Mathematical Medicine and Biology Advance Access published online on September 4, 2009
Mathematical Medicine and Biology, doi:10.1093/imammb/dqp018
Survival thresholds and mortality rates in adaptive dynamics: conciliating deterministic and stochastic simulations

Laboratoire Jacques-Louis Lions, UMR 7598, UPMC Univ Paris 06, F-75005 Paris, France, Institut Universitaire de France and Laboratoire Jacques-Louis Lions, UMR 7598, CNRS, F-75005 Paris, France

Laboratoire de Microbiologie, Géochimie et Écologie Marines, UMR 6117, Centre d'Océanologie de Marseille, Université de la Méditerranée—CNRS, Campus de Luminy, Case 901, 13288 Marseille Cedex 09, France
Email: benoit.perthame{at}upmc.fr
Email: mathias.gauduchon{at}univmed.fr
Received on January 20, 2009. Revised on April 16, 2009. Accepted on July 27, 2009.
Deterministic population models for adaptive dynamics are derived mathematically from individual-centred stochastic models in the limit of large populations. However, it is common that numerical simulations of both models fit poorly and give rather different behaviours in terms of evolution speeds and branching patterns. Stochastic simulations involve extinction phenomenon operating through demographic stochasticity, when the number of individual units is small. Focusing on the class of integro-differential adaptive models, we include a similar notion in the deterministic formulations, a survival threshold, which allows phenotypical traits in the population to vanish when represented by few individuals. Based on numerical simulations, we show that the survival threshold changes drastically the solution; (i) the evolution speed is much slower, (ii) the branching patterns are reduced continuously and (iii) these patterns are comparable to those obtained with stochastic simulations. The rescaled models can also be analysed theoretically. One can recover the concentration phenomena on well-separated Dirac masses through the constrained Hamilton–Jacobi equation in the limit of small mutations and large observation times.
Keywords: evolution; adaptative dynamics; Hamilton–Jacobi equation; asymptotic analysis; demographic stochasticity; individual-based model; evolutionary branching