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10.3 Model Results
Now the model is complete and can be used to develop a base case model of zebra
mussel growth in our lake. The base case model uses average values for model
parameters published in the literature 2 . You will find that data in the model equations
at the end of the chapter.
The results of the base case model can be compared with alternative scenarios to
determine the impact and sensitivity of various parameters on the growth patterns.
Such a procedure is important if some data are unknown or unavailable, or if there
is uncertainty surrounding parameter estimates.
For a sensitivity analysis, vary the value for SUBSTRATE PERCENT between
50% and 90% and the death rates for the first three age classes within the intervals
listed in Table 10.1:
Change only one parameter value at a time.
The base case growth, density, and lake turnover pathways are shown in
Figure 10.5. We have assumed that the initial invading population consists of
100 juveniles. In the early years, population grows exponentially and reaches a
total population peak of 8
08 10 8 mussels in year thirteen. The population then
oscillates with decreasing extremes toward a steady state population of 7
.
79 10 8 .
Population density follows the same pattern as total population growth. Density
peaks at 834 mussels
.
m 2
m 2 .
/
and stabilizes at 772 mussels
/
Table 10.1
Minimum
Maximum
DEATH RATE 1
0.06
0.12
DEATH RATE 2
0.09
0.15
DEATH RATE 3
0.18
0.18
2 See, for example: Bij de Vaate, A. 1991. Distribution and Aspects of Population Dynamics
of the Zebra Mussel, Dreissena polymorpha (Pallas, 1771), in the Lake Ijsselmeer Area (The
Netherlands). Oecologia Vol. 86, pp. 40-50; Griffiths, R.W., W.P. Kovalak, and D.W. Schloesser.
1989. The Zebra Mussel, Dreissena polymorpha , in North America: Impact on Raw Water Users,
in Proceedings: EPRI Service Water System Reliability Improvement Seminar . Electric Power Re-
search Institute, Palo Alto, CA, pp. 11-27; Griffiths, R.W., D.W. Schloesser, J.H. Leach, and
W.P. Kovalak. 1991. Distribution and Dispersal of the Zebra Mussel ( Dreissena polymorpha )inthe
Great Lakes Region, Canadian Journal of Fisheries and Aquatic Science, Vol. 48, pp. 1381-1388;
Haag, W.R. and D.W. Garton. 1992. Synchronous Spawning in a Recently Established Popula-
tion of the Zebra Mussel, Dreissena polymorpha , in Western Lake Erie, USA., Hydrobiologia ,
Vol. 234, pp. 103-110; Kryger, J. and H.U. Riisgard. 1988. Filtration Rate Capacities in 6 Species
of European Freshwater Bivalves., Oecologia , Vol. 77, pp. 34-38; Mackie, G. 1991. Biology of
the Exotic Zebra Mussel, Dreissena polymorpha , in Relation to Native Bivalves and its Potential
Impact in Lake St. Clair, Hydrobiologia, Vol. 219, pp. 251-268; Strayer, D.L. 1991. Projected
Distribution of the Zebra Mussel, Dreissena polymorpha , in North America, Canadian Journal of
Fisheries and Aquatic Science, Vol. 48, pp. 1389-1395.
 
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