PHYSIOLOGY AND ECOLOGY 35 
same species (man). He suggests that the social psychology of man 
may be traced to the inter-psychology and physiology of the lower 
animals. If this is true, then we can be more certain that the inter- 
psychology of the higher forms has developed from the inter-physiology 
of the lower forms (55 and citations). To this should be added the 
behavior between different species, while acting or living together as 
one. In the steppes ecologically similar animals frequently act as one 
species. Mr. Roosevelt has said that one of the most interesting features 
of African wild life is a close association and companionship often seen 
between totally different species of game (3). Mr. Roosevelt shows 
the zebra and hartebeest herding together. (6) Inter-mores physiology 
(between ecologically dissimilar forms, or antagonistic forms).—The 
relations of animals of different size, habits, etc., to one another involve 
some of the most striking features of behavior. Much of the behavior 
which tends to protect animals from enemies falls under this head.! 
In all cases of modification of behavior by the physical environment 
or by relations to other animals of the community and in all cases where 
the habitat is selected, the habitat is the mold into which the organism 
fits. The study and analysis of the habitat is a necessity as soon as the 
selection of habitat and the adjustment of behavior and physiological makeup 
to the environment are shown to be general facts. Since habitats are differ- 
ent, animal communities occupying different habitats are physiologically 
different for the reasons just given. 
The relations of the animals which make up communities are 
relations of life histories. The life histories of the different species are so 
adjusted to conditions that all animals do not reach maturity and greatest 
abundance at the same time. Some species continue throughout the 
season; for example, mammals because of their long lives, and some 
species of aphids or. copepods because of their great fecundity and 
peculiar physiological makeup. There is a succession of mature or 
breeding animals with the change of season. A similar phenomenon 
is noticeable in plants. Such succession is called seasonal succession 
(47, 56). Different species of the same community come into relation 
at different seasons of the year. 
Communities are systems of correlated working parts. Changes are 
going on all the time as a sort of rhythm much like the rhythm of activity 
in our own bodies related to day and night. In addition to this, com- 
munities grow by the addition of more species, decline, and finally 
tIt is at this point that ecology comes into contact with the theories of natural 
selection, adaptation, mimicry, etc. 
