THE study of the relationship of animals to each other is termed Ecology. Ecology means scientific field natural history. It is the same as natural history, but endeavours to be more accurate and precise. It deals with the law of living things in relation to other living things, and with the relations of animals to their environment, but is connected with a great many other subjects. It seeks to make use of, to give some definite form to, the very large number of observations which have been accumulated during the last few hundred years by field naturalists interested in live animals. Perhaps the greatest number of these observations have been made on insects.
Not much work has been done in animal ecology so far, as during the latter half of the nineteenth century zoologists, entomologists and naturalists generally, took more interest in other aspects of animals, and most of the older work dealt chiefly with attempts to help prove the theory of natural selection. Botanists, however, have developed further the scientific study of the relations between plants and their environment. Ecology is endeavouring to solve some of the urgent practical problems which keep cropping up everywhere as the result of man’s interference with the animal and plant life around him.
Different sets of animals are peculiar to different localities, and in the course of evolution the animals become more and more adapted to their surroundings, and are thus specially fitted for the conditions under which they live. They become adapted to climatic and other physical and chemical factors, such as the type of food which is available, the kind of enemies with which they have to deal, and to various communities or associations of plant.
The personnel of every community of animals is constantly changing with the seasons, the weather, and so on, though the changes may be gradual over immense periods, as they were during the advance and retreat of the Ice Age. On the other hand, the changes may be on a small scale.
J. D. Brown observed for several years the inhabitants of a hole in a beech tree, and the succession of the creatures who used it. In the first place, an owl used it for nesting purposes, but as the tissues of the tree grew round the entrance to the hole, it became too small for owls to enter, and their place was then taken by nesting starlings. Later the hole grew so small that no birds could enter, and it was occupied by a colony of wasps. Finally the entrance hole was completely closed up.
The writer also, for ten years, kept under observation a hollow birch tree and noted how soon a new ants’ nest became infested with ants’ guests. On August 27th, 1915, a fierce battle was witnessed at Woking between workers of the shining black ant and the subterranean yellow ant. The ants were all around the foot of a hollow birch tree in which the yellow ant was nesting; hundreds of yellow ants lay dead, many dead ones were fastened by their mandibles to the legs and antennas of live black workers, and some workers of both lay dead, joined inextricably together during their death struggle. A few live yellow ants were still fighting with the black ones, but the colony of the former appeared to have been practically exterminated.
The black ants finally established their colony in the hollow birch tree, building a carton nest at the roots of the tree. As it seemed a good opportunity to note how soon different ant guests came to a new nest, the tree was visited regularly for ten years, and by July 29th, 1925, thirty-eight different species of guests were noted.
The gradual extermination of our British red squirrel by the presence of the introduced American grey squirrel is an example of a change which is now taking place.