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Climate Change 

August 12, 2007

Models: CEG

2_times_diversity_network.pngWelcome back to models. I’ve been thinking about how to proceed with this thread, and I’ve developed three objectives:

  1. Explain more about model construction, use, and limitations, using a model that I’ve developed myself. This model, CEG, is designed to examine the responses of biological communities and ecosystems to disruptions of various sorts, on the large-scale.
  2. Open source” (of which I am BIG fan) the model, in the sense that I would like feedback (no pun intended) from you, the blog readers, regarding questions to be addressed, and modifications to be made to the model. In other words, I’d like us to generate some experiments as a community!
  3. I would very much like to bring this model, and the work that we’ve applied it to, to the general public, and we (myself and collaborators) have been thinking long and hard on the best ways to do this. The end-product would be something that would form part of the public offering of the California Academy of Sciences, whether an exhibit, visual show, online experience, etc. I’d like to open this effort also to the community, and as we discuss the model and play with it, let’s see what ideas could perhaps be generated. What would you like to see? What do you think would be most informative, exciting, educational?

So let’s begin the process now! Let’s hear your questions, and as I explain the model and objectives, let’s hear your ideas!

Okay, a brief introduction to CEG. CEG stands for Cascading Extinction on Graphs, and is actually a body of theory that seeks to understand the role of community structure in extinction. No species is an independent unit, and change in one species is likely to affect other members of the biological community, either directly or indirectly. CEG represents communities as graphs (read more here, and take a look at the figure), where the nodes are species, and the links or edges between species represent trophic (“predator-prey”) interactions. The most basic version of CEG examines what happens when we remove a species from the community or graph. Is there a cascade of effects? Does the community eventually settle down to a new stable state, or at what point will (or can) the community unravel or collapse entirely? These are not really new questions, but we are asking them in a new way, and with new implications. So far we’ve examined mostly paleocommunities from the distant past, but we are beginning to “look to the future”. You can read a bit more about CEG here and here (sorry, but I can post only the first pages of these publications). I will also make a recent presentation available online; soon.

Next time, we’ll go through the exercise of actually beginning development of the model. We’ll also keep climate change models in mind, and refer to them often.

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Filed under: Climate Change — Peter @ 11:31 am


  1. Hi Peter,

    Very interesting model and thanks for sharing it.

    I was checking out your blog while writing a post on the climate exhibit at CAC from my visit last week (see http://blog.ifpeople.net ) when I found this post. I thought you might be interested to know about Climate Interactive, a project that is creating an open source community around climate models, and specifically the learning simulations created for them.

    They are specifically working on systems dynamics models and are leveraging the online software of Forio.com for allowing users to interact with them. Forio allows anyone to use the simulation online (no need for proprietary desktop software to run it).

    Anyway, have a look at climateinteractive.org for some info (this site is getting replaced soon). Another good place is their blog – http://climateinteractive.wordpress.com .


    Comment by Christopher Johnson — October 30, 2008 @ 7:39 pm

  2. Hi Peter,

    Very interesting model and thanks for sharing it.
    Anyway, have a look at climateinteractive.org for some info (this site is getting replaced soon).

    Comment by Denis — August 24, 2010 @ 11:22 am

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