66
4. Epidemics in the Marine System
TOTAL POPULATION
o
NETBIRTHS
MORTALITY RATE DEATH
CONTACT RATE
INFECTED
FIGURE 4.12
LOSS OFIMMUNITY IMMUNE
RECOVERY
susceptible individuals entering the system, the disease is perpetuated,
rather than disappearing from the population. Figure 4.13 confirms this
expectation.
Have we gained anything new from explicitly induding the natural birth
and death processes into our model? We have introduced another feature
into the model , and in response our results differ-the disease continues to
2:
3:
4'
3:
4'
1: IMMUNE
4000 .00
2000 .00
I
/
/A\A\\AVhV
v
(\
r. n r-. n rv n n ,..... (\ n ,, '
i
--l
4: TOTAL POPULATION
3: SUSCEPTIBLE
2: INFECTED
w V V'
400 .00
t )IV W lJ v. 3
100.00
0.00
0.00
300 .00
3:
200.00
Weeks
FIGURE 4.13