BIOTIC FACTORS IN RELATION TO INDIVIDUALS 



227 



understandable on the assumption that the 

 coral snakes can develop the color patterns 

 called for by their hereditary mechanisms 

 without effective control by selection pres- 

 sures of either their physical or bioUc envi- 



ronment. Here mutation pressures that af- 

 fect color patterns reign, httle controlled by 

 enviionmental checks. 



Related matters will be discussed in 

 Section V. 



17. BIOTIC FACTORS IN RELATION TO INDIVIDUALS 



It has been objected that the ecology of 

 individual animals, as autecology, is logi- 

 cally a contradiction in terms; but the ad- 

 vantages of prehminary analysis appear to 

 outweigh this consideration. It may be 

 pointed out that a single isopod moving up- 

 stream with no other isopod within several 

 yards has relations to its physical environ- 

 ment as an individual; this may be an ex- 

 treme case, but in such instances autecology 

 is logical and real. The difficulties involved 

 in the dissociation from each other of the 

 biotic factors of the environment, and in the 

 analysis of these factors, are obviously much 

 greater than is the case with the inorganic 

 physicochemical conditions. The inorganic 

 factors, indeed, merge with the biotic in 

 the field of organic chemistry; witness our 

 consideration of the organic constituents of 

 soil, water, and air. The overlap of the 

 biotic with the nonliving factors is as fol- 

 lows: 



evolutionary origin. The subject matter of 

 the section on "Biotic Factors in Autecol- 

 ogy" in Chapman's Animal Ecology, which 

 deals with the analysis of the biotic poten- 

 tial, is referred by us to the section on 

 populations (see Chap. 22). 



MICROCLIMATES AND THE PLANT 

 MATRIX 



The fundamental dichotomy of organisms 

 into plants and animals with only a small 

 persisting overlap in a few types of micro- 

 organisms and in the slime-molds, is of 

 basic importance for the consideration of 

 the modification of animal habitats by the 

 biotic environmental factors. Animals five 

 in a plant environment referred to by Cle- 

 ments and Shelford (1939) as the plant 

 matrix, and tliis forms a logical, though per- 

 haps a somewhat artificial justification for a 

 treatment of animal ecology as distinct 

 from plant ecology. Even the major com- 



NonHving 



Biotic 



Living organisms 



Nonliving 

 organic matter 



Inorganic 

 matter 



In the present section the discussion of the 

 biotic factors in the environment must ac- 

 cordingly lean heavily on the organic por- 

 tion of the preceding section, and in many 

 cases we shall require little more than men- 

 tion of the topics involved, which either 

 have already been discussed, or are to be 

 treated more extensively in connection with 

 the organization of populations, or with 

 the community, or with evolution. 



Our account of the biotic factors in the 

 environment of animals will deal with shel- 

 ter relations, with the energy relations of 

 the food supply, with the series of relations 

 grouped under symbiosis (including para- 

 sitism), and with disease, in so far as these 

 various elements can be dissociated from 

 the community complex and from their 



munities of land animals are obviously 

 dominated by the major divisions of the 

 plant environment into forest, grassland, 

 desert, and tundra. The total relations of 

 animals to aquatic plants are much modi- 

 fied, as compared with terrestrial communi- 

 ties, by the importance of the role played 

 by plant plankters. The aquatic plant 

 matrix in aquatic habitats resembles its ter- 

 restrial counterpart in stands of rooted vege- 

 tation or in the dense, floating mats that 

 characterize some ponds and lakes and at- 

 tain an acme of development in the oceanic 

 reaches of Sargasso seas. The gigantic 

 rooted algae of the Laminaria type may 

 form submarine forests comparable in 

 height with the sequoias. 



Modifications of the physicochemical en- 



