Transcript Ants At Work by Deborah Gordon

Ants At Work
Fres 1010, Fall 2005
Complex Adaptive Systems
Lecture 2
Eileen Kraemer
Why study ants?
 How are these related?
 Behavior
of individual ants (microbehavior)
 Overall behavior of colony
 An emergent, self-organizing system
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
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.
3 Distinct Levels of Ants
 Queen Ants
 Worker Ants
 Sterile Females
 Male Ants
Queen Ants
 Not an authority figure; doesn’t decide
which worker does what
 Lays eggs
 Fed and cared for by “interior” workers
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
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.
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
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
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
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

Ants also …
 Find the shortest distance to a food
source
 Prioritize food sources
 Switch from nest-building to foraging to
raising ant pupae
How ???
 How do they know to do that???
 How do they accomplish it?
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
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?
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
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.”
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???
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
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.
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
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
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
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.
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
Stages in Colony Development
 Infancy
 Adolescence
 Maturity
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.
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?
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
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
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
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.