Ecological Stoichiometry as an Integrative Framework in Stream Fish Ecology
Peter B. McIntyre and Alexander S. Flecker
Abstract.—Ecological stoichiometry refers to the relative availability of elements in ecosystems as both an influence upon and result of ecological interactions. Nutrient ratios have long been analyzed in primary producers, but their application to animals is more recent. Here, we summarize the ecological stoichiometry framework and highlight three key contexts in stream fish ecology: body stoichiometry, dietary stoichiometry, and roles in ecosystem nutrient cycling. Elemental demands for growth depend directly upon the stoichiometry of carbon and nutrients in body tissues. Body stoichiometry varies widely among the dozens of stream fish species for which data are available and exhibits some phylogenetic and size-based patterns. Due to the variety of foods consumed by stream fishes, the stoichiometry of their diets also varies widely. Consuming foods with high carbon:nutrient ratios can produce phosphorus-limited growth in algivores and potentially in insectivores as well. These expectations contrast with the prevailing belief that energy intake is the key nutritional control on growth of most fishes. Ingested nutrients that are not incorporated into body tissues must be defecated or excreted. These waste products can be a critical component of ecosystem nutrient cycles and offer the opportunity for species identity to affect ecosystem functioning. We argue that ecological stoichiometry provides an integrative framework for merging perspectives across individual, population, community, and ecosystem levels. Broader application of this approach to stream fishes will offer particular insight into consumer–resource interactions and ecosystem dynamics.