Ants At Work

1. Ants At Work Fres 1010, Fall 2005 Complex Adaptive Systems Lecture 2 Eileen Kraemer

2. Why study ants? • How are these related? • Behavior of individual ants (microbehavior) • Overall behavior of colony • An emergent, self-organizing system

3. Deborah Gordon • Researcher at Stanford University • Tracks life cycles of ant colonies, following them year after year as they • Look for food • Compete with other colonies • Mate with other colonies • Author of Ants at Work: How an Insect Colony is Organized

4. Various Networks of Ants • Networks and connections within the ant colony. • Networks of trails and paths to food outside the colony. • Networking and connections with neighboring ant colonies.

5. 3 Distinct Levels of Ants • Queen Ants • Worker Ants • Sterile Females • Male Ants

6. Queen Ants • Not an authority figure; doesn’t decide which worker does what • Lays eggs • Fed and cared for by “interior” workers

7. The “Escape Hatch” • In case of disturbance, interior workers carry the Queen Ant down a passageway that leads two feet underground • Why? • Queen Ant “orders” them to? • Their genes “tell them to” – it is in the best interest of the colony (and the colony’s gene pool) because the Queen is responsible for giving birth to members of the colony

8. Working Ants and Daily Chores • Interior Workers • Tend to the Queen and brood (eggs, larvae, and pupae) • Nest Maintenance • Open and close entrances to the nest • Maintain all structures and pathways within the colony • Patrollers • Designate the foraging paths for the day • Foragers • Follow paths designated for them to gather food for the colony • Midden Workers • Manage the refuse pile, also known as the Midden • The Midden also seems to have a significant relation to how the ants find their colony.

9. Allocation of Tasks • No source of leadership • Queen is only there to reproduce, not to control the colony • As conditions change emphasis on certain jobs change • Workers are moved from one task to another depending on the need for workers • Ex. If there are serious issues with nest maintenance, some foragers will switch to nest maintenance until the problem is solved. • Foraging is the most important task and will call for workers before any other task

10. Foraging Paths and Trails • Mature colonies can have up to 8 customary foraging trails • However, patrolling ants generally do not send foraging ants to the same trail as the day before • Younger colonies are more likely to send their foraging ants to a rich food source they had once found

11. Foraging Paths (continued) • Larger colonies don’t necessarily cover larger areas, but get more food because they have more workers • Paths are very adaptable • They grow into more intricate paths with the growth of the workforce • A small workforce changes the paths to a more standard construct to cover area more effectively

12. Ants partition their living space • Ants take trash from food they’ve collected and deposit it in the midden (garbage dump) • Ant carcasses piled into a “cemetery” • In closed environment: • Cemetery is farthest point from colony • Midden is half-way between cemetery and colony

13. Ants also … • Find the shortest distance to a food source • Prioritize food sources • Switch from nest-building to foraging to raising ant pupae

14. How ??? • How do they know to do that??? • How do they accomplish it?

15. How do they do that? • Swarm logic: “thousands of ants, each limited to a meager vocabulary of pheromones and minimal cognitive skills collectively engage in nuanced and improvisational problem-solving.” • Individual ants assess local conditions and respond, interactions among ants result in global (colony) behavior

16. Foraging <-> colony size • Number of ants foraging for food is constantly adjusted, based on: • Overall colony size • Food available in surrounding area • Presence of other colonies in vicinity • How do ants know to change jobs?

17. Ants communicate • Pheromones (semiochemicals) • Secreted from sternal and rectal glands • Play the central role in the organization of colonies (Wilson & Holldobler) • Also regurgitate recently digested food • Tactile

18. Pheromones can signal: • Task-recognition • “I’m on foraging duty.” • Trail attraction • “There’s food over here!” • Alarm behavior • “Run away!” • Necrophoric behavior • “Let’s get rid of these dead ants.”

19. Seems too simple …. • Can also detect gradients in pheromones • Essential for forming food delivery lines • Provides directional information • Can also detect frequency of detection • Encounter 10 other foraging ants/hour -> keep at it • Encounter 100 other foraging ants/hour -> change jobs • Estimate size of colony by statistical sampling of encounters???

20. Principles for deriving global intelligence from local interactions • More is different • Ignorance is useful • Encourage random encounters • Look for patterns in the signs • Pay attention to your neighbors

21. More is different • Must have a critical mass of ants for colony to make intelligent assessments of local state • 10 ants – not enough for interactions to happen frequently enough for organized behavior to emerge • 2000 ants – that’s enough! • Ants don’t “know” they’re prioritizing pathways between different food sources by laying down pheromones • … and we wouldn’t know either if we only studied individual ants …it is only by observing entire system that behavior becomes apparent.

22. Ignorance is useful • Each ant follows simple rules • Complex analysis not required of individual ants; don’t become too finely tuned …. • Variations in response among ants helps to smooth transitions of colony behavior

23. Encourage random encounters • Colonies rely on random interaction of ants exploring space without any predefined orders. • Arbitrary pair-wise encounters; large number of encounters allows individuals to gauge system state • Response of individuals combine to alter system state • Supports adaptation to new environmental conditions

24. Look for patterns in the signs • Ants have small vocabulary • Rely on patterns in semiochemicals they detect • Gradient in pheromone trail -> leads to food source • High ratio of nest-builders to foragers in other ants they encounter -> switch to foraging

25. Pay attention to your neighbors • Local information can lead to global wisdom. • Primary mechanism of swarm logic is the interaction of neighboring ants in the field.

26. Life Cycles • Colony Life Cycles • Form when a New Queen mates with a Male from another parent colony, and then forms her own colony • Generally last about 15 years • Can exist as long as the Queen can continue reproducing female workers • Individual Ant Life Cycles • Queen: 15- 20 years • Males: A few weeks (long enough to reproduce) • Female Workers: About 1 year

27. Stages in Colony Development • Infancy • Adolescence • Maturity

28. Differences among life stages • Younger colonies are more fickle than older colonies – may respond differently from week to week. • Encounters with other colonies: • Older colonies avoid interaction. • Younger colonies more aggressive.

29. Are the ants older too? • Male ants live only one day. • Worker ants live about 12 months. • Queen ant lives for years. • So, if the ants are just as young, why does an older colony behave differently from a younger colony?

30. Connections with Other Colonies • Workers can recognize ants from their own colony by a colony specific scent • When foragers from different colonies meet, those foraging trails will be used less and less, and seen as space lost to competition • Certain foragers specialize in fighting, and do not usually go out unless large number of foragers are out

31. Older Colonies vs. Younger Colonies • Older colonies are more likely to interact with other colonies • Colonies remain about the same size • Once colonies reach the 2-year mark they are likely to keep the size of their nest the same • More ants are sent out from the older colony • Older colonies also send their foragers out farther distance

32. Natural Response to Strangers • Ants respond to the rate of interaction with non-nestmates • Sight not good, use contact rate to determine the density of non-nestmates • Ants will try to maintain density through clustering when they feel contact rate is low • Contact rate directly correlates with density of nestmates • Low contact rates indicates high numbers of mates present • High contact rates indicate low number of mates present

33. Sources Used • Gordon, D. (1999). Ants at work. New York, NY: The Free Press. • Foster, D. (2001) An ant’s life. Retrieved from the World Wide Web on November 13, 2002. • Library.Thinkquest.org. (?). Insects. Retrieved from the World Wide Web on November 13, 2002. • The University of Georgia College of Agricultural and Environmental Sciences. (2000). Managing imported fire ants in urban areas. Retrieved from the World Wide Web on November 13, 2002.