Ned is right in one respect, IBMs are conceptually straightforward and easy to understand, but there are lots of pitfalls along the way. One is that they are computer-intensive and can be very slow to run. A more important problem is that it is easy to make mistakes in setting up the problem. I recall one paper I reviewed which illustrated the method with the old fox-rabbit system beloved by Lotka-Volterra theorists, but the foxes ended up starving to death even though there were rabbits within 100 m - it was just to hard to get the search algorithm right.
To be fair, IBMs are most often used to model spatial effects (moving from one grid cell to another) and these are very difficult to get right. Spatial models are probably the hardest to build due to the problems of understanding and predicting how animals will move around. That is why there are really no spatial fisheries models to speak of. If anyone wants to experiment with IBMs without getting into the heavy programming that they often involve, I recommend the free modelling package NetLogo from Northwestern U. which is easy to use and will get you into the field relatively painlessly. I took a complicated C++ model of the North Sea that I developed with two other colleagues and came up with a NetLogo approximation in an afternoon (the model is on their website - I don't have the URL handy since I live in the country far from broadband, but do a search on NetLogo to find it.). Someone asked for the Starfield citation, he has written quite a few books and papers, but his classic is: Starfield, A.M. and A.L. Bleloch. 1991. Building Models for Conservation and Wildlife Management. Second edition, The Burgess Press, Edina, Minnesota. It's hard to find and the title is awful, but it's a really good book. I particularly like his concept of "frames" which offers a way to deal with discontinuities such as metamorphosis. I guess I'll put in a plug for one of my own papers, Silvert, William. 2001. Modelling as a Discipline. Int. J. General Systems 30: 261-282. A Polish translation was published in the "Projektowanie i Systemy" volume XVII in 2004, and the PDF (of the English version) is on the web at http://bill.silvert.org/pdf. Bill Silvert ----- Original Message ----- From: "Ned Dochtermann" <[EMAIL PROTECTED]> To: <ECOLOG-L@LISTSERV.UMD.EDU> Sent: Monday, March 06, 2006 7:23 PM Subject: Re: math modelling > To follow on the below post, DeAngelis and Mooj (2005) provide a concise > overview of individually-based models (IBMs). IBMs have several advantages > over other approaches. First, they emphasize the conceptual model > underlying > the system you're attempting to understand. Second they, obviously, > operate > at the level of the individual which arguably is where many/most > ecological > and evolutionary processes should be approached from. Finally, they are > far > more accessible for those of us that may not have the mathematical skills > we'd desire or required of other approaches...
