THE ENVIRONMENT 



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TABLE 17.1 RELATIONSHIPS AMONG ECOLOGICAL FACTORS AND ORGANISMS 



Tertiary Foctors 



Secondary Factors 



Primary Factors 



Life 



Topography 

 Latitude 

 Relief 

 Distribution 



Biotic factors 



Precipitation 



Wind 



Soil structure 



Biotic factors 



General climate 



Temperature 



Water 



Light 



Air 



Wind 



Nutrients 



Biotic factors 



The various factors 

 affect ecological 

 amplitude or are 

 the sources of 

 particular needs 



Discussion of ecological factors, owing to their 

 interrelations, requires some repetition. However, 

 this may be welcome because even a superficial 

 treatment of factors is somewhat complex. 



MICROHABITAT 



Further discussions of physical and biotic factors 

 may lead to the implication that an individual en- 

 vironment is a large area of ecological homogeneity. 

 Nothing could be further from what exists in nature, 

 because factors work in combination to produce very 

 minute as well as fairly large distinctive units. The 

 minute areas, or microhabitats are likely to be over- 

 looked. For example, the fact might be disregarded 

 that difTerent sides of a fallen tree or of a leaf have 

 unlike microenvironments and organisms. 



Although the large, more conventional habitats em- 

 phasize the importance of horizontal distribution of 

 environmental factors, one kind of microhabitat, 

 layers, stresses the vertical zonation of factors. These 

 microhabitats portray the ecological uniqueness of 

 trees, shrubs, herbs, mosses, leaf litter, and tiers of 

 the soil. Often a surface microhabitat is much dii- 

 ferent from one underground. For example, when 

 the substrate is covered with snow and few organisms 

 are active upon the surface, the organisms under- 

 ground in their insulated, warmer microhabitat may 

 be quite active. 



The presence or absence of individual microhabi- 

 tats is likely to be very important in animal occur- 

 rence. An animal may be most closely associated not 

 with a plant community or any major portion of a 

 habitat, but with being under objects, in moist situa- 

 tions, in sandy soil, on a particular species of plant. 



or even on a limited part of a single plant species. 

 Such places usually are not studied in detail; how- 

 ever, the serious student must locate these micro- 

 habitats. The only way that it can be done is to make 

 careful records of the exact place in which an animal 

 is found. This place also must be described accord- 

 ing to the details of the ecological factors that are 

 present. 



An appreciation of many possible microhabitats in 

 any locality is gained even by a superficial examina- 

 tion of a conventional habitat. (The word '"habitat" 

 is all inclusive; microhabitats and conventional habi- 

 tats are both habitats). For example, in a woodland 

 one can usually find trees, shrubs, herbs, mosses, 

 climbers, epiphytes, saprophytes, and parasites. Each 

 of these plant layers possesses difl'erent species and 

 ecological factors, and even different parts of a single 

 layer contain unlike microhabitats. The parts of a 

 tree provide variations in environment, hence many 

 habitats, for organisms. If the bark of a tree is stud- 

 ied, the outer surface, cracks, and bark interior are 

 the more obvious sites of unique microhabitats and 

 species. 



Certain microhabitats might be overlooked. In a 

 woodland one can usually find logs, boards, and/or 

 rocks upon the ground. Different organisms are 

 found under or within these objects. Also, it fre- 

 quently is profitable to examine any litter that may 

 be under these objects. In addition, the ground be- 

 neath most woodlands is covered by decaying plant 

 remains that are forming humus. Decaying organic 

 remains of different thickness, moisture content, and 

 stage of decomposition generally support unlike or- 

 ganisms, and often there is a layering of different 

 species within a single layer of thick humus. Finally, 

 unlike conditions are found in both soil variations 

 and layers within any soil. 



