SEVENTH ANNUAL MEETING 



79 



THE PHYSIOLOGICAL AGREEMENT AMONG THE 

 ANIMALS OF ANIMAL COMMUNITIES 



BY V. E. SHELFORD, UNIVERSITY OF ILLINOIS 



All the animals occupying a relatively uniform habitat con- 

 stitute an animal community. A physiological agreement exists 

 among the animals of communities. The object of this investi- 

 gation was to determine the extent and character of such agree- 

 ment with particular reference to the rapids community of a 

 large creek. Considering the community as a whole there is 



POSITIVE REACTIONS 



HYDROPSYCHE OH RAPIDS COMMUNITY 



SPECIES 

 (IHfOSTOMA 



CAMBARUS 

 G0NI08ASIS 

 HYOROPSYCHl 

 ARGIA 



20 40 60 80 



tun 



HtPlAGfMNAl 

 PSEPHENUS E 



^TRONG CURRENT 

 POSITIVE ( 



REACTIONS TO^HARO BOTTOM 



VMIOIUM UGHI 



STRATA 



^OPEN WATfB 

 (AMONG 



ON STONES 



UNDER STONES 



UNDER STONES glV^ AMONG STONES MM 



ON STONES liijiiiJN WEAK LIGHT HH 



STRONG LIGHT Ejggj KINAESTHESIA M 



Figure 8 

 Biol. Bull. Vol.. XXVI, p. 313. Fig. 40. 



(1) a general agreement in reactions to certain factors; (2) 

 disagreement in respect to factors differing in intensity ver- 

 tically, and (2) a sharp difference between the rapids com- 

 munity and other communities. 



Figures 8 and 9 are introduced to show the character of the 

 agreement and disagreement in a rapids community, and the 

 fact that the pool community is different but remains un- 

 solved. Noting first figure 8, we note a noteworthy agreement 

 in reaction to bottom and to current. The preference for hard 

 bottom in these experiments means the avoidance of sand as 

 sand and hard bottom were present in the experiment. Animals 

 living under stones were under stones in darkness in the ex- 

 periment. The snail (Goniobasis) which lives on stones was 

 found on stones in the .experiment. The darter (Etheostom-a) 

 and the crayfish (Cambarus) which live among stones were 

 found among stones in the experiment. Thus the different an- 

 imals differ in their reactions to bottom and are in disagree- 

 ment with reference to their vertical distribution in nature. 

 Turning to reactions to light we find a comparable difference. 



