All organisms are composed of multiple chemical elements such as carbon, nitrogen, and phosphorus. Recent research in the area known as ecological stoichiometry has highlighted the ecological importance of the relative abundance of chemical constituents, known to vary considerably among species and across trophic levels. However, most theoeretical studies in ecology have until very recently ignored the sources and consequences of this chemical heterogeneity. The investigator and his colleagues undertake theoretical investigations of ecological stoichiometry. They develop a relatively new theoretical framework for ecological dynamics that explicitly incorporates stoichiometric constraints. This base model involves a stoichiometric counterpart of the familiar Rosenzweig-MacArthur equations in which the effective carrying capacity of the resource species and the transfer efficiency of the consumer species are constrained by stoichiometric principles. Introduction of stoichiometric considerations in these equations (here, akin to "food quality") allows for a rich array of ecologically realistic dynamics, including deterministic extinction of the consumer species when resources are abundant but of poor quality. They expand this model in five different directions, to explore ecological realities (i.e., complications) whose consideration has proved illuminating in other, non-stoichiometric settings. Specifically, they analyze the dynamics of 1) a multi-nutrient model; 2) trophically complex models in which multiple consumer species share a resource; 3) time delays in nutrient recycling that are a realistic component of terrestrial ecosystems; 4) two patch models featuring habitat heterogeneity and dispersal of the consumer; and 5) age structured models in which juvenile and adult consumers differ in their nutrient requirements. The project aims to provide an analytically rigorous foundation for burgeoning empirical research into ecological stoichiometry. All living things, including humans, are constructed of approximately the same set of basic building blocks, chemical elements such as carbon (C), nitrogen (N), phosphorus (P), and several dozen more in smaller amounts. However, different organisms contain different proportions of these key elements in their biomass and thus must extract these elements from their environment to differing degrees. In many situations, the environment does not provide these key nutrient elements in the abundance and proportions that are optimal for organism growth and reproduction. Thus, the chemical environment of life may set limits on the success of organisms in various situations. In this project the investigators use mathematical models to simulate the flow of multiple chemical elements in natural food webs to better understand how the requirements of living things for multiple chemical elements establish key feedbacks between the living and non-living world. This work is important for two reasons. First, it may provide a better fundamental understanding of how chemical elements move through food webs. Second, improved fundamental knowledge of how nutrients move in the environment and how to simulate those movements with mathematical tools may help predict and manage natural and human-dominated ecosystems, including those affected by nutrient inputs from human activities (e.g. N and P inputs from fertilizer, sewage) or by global change (e.g. effects of increased atmospheric carbon dioxide on C and nutrient flow in the environment).
