isee systems
STELLA
lynx-hares.stmx
(C) 2013 by isee systems, inc.
0
60
0.125
5E4
Initially, there are 50000 hares in the ecosystem.
hare_births
hare_deaths
Hares*hare_birth_fraction
A compounding process is used to depict hare births. The births flow is defined as the product of Hares and their natality. This process works just like compounding interest in a savings account.
Lynx*hares_killed_per_lynx
In this external resource process, lynx are the resource underwriting the consumption of hares. Each lynx has a productivity, given by hare kills per lynx.
1250
Initially, there are 1250 lynx.
lynx_births
lynx_deaths
one_time_lynx_harvest
Lynx*lynx_birth_fraction
A compounding process is used to depict lynx births. The births flow is defined as the product of lynx and their natality. This process works just like compounding interest in a savings account.
Lynx*lynx_death_fraction
This is a draining process. Some fraction of the lynx population will die each year. The portion that dies, in turn, depends on the density of hares in the ecosystem.
PULSE(size_of_1_time_lynx_harvest, 4, 1e3)
This test input uses a PULSE function to remove some number of Lynx from the system at time 4. This harvesting effectively knocks the system out of steady state, thus enabiling its latent dynamics to unfold.
1.25
Each hare in the ecosystem is assumed to produce 1.25 offspring (on average) per year.
Hares/area
This equation calculates the average density of hares in the ecosystem.
1E3
The area of the ecosystem is defined as 1000 hectares.
0.25
On average, each lynx will generate .25 offspring per year.
1
hare_density
.94,.66,.4,.35,.3,.25,.2,.15,.1,.07,.05
hare_density
The number of hares killed per lynx (per year) increases with the density of hares in the ecosystem. Note that when density is 0 (there are no hares), kills per lynx per year must be 0.
0,50,100,150,200,250,300,350,400,450,500
hare_birth_fraction
hare_births
Hares
hare_births
Hares
hare_density
area
hare_density
hare_density
hares_killed_per_lynx
hare_density
lynx_death_fraction
hares_killed_per_lynx
hare_deaths
lynx_death_fraction
lynx_deaths
Lynx
lynx_deaths
Lynx
hare_deaths
Lynx
lynx_births
lynx_birth_fraction
lynx_births
size_of_1_time_lynx_harvest
one_time_lynx_harvest
flow
value
IF value THEN MAX(flow, 0) ELSE flow