Ecological Succession

Fishes have definite habitat preferences which cause them to be definitely arranged in streams which have a graded series of conditions from mouth to source. 2. Beginning at the sources of the streams of the developmental series considered, we find the same species represented in essentially the same order in all the streams, in so far as the series of conditions is present. The only species in the youngest stream is the same as the species nearest the sources of the larger streams. 3. Migration of conditions for breeding is an important cause of fish migration, but fish reactions outside the breeding season may be often more important than movement of conditions necessary for breeding over the route of migration. Migration may even be due to reactions to a single factor. 4. Fish entering a stream will take a position in the stream suited to their ecological constitution without regard to the time and mode of origin of these conditions. 5. There is a succession of ecological types over a given point. Ecological succession is based on similar mores (physiology, behavior, habits and mode of life) of fish communities as a whole or comparable species of communities. 6. Physiographic analysis locates the animal in its environment and is but a method of studying the organism as a whole and a basis for proceeding to its analysis.1