34 ENVIRONMENTAL RELATIONS 
environmental complex is selected by a number of species. All of the 
animals of a given habitat constitute what is known as an animal 
community; all the life (plant and animal) is a biota. It follows that 
there is often a certain physiological or ecological similarity in the species 
which select the same or similar habitats. When not ecologically 
similar, animals living in the same or similar habitats are usually 
ecologically equivalent, i.e., they meet the same conditions in different ways. 
For example, in a swift stream, the small fishes known as darters maintain 
themselves against the swift current by their strong swimming powers 
and by orienting against the current (positive rheotaxis). The snails 
(Goniobasis) are able to maintain themselves because of the strength of 
their foot and positive rheotaxis. The darters and snails are ecologically 
equivalent with respect to current. 
There is a marked agreement of all the animals of this community in 
their reactions to the factors encountered in the stream. This agreement 
is due (a) to the selection of the habitat through innate (instinctive) 
behavior (40, 49, 54, 55), and (b) to the adjustment of behavior to the 
conditions through the effects of physical factors and through formation of 
habits and associations (44, 53). 
Animals of the same species show behavior differences in different 
habitats (44, chap. xxi; 55, p. 584; 53). Bohn found that the sea 
anemones living near the surface of the sea, where the wave and tide 
action are strongest, showed more marked rhythms of behavior in relation 
to tide than those living lower down where the action of the tide and 
waves is less marked (53a, p. 156; 53 0, p. 155). These rhythms dis- 
appeared slowly when the animals were removed from the tide to the 
aquarium. Many such cases are probably to be found in the natural- 
history literature. For example, the chipmunk differs in behavior under 
different conditions (21, p. 523). Abbot (53c, p. 104) makes a similar 
statement about fish. It is apparent then that one species may have 
several mores. Different species may sometimes have identical mores; 
these cases are usually separated geographically (55, p. 604). In 
addition to these relations, the relation of ecology to species is largely a 
matter of language, names being necessary as a means of referring to 
animals. 
The physiological and behavior relations of animals in the same 
community are of much importance and are included under (a) inter- 
physiology or psychology and (b) inter-mores physiology or psychology. 
(a) Inter-physiology.—Tarde (55, citations) is the author of the idea of 
inter-psychology—the psychology of the relations of individuals of the 
