size: 5036KB - Crocodile Specialist Group

Points 1-5 below describe the construction of the population'
Points 6 anal 7 explain how the samptes vere caught.
1. Each siliulated crocodile in our population is
constructed to have a knor,in aqe (rneasured in days) and a known
total length (heasured in centimeters) .
2. The sinulated population of crocodilians l^tas created
and 'tgrownl according to a formula that gives predicted total
Iength at tine t (PTLt) as a function of age (t) and 4 growth
paramecers:
PTLI =
[Sa1_m
-(S"t"' - n),
So1'n)e(_211+n]t/r)11/(1
where s^ is asyrnptotic fength, ir'is the curve shape parameter,
s^ is ldnqth -loqarithhs, at time zero (hatchling tength), e is the base of
nhtural
t is tine, and T is the grouth-rate
paraheter a: expressed by Brisbln et al. (1986). For this
sinulated population we chose parameter values approximatefy
equal to those estirnated for a south Florida population of
crocodvlus acutus.
'
3. originafly this sinutated population had one animal
at ewery even-day age from 2 days to 8000 days. Then each
sihulatad animal was assigned a "survival probabitity." This
probability decreases r.rith age in such a vray that:
by
a. From t=o to t=36o, survival probability, P, is gliven
P = (o.998076)t;
i.e., about half of the anihals night be expected to die off by
one year of age.
given -
b. Frorn t= 361 to t = a000, survival probability rs
by
F = (0.5)*(o.999711)t'360 -
i.e., aninals that reach one year of age rnight be expected to
ffdecay outl by about IOZ/YeaY.
4. Aninals were "kill-ed off'r according to their P (or
survival probability, as described above) by conparison aqainst
r Many readers wilf recognize the above equation as the
fuII, four-pararneter Richards node1. S" i.s set at 400cm; n 1s
set at 0.273; s" is set at 3ocn; t (agel is measured in days;
T is set at 6000 days. Given these parameter values, the
equation sinplifies to approxinately
PTLr = 177,929-(66.075)*EXP(-o.ooo4243'rt) l^1.3755