Ecological Economics 31 (1999) 227 – 242 ANALYSIS Human – ecosystem interactions: a dynamic integrated model Bobbi Low a, *, Robert Costanza b , Elinor Ostrom c , James Wilson d , Carl P. Simon e a School of Natural Resources and Enironment, Uniersity of Michigan, Dana Building, 430 East Uniersity, Ann Arbor, MI 48109 -1115, USA b Uniersity of Maryland Institute for Ecological Economics, Center for Enironmental Science, Uniersity of Maryland, Box 38, Solomons, MD 20688 -0038, USA c Workshop in Political Theory and Policy Analysis, Indiana Uniersity, 513 North Park, Bloomington, IN 47408 -3895, USA d School of Marine Sciences, Uniersity of Maine, 5782 Winslow Hall, Orono, ME 04469 -5782, USA e Mathematics, Economics, and Public Policy, Uniersity of Michigan, 412 Lorch Hall, Ann Arbor, MI 48109 -1220, USA Abstract We develop an interactive simulation model that links ecological and economic systems, and explore the dynamics of harvest patterns as they simultaneously affect natural and human capital. Our models represent both single and multiple systems. The level of natural capital is influenced by interactions of (1) natural capital growth and (non-human influenced) depletion, (2) ecological fluctuations, (3) harvest rules, and (4) biological transfers from one ecological system to another. We focus first on isolated systems in which there are no biological transfers between units and humans rely for subsistence on the resource; thus both the economic and ecological portions of the system are relatively independent of other systems. In this case, the maximum sustainable harvest rate depends on the local carrying capacity, the stock growth rate, and fluctuations in such ecological variables as rainfall and temperature, which are ‘extrinsic’ to the stock – human harvest, but nonetheless affect stock levels. Next, we address spatially complex situations in which biological resources move from one spatial unit to others. In these models, the greater the potential movement of stocks across ecosystems, the more any particular human sub-system can increase its harvesting rate without danger of its own collapse — although at a cost to neighboring subsystems. © 1999 Elsevier Science B.V. All rights reserved. www.elsevier.com/locate/ecolecon 1. Introduction Managing human use of important ecosystem resources to be sustainable can clearly be prob- lematic (McCay and Acheson, 1987; Ludwig et al., 1993; Jansson et al., 1994). We mine ocean and coastal ecosystems to provide important bio- logical resources — fish, whales, and lobsters, for example — yet these ecosystems remain particu- larly intractable for sustainable resource manage- ment. Both resource stocks and harvesters may cross boundaries; it is difficult-to-impossible to * Corresponding author. 0921-8009/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII:S0921-8009(99)00081-6