COMMUNITY ORGANIZATION: PERIODISM 



541 



aflFects the community, we are not con- 

 cerned with an encyclopedic catalogue of 

 the several migrating species and their 

 particular problems; nor with the evaluation 

 of exogenous influences such as the in- 

 tensity of hght, length of daylight periods, 

 and available food; nor with endogenous 

 factors, such as the deposition of fat, habit, 

 and hormone production (Rowan, 1926, 



latter point is illustrated by the migration 

 of mule deer (Odocoileus hemiomis) in the 

 mountainous regions of the western United 

 States (Russell, 1932). These deer in the 

 Yellowstone and Yosemite regions occupy 

 distinct summer and winter ranges. The 

 migration routes vary from 10 to 60 miles 

 in length. In the spring the deer move into 

 the higher altitudes, and in the autumn 



BREEDING RANGE 

 ^'//J WINTER HOME 



Fig. 186. Seasonal march of isotherm fronts and the vernal migration of the black and white 



warbler. (Modified from Lincoln.) 



1929, 1932; Wolfson, 1945). The resulting 

 balance between these and other external 

 and internal stimuU causes the individual 

 organism to move into and out of the sev- 

 eral communities with which it is associated. 

 The stimuli effective for one species may 

 not be effective, either in kind or degree, 

 for another species; and the stimuli effective 

 for one part of an annual movement may 

 not be effective for another part of the 

 same movement in a given species. This 



they reverse this movement. Although 

 mating behavior and birth of young deer 

 are correlated with this seasonal movement, 

 no causative relationship has been demon- 

 strated between these organismal activities 

 and the phenomena associated with migra- 

 tion. The deer become restless on their 

 summer range with the onset of early snow 

 storms and a drop in temperature. Fall 

 migration to the lower winter range ap- 

 pears to be initiated by heavy snowfall. The 



