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2.13 Collective Behavior
Discussion
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Instructions
In this simulator, you will be playing with a stripped down version of nest site selection in Temnothorax ant colonies. As you learned in the lecture, the first nest site to reach a critical density (known as quorum) wins the competition. How does an individual ant know if quorum has been met? Does it count up all the ants in the nest and divide by the nest area? Of course not. But then, how do ants sense quorum?The simulation will provide some guiding questions leading to the challenge for you to determine the “rule” that is being used by individual ants to sense quorum.
Collective Decision Making in Temnothorax Ant Colonies
Questions
What is the rule that governs how a quorum is reached? What else did you observe? What did you learn from the simulation? What questions do you have that remain unanswered? -
Observations:
1) ants turn red when they bump into the wall of the nest or they bump into another red ant
2) ants turn black after a certain number (x) of steps if they don’t bump into the wall or bump into another ant after x steps
3) progress bar increases with every red ant that leaves the nest before turning black
4) nests with smaller radius and wider apertures perform better maximising the number of red ants leaving the nest before turning black
Question:
1) why is there a rule that ants turn black in Observation (2)? Do they forget it’s a good nest after a certain time represented by x steps?-
Hi Johann,
Your assessment is basically correct. The rules that govern the simulator are as follows:
1) Ants turn red when they bump into other ants – this represents the “excited state”
2) Ants return to black if a certain amount of time passes without contact with another ant – this is the “ground state”
3) If an ant exits in the excited state the progress bar increments – this represents recruitment to this nestThe reason ants decay from red to black is because the goal is to sense “quorum” which is a density-dependent effect. When an ant is in the excited state, it thinks that the nest must have a high density because it just encountered another ant. However, if the nest is really low density then a long amount of time passes before the ant encounters another ant. Thus, the decay from the excited state allows ants to properly estimate nest density. High-density nests will keep the ants in the excited state (small nests with extremely small apertures will be filled with red ants) whereas low-density nests will lead to ants leaving in the ground state (large nests with large apertures).
To us, this is an odd way to estimate density but to ants, it is a cognitively simple way to get a decent estimate for density. In fact, the ants don’t even need to know that they are measuring density. Instead, all they need to know is whether or not, at the time of exit, they have recently been “stimulated” by another. If so, they take this excitement into their recruitment behavior (presumably).
Best,
Jake
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Based on my experience with the simulator I have determined a few basic rules:
1. Ants are generated at the entrance to a nest and are colored black
2. If ant bumps into the walls of the nest or another black ant sufficiently many times, it will turn red
3. If a black ant bumps into a red ant, it will turn red
4. If a red ant leaves the nest, the progress bar increasesThese rules simulate a temnothorax ant colony exploring possible nest candidates. When a black ant is generated at the entrance to the nest, it simulates an ant brought into the nest by tandem running. An ant that is satisfied with the nest turns red, and if a red ant leaves the nest, it means it has started to carry ants into the nest. Therefore the progress bar of the nest increases, bringing it closer to quorum. Whichever nest candidate reaches quorum first “win’s”, which means the entire colony will be moving in soon.
I share the same question as Johann; why do red ants turn black after a certain number of steps? Are they not satisfied with the nest anymore?
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HI Akshansh,
Yes! The ants are no longer satisfied with the nest. This way of decision making is known as “Temporal Discounting” and it is something you and I both do as well. The basic idea is that immediately after being stimulated we are the most excited to take action but, as time passes, the strength of the stimulus fades and we become less interested in whatever action we were thinking about taking. For example, immediately after a tragedy there is almost always talk about what actions can be taken to avoid the repeat of such a tragedy in the future but, as time passes, the pain wears off and people become less likely to make any change.
For the ants, Temporal Discounting basically serves as a simple way to be “excited” about transporting. If they bump into another ant inside the nest, they (presumably) think this nest must be a good one I want to recruit to it but, if too much time passes, this enthusiasm fades and if they will not transport upon exit. This simple mechanism actually serves as a way for ants to recruit to nests with high density, which is the goal of quorum sensing.
This is due to the fact that high-density nests will keep ants in the excited state whereas low-density nests allow ants to decay back to the ground state before exiting. The reason ants want to recruit to high-density nests is because high-density implies lots of previous recruitment behavior, which is basically like lots of votes in favor of a given nest. A high density means a lot of votes for a nest, and that means the nest is likely a good one to recruit to.
Best,
Jake
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