ANZIAM  J.  48 (2006), 1-10
Freely forming groups: Trying to be rare

Michael Baake
  Fakultät für Mathematik
  Univinersität Bielefeld
  Box 100131
  33501 Bielefeld
  Germany
  mbaake@math.uni-bielefeld.de
Uwe Grimm
  Department of Mathematics
  The Open University
  Walton Hall
  Milton Keynes MK7 6AA
  UK
  u.g.grimm@open.ac.uk
and
Harald Jockusch
  Fakultät für Biologie
  Univinersität Bielefeld
  Box 100131
  33501 Bielefeld
  Germany
  h.jockusch@uni-bielefeld.de


Abstract
A simple weakly frequency dependent model for the dynamics of a population with a finite number of types is proposed, based upon an advantage of being rare. In the infinite population limit, this model gives rise to a non-smooth dynamical system that reaches its globally stable equilibrium in finite time. This dynamical system is sufficiently simple to permit an explicit solution, built piecewise from solutions of the logistic equation in continuous time. It displays an interesting tree-like structure of coalescing components.
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