ECOLOGICAL STOICHIOMETRY: SPATIAL-TEMPORAL CONSTRAINTS, TRANSPORT PROCESSES, AND GLOBAL INTEGRATION

Ecological interactions and organic evolution have made biotic stoichiometry a major force in shaping global chemistry and physics over geological time. Biological stoichiometry underlies global properties such as the oxygenation of the oceans and atmosphere; the abundance of present-day chemical suites of nitrogen, sulfur, iron, and other elements; and the radiative energy balance of the atmosphere. These effects on environmental chemistry began as early as 3,500 Ma and have changed through time in response to combinations of geological conditions and biological evolution. The chemical interaction between the abiotic and biotic components of the biosphere is referred to by ecologists as “ecological stoichiometry.” This subfield of ecology has led to an understanding of how the abiotic environment controls the species composition and ecological functions of the local ecosystem on one hand, and how biotic activities of that ecosystem alter the abiotic environment on the other hand--a classic case of circular causal loop control.

The phenomena comprising ecological stoichiometry vary in relative importance in different environmental and ecological situations, however. While a low resolution geography of contemporary, biological contribution to biospheric chemistry can be mapped at the global scale, an assessment of ecological stoichiometry at a more local scale is highly dependent on spatial and temporal time frames of observation as well as the ways that system boundaries are defined. To a considerable extent, the critical importance of spatial-temporal scales is dependent on the strength and timing of transport processes into and out of defined systems. Because of translocation conditions and events, biological control of environmental chemistry may be ephemeral at the local scale, while, through integration of spatial-temporal variation, still be of millennial consequence at the global scale.

This paper addresses what criteria and metrics are necessary for determining the relative importance of geochemical versus biochemical control of environmental geochemistry at different spatial-temporal scales. It explores the roles of different transport mechanisms and the geography of translocation, sequestration, and turnover times.