COMMUNITY ORGANIZATION: PERIODISM 



549 



tance from the activity under examination. 

 A striking example is found in the work 

 of Philip (1927) in the Crystal Lake com- 

 munity in Minnesota. Philip found a 

 marked diel rhythm in hydrogen ion con- 

 centration. The amplitude increased regu- 

 larly from open water, to the water sur- 

 rounding algal mats, and culminated with- 

 in the mats per se (Fig. 188). These three 

 rhythms show a rising alkalinity of the 

 water to a midday peak, and a falling al- 

 kalinity into the crepuscular period. The 

 rhythrnic shift in pH is a result of both 



the mat, so that we have still another 

 example of both inanimate and animate 

 portions of the community affecting 

 each other in the diel cycle. The photo- 

 synthesis of the algae will later directly 

 affect (1) the population of the algae, (2) 

 the algal herbivores, and (3) indirectly af- 

 fect the predators, through the highest 

 trophic level. This is in addition to any 

 stimulus that the pH cycle may have upon 

 the behavior of individual animals. 



Coordinated studies of the animals of a 

 given community, or of a portion thereof. 



F.C 



100% 



6 



5 

 4 

 3 

 2 

 I 

 



rhTf 



% 



100 



90 



80 



70 



lOQ 



90 



80 



70. 



CENTROLENE 

 LESSER TINAMOU 



CENTROLENE 

 LESSER TINAMOU 



DAWN 



DUSK 



1 



56789 10 II 12 123456789 10 II 12 I 2345 

 AM N PM M AM 



JULY 18 JULY 19 



Fig. 190. Diel cycle in vocalization in a clearing in the upland forest on Barro Colorado 

 Island, Panama Canal Zone. Dawn and dusk (2 foot-candles) are accompanied by change 

 in activity of typical animals: diurnal toucans begin calling shortly after dawn, continue 

 through day, and give their last call shortly after dusk; nocturnal tree frogs (Centrolene) and 

 lesser tinamou stop vocalization just before dawn, and begin shortly after dusk. (After O. 

 Park.) 



physical and biological community factors. 

 With the gradual rise in water temperature 

 of the surface stratum, some carbon dioxide 

 is driven off, with a peak loss in midafter- 

 noon; with the gradual fall in water tem- 

 perature, there is an increased solubility of 

 atmospheric carbon dioxide, and corre- 

 sponding loss of alkalinity as evening sets in. 

 This basic temperature and carbon dioxide 

 rhythm underlies each of the curves in the 

 figure. As the light intensity increases 

 through the morning, there is a correspond- 

 ing increase in algal photosynthesis and a 

 further rise in the pH as the carbon dioxide 

 in the water is utilized. This biological proc- 

 ess affects not only the medium in the 

 algal mat, but also the medium around 



are relatively few. These include an early 

 study of the insect fauna of a Minnesota 

 sand dune (Chapman, Mickel, Parker, Mil- 

 ler, and Kelley, 1926); diel activity of a 

 number of species of animals in a beech- 

 sugar maple forest in northeastern Ohio 

 (Park, Lockett, and Myers, 1931) and in 

 a similar community in northern Indiana 

 (Park and Strohecker, 1936); rhythmic 

 fluctuation in abundance of insects in a 

 prairie near Norman, Oklahoma (Carpen- 

 ter, 1936); and a relatively concentrated 

 study of the Barro Colorado Island rain 

 forest in the Panama Canal Zone (Allee, 

 1926, 1926a; O. Park, 1938; Park, Barden, 

 and Wilhams, 1940). In all these studies 

 there was a correlation between the physi- 



