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Selina S. Heppell, Deborah T. Crouse, and Larry B. Crowder
proportional parameter perturbations that would be associated with interactions
with Rainbow Trout. Finally, the authors asked what magnitude of perturbations
of suites of parameters associated with each ecological pressure were necessary to
cause local extinctions.
Patterns in reproductive value among size classes and the damping effect of
density-dependent survival in small fish led to high sensitivity values for survival
of large juveniles and small adults and growth rates of small juveniles. Although
equilibrium population size was relatively robust to changes in survival rates of
most size classes, it was sensitive to changes in survival of fish in classes 60–
100 mm and 101–140 mm (Fig. 10.4a). This roughly corresponds to Brook Trout
late in their first growing season and early in their second growing season. An
increase in survival of these fish resulted in an increase in equilibrium population
size. Both measures of size distribution (number and proportion of large fish)
Figure 10.4. Sensitivity of population size (a), number of large fish (b), and proportion of
large fish (c) to changes in stage-specific survival in a density-dependent matrix model of
Brook Trout. Density-dependent survival of age 0 fish (larvae, 21–60 mm and 61–100 mm)
was dependent on size and the number of age 0 fish. Points represent results from model
runs with various levels of density dependence. (From Marschall and Crowder 1996; used
with permission.)
Selina S. Heppell, Deborah T. Crouse, and Larry B. Crowder
proportional parameter perturbations that would be associated with interactions
with Rainbow Trout. Finally, the authors asked what magnitude of perturbations
of suites of parameters associated with each ecological pressure were necessary to
cause local extinctions.
Patterns in reproductive value among size classes and the damping effect of
density-dependent survival in small fish led to high sensitivity values for survival
of large juveniles and small adults and growth rates of small juveniles. Although
equilibrium population size was relatively robust to changes in survival rates of
most size classes, it was sensitive to changes in survival of fish in classes 60–
100 mm and 101–140 mm (Fig. 10.4a). This roughly corresponds to Brook Trout
late in their first growing season and early in their second growing season. An
increase in survival of these fish resulted in an increase in equilibrium population
size. Both measures of size distribution (number and proportion of large fish)
Figure 10.4. Sensitivity of population size (a), number of large fish (b), and proportion of
large fish (c) to changes in stage-specific survival in a density-dependent matrix model of
Brook Trout. Density-dependent survival of age 0 fish (larvae, 21–60 mm and 61–100 mm)
was dependent on size and the number of age 0 fish. Points represent results from model
runs with various levels of density dependence. (From Marschall and Crowder 1996; used
with permission.)