Living things cover the face of the earth from the torrid sands of the desert to the cold wastes of the Arctic, and every variation in environment develops a closely knit community of plants and animals. They are the ones best adapted to living where they do, or they may have been the first to arrive there, filling all available homesites and monopolizing the food and water supply to create a “closed” community. In each environment, a delicate balance is established between its various residents and between them and their surroundings. The study of all these interrelationships is called “ecology.” Beginning with the environment, we have seen in our brief look at the origins of Castle Neck how drastically an area can be altered as conditions change on the earth’s surface. Environment is affected in other ways, too. Man’s activity can change it almost overnight as a bulldozer clears land for a housing development, a dam alters the flow or course of a river, or careless disposal of a cigarette or campfire lays waste to acres of woodland. Or, as in the slow development of a forest, the growth of the trees themselves can change the environment, the maturity of one species whose seedlings require sunlight contributing to the growth of those better adapted to shade. If you should watch an old abandoned pasture over a period of many years, you could see environment gradually altered. First there are the mosses and grasses that create a fertile soil. Then come the Poplars and shrubs. As these grow they offer shade where Pines and, finally, the broad-leaved trees can flourish. This change in vegetation will also bring about a change in the resident animal communities. When parts of Castle Neck were rich farmland, specialized forms of life which thrive in that type of environment were abundant there. We have only to look at Castle Hill, just a few hundred yards from the dunes, or at some of the swamps that dot the Neck to see how different are the inhabitants from those of the dunes. On the Hill live the Oaks, Maples, Jumping Mice, Raccoons, and Toads, plants and animals that would be misfits indeed—if they could live at all—in the world of moving sand. Maples and Oaks, relics of the time when the dune area was fertile, may still be found dying and being buried over by drifting sand. Now it is a different community of plants and animals living here. The continually shifting sand and the scarcity of water limit the variety of life found, but each dune dweller is specially adapted to this homesite, and no matter how lush, green, and more attractive a neighboring meadow may look to us, many of these specialized organisms could not survive there at all.