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Ants Ants Complex



Complex Adaptive Systems, CS 591
        April 16, 2008
    Prof. Melanie Moses
                   Basic Ant Biology
• All ants are eusocial
    – The colony is the unit of selection
        • Queen(s): reproducers, not masterminds
        • Reproductives: winged male and female alates
        • Workers: female, short lived compared to queens
    – Genetic sex determination
        • Haplodiploidy
        • Sociobiology
    – Division of labor:
        • All males are reproductive
        • female caste determined by environment & larval feeding
        • Allows learning, farming, herding, fishing(?!)…
• Communication primarily through pheromones
• Self organization (dumb ants, smart colonies)
Weaver Ants
                            Ant Diversity
“Lean against a tree almost anywhere, and the first creature that crawls on you
   will probably be an ant.” Holldobler and Wilson, Journey to the Ants (1995)
• In the world: 1016 ants; 10,000 spp.
• Colony size: ~10 to 10 million workers per colony
• Diversity decreases with latitude
• Ants live everywhere
    –   Soils
    –   Leaf litter
    –   Tree canopy
    –   In or under logs, rocks,sidewalk cracks, your house
• Ants eat everything
    –   Seeds
    –   Nectar (honey pots)
    –   Leaves/fungus
    –   Other insects (esp. termites)
    –   Each other
The New World Atta
    Leaf cutters
        Army Ants

Photos by Steven Holt
Army Ants

            Photos by Alex Wild
            SWRS, Portal, AZ
                     Worker castes
“Human societies send their young men to war, and colonies
  send their old ladies.” Holldobler and Wilson, The Ants (1990)

Old workers take on dangerous tasks
Many spp have morphological differences in castes
Trend toward increasing caste differentiation in large colonies
   –   Foragers
   –   Nurses
   –   Soldiers,
   –   Scouts & patrollers
   –   Nest maintenance workers
   –   Repletes
               Ant Colony Lifecycle

•   Queens and males fly from nests to mate
•   Male dies
•   Queen mates 1+ times, drops wings, digs nest
•   1st season: queen may forage or rely on stored fat
•   After 1st workers emerge: queen remains in nest
•   First workers forage to feed themselves and the queen
•   Very high mortality of juvenile colonies
Ant Mating
                   Ant Movement
• Migration by founding queens
• Colony movements
   – Relocations
   – Polydomous colonies
   – Army ants/bivouacs
• Worker movements
   – Patrollers
   – Nest maintenance, midden work
   – Foragers
• Foraging with pheromones:
   – information exchange, “stigmergy”, positive feedbacks & the
     social optimum
Desert Seed Harvesters
                  Pogonomyrmex spp.
•   Monogynous, monodomous, monomorphic
•   Stationary colonies
•   Sterile workers
•   Similar
    – behavior
    – diet (seeds, termites)
    – ant size (13-23 mg)
• Foraging period set by temperature & humidity
• Colony lifespan: up to 20 years
• Guilds of spp. associated w/ climate & elevation (Johnson
Colony size

                                                       2003 & 2004
                                                       Sevilleta LTER
      2003 Portal, AZ

P. desertorum            P. maricopa               P. rugosus
40-100 foragers/colony   150-250 foragers/colony   1500-2500 foragers/colony
                 Foraging in Ant Colonies

Workers organize to increase the survival and reproduction of the colony without
  central control

Colony metabolism is determined by foraging success:
   foragers collect all of the food that the colony consumes

Colony population size ranges from 10 to 10 million
    There are costs and benefits to increased size

How does colony size influence acquisition of energy and information?
  How do foraging networks scale with the size of the colony?
  How does network scaling affect colony behavior?

Model and field study of Pogonomyrmex (seed harvesting ants)
                 Big colonies need big territories

Longer foraging trips require more energy & reduce energy intake rates

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