570 



THE COMMUNITY 



of microseral or minor successions that take 

 place within larger communities.* 



In forest communities there are many 

 generally similar microseres. Thus the fungi 

 that sprout from the rich leaf mold, as well 

 as the bracket fungi growing on trees and 

 decomposing logs, pass through a sequence 

 of relatively short serai stages (O. Park, 

 1931a), and the more protracted microsere 

 of the fallen tree is well known (Shelford, 

 1913; Blackman and Stage, 1924; Savely, 

 1939; Daggy, 1946). The decaying fungus 

 and log, like the aging dung, eventually 

 lose their individuaUty and enter a mound- 

 ing period in which their substance is 

 gradually incorporated into the community 

 floor. In such microseres there can be no 

 permanent end product, or climax stage; 

 this latter is not possible where the micro- 

 habitat becomes a part of the larger whole, 

 and such a differentiation of function be- 

 comes a criterion for separation of microsere 

 from sere. 



The microhabitat may disappear by re- 

 newed growth of its immediate environ- 

 ment. An example of this interesting phe- 

 nomenon is provided by the observations of 

 J. D. Brown, who watched the occupants 

 of a tree hole for some years (Elton, 1927). 

 At first the hollow in a beech tree was used 

 by a nesting owl, but as the tree tissues 

 grew, the entrance became too small for 

 the owls and the hole was taken over by 

 nesting starlings. Later on, the hole had 

 a still further contracted opening, so that no 

 birds could enter the hollow within, and 

 wasps colonized the cavity. Finally, the 

 growth of the tree completely closed the 

 entrance. 



Tree holes have been discussed pre- 

 viously (p. 485) in general terms as 

 habitats of the forest community. Such 

 holes have their own micro-food webs, and 

 are involved in a tree hole microsere. Briefly, 

 in instances where the cavity is not closed, 

 this microsere eventually passes into the 

 microsere of the decomposing log. If the 



** A neglected microsere is that of carrion. 

 Decomposing bodies of fishes washed ashore, 

 and the remains of dead reptiles, birds, and 

 mammals, are especially well suited for research 

 in this connection. Associated with changes in 

 the chemistry of the flesh are numerous prob- 

 lems involving bacterial activities, carrion 

 biocoenoses, and the microseral succession of 

 the carrion fauna. 



tree closes the cavity or the orifice, the en- 

 closed bacteria and fungi may destroy the 

 tree, as such, in which case the tree hole 

 microsere also merges in the decomposing 

 log microsere. Still later, the rotten, 

 mounded log eventually becomes incor- 

 porated in the forest floor stratum, and its 

 substance is partially or wholly utifized in 

 the growth of other generations of forest 

 plants, and still later of forest animals, in 

 the complex process of community develop- 

 ment. 



Within the major marine community 

 there is a well-developed succession in the 

 growth of the coral reef community or 

 habitat. Thus corals may build upward 

 within fixed hmits. These coelenterates may 

 not continue the reef above the sea surface, 

 and when this point is reached, the animal- 

 formed, calcareous substrate is invaded by 

 other organisms. The reef fonn itself is 

 related to its position in the sea. For ex- 

 ample, many pioneer coralUne species, as 

 well as other animals that occupy exposed 

 reefs, differ in growth form from those 

 that five in sheltered lagoons. The exposed 

 reef corals usually form flat incrustations, 

 whereas the lagoon corals are more often 

 arborescent (Darwin, 1842; Vaughan, 

 1919; Pearse, 1939). 



There are numerous other examples of 

 succession in aquatic communities, as, for 

 example, the successional development of 

 bottom organisms in the profundal stratum 

 of water-supply reservoirs (Fig. 208) de- 

 scribed by Gersbacher (1937), and the 

 succession taking place in the marine 

 littoral of Monterey Bay, California, 

 described by Hewatt (1935, 1937). Hewatt 

 finds that any clean area is first colonized 

 with a film of algae (1); alga-eating 

 animals, such as limpets (2), then ap- 

 pear; next, a variety of animals, includ- 

 ing mussels, gooseneck barnacles, and 

 rock barnacles attach themselves, during 

 their respective spawning seasons, to the 

 relatively pioneer surface (3); gradually 

 these sessile animals occupy most of the sur- 

 face exposed, and so render the area less 

 available for the larger limpets, which 

 limpets move on, into a still higher httoral 

 zone, where mussels and barnacles are not 

 able to flourish (4). 



Up to this point we have been con- 

 cerned more especially with details of suc- 

 cession than with the general view of the 



