74 REACTION: THE INFLUENCE OF COMMUNITY ON HABITAT 



(1907), or about 1 to each 3 square centimeters. Since many species 

 produce several generations in a year and others do not appear in the 

 summer aspect at all, the total number annually must be much larger, 

 probably reaching 1 or 2 per scjuare centimeter. 



It seems probable that the contribution made by excreta is more 

 evenly distributed in general than the bodies of animals, though just 



Fig. 15.— Diagram of a typical den of the banner-tailed kangaroo rat (Dipo- 

 domys spectabilis Mer.). Double shading indicates where one portion of tunnel 

 lies above another and solid black a three-story arrangement; A, B, C, etc., 

 active openings to surface; N, nest chamber; S, storage; OS, old storage; Y, 

 probably an old nest chamber; Z, old, unused, or partially plugged openings. 

 (After Vorhies and Taylor, 1922.) 



as little is known of its amount, apart from guano and similar deposits. 

 A large ungulate will distribute a considerable amount of excrement 

 in the course of a lifetime, as the "buffalo chips" of the Great Plains 

 demonstrate, but the absence of accumulation renders this much less 

 conspicuous than in the rookeries of birds, bats, etc. Concentration 

 also occurs in respect to many rodents, especially in relation to sani- 

 tation, and the intensity of the reaction can be estimated from pellet 



