Survival of Peromyscus in Relation to Environmental Temperature and Acclimation at High and Low Temperatures

The impotrtance of temperature as an environmental factor affecting the behavior, physiology, and ecological relaionships of various organisms has long been recognized. Much emphasis is still placed upon the immediate quantitative aspects relating temperature to various biological processes (for excellent reviews of this literature see Belehradek, 1935; Luyet & Gehenio, 1940). Not much attention has been devoted, however, to the adjustments which various species make to changes in temperature which are prolonged and for which the terms and are customarily employed. The term, adaptation, is quite frequently used synonymously with acclimation and acclimatization but is not as desirable, since it is most often used by physiologists in connection with rapid adjustments which may take place in a matter of minutes or hours as contrasted with the slower adjustments involved in acclimation and acclimatization. Some confusion may also arise from the use of the term in connection with morphological evolutionary changes. The usage of the terms, acclimation and acclimatization, is also not uniform, although the former had best refer to short term adjustments taking place over a period of weeks or months or within the lifetime of the individual, while the latter should be reserved for long term adjustments which in. volve evolutionary changes over generations as the result of selection by the environment. The present investigation has been concerned with the extent to which some of the smaller mammals may become acclimated to high and low environmental temperatures and the influence which such acclimation may have on their geographical and ecological distributions, populations, and behavior under natural con1itions. The study has also been concerned with adjustments to seasonal rhythms in climate and the possible effect of temperature on variations in population level. Major consideration has been given to the northern white-footed mouse, Peromyscus leucopus noveboracensis (Fischer), also called wood-mouse and