310


model are given in the legend. Values for constants used

in the execution of the program are listed with sources in

Appendix Table C-10. The forcing function, land surface

covered by water, was generated by the water model (Figure

14) and can be seen in Figure 61. In Model III as in the

previous models, only water surface area was changed to

distinguish present conditions from primitive conditions.

 Simulations from Model III under the drained and

undrained conditions are shown in Figures 78 and 80. In

Figure 78A, prey fish density varies according to the

extent and time of water coverage but is also affected by

prey fish stock at the beginning of the wet season. In the

simulations under present conditions, interactions between

prey fish density (Figure 78A) and predator fish biomass

(Figure 78B) are apparent. Predator fish populations grow

when prey populations are high, but expanded predator

populations cause prey fish populations to decline.

Predator fish populations are favored by a series of wet

years, and almost absent during dry years. Similarly,

predator fish population levels are much lower under

present conditions than under primitive conditions.

Predator fish populations under present conditions are not

large enough to have a significant effect on prey

populations. The difference in predator population levels

between primitive and present conditions is responsible for

the several instances in the simulations when prey

populations are higher under present conditions than under