Biological Inspiration: Ants

1. Biological Inspiration:Ants By Adam Feldman

2. “Encounter Patterns” in Ant Colonies • Ants communicate through the use of pheromones perceived through their antennae • For example, determines if another is a nestmate • Study antennal contact between workers • ‘Antennal contact’ refers to brief contact between the antennae of two ants

3. Experiment 1 • Is a pattern of antennal contact a characteristic of the behavior of an ant colony? • Examine 3 species of ants: Myrmica rubra, Solenopsis invicta (the fire ant), and Lasius fuliginosus • How does each species vary antennal contact behavior in response to the presence of food?

4. Experiment 2 • Does antennal contact help determine ant density? • How does antennal contact rate vary as ant density varies? • ‘Contact rate’ defined as the number of contacts per ant, per unit time • Only L. fuliginosus workers used in the remainder of the experiments

5. Experiment 3 • How is the rate of antennal contacts affected by the change of ant density? • How does behavior change with the introduction of ants which are non-nestmates? • Contact Rate • Speed of movement

6. Differences in Contact Rate by Species(Method) • Each colony lives in an isolated environment • 12x23cm plastic arena with Fluon walls • Divided into four regions – food, nest, two empty • Colonies consist only of worker ants – no queen or brood (except S. invicta which contain both) • Experiments do not begin until the colony has been in its arena for at least a week

7. Differences in Contact Rate by Species(Results) • Contact rates highest in L. fuliginosus • Largest of the three species • M. rubra increased contact between returning foragers and preceding ant trail formation • Antennal contact is involved in forager recruitment • S. invicta increased contact where food is found • Foragers recruited from nearby ants • Contrasts with bee behavior

8. Attraction to Edges(Method) • Ants displayed a tendency to gather at the arena edges • Attraction to arena edges • Movement to edges designed to facilitate higher local density • Experiment in arena without edges • Create arena on the surface of a sphere • Two attempts correspond to size of smallest square arenas

9. Attraction to Edges(Results) • Ants displayed an attraction to arena edges • As ant density decreased, clustering increased, especially at the arena edges • As arena size increased quadratically, edge size only increased linearly • By staying at the edges, ants could maintain local density • Aggregation in edgeless arena • Indicates that maintaining density is the reason for clustering, not affinity for the edges

10. Tendency to Aggregate(Methods) • Suppose ants’ tendency to aggregate (cluster) related to desire to control contact rate • Ants must be able to see (or otherwise sense) each other before deciding to initiate a contact • Measure the average scanning distance of an ant • From what distance can one ant detect the presence of another

11. Tendency to Aggregate (Results) • Appears that ants can detect one another at distances up to 1.2cm • Ants closer than this turned towards each other much more than statistically likely • Ants farther than this behaved as though no other ant was present • Ants can indeed control contact rate by choosing in advance whether or not to approach another ant

12. Contact Rate vs. Density(Methods) • Changes of ant density • Three ant groups – 100, 200, and 450 workers each • Four square arenas – 25cm, 50cm, 75cm, and 100cm • Each arena divided into 6.25x6.25cm grid squares • The contact rate in each grid square was determined, so Local Contact Rate could be studied separately from Overall Contact Rate

13. Contact Rate vs. Density(Results) • Overall Contact Rate • If contacts were purely random (collisions), overall contact rate would increase linearly with density • While contact rate did increase with density at very low densities, it leveled off as density further increased • Thus, statistically, overall contact rate could not be determined by random collisions

14. Contact Rate vs. Density(Results) • Local Contact Rate • Did not increase with density • Even at the local scale (one grid square), contact rate did not follow a model of random behavior • Clearly, local contact rate is determined by design of the colony, not through any random element

15. Contact Rate vs. Density(Results) • Comparing Overall & Local Contact Rates • Both locally and globally, ants control contact rate by preventing or encouraging contacts with nearby ants depending on density • Contact rate easier to regulate on flat surface than sphere • Aggregating along an edge provides “protection” against too many contacts • Edgeless arenas create two dimensional clusters

16. New Ant Encounters: Contact Rate(Methods) • Start with a host group and add new ants • Host group 35 or 75 ants from colony A • Add 15 ants from either colony A or colony B • Observe contacts of host group prior to addition of new ants and for 10 minutes after • Observe contacts of new ants from moment of addition until 10 minutes have passed • Examine immediate (1-3 minutes after addition) and lasting (5-10 minutes) changes in behavior

17. Contact Rate: New Ant Encounters(Results) • Response of host ants depend on rate of contact with added ants • Contact rate increased if higher proportion of new ants encountered • Experiments with 35 host ants showed more impact than experiments with 75 host ants, as did experiments with non-nestmates (colony B) • New ants not avoided • Behavior returns to normal within 5 minutes

18. New Ant Encounters: Speed(Methods) • Increases in speed of movement may be the cause for any increased contact rate upon adding new ants • New ant experiments are re-examined (via videotape), with attention paid to ant speed

19. Speed: New Ant Encounters(Results) • New ants moved much faster than host ants, especially if they were non-nestmates • However, speed changes did NOT account for changes in contact rate • Even undisturbed ants varied their speed greatly from minute to minute • Highest speed resulted from experiment involving 75 host ants and 15 non-nestmates • Not the same experiment as the highest contact rate

20. Conclusion • Different species of ants will display different patterns of antennal contact • Corresponds to other species-specific differences • S. invicta (colonizing species) increase contacts if food is found while L. fuliginosus (stable, old colonies) do not • Contact rate must be important • Ants attempt to regulate it • One way, by detecting each other from up to 1.2cm away

21. Conclusion • Ants regulate contact rate to keep it fairly constant, despite density changes • Maintaining contact rate plays a role in colony organization by causing aggregations to result • Information transmitted by a contact can affect colony decision making • Ant can change behavior based on who is encountered (forager vs. nest maintainer) • Follows bee model (forager vs. nectar storer)

22. Conclusion • Ant behavior is dictated by the proportion (not the number) of non-nestmates encountered • Contact rate increases up to three fold upon introduction of non-nestmates • Increase only lasts for several minutes • Speed could account for this increase • Findings indicate it is not the only relevant mechanism • Ants cause this increase by choosing how many nearby ants to approach • Motivation: Quickly judge danger (lost vs. attack)

23. Conclusion • Limitations • Specialized domain • Authors repeatedly stress that laboratory nature could alter results from real world values • Lack of queen & brood, trying to escape arena, etc • Admitted imperfect counting techniques