Stata Technical Bulletin
31
Population density
O Prey population (n) д Predator population (n)
900
800
700
600
500
400
900
800
700
600
500
400
Figure 3
Figure 4
Figure 3 shows the simulations of the Volterra model of prey-predator interactions. In the top panel, no delay between predation and predator birth is
assumed. In the bottom panel, a time lag of 0.3 years is assumed to exist between predation and the new births. Figure 4 shows the growth process
of an organism, without limitations (a) and with a maximum value obtainable (b).
Figure 5
O Warm water flux (l/s)
2
(a)
Topt
1.5
1
5
cold water flux
15
.5
0
•30
•20
10
50
30
20
10
0
2
4
6
8
10 12
S Shower water temperature
50
•40 1.5
1
.5
0
•50 2
40
30
20
10
0
2
4
6
8
10 12
2
40 1.5
1
.5
0
50
40
30
20
10
0
2
4
6
8
10 12
Figure 6
Time (s)
Figure 5 shows the growth process of an organism, switch-off (a) and switch-on (b) effects of the SWTC function. Figure 6 shows the shower water
temperature regulation: a) perfect (no delay); b) long pipe (constant information delay); c) long pipe (information delay, variable as a function of total
flux); d) lizard adjusting (material delay, variable as a function of the mixed water temperature).
References
ACSL. 1987. Advanced Continuous Simulation Language, User Guide/Reference manual, Edition 4.1. Concord, MA: Mitchell and Gauthier Assoc.
Brennan, R. D., C. T. De Wit, W. A. Williams, and E. V. Quattrin. 1970. The Utility of a Digital Simulation Language for Ecological Modeling.
Oecologia (Berlin) 4: 113-132.
Dent, J. B. and M. J. Blackie. 1979. System Simulation in Agriculture. London: Applied Science Publishers.
de Wit C. T. and J. Goudriaan. 1978. Simulation of ecological processes. Wageningen: PUDOC.
Ferrari, T. J. 1978. Elements of System-Dynamics Simulation—A textbook with exercises. Wageningen: PUDOC.
Forrester, J. W. 1968. Principles of Systems. Cambridge: MIT Press.
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