Community Composition 415 



rotten log, or in the debris washed up on the sliore of a lake constitute 

 still smaller biocenoses. Characteristic communities occupy even 

 more minute microhabitats in the area such as a crevice in a ledge, 

 or the water in a pitcher plant. We thus have communities within 

 communities. The epiphytes, epizoans, and parasites of an animal 

 or a plant may also be thought of as comprising a biocenose. An 

 apple tree and the plants and animals that live on it and in it illustrate 

 a special community of this sort. A horseshoe crab with the dozen 

 or so species of mollusks, worms, and barnacles attached to its shell 

 exemplify a microcommunity, as do the fauna and flora of a cow's 

 stomach. 



The number of species and the population abundance in communi- 

 ties also vary greatly. While maintaining the necessary quantitative 

 relationships among the consumers and the producers in the eco- 

 system, the inhabitants of an area often include a wide range of densi- 

 ties. Furthermore, each component in the ecosystem may be repre- 

 sented by one, a few, or many species. Biotopes with extreme con- 

 ditions and little food, such as a rock desert or an ocean deep, gen- 

 erally support few species and relatively few individuals of each 

 species. The relatively small number of both species and individuals 

 in the badlands sections of southwestern United States is familiar to 

 those who have crossed these areas. In other severe habitats suffi- 

 cient energy and nutritive materials are sometimes available to allow 

 huge populations to develop although only a few species are able to 

 survive. In the relatively simple biocenose on Bear Island in the 

 Arctic Zone some of the smaller plants and animals are very abun- 

 dant (Elton, 1939). 



Under more equable climates larger numbers of species generally 

 become interrelated in community groups; each species is usually 

 rather meagerly represented, but sometimes the abundance of certain 

 species is great. The food relations of the North Sea herring are 

 known to involve a great number of species (Fig. 11.6)— some rep- 

 resented by very large populations— and these food species form 

 only a portion of the whole community of which the herring is a 

 member. A bed of kelp {Nereocysfis hietkeano) in Carmel Bay, 

 California, was found by Andrews ( 1945 ) to form the matrix of a 

 community that included 40 species of invertebrates, several kinds 

 of fishes, and numerous attached algae, protozoans, and bacteria, as 

 well as associated species of phytoplankton and zooplankton. 



Few complete enumerations have been made of both the plants and 

 animals in even the simplest situations and none in complicated 

 biotopes— especially in those with elaborate populations of micro- 



