Fish & Food Webs
Food webs are one of the core thematic frameworks in the ecological sciences. Broadly defined, food webs are special descriptions of biological communities focused on trophic interactions between consumers and resources. They provide a means of analyzing interrelationships among community structure, stability, and ecosystem processes, and how these attributes are influenced by environmental change and disturbance (DeAngelis 1992). These depictions of feeding relationships can provide insight into almost every area of ecological research, ranging from population dynamics to the cycling of nutrients through ecosystems. Organisms comprising food webs live in a spatially heterogeneous world in which habitats vary greatly in productivity, resource abundance, and consumer behavior and demography. Food webs and river drainages represent hierarchical networks and complex adaptive systems. Well- functioning food webs are fundamental in sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. In this multicontinental, hierarchical study, we will assess food web structure of different river functional process zones (see Hydrogeomorphic Analysis) by compound specific stable isotope analysis (CSIA) of amino acids. The analytical advantage of δ15N CSIA is that the focal consumer contains information on both the basal signature of the primary producer and the number of trophic transfers, eliminating the need for separate signatures from a primary producer. This allows us to determine trophic position and food chain length of consumers in the river. Additionally, naturally occurring δ13C patterns among amino acids can distinguish between multiple aquatic and terrestrial primary production sources. Consumers retain this “isotope fingerprint,” allowing us to trace the carbon sources through the food web using a Bayesian mixing model.