11 .7. Questions and Tasks
229
FITNESS = IF EAT_PER_BIRD < A THEN (EAT_PER_BIRD /A)
ELSE 1 {EGGS PER BIRD/EGGS PER BIRD}
BIRD_DEATH_RATE = GRAPH(EAT_PER_BIRD)
(0.00, 0.85), (27000, 0 .685), (54000, 0.58 ), (81000 ,
0.525) , (108000, 0 .475), (135000 , 0 .45), (162000,
0 .425), (189000, 0 .405), (216000, 0 .39), (243000,
0.39), (270000, 0 .39)
CRAB EGGS MODULE
CRAB_EGGS(t) = CRAB_EGGS(t-dt) + (SPAWNINGBIRD_PREDATION-EGG_FAILURES-EGGS_INTO_CRABS) * dt
INIT CRAB_EGGS = 162957963320 {EGGS}
INFLOWS:
SPAWNING = ADULT_CRABS[FEMALE]*FERTILITY {IF
CARRYING_CAPACITY(ADULT_CRABS[MALE]+ADULT_CRABS[FEMALE)> 0 THEN
ADULT_CRABS[FEMALE]*FERTILITY
ELSE (.5*(ADULT_CRABS[FEMALE]*FERTILITY»)}
OUTFLOWS :
BIRD_PREDATION = BIRDS*EAT_PER_BIRD {EGGS PER SEASON}
EGG_FAILURES = CRAB_EGGS-EGGS_INTO_CRABS-BIRD_PREDATION
{EGGS PER SEASON}
EGGS_INTO_CRABS = IF
(ADULT_CRABS [MALE]+ADULT_CRABS [FEMALE]) >
CARRYING_CAPACITY THEN
((CRAB_EGGS*BIRTH_SUCCESS) /((ADULT_CRABS[MALE]+ADULT_CR
ABS[FEMALE]) /CARRYING_CAPACITY» ELSE
(BIRTH_SUCCESS*CRAB_EGGS)
A = 135000
BIRTH_SUCCESS = 0.00002272727273
CARRYING_CAPACITY = 2500000 {CRABS PER AREA}
EAT_PER_BIRD = IF EGGS_PER_BIRD > = A THEN A ELSE
(A*(EGGS_PER_BIRD /A» {EGGS PER BIRD}
EGGS_PER_BIRD = IF BIRDS > 0 THEN CRAB_EGGS /BIRDS ELSE
o {EGGS PER BIRD}
FERTILITY = 88000 {EGGS PER FEMALE CRAB}
TOTAL_ADULT_CRABS = ADULT_CRABS [MALE] +
ADULT_CRABS [FEMALE]
JUVENILE HORSESHOE CRAB MODULE
JUVENILE_CRABS(t) = JUVENILE_CRABS(t-dt) + (BIRTHSJUV_DEATH-JUVENILES_TO_ADULTS) * dt