Individual-based physiologically structured population and community models

Individual-based, physiologically structured models of populations and communities are constructed from growth models of individuals, McKendrick-von Foerster type partial differential equation population models which include the individual models, and appropriate interactions between the populations in the community. The individual growth model, based on an energy budget, can be formulated in a modular way using mechanistic models of the tasks involved in such processes as feeding, digestion, work, maintenance, and reproduction. The population model consists of an arbitrary number of subpopulation models representing intraspecific competition between ecotypes. The subpopulation models are coupled together through density dependence in growth, birth, and mortality rates. This metapopulation model exhibits competitive exclusion with respect to ecotypes in a nongenetic form of "survival of the fittest." The fitness of an ecotype is measured by the product of its birth rate and survivorship. A mathematical method of determining experimental mesocosm size is illustrated by scaling both aggregated and structured predator-prey models. The extinction threshold in the structured predator-prey model is defined and computed for different levels of toxicant and different parameters of size-dependent predation.