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from infection at 92%. Each scenario was initialized with 10 ticks of which on average
5 were infected, and the simulation was run 25 times each for 10 years. For Scenario
1 and 2, the tick population was established, but the disease died out within two
years for all simulation runs. For Scenario 3, both the tick population and the disease
remained in the system at the end of all but one simulation. For Scenario 4, even with
a reduction in fecundity of 92% for infected females, both the tick population and the
disease remained in the system at the end of all simulations. This demonstrates the
significant impact of transovarial transmission on the establishment of a tick-borne
disease in a new area.
Exercise 4.43.
Using the ODD Template of Grimm et al. [
65
] provided here and
demonstrated in this section, return to your favoritemodel in this chapter and complete
the ODD Template for that model.
1.
Purpose
Question: What is the purpose of the model?
2.
Entities, state variables, and scales
Questions: What kinds of entities are in the model? By what state variables, or
attributes, are these entities characterized? What are the temporal and spatial
resolutions and extents of the model? Most ABMs include the following types
of entities:
Agents/individuals
Spatial units (e.g., grid cells)
Environment
Collectives
3.
Process overview and scheduling
Questions: Who (i.e., what entity) does what, and in what order? When are state
variables updated? How is time modeled, as discrete steps or as a continuum
over which both continuous processes and discrete events can occur? Except
for very simple schedules, one should use pseudo-code to describe the schedule
in every detail, so that the model can be re-implemented from this code. Ide-
ally, the pseudo-code corresponds fully to the actual code used in the program
implementing the ABM.
4.
Design concepts
Questions: There are eleven design concepts. Most of these were discussed exten-
sively by Railsback (2001) and Grimm and Railsback (2005; Chapter. 5), and
are summarized here via the following questions:
a.
Basic principles. Which general concepts, theories, hypotheses, or model-
ing approaches are underlying the model's design?
b.
Emergence. What key results or outputs of the model are modeled as emerg-
ing from the adaptive traits, or behaviors, of individuals?
c.
Adaptation. What adaptive traits do the individuals have? What rules do
they have for making decisions or changing behavior in response to changes
in themselves or their environment?
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