Living Habits of Reptiles (Part 7)

Reptiles are well represented in the desert. Besides the sand-swimmers, there are many that live under rocks and in crevices. Others live in holes in the ground. Very few of these are underground foragers, however, since in deserts there is very little food, either plant or animal, beneath the surface. Most of them are nocturnal and come to the surface to hunt when the sun goes down, although in some cold deserts the routine is reversed. A well-made permanent burrow is a limited bit of favorable environment, and various kinds of interloping creatures are often drawn to it and live there more or less in intimacy and harmony. A classic example is the burrow of the gopher tortoise in the south-eastern United States, inhabited quite regularly by rattlesnakes, indigo snakes, two kinds of lizards, the gopher frog, various small mammals and a great many insects. Some of these guests go in merely to elude a pursuer.

Other reptiles habitually occupy the burrows of various other kinds of animals. Ant galleries and termite nests have special snake and lizard guests. On the dry Pacific slope of Central America much of the reptile fauna can be found at one time or another enjoying the hospitality offered by the burrows of tarantulas, leaf-cutting ants or armadillos.

The range of an animal can be shown on a map. Its habitat cannot. You can plot the distribution of the sort of topography or vegetation or climate in which an animal may be expected to occur, but this would show little about the character of the habitat. A habitat is a place; but it is also the sum of the conditions that make the place easy or hard to live in. These conditions are partly physical and partly biological. Some can readily be seen or measured, but some are subtle or hidden.

In the physical environment of the land one of the clear-cut problem encountered by reptiles, whose ancestors came out of the water, was the danger of drying up. It was this danger that was behind the evolution of the famous shelled reptilian egg, and the same danger imposed the selective pressures that brought changes in the body of the animal itself. It caused reptiles to evolve a horny epidermal covering to cut down evaporation of their body water. This covering, laid on in the form of scales or plates, does not prevent all loss of water. A reptile is perfectly capable of drying up, but the scales do slow down the process to the point where reptiles are able to live in the driest places on earth if they live carefully. The epidermal layer is periodically shed. In snakes and in a few lizards it tends to come off in one piece, the cast skin faithfully reproducing the surface sculpturing of the animal's body, even down to the spectacle over the eyes. In other lizards the skin comes off in patches. In some kinds of turtles the horny scales of the shell surface fall off, but in others they pile up, and unless worn away show peripheral growth rings. In regions with well-marked seasons these rings may be of some value in determining the age of the turtle.

Go To Page: 1 2

Articles in this Topic    Discussions in this Topic