Guide to the study of animal ecology

by Charles C. Adams

Ecology has no aim, but ecologists have. The problems of the ecologist are not fundamentally different from those of any other kind of naturalist. The superficial differences in aim are due to the different points of view, or methods of approach, rather than to any essential difference in the character of the problems.

The essentially biological core of ecology may be best shown by considering the relation which this science bears to other branches of biology, a relation which has been admirably expressed by the eminent physiologist, Burdon-Sanderson (’94, pp. 438-439), as follows:

“Now the first thing that strikes us in beginning to think about the activities of an organism is that they are naturally distinguishable into two kinds, according as we consider the action of the whole organism in its relation to the external world or to other organisms, or the action of the parts or organs in their relation to each other. The distinction to which we are thus led between the internal and external relation of plants and animals has of course always existed, but has only lately come into such prominence that it divides biologists more or less completely into two camps—on the one hand those who make it their aim to investigate the actions of the organism and its parts by the accepted methods of physics and chemistry, carrying this investigation as far as the conditions under which each process manifests itself will permit; on the other, those who interest themselves rather in considering the place which each organism occupies, and the part which it plays in the economy of nature. It is apparent that the two lines of inquiry, although they equally relate to what the organism does, rather than to what it is, and therefore both have equal right to be included in the one great science of life, or biology, yet lead in directions which are scarcely even parallel. So marked, indeed, is the distinction, that Professor Haeckel some twenty years ago proposed to separate the study of organisms with reference to their place in nature under the designation of ‘œcology,’ defining it as comprising ‘the relations of the animal to its organic as well as to its inorganic environment, particularly its friendly or hostile relations to those animals or plants with which it comes into direct contact.’[1] Whether this term expresses it or not, the distinction is a fundamental one. Whether with the œcologist we regard the organism in relation to the world, or with the physiologist as a wonderful complex of vital energies, the two branches have this in common, that both studies fix their attention, not on stuffed animals, butterflies in cases, or even microscopical sections of the animal or plant body—all of which relate to the framework of life—but on life itself.”

[1] These he identifies with “those complicated mutual relations which Darwin designates as conditions of the struggle for existence.” Along with chorology—the distribution of animals—œcology constitutes what he calls Relations-physiologie. Haeckel, “Entwickelungsgang u. Aufgaben der Zoologie,” Jenaische Zeitschr., 1869, Vol. V, p. 353.

The quotations from Brooks, on a preceding page, show even more explicitly the intimate relation which exists between biology and ecology. At first glance they may seem to prove almost too much—that biology and ecology are synonymous. They show at least that ecology is concerned with fundamental biological problems—the responses of organisms to their complete environments.

The relations which different branches of ecology bear to one another may be discussed under three headings, individual, aggregate, and associational ecology. These phases are superficially so distinct that students of one branch may be almost unaware of the existence of the coördinate branches and may not realize that each is a part of the larger unit.

Individual Ecology.—The study of individual ecology is the investigation of the development (process of formation) of the structure, function, and behavior of a given individual or kind of animal from the standpoint of its relations and responses to the complete environment. All ecologically significant facts should be considered. Such a study may be devoted to an animal, as, for example, a bumblebee, a crawfish, or a garter snake, and may be limited to a single habitat or locality, or extended throughout the entire geographic range of an animal. From this standpoint the individual studied becomes the hub of the microcosm, from which all relations and responses radiate. Most of the physiological studies of ecological bearing and many investigations of animal behavior have been made from this viewpoint. The organism is thus considered as an agent which, transforming and utilizing substance and energy, produces a varied number of physiological conditions and forms of activity, which in turn furnish the basis for the constant process of response between the organism and its environment.

Aggregate Ecology.—The study of aggregate ecology is the investigation of the ecological development, relations, and responses of animals based upon hereditary or taxonomic units, as in a family community, or in genera, families, orders, etc. These groups or aggregates are made the basis for the ecologic study, as a hive of bees, birds, dragon flies (Odonata), the genus Bombus. From this approach the activities and responses of the group are traced throughout all environments and associations within the area studied, or throughout the world, and its responses and adjustments to the whole environment receive primary attention. The hereditary or taxonomic unit is here the hub of the microcosm. Perhaps most of the contributions to ecology by the taxonomists are made from this standpoint. Here also the aggregate is considered as an agent or entity which produces many kinds of activities and adjustments to the environment.

Associational Ecology.—Associational ecology is devoted to the investigation of the development, interrelations, and responses of animals which are grouped or associated in the same habitats and environments. In this case the associates in a given association and habitat are considered as a unit, whose activities and interrelations and responses are investigated in the same manner as if it were a single animal. The interactions among members of an association are to be compared to the similar relations existing between the different cells, organs, or activities of a single individual. Such groupings have a composition which has developed into an arrangement, or “spacing,” of individuals within it, and which produces a particular plan or pattern, as a result of the innumerable responsive activities on the part of the individuals which live together. For example, when the animals living in a small brook, the littoral zone of a lake, in a colony of breeding gulls, or on the floor of a forest, are treated as a unit, the entire history of the animals in the habitat is considered as a response to the conditions of life.

In this form of study the association becomes the center of all radiating relations and responses. Such an association is an agent which transforms substance and energy, producing varied physiological conditions and responses in the continuous process of adjustment “which constitutes life.” The physiological needs and states of an association have as real existence in individual animals as have similar needs in the cell or cells which compose the animal body. The mere statement of the facts of such relations is enough to make valid such a comparison.