PHYSIOLOGY AND ECOLOGY 33 
distinguished from the more special physiology of organs (13, 51). With 
these limitations upon the term physiology, what may be termed 
physiological life histories (52) covers much of the field. Under this 
head fall matters of rate of metabolism, latency of eggs, time and condi- 
tion of reproduction, necessary conditions for existence, and especially 
behavior in relation to the conditions of existence. Reactions of the 
animal maintain it in its normal environment; reactions are dependent 
upon rate of metabolism (53 and citations), which may be modified by 
external conditions. Behavior reactions throughout the life cycle are a 
good index of a physiological life history. 
If we knew the physiological life histories of a majority of animals, 
most other ecological problems would be easy of solution. The chief 
difficulty in ecological work is our lack of knowledge of physiological life 
histories. With elaborate facilities these may be worked out in a 
laboratory. Ecology, however, considers physiological life histories 
primarily in nature, and for this reason the central problem of ecology 
is the mores (13) problem. This may be defined as the problem of 
physiological life histories in relation to natural environments together 
with that of the relations of organisms in communities. The latter is 
not a part of physiological life histories, the mores conception being the 
broader. An ecological classification is a classification upon a physio- 
logical basis, but since structure and physiology are inseparable, we 
must not forget the relations of structure to ecology and to ecological 
classification." 
V. COMMUNITIES AND BIOTA 
I. BASIS 
Animals select their habitats probably by trial and error. The simple 
fact of selection is, we believe, familiar to all naturalists. A given 
of natural history. There has never been any attempt to organize natural history 
and physiological data into a science under the head of ethology, biology, or bio- 
nomics, and the use of these terms will not seem justified until the materials to which 
they have been applied are organized into a science. 
2) 66 
t Mores (Latin singular mos), “behavior,” ‘‘habits,” “customs”; admissible here 
because behavior is a good index of physiological conditions and constitutes the 
dominant phenomenon of a physiological life history and of community relations. 
We have used this term just as form and forms are used in biology, in one sense to 
apply to the general ecological attributes of motile organisms; in another sense to 
animals or groups of animals possessing particular ecological attributes. When applied 
in this latter sense to single animals or a single group of animals the plural is used in 
a singular construction. This seems preferable to using the singular form mos which 
has a different meaning and introduces a second word. The organism is viewed as a 
complex of activities and processes and mores is therefore a plural conception. ; Al m~ 
