Systems dynamics is one approach to modelling the dynamics of ecological and economic systems, which usually interact strongly with each other. External free source software links Simile (http://www.ierm.ed.ac.uk/simile/) (free for research, educational and personal use) http://www.suite101.com/article.cfm/scientific_computing/85003 Mailing lists System Dynamics Mailing List (http://www.vensim.com/sdmail/sdinfo.html) Computer Simulation in Social Sciences (http://www.jiscmail.ac.uk/lists/simsoc.htmlSIMSOC)