The Cook Book
Recipe for the week of January 15 - 21
CAM8 hits the road: EcoMachines at SFI
- Our CAM8 mixmaster has been basking in the bright sun and 60 degree
temperatures of New Mexico while attending a workshop on ecological modeling at the
Santa Fe Institute. This week's soup shows
SFI's new home on Hyde Park Road. I will testify to the blue skies,
but cannot speak to the significance of the strangely attractive cosmic TV
antennae. For the record, we reproduce the schedule of the workshop and
abstracts of the invited talks below.
ECOMACHINES AND SPATIAL MODELING
IN ECOLOGY AND BIOLOGY
January 13-16, 1996
Santa Fe Institute
Santa Fe, New Mexico
Sponsored by SFI, with additional funding from the National Science
Foundation
SATURDAY
12:00
LUNCH
1:00 - 2:00
Levin: Evolution in structured environments
2:15 - 3:15
Kinzig: Selection of Microorganisms in Spatially Heterogeneous Environments
& Implications for Plant Access to Nitrogen
COFFEE
3:45 - 4:45
Durrett: When is Space Important in Modelling?
SUNDAY
8:30
COFFEE
9:15 - 10:15
Ray: Natural Evolution in the Digital Medium - not a model
10:45 - 11:45
Reynolds: Behavior Models in Animation and Games
12:00
LUNCH
1:00
SELF-ORGANIZED OUTINGS
Options, subject to interest and self-transport,
with approximate cost, are:
Bandelier National Monument: 16th century cliff dwellings
($5)
Bradbury Science Museum: history of the Los Alamos Lab
($2)
Santa Fe Detours: guided walking tour of town ($10)
Santa Fe School of Cooking: a class on tapas ($42.50)
A Santa Fe Art Museum exhibit: to be announced ($5)
NFC Title Game: margaritas might assuage the Pack's demise (??)
Read your email at SFI!: how pathetic... (free)
7:00
WORKSHOP DINNER
La Tertulia
416 Agua Fria, (505) 988-2769
( Cash bar )
MONDAY
8:30
COFFEE
9:15 - 10:15
Gerhardt & Schuster: Cellular Automata -
mathematical amusements or efficient tools of science?
10:45 - 11:45
Boerlijst: Selfstructuring - a substrate for evolution
12:00
LUNCH
1:00 - 2:00
Caswell, Etter & Hill: Cellular Automaton Models for
Ecological Interactions in Patchy Environments
2:15 - 3:15
Kapral: Fluctuations, Oscillations and Patterns in Biochemical Systems
COFFEE
3:45 - 4:45
Fisch, Griffeath, Evans & Klopfer: The CAM8 as an EcoMachine -
some preliminary experiments
7:00
SHOW & TELL with Pizza
TUESDAY
8:30
COFFEE
9:00 - 10:00
Langton: The Swarm Simulation System
10:15 - 11:15
Kauffmann: Coevolution to the "Edge of Chaos"? -
tentative evidence for a general attractor
11:30
LUNCH
ABSTRACTS
Selfstructuring - a substrate for evolution
Maarten Boerlijst
- In the study of evolution selfstructuring and evolutionary processes
are themes that are usually studied separately. In this talk we
demonstrate that spatial selfstructuring can profoundly change the
outcome of evolutionary processes; for instance, positive selection for
"altruistic" features becomes possible. We study various systems,
ranging from abstract models for the evolution of cooperation, to
hypercycle models for pre-biotic evolution, ecological models for
predator-prey interactions, and models for aggregation in the slime
mould Dictyostelium discoideum.
- We show that spatial selfstructuring does not only change the
population dynamics, but it can also change the direction of
selection. Furthermore, we often observe selection towards a phase
transition in the spatial pattern. We argue that evolution can use such
selfstructuring patterns as a valuable source of information for
creating new possibilities for life. Once a selfstructuring pattern is
present it can "trap" the evolutionary dynamics in that they become
subordinate to the dynamics of the newly emerged pattern. To consider
selfstructuring patterns as "constraints" is, however, in our opinion a
gross underestimation of the creative and guiding power of
selfstructuring phenomena in the evolution of life.
Cellular Automaton Models for Ecological Interactions in Patchy
Environments
Hal Caswell, Ron Etter, and Mark Hill
- Cellular automaton (CA) models for ecological processes come in two varieties:
those in which the units at each point of the underlying lattice are individuals,
and those in which they are patches of habitat. Individual-based CA models can
follow individuals in a Lagrangian fashion, whereas the patch-based models take an
Eulerian approach. This talk will report on some of our work on patch-based models.
The construction of these models depends on a partitioning of the phase space into
discrete regions (e.g., presence-absence), and reducing the dynamics to a set of
transition rules. In our models, these transition rules are nonlinear,
discrete-time Markov chains. Because the models describe patches, in which
multiple species may maintain populations, ecological interactions appear in the
transition rules within patches, rather than in the interaction of adjacent patches.
We will present some results for competition, predator-prey interactions,
and the effects of habitat fragmentation on population persistence.
When is Space Important in Modelling?
Rick Durrett
- We will answer the question in the title by considering
three systems that model the interaction of (1) two strains
of the barley yellow dwarf virus, (2) two strains of E. coli, one
which produces colicin and one that is sensitive to it, (3) two
genotypes in a hybrid zone.
Cellular Automata - mathematical amusements or efficient tools of
science?
Martin Gerhardt and Heike Schuster
- They were born in the 50's by John von Neumann, awakened to LIFE
by Conway, and experienced their childhood with the help of computers
in the 80's, serving mostly as nice "pattern makers" and amusing
toys for scientists. Nowadays, cellular automata have more and more
grown up to serious simulation tools for modelling natural systems,
unifying the advantages of efficient computation and an intuitively
accessible approach for the complex mechanisms of self-organization
in decentralized systems.
- One of the best examples of this development can be found in
excitable media - ranging from the chemical Belousov-Zhabotinsky
reaction to life-threatening arrythmia of the human heart.
By providing not only qualitatively, but also quantitatively reliable
results, cellular automata open up new perspectives for future
simulation of natural systems.
The CAM8 as an EcoMachine - some preliminary experiments
Robert Fisch, David Griffeath, Kellie Evans, and Eric
Klopfer
- We will demonstrate the CAM8 cellular automaton machine, designed
and developed by Norm Margolus at MIT, as a simulation tool for
biomathematical prototypes. Simple experiments will be presented to
illustrate phase separation, nonlinear growth, complex self-organization
along the phase boundaries of a several-dimesnional parameter space,
and some density-dependent multi-species predator-prey models.
Coevolution to the "Edge of Chaos"? - tentative evidence for a
general attractor
Stuart Kauffman
- The metaphor of evolution on a "fitness landscape" reaches back
at least to Sewall Wright in 1932. In a coevolutionary process, most
commonly modeled in terms of evolutionary game theory as introduced by
Maynard Smith in 1973, the set of strategies of an organism consists in
its set of genotypes. The payoff to each organism is a function of its
current strategy and the strategy of its coevoltionary partners. If each
agent can only make "local moves" in its strategy space, for example,
changing by single mutation variants, then each agent can be thought of
as evolving on a fitness landscape that may be persistently deformed by
the adaptive moves of other agents. Two regimes generically exist in
such systems: 1) An ordered regime exists where each agent reaches a local
peak in its fitness landscape consistent with the peaks attained by its
coevolving partners. This is a "local Nash" equilibrium and an analogue
to Maynard Smith's "evolutionary stable strategies". 2) A chaotic or
disordered regime exists where agents keep "hill climbing" on ever
deforming landscapes. This is the analogue of the "Red Queen" regime.
- A coevolutionary process, therefore, depends upon the ruggedness
of the fitness landscapes each agent explores, and how richly coupled
landscapes are with a few or many other ecosystem "neighbors". These
couplings govern how dramatically each agent's landscape deforms due to
the adaptive moves of other agents.
- I will discuss recent results based on a spin-glass family
(the NK family) of coupled rugged fitness landscapes, where the agents are
able: 1) to evolve ON their deforming landscapes; 2) to evolve the very
ruggedness of their own landscapes; 3) to invade one another's niches and
thereby drive the invaded player "extinct" while "speciating" a copy of
the invader if it is fitter than the invaded player. By mechanism 3) players
with "good" landscape ruggedness are replicators, carrying "good landscape"
structures with them.
- Our results show that in such model ecosystems, as if by an
invisible hand, each agent (species) evolves the ruggedness of its own
fitness landscape for its own advantage such that the mean fitness is
sharply increased (maximized?), the probability of extinction is sharply
decreased (minimized?), yet a power law distribution of avalanches of
small and large extinction and speciation events propagate through the
ecosystem. These model results fit the current best, but still
questionable, estimates of the distribution of sizes of extinction
events in the Record, and the life time distributions of Genera. The
same results fit extinction avalanche distributions in "Tierra". And the
same model seems to fit qualitatively to economic concepts concerning
Schumpeterian "gales of creative destruction" and firm life-time
distributions. Thus, the model suggests a general attractor for
coevolving complex systems in the biosphere and econosphere.
- Reference: At Home in the Universe. Oxford University Press, 1995.
Fluctuations, Oscillations and Patterns in Biochemical
Systems
Raymond Kapral
- The role of internal fluctuations on reaction-diffusion dynamics
will be described. The emphasis will be on the character of the
spatial and temporal dynamics in systems with small populations
of reactive species, such as reactions occurring in single
cells or even population dynamics where the numbers of individual
species is not large. Questions concerning the applicability of
macroscopic reaction-diffusion models and the effects of
fluctuations on reaction rates and pattern formation
processes will be addressed.
- Lattice-gas cellular automaton models will be used to investigate
these questions. A lattice-gas model whose mean field limit is the
FitzHugh-Nagumo equation will be described and used to illustrate
fluctuation effects on pattern formation resulting from front propagation
and instability. Lattice gas models for systems whose mean field
limit yields chaotic dynamics will also be discussed.
Selection of Microorganisms in Spatially Heterogeneous
Environments
& Implications for Plant Access to Nitrogen
Ann Kinzig
- Microorganisms can create spatial heterogeneities in the soil system and
engineer favorable nitrogen and carbon environments for themselves.
Simulations show that these self-created heterogeneities can lead to
selection of microbial types differing from those found in a homogeneous
environment. Moreover, plant access to nitrogen is frequently increased
due to selection of mutualistic microorganisms in this heterogeneous
environment, and plants can evolve strategies to exploit the
heterogeneities and increase population densities of favorable microbial
types.
The Swarm Simulation System
Chris Langton
- Swarm is a general purpose simulation package for the investigation
of concurrent, distributed systems: systems in which hundreds or
thousands of autonomous agents interact with one another and with
a dynamically changing environment. Swarm provides general
purpose utilities for designing, implementing, running, and analyzing
such multi-agent systems.
- I'll talk about the architecture of Swarm and give examples
of applications in ecology, economics, and other domains.
Evolution in structured environments
Simon Levin
- It will be shown by example that the evolution of a wide variety
of phenotypic traits of ecological importance can occur only
in a spatially structured environment. Examples will be given
of altruistic behavior, such as prudent predation, reduced parasitic
virulence and reduced exploitation rates, as well as of spiteful
behavior such as allelopathy. Interacting particle systems will serve
as the mathematical tool of choice, and methods will be introduced
for analysis and scaling.
Natural Evolution in the Digital Medium - not a model
Tom Ray
- Life on Earth is the product of evolution by natural selection
operating in the medium of carbon chemistry. However, in theory,
the process of evolution is neither limited to occuring on the
Earth, nor in carbon chemistry. Just as it may occur on other
planets, it may also operate in other media, such as the medium
of digital computation. And just as evolution on other planets
is not a model of life on Earth, nor is natural evolution in the
digital medium.
Behavior Models in Animation and Games
Craig Reynolds
- This talk will review some simple models of volition and behavior,
particularly related to the path a simulated creature steers
through its world. Examples will include systems constructed by
hand, such as the Boids model (of flocking, herding, and schooling)
and a behavioral model of hockey players. Also included will be
behavioral models constructed by evolutionary computation, such as
for corridor following and for the game of tag.
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Last modified: January 11, 1996 by Kimberly Bodelson
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