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<br />Squawfish Population Viability Analysis --July 1993 <br /> <br />Page 32 <br /> <br />,... <br />+ <br />- <br /> <br /> <br />t Degree of <br />, Resilence <br /> <br />Q) <br />E <br />i= <br /> <br />15 <br />Q) <br />N <br />Ci5 <br />c: <br />o <br />:;:: <br />cu <br />:J <br />a. <br />o <br />a. <br /> <br />Population Size at Time t <br /> <br />Figure 3.2. Speculation on the change of carrying capacity after white man <br />disturbed the Colorado squawfish. The curves represent a biological <br />mapping from the current adult density to the density one time step into the <br />future. K is the amount of adult biomass per unit length of river in the <br />upper Colorado River Basin. The size of the time step is arbitrary. <br />Resilence is the maximal separation between the 45 degree line and the <br />growth function line, F(e). <br /> <br />3.3 Population Resilience <br /> <br />An ecological equilibrium point has two properties: its numerical value and <br />its stability to disturbance from this value. Ecological stability analysis has <br />been approached from various angles. C. S. Holling has spoken of <br />"resilience," which he defines as the ability to rebound from a fairly major <br />disturbance. This is distinct from the normal mathematical stability <br />analysis that is only performed (through eigenvector techniques) in a <br />neighborhood of the equilibrium point). Assume that something like the <br />relationship sketched in Figure 3.2 holds for the squawfish. Not only is the <br />carrying capacity much lower, but also the maximal percentage rate of <br />population growth is reduced. This is indicated in the graph by the fact <br />that the discrete dynamic function line remains closer to the 45 degree line. <br />This means that it could take absolutely longer for the population to return <br />