Theoretical Frameworks for Ecological Dynamics Subject to Stoichiometric Constraints

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Kuang0077790 All organisms are composed of multiple chemical elementssuch as carbon, nitrogen, and phosphorus. Recent research in thearea known as ecological stoichiometry has highlighted theecological importance of the relative abundance of chemicalconstituents, known to vary considerably among species and acrosstrophic levels. However, most theoeretical studies in ecologyhave until very recently ignored the sources and consequences ofthis chemical heterogeneity. The investigator and his colleaguesundertake theoretical investigations of ecological stoichiometry.They develop a relatively new theoretical framework forecological dynamics that explicitly incorporates stoichiometricconstraints. This base model involves a stoichiometriccounterpart of the familiar Rosenzweig-MacArthur equations inwhich the effective carrying capacity of the resource species andthe transfer efficiency of the consumer species are constrainedby stoichiometric principles. Introduction of stoichiometricconsiderations in these equations (here, akin to "food quality")allows for a rich array of ecologically realistic dynamics,including deterministic extinction of the consumer species whenresources are abundant but of poor quality. They expand thismodel in five different directions, to explore ecologicalrealities (i.e., complications) whose consideration has provedilluminating in other, non-stoichiometric settings. Specifically,they analyze the dynamics of 1) a multi-nutrient model; 2)trophically complex models in which multiple consumer speciesshare a resource; 3) time delays in nutrient recycling that are arealistic component of terrestrial ecosystems; 4) two patchmodels featuring habitat heterogeneity and dispersal of theconsumer; and 5) age structured models in which juvenile andadult consumers differ in their nutrient requirements. Theproject aims to provide an analytically rigorous foundation forburgeoning empirical research into ecological stoichiometry. All living things, including humans, are constructed ofapproximately the same set of basic building blocks, chemicalelements such as carbon (C), nitrogen (N), phosphorus (P), andseveral dozen more in smaller amounts. However, differentorganisms contain different proportions of these key elements intheir biomass and thus must extract these elements from theirenvironment to differing degrees. In many situations, theenvironment does not provide these key nutrient elements in theabundance and proportions that are optimal for organism growthand reproduction. Thus, the chemical environment of life may setlimits on the success of organisms in various situations. In thisproject the investigators use mathematical models to simulate theflow of multiple chemical elements in natural food webs to betterunderstand how the requirements of living things for multiplechemical elements establish key feedbacks between the living andnon-living world. This work is important for two reasons. First,it may provide a better fundamental understanding of how chemicalelements move through food webs. Second, improved fundamentalknowledge of how nutrients move in the environment and how tosimulate those movements with mathematical tools may help predictand manage natural and human-dominated ecosystems, includingthose affected by nutrient inputs from human activities (e.g. Nand P inputs from fertilizer, sewage) or by global change (e.g.effects of increased atmospheric carbon dioxide on C and nutrientflow in the environment).