COMMUNITY ORGANIZATION: METABOLISM 



515 



ment of the food web, among other in- 

 fluences, results in loss of equilibrium in 

 the metabolism of the whole community. 

 Unbalance so created first affects a partic- 

 ular food chain, or several closely associated 

 chains, and affects last those parts of the 

 web ecologically farthest from the initial 

 state of unbalance. Tliis may bring to mind 

 the famiUar analogy of tossing a pebble 

 into a pond and watcliing the concentric, 

 ever-widening circles of disturbance on the 

 surface of the water. 



This useful analogy is not so appHcable 

 as it sounds. In the first place, the dis- 

 turbance in the pond travels at decreasing 

 force through distance, whereas disturbance 

 in the food web may or may not do so, 

 depending upon numerous influences. For 

 example, if a key organism or key industry 

 is affected, the unbalance will progress at 

 the same, or increasing, force to the Limits 

 of the food web. If the community involved 

 is unable to adjust or otherwise ameliorate 

 this initial disturbance, such initial un- 

 balance will destroy the community. Con- 

 sequently, unlike the pebble-pond analogy, 

 not only the initial force of the disturbances 

 and the initial location of the unbalance in 

 the food web are to be considered, but the 

 ecological importance of the food niche 

 must be appreciated. 



This is just as true of large metropolitan 

 communities as it is of a pond or forest. 

 For example, a work stoppage in the manu- 

 facture of a luxury food or a relatively 

 minor manufactured article such as hair- 

 pins may cause inconvenience. The force 

 of the disturbance (as measured by the 

 number of hairpins available in proportion 

 to the demand for the article) may be dis- 

 sipated or quickly buffered by adjustment 

 (employment of substitutes) and such an 

 initial economic disturbance may not call 

 forth a vigorous response. On the other 

 hand, if a work stoppage in the production 

 or transportation of a vital fuel or food 

 product occurs, the force is quickly felt by 

 the entire community, and the response is 

 rapid, vigorous, and diverse. 



It will also be recalled that impairment 

 or destruction of a link in a food chain 

 affects both adjacent links (p. 372). Con- 

 sequently the initial disturbance sets in 

 motion two complex stimuli. This is a 

 still further removal from the pebble-pond 

 analogy. 



In many recent instances man has created 

 unbalance. One interesting example, in 

 which man served in a dual role of first 

 a link in a primitive food chain and later 

 as an economic Unk, is described by 

 Haviland (1926) and Elton (1927). lu 

 Siberia, in the region of the Yenisei drain- 

 age basin and estuary, one of the chains in 

 the food web consists of (1) reindeer moss 

 (a lichen) — (2) reindeer— (3) man. The 

 Hchen pastures form the chief food of the 

 reindeer, and these plants influence both 

 the range and abundance of this animal, 

 Siberian man at first was almost wholly 

 dependent upon the reindeer. It afforded 

 him food, hide-clothing, thread from 

 sinews, and needles from sharpened bone 

 spUnters. In this chain, man is a simple 

 ecologic link. With the increasing de- 

 mand for furs, Siberian man increased 

 his occasional killing of arctic foxes to a 

 professional status and, thereby, became 

 a new link in another food chain of the 

 Siberian food web, namely, (1) natural 

 grasses— (2) arctic hare and/or lemming 

 — (3) arctic fox— (4) man. He also 

 served to connect both these chains with 

 the involved economic chain which in- 

 cluded the fur markets of such cities as 

 Paris, London and New York. Here Siberian 

 man is more than a food niche. He has 

 become an economic entity, and desires 

 more than reindeer steak. This "more" can 

 be obtained by barter for fox pelts, and 

 certain products of civihzation become 

 necessities in his eyes. But the fox popu- 

 lation fluctuates with the lemming popu- 

 lation as a rule, causing fluctuation in pelt- 

 taking and in the amount of manufactured 

 articles he can buy, and influencing the 

 price of finished fox fur. 



Man not only is directly involved in 

 natural food chains, as we have just seen, 

 but he also exerts a profound indirect in- 

 fluence upon natural community food webs 

 in which he does not occupy a feeding 

 niche (Gustafson et al., 1947; DeTurk, 

 1948; Osborn, 1948; Vogt, 1948). His 

 activities create unbalance in river com- 

 munities by pollution from sewage (Forbes 

 and Richardson, 1919; Buswell and Boruff, 

 1931; Thompson, 1931) and from manu- 

 facturing wastes. Indiscriminate lum- 

 bering upsets the food web of forest com- 

 munities, and, at the same time, makes 

 available increased space for those grass- 



