Hioseres may occur on a small scale in microhabi- 

 tats as well as in major ones. When hay infusions, 

 prepared in the laboratory, are seeded with repre- 

 sentative protozoans, the order of appearance of 

 maximum or peak fwpulations in the various species 

 is bacteria and monads, Colpoda. hypotrichates, 

 Paramecium. I'orticcUa. and Amoeba. Disappear- 

 ance of species is in the same order, except that 

 Amoeba precede Paramecium and I'orticcUa. Algae 

 may come in at the tinal stage, so that a more or less 

 balanced community is established. The succession of 

 species appears a result of the higher reproductive 

 rate of earlier species, and to the fact that the excreta 

 of at least some forms, especially the hypotrichates 

 and Paramecium, are toxic to them (WoodruiT 1912, 

 1913, Eddy 1928). 



Another common microsere occurs in the death 

 and decay of trees (Graham 1925, Ingles 1931, 

 Savely 1939). The sequence of animal species pres- 

 ent as decay progresses depends on the species of tree, 

 the community in which the tree occurs, the climate, 

 and the geographic locality. The following stages 

 have been recognized : 1 ) tree dying, but still with 

 leaves and sap; 2) tree recently dead, bark beginning 

 to loosen, termites and other insects boring into 

 wood: 3) wood well seasoned, bark very loose or off. 



wood borers still predominant ; 4 ) wood softened and 

 permeated with fungus : fungus beetles, elaterids, and 

 IKissalids common; 5) wood largely disintegrated 

 and crumbly, snails and millipedes, occur. Wilson 

 (1959), working in New Guinea rain forests, sub- 

 divides stages Z--' in a difTerent manner, each of which 

 he names after characteristic insects found: 2) 

 scolytid, 3) cucujid, 4) zora])teran, 5) passalid, and 

 6) staphylinid. Each stage also has a significantly 

 different aggregation of resident ants. I'-ventualiy the 

 decaying log becomes a part of the forest floor, and 

 the animal species then present are those in general 

 occurrence. 



Climatic succession 



With changes in climate, environmental condi- 

 tions often surpass the limits of tolerance of estab- 

 lished plants and animals. The result is the replace- 

 ment of the existent community by another. 



A most interesting clisere is the one that has oc- 

 curred since the northward retreat of the continental 

 glacier of Pleistocene time (Sears 1948, Deevey 1949, 

 Table 21-1 ). .Stages in this clisere may be detected 



FIG. 3-2 The types of frees 

 which have lived and died during 

 fho pasf few thousand years in 

 Quebec. Instrument taking bor- 

 ings of lake bottom for pollen 

 samples is operated from a boat. 

 Symbols representing different 

 pollen grains and the percentage 

 which each species constitutes in 

 the total are shown at the left. 

 The type of climate indicated by 

 the prevailing vegetation at 

 the time is shown at the right 

 (Wilson 1952). 



The biotic community 23 



