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Complexity: Ch. 1

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Broad Examples

• Insect colonies•The brain•The immune system•Economies•The World-wide Web

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Breaking Ranks Temporarily

•We’re going to leave the book’s systematic development for a while and take a closer look at one particular type of complex system.• This will give us a chance to introduce several topics that will be continuing themes in the course.• And it’s sometimes more interesting.

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Eusocial Animals

•Highly evolved level of organization• cooperative care for immature members•multiple generations in a colony• both reproductive and non-reproductive members

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Some Eusocial Animals

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naked mole rat

parasitic shrimp

antsbees

wasps

termites

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Eusocial Insects

• 1.9 million animal species described so far• probably 8-30 million total• about one half are insects: 4-15 million• about 1% are eusocial: 100,000

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Eusocial Insects

•Dominant role in most land ecosystems•Ultimate superorganisms• principal predators• principal scavengers• aerate soil• food for other animals

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Ants

• Entire colony is a single superorganism on which evolutionary selection operates.• organizations vary greatly• number of queens• size of colony, including

supercolonies of several hundred million members• reproductive practices• foraging practices

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I’d like you to meet a young lady from a very

interesting family

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A member of a eusocial ant species

Leafc

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Attine Distribution

• tropical regions of Mexico, Central America, South America, southern U.S.• as far north as the New Jersey Pine

Barrens• as far south as central Argentina• Attines appear to have a single

ancestor species: agriculture in the New World was probably invented just once, shortly after South America separated from Africa. 10

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Attine Agriculture

• human agriculture about 10,000 years ago• attine agriculture about 60 million

years ago (six thousand times more ancient)• fungus agriculture developed by• termites in the Old World• attine (leafcutter) ants in the New

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Atta cephalotes (Costa Rica)

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Atta Texana Nest Model

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Colombia: $40/lb

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To see a live leafcutter colony

• cross the bridge into Vermont,• turn left,• and visit

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How Do Attine Colonies Work?

•Good question• Intensely studied

We’re going to look at a few

models

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All models are wrongbut some are useful.

- George Box, 1976

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Two broad motives for modeling

One is to accurately represent reality:

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Two broad motives for modeling

The other is to discover the origins of some essential features of reality

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Which is what we’ll do here

Agent-based Modeling•Create a world with a bunch of ants (agents) in it•Assign behavioral rules to the ants•Start the clock ticking

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Ant Rules

• If she has food and is at the nest• drop off the food.

• Otherwise if she has food• head for the nest.

• Otherwise if she finds food• pick up a piece.

• Otherwise• wander randomly around.

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The Universe

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Early days in the Universe

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Now let’s take a look at some simulations in NetLogo

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What have we seen?

• Individual ants have very small behavioral repertoire•A small set of rules leads to the emergence of “coordinated” behavior• Information exchange (chemical trails) increases efficiency 26

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Properties of Complex Systems

•Complex collective

behavior

• Information processing

•Adaptation27

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Mitchell’s Definition

A complex system is one in which large networks of independent components with simple rules create•complex collective behavior• information processing systems•adaptive change

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