COMMUNITY ORGANIZATION: METABOLISM 



495 



variety of forest habitats, and the selective 

 action of these habitats on the bird popu- 

 lations of the several forest communities. 

 Many influences are discussed by these 

 authors. Thus food may be the predomi- 

 nant factor (crossbill, p. 586), or the 

 feeding habit (flycatchers), or the song 

 post (blackcap), or nesting site (hole- 

 nesters), or nest-building material (night- 

 ingale), or roosting place (pheasant). 



Microclimate may be important in local 

 segregation, but is a difficult factor to 

 evaluate (Kendeigh, 1945; Moreau, 1934). 



Kendeigh (1945) analysed the restric- 

 tion of birds, especially warblers, during 

 the breeding season, near Albany, New 

 York. In this study four types of communi- 

 ties were involved: grassy fields, mixed 

 shrubs and small trees, hemlock-beech for- 

 ests, and beech-sugar maple-hemlock for- 

 ests. He concluded that the selection of 

 shrubby fields or forests rather than grass- 

 land was correlated with more elevated 

 positions for (1) feeding areas, (2) nest 



sites, and (3) song posts; that the selection 

 of forests rather than shrubby fields was 

 conelated with (1) avoidance of high 

 Ught intensity, and (2) greater restriction 

 of free movement; and that selection of 

 either evergreen or deciduous forest is cor- 

 related with the size and shape of leaves 

 and their arrangement on the twig, rather 

 than with persistence of foUage, microcH- 

 mate, or food supply. Finally, this author 

 believes that patterns of behavior through 

 succeeding bird generations stabilize the 

 local segregation of species into difiEerent 

 community types, and into their several 

 habitat and stratal positions in these types. 

 In the preceding pages the forest com- 

 munity has been discussed, where feasible, 

 in terms of each stratum. As in the grass- 

 land community (Tables 35 and 36), the 

 principle of geographic stratal equiva- 

 lence is readily demonstrated. In Table 40 

 a few stratal categories are listed to empha- 

 size further the importance of this view- 

 point. 



27. COMMUNITY ORGANIZATION: METABOLISM 



One of the fundamental causes of the 

 adaptive utilization of the space-time com- 

 munity lattice is the drive for nourishment. 

 An organism must eat to Hve, and the 

 food it consumes maintains the balance be- 

 tween physiological input and output of 

 energy. Since food must be obtained from 

 the environment and since there is a limit 

 to the productivity of any given area, 

 there is not enough food to maintain an un- 

 limited number of organisms, even though 

 in actual life food may not set the primary 

 limits to population density. The food sup- 

 ply of a community, and the relative avail- 

 ability of various food elements for the 

 several species populations cooperating in 

 community maintenance become limiting 

 influences governing community size and 

 complexity and the density of the popula- 

 tions whose intertwining makes up the 

 major community. 



Since species have specific protoplasms 

 and inherit specific physiological require- 

 ments, their ecological needs are necessar- 

 ily more or less specific. These environmen- 

 tal adjustments must be made through the 

 agency of both general and particular 

 modifications of structure and function. In- 



evitably, the survival of the species de- 

 pends upon its association with foods sufii- 

 cient to meet these requirements. In the 

 overwhelming majority of organisms this 

 is accomplished by each species becoming 

 a member of a food-feeder nexus. These 

 natural, cooperative groups are relatively 

 self-sufficient, and the component species 

 populations are spatially integrated and 

 stratified. 



These subcommunities appear to be a 

 series of interwoven elements, and their col- 

 lective effect may be Hkened to the total 

 effect of the physiological processes of an 

 individual organism. The sum total of the 

 organismal nutritional and assimilative re- 

 sponses of the community may be consid- 

 ered to be the metabolism of the com- 

 munity, just as the sum total of the phys- 

 icochemical processes in the organism is 

 thought of as the metabolism of the individ- 

 ual. In both instances these metabolic 

 wholes are composed of spatially integrated 

 and stratified responses. 



We are only at the threshold of compre- 

 hension of the community. No complete 

 analysis of even a simple food chain, or 

 food web, is possible until intraspecies 



