The Ecology of Agglomeration and
the Rise of Chaco Great Houses

Vernon, McCool, Brewer, Codding, Ortman

What is a Chaco great house?

Why are they built in these areas?

Why are they built at these times?

Familiar hypotheses

  1. Natural advantages
    Environment offers 🌳 resources, soil, 🌤️ climate️,💧 water!
  1. Agglomeration effects
    Density offers 🚚 reduced transport costs, 👷 available labor️, and 🧪 knowledge spill-overs
  1. But cities are costly, too!
    More people means 🤼‍competition for jobs, 📈 higher rents, 🍷 expensive food, and 😬 more people

Clustering is costly!

IFD tells us that habitat suitability is negative density dependent, so how do we get agglomeration effects?

Allee effects are unstable

Positive effects at low density are eventually overwhelmed by competition.

But, unequal effects may be self-reinforcing

Given circumscription, the productivity of an unequal system will increase relative to alternative arrangements.


Can explore this process by looking for times and places where great houses and pueblos co-occur.

Unit of analysis

⚠️ These results are preliminary!
  1. Still experimenting with hyper-parameters.
  2. Just an intercept-only model for now.

Spatial random effects

Temporal random effects

Covariance of spatio-temporal weights


  1. Results are suggestive 🤔 but inconclusive.
  2. Potential regional trends 🌎 need more consideration.
  3. Need to incorporate environmental covariates 🌳.
  4. And so many other things…


  • Joan Brenner-Coltrain
  • Link O’Brennan
  • Josh Watts
  • R. Kyle Bocinsky