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 is not important. It also assumes that growth of bird

 biomass is proportional only to fish density, and that the

 number of potentially breeding birds at the beginning of

 the nesting season is not important. Note that there is no

 feedback from the fish compartment to the multiplier on

 fish growth or from the bird compartment on food

 consumption.

 The structure of Model I suggests a system's

homeostasis in which fish recruitment and growth rates are

adjusted to counteract variation in initial fish stock.

When initial fish stock is low, recruitment and growth

rates are high; when initial fish stock is high,

recruitment and growth rates are lower. This model also

suggests that breeding activity is not limited by the

number of birds capable of breeding. It assumes that the

number of breeding birds is unlimited relative to the level

of breeding activity that can be supported by th.e system.

None of these assumptions is unrealistic if, in the prey

population, survival of young is inversely proportional to

the density of adults and if, in the predator population,

isolation from other breeding populations of the same

species is not complete.

 In Model II (Figure 12) growth and survival rates of

fish stocks the previous year are factors in determining

the rate at which fish biomass increases. Equations for

Model II are shown in the legend to Figure 12.