Positional Communication and Private Information in ... · What can we learn from biological models...

Positional Communication and Private Information in Honeybee Foraging Models

Peter Bailis, Radhika Nagpal, and Justin Werfel

HarvardSchool of Engineeringand Applied Sciences

ANTS 2010: September 8, 2010

Peter Bailis - Harvard University 2010

Harvard RoboBees ProjectGoal: Build swarms of micro-robotic insect pollinators

What tradeoffs do we need to make between complexity and performance?

What can we learn from biological models about bee behavior?

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Collective Honeybee BehaviorHoneybee colonies exhibit amazing collective behavior

• Large-scale (20-30K), decentralized multi-agent coordination using extremely simple mechanisms

• Foraging: dynamic task allocation across changing environments (bees to known sources)

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How Bees Communicate: Waggle Dance

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Direction



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Direction

Distance



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Direction

Distance

Duration ~= Quality


Recent Controversy

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Recent Controversy

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Does the dance increase efficiency?


Recent Controversy

Recent study: 93% of foragers studied relied on private information about food sources instead of following a dance’s cues [Grüter et al., 2008, Proc. R. Soc. Lond. B Biol.]

Lack of location information often does not affect colony success [Sherman and Visscher, 2002, Nature]

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Recent Controversy

Recent study: 93% of foragers studied relied on private information about food sources instead of following a dance’s cues [Grüter et al., 2008, Proc. R. Soc. Lond. B Biol.]

Lack of location information often does not affect colony success [Sherman and Visscher, 2002, Nature]

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New theory: shared information is a backup for private information [Grüter and Farina, March 2009, Trends in Ecology and Evolution]



Critical response: results are inconclusive [Brockmann and Sen Sarma, November 2009, Trends in Ecology and Evolution]:

“...there has not been a rigorous analysis to date of how to assess correctly the efficiency of the dance language or any other symbolic system that communicates spatial information”

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Is sharing position information more useful than relying on private information, and when?

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Key Question


Key Variables

We explore the effect of the food’s

•Distribution: Clustered or scattered

•Density: Many or few food sources

•Quality: Homogeneous or heterogeneous

•Quantity: Amount of food per source

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Outline

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Motivation: Why bees and why foraging?

Design: Foraging model

Evaluation: Simulation and results

Discussion


Model

Goal: Accurately represent salient details of bee foraging as described in literature

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World

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Hive


Food Distribution

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Flowers added at fixed rate


Flower Quality

Capacity: fixed number of visits

Nectar value: 1 or 4 sugar units per visit [Dornhaus et. al., Behavioral Ecology and Sociobiology, 2006]

Overall flower quality metric:

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(Distance from Hive)

(Maximum Distance)(Nectar Value)*(1- )

[Seeley, Wisdom of the Hive, 1996]


Bee

Bee Model

• Inaccurate flight, limited energy and memory

Bee Roles

•Dynamic transitions

Shared versus Private Information

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Bee Roles

Scout: look for new food sources, remember best one

Forager: move to and collect food from known source; if known source not present, search for replacement

Unemployed: no known food source, wait in hive to be recruited

[Similar to de Vries and Biesmeijer, Behavioral Ecology and Sociobiology, 1998, and others]

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Lévy Flight

16[Reynolds, Physics Letters A, 2006]


Role Transitions

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Dance Threshold

Forage Threshold

Qua

lity


Role Transitions

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Dance Threshold

Forage Threshold

Advertise flower

Qua

lity


Role Transitions

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Dance Threshold

Forage Threshold

Advertise flower

Qua

lity

Continue to forage


Role Transitions

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Dance Threshold

Forage Threshold

Advertise flower

Qua

lity

Continue to forage

Become unemployed


Role Transitions

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Dance Threshold

Forage Threshold

Small probability of scouting

Advertise flower

Qua

lity

Continue to forage

Become unemployed


Communication Models

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SharePosition



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SharePosition PrivatePosition



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SharePosition PrivatePosition

Previously encountered,

Privately remembered

sources



SharePosition: Recruits forage at location specified by dance

PrivatePosition: Recruits forage at previously known location, or, if they have none, become scouts

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SharePosition: Recruits forage at location specified by dance

PrivatePosition: Recruits forage at previously known location, or, if they have none, become scouts

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Two extremes


Outline

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Discussion


Overall Efficiency

Efficiency metric:

Food gathered / Energy expended

Default comparison:

PrivatePosition to SharePosition

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Overall Efficiency

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Overall Efficiency

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PrivatePosition better


Overall Efficiency

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PrivatePosition better

SharePosition better


Overall Efficiency

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Low (20 trips)Flower Capacities


Overall Efficiency

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PrivatePosition can be more efficient than SharePosition!



Overall Efficiency

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Medium (60 trips)Low (20 trips)

Flower Capacities


Overall Efficiency

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Medium (60 trips)High (200 trips)



Overall Efficiency

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Medium (60 trips)High (200 trips)


...but isn’t always more

efficient!


Relative performance depends heavily on environment

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Known Food Sources

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Known Food Sources

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PrivatePosition harvests from many more

sources


Known Food Sources

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PrivatePosition harvests from many more

sources

Capacity 20 trips


Oversubscription

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Oversubscription

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Yum!

Yum!


Oversubscription

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Oversubscription

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(Potentially many) wasted trips!


Foraging at more food sources results in greater diversity in forager allocation

• Low capacities result in high oversubscription--more wasted trips!

•With higher capacities, oversubscription costs are amortized across more trips

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Unsuccessful Trips

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Efficiency, Revisited

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Low (20 trips)Medium (60 trips)High (200 trips)

Flower Capacities


Efficiency, Revisited

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As generation rates increase,

chance of finding replacement flower after depletion


Flower Capacities


Clustered Efficiency

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Flower Capacities



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Efficiency again depends on

environment!


Flower Capacities



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In clustered world, harder to find additional flower once

cluster is depleted

Efficiency again depends on

environment!


Flower Capacities


Observation: under this model, clusters are essentially super-food sources

•Depletion and recovery speeds determined by flower generation rate

Clustered world is analogous to having ten super-flowers; location matters

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PrivatePosition’s successes are due to its diversity of sources

• Reduces oversubscription problem

•With higher amounts of food, and when food is easy to find or geographically correlated, less advantageous

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Heterogenous Worlds

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50% each quality


Efficiency

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Flower Capacities


Efficiency

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SharePosition concentrates its efforts on fewer, but higher quality

sources


Flower Capacities


Efficiency

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Flower Capacities


Efficiency

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Again, SharePosition is

better in heterogenous

worlds...


Flower Capacities


Summary

PrivatePosition is better in worlds with:

• Fast source depletion

•Many easy-to-find sources

SharePosition is better in worlds with:

• Low risk of oversubscribing sources

•Heterogeneous source qualities

• Few hard-to-find sources

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Outline

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Discussion


Discussion

Effectiveness depends on a careful balance between

having a diversity of food sources, decreasing the risk of oversubscribing them and wasting energy and

concentrating efforts on the best sources

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Discussion

However, PrivatePosition can outperform SharePosition by over 35%

This supports Grüter’s hypothesis regarding the role of private information in forager allocation

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RoboBees

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•Open Questions:

•How complex do agents need to be?

•What communication capabilities are necessary?


Conclusion

Relying on private information in bee foraging can be advantageous in several environment types due to an increased diversity in food sources

• This supports recent claims about the role of the waggle dance and private information

• Relative efficiency dependent on many environmental factors

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Thank YouData and open source (GPL) code:

http://eecs.harvard.edu/~pbailis/beesim/

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Conclusion

Relying on private information in bee foraging can be advantageous in several environment types due to an increased diversity in food sources

• This supports recent claims about the role of the waggle dance and private information

• Relative efficiency dependent on many environmental factors

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Peter Bailis - Harvard University 2010 43

Positional Communication and Private Information in ... · What can we learn from biological models...

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