NetLogo User Community Models
by (Submitted: 05/01/2012)
This is an agent-based simulation of the classic "diet breadth model" of optimal foraging theory (see Foley 1985).
SETUP: Initialize the number of foragers and total number of prey.
FORAGERS: One or more foragers (<init-foragers> selected by the user) are placed randomly and given 100 energy units (eu's) to start with. Each forager begins to move in random directions; each cell moved costs the forager 1 energy unit.
PREY: Prey (total determined by <init-prey>, selected by the user) are placed randomly and move randomly. Up to 4 distinct prey species can be defined. The user selects the relative density of the species, its food value (when consumed by a forager), and the costs to process the species before it can be eaten. Prey are ranked according to their net food value = gross food value - processing costs.
FORAGING: When a forager encounters prey, she/he decides whether to take it or continue searching for prey. If she/he is not very hungry (energy >= 85), she/he will only take the 1st ranked prey; if she/he is hungrier (energy 70-85), she/he will take 1st or 2nd order prey; if she/he is even hungrier (energy 55-70, she/he will take prey ranked 1st through 3rd; if she/he is very hungry (energy < 55), she/he will take any prey. On taking any prey, the forager received the net food value. A patch turns red briefly to mark when a prey is taken.
MONITORING DIET BREADTH: The species of any prey taken is added to the beginning of a running list of the 10 most recent prey taken; if the length of the list is over 10, the last prey on the list is removed. The number of different prey species in the list is monitored as diet breadth.
HOW TO USE IT
Set the options (see above). Press "setup". Then press "run".
THINGS TO TRY
Try changing the density of the 1st ranked species or of other species. What happens to diet diversity? Try changing the food values in each cell or the distance moved by each forger each cycle. The classic diet breadth model considers only one forager. What happens if more than one forager are placed in the simulation?
EXTENDING THE MODEL
Other OFT models could be simulated in this way.
CREDITS AND REFERENCES
C. Michael Barton, Arizona State University
For an overview of OFT models, see Foley, R. (1985). Optimality theory in anthropology. Man, 20, 222-242.
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