consumer assemblage and the number of 

 different species in the assemblage, 

 feeding relationships can be complex. All 

 of the pathways shown have been verified 

 by feeding observations or gut content 

 studies, and in addition, Fankboner (1976) 

 and Fankboner and Druehl (1976) have shown 

 that at least two invertebrates can use 

 dissolved organic matter produced by 

 Macrocystis integrifolia . 



Biomass, densities, and feeding 

 observations have been used by Pearse and 

 Hines (1976) to construct a 

 semi-quantitative food web for the Point 

 Cabrillo kelp forest that shows standing 

 stocks and feeding relationships (Figure 

 12). 



In our view, productivity and energy 

 flow in communities are a consequence, not 

 a cause, of population and community 

 structure. As a subdiscipl ine of ecology 

 they may be of interest in their own 

 right, but they have contributed little to 

 our understanding of community structure 

 and dynamics. Moreover, food webs 

 constructed from energy flow studies can 

 be misleading as they may be interpreted 

 as "control webs"; because A eats B, A 

 controls the population's size and/or 

 distribution of B. Such a misinterpre- 

 tation of food webs has, no doubt, 

 contributed to the popular notion 

 (probably misconception -- see Ehrlich and 

 Birch 1967, Connell and Sousa 1983, Wiens 

 1984) that "nature is in balance." 



I vermetids snails abalone bat stars sea urchins crabs 



50 000 200. 4.000 5.000 



Av- 



detritus grazing 



Cystoseira \ giant kelp / 



2.000 500 



(veg: 500 kg) (3,000 kg) 



(net production: 24,000 kg/yr) 



red algae 

 (1.500 kg) 



Figure 12. A food web for the Point Cab- 

 rillo kelp forest near Monterey. Numbers 

 give approximate number of organisms/ 

 1000 m 2 . Numbers in parentheses give 

 approximate wet weight/1000 m 2 (from 

 Pearse and Hines 1976). 



Populations may be regulated by predators 

 or grazers, but they can also be regulated 

 by a variety of other processes. Figure 

 13 illustrates some of the "control" 

 possibilities discussed in detail 

 elsewhere in this profile (see especially 

 Chapters 2 and 5), many of which are not 

 easily measured in equivalent energy units 

 (e.g., a storm removing a large quantity 

 of kelp or killing sea urchins), or affect 

 such small amounts of energy that they are 

 not usually considered in even a detailed 

 energy flow analysis (e.g., spore or 

 larval removal by filter feeders). 



41 



