Human-ecosystem interactions: a dynamic integrated model

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. (C) 1999 Elsevier Science B.V. All rights reserved.