Beginners Interactive NetLogo Dictionary (BIND)
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NetLogo User Community Models
# Model of Spatial Dynamics of Desert Locust Populations
## WHAT IS IT?
The locusts species __Schistocerca gregaria__ has two lifestyle phases to deal with environmental changes that exhibit their own behavior. They live on grass patches in the desert. High density populations will trigger a phase change and "gregarious" locusts appear. They form swarms and search the desert for food. When they find a grass patch they will land and start to eat. After distributing over the patch the phase change may trigger again as the density reduces. Then "solitary" locusts will roam the area on their own looking for food.
## HOW IT WORKS
The solitary locusts (phase 1) will avoid contact with each other and turn around when encountering other locusts. However, their priority is finding food such they can reproduce. Otherwise they randomly walk around.
Their interaction with the environment will trigger a phase change. At some point locusts will have finished eating up a whole grass patch. Then they are stuck together in the desert and have a lot of contact with each other. Their memory of encounters will increase and when it hits a certain threshold individuals turn into a gregarious locust (change of breed).
Now the gregarious locusts (phase 2) have very different behavior. Their top priority remains finding food to reproduce. But if there is no food around them, they will flock and form a swarm with their neighboring gregarious locusts. (Here we copied and adapted code from “Flocking” in the NetLogo Models Library that uses a lot of trigonometry.)
The flock moves faster and more energy efficient than single locusts. The goal of the flock is to find food and they can sense grass patches over long distances. Flocking locusts will stay together, and some swarms also merge to become a larger swarm if they are close together.
Once a flock finds a grass patch and lands, the gregarious locusts will start to look for food on their own. This behavior may reduce their encounter memory and they may turn back into solitary phase.
- We introduced individual age such that locusts cannot carry on with this behavior forever
## HOW TO USE IT
The most interesting parameter to experiment with is `rain-interval`. Swarms will endure the dry periods better than solitary locusts.
(how to use the model, including a description of each of the items in the Interface tab)
## THINGS TO NOTICE
Enjoy observing the locusts living their life and periodically changing their behaviour through interaction with their environment.
## THINGS TO TRY
(suggested things for the user to try to do (move sliders, switches, etc.) with the model)
## EXTENDING THE MODEL
One possibility of extension would be to implement a switch to generate a space with evenly distributed grass instead of randomly placed patches.
How to implement the `break` in the `foreach` loop of the `eat` procedure?? Please contact me if you find out haha
## NETLOGO FEATURES
(interesting or unusual features of NetLogo that the model uses, particularly in the Code tab; or where workarounds were needed for missing features)
## RELATED MODELS
We copied and adapted the flocking behavior code from the NetLogo Models Library/Biology/Flocking.
## CREDITS AND REFERENCES
Authors: Jeremy Cook and Clemens Wager
### Background knowledge
Collett et al. 1998 PNAS https://www.ncbi.nlm.nih.gov/pmc/articles/PMC23706/
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