Database Reference
In-Depth Information
DEATH J
DEATH A1
DEATH A 2
DEATH RATE 1
DEATH RATE 2
DEATH RATE 3
GROWTH 1
GROWTH 2
SURVIVE
JUVENILE
ADULT 1
ADULT 2
SURVIVE POT
GROWTH 3
TOTAL POPULATION
ADULT 3
SUSTAINABLE POPULATION
ADULT 2
ADULT 3
ADULT 1
DEATH A3
ATTACH RATE
SURVIVE POT
FECUNDITY 1
SEX RATIO
FECUNDITY 3
FECUNDITY 2
Fig. 10.1
At first glance, it appears that the sustainable population will not be exceeded.
However, due to the way in which the populations move between cohorts, the total
population does, in fact, overshoot the sustainable level in certain years. Adult pop-
ulations die at certain rates between years; the surviving population grows to a new
average size and enters the next cohort. At the end of the fourth year, it is assumed
that the entire generation dies out. The sustainability module of the model is shown
in Figure 10.2.
The sustainability module determines the equilibrium population level that is
expected to be reached over the long term. The key parameter that determines this
level is the availability of suitable substrate material upon which the mussels can
attach. Zebra mussels require hard substrates and cannot live in muddy conditions.
Other potentially limiting factors, such as calcium deficiency or extremes in water
temperature or nutrient availability, are not considered here.
