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Interpretation

The existence of a carrying capacity reduces the equilibrium value for the resource by a factor of relative to the harvesting equilibrium, , of section 2. Alternatively, harvesting reduces the level of the natural resource by a factor of relative to the carrying capacity.

The absolute value of the real part of , which determines the strength of the attraction towards the equilibrium, is strongly increased when the carrying capacity is of the same order as the harvesting equilibrium . It can be observed on the time plot of figure 5 that the carrying capacity limits the upward oscillation of the resource, thus limiting the overshoot and the subsequent backlash. This corresponds to the results shown in figure 14: the resource depletion curve for a carrying capacity of five times the harvesting equilibrium is well above the same curve in the absence of a carrying capacity. In other words, if resources were harvested at a rate such that the harvesting equilibrium were of the same order of magnitude as the carrying capacity then resource depletion would not be a big issue, even for small values of .

Using equation 26, the linear fragility of the system is now given by

 

The variations of f with are represented on figure 7.

  
Figure 7: Linear fragility, defined in the text as the ratio between relative resource depletion to initial relative capital distance to equilibrium (see figure 3) is represented as a function of , the ratio of the carrying capacity to the harvesting equilibrium for a coefficient of 0.1. Computation is done according to equation 28. Resource depletion is strongly attenuated by the existence of a carrying capacity of the same order as the harvesting equilibrium.

The stronger attenuation of the oscillations by the carrying capacity is accompanied by a decrease in the size of the region in which oscillations occur. The following values of limit the oscillation region:

 

For instance, when the carrying capacity m is large compared to the harvesting equilibrium , the upper range in of the oscillatory region is decreased to instead of the limit of 8 which was found for the system without carrying capacity.



next up previous
Next: Prices Up: Carrying capacity Previous: Algebraic approach



weisbuch
Fri Feb 7 13:18:37 GMT+0100 1997