Biology Reference
In-Depth Information
to be equal, and set
grass-energy
and
weed-energy
to be equal as well. What
do you think will happen to the population levels now? Determine slider values so
that the following situations occur:
a.
The grass and weeds stay at (roughly) the same level (as shown in the plot
window).
b.
The weed levels (as shown in the plot window) are higher than the rabbit levels
and the rabbits die out.
c.
The weed levels (as shown in the plot window) are higher than the rabbit levels
and the rabbits do not die out.
Exercise 5.2.
Set
weed-grow-rate
and
weed-energy-level
to 0, and
grass-grow-rate
and
grass-energy
to 5 if they are not already at those
levels. Set
birth-threshold
to 15, and press
setup
and
go
to restart the sim-
ulation. As the simulation runs, gradually decrease
birth-threshold
to 10, and
then to 5. You will notice in the plot window that the rabbit population oscillates at a
higher amplitude as you decrease
birth-threshold
. Why does this happen? As
you further decrease
birth-threshold
to 2 or 1, the rabbits die out. Why does
this happen?
Exercise 5.3.
Right-click on the graphical interface and select
Edit…
. Notice
that the boxes labeled
'World wraps horizontally'
and
'World wraps
vertically'
are checked. This means that when a rabbit moves left from a left-
most patch, it will reappear on the corresponding right-most patch (and similarly if
the rabbit moves vertically from a top-most patch). If you uncheck those boxes, the
rabbits will be bound by the edges of the map (so we can think of them as being
“fenced in”). What effect does checking these boxes have on the rabbits? What effect
does it have on the grass?
Exercise 5.4.
By altering the code in the “Code” tab, change the patches in the
model so that there is a river three patches wide that separates the field into two
halves (this can be done by altering the code in the
grow-grass-and-weeds
function). Ensure that grass and weeds cannot grow in the river. Alter the
setup
function so that rabbits cannot begin in the river, and alter the
death
function so
that a rabbit dies if it goes into the river. What effect does this have on the rabbit
population over time?
5.4
AN INTRODUCTION TO AGENT-BASED MODELS
Mathematical modeling is a method of encoding relationships and interactions in a
natural or engineered system into a formalized system; the models can then be studied
and analyzed using a variety of mathematical approaches. Models allow researchers
from a wide variety of disciplines to examine systems and their emergent behavior.
For example, a model may be used in order to make predictions about the future
behavior of a system, or it may be used to solve a complicated problem explicitly.
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