know, the conditions under which it alone applies are almost never found. Extraneous factors nearly always complicate the simple fundamental relation between time and spread.

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