Biochemical tracers reveal intra-specific differences in the food webs utilized by individual seabirds

Abstract

Food web structure regulates the pathways and Xow rates of energy, nutrients, and contaminants to top predators. Ecologically and physiologically meaningful biochemical tracers provide a means to characterize and quantify these transfers within food webs. In this study, changes in the ratios of stable N isotopes (e.g., 15 N), fatty acids (FA), and persistent contaminants were used to trace food web pathways utilized by herring gulls (Larus argentatus) breeding along the shores of the St Lawrence River, Canada. Egg 15 N values varied signiWcantly among years and were used as an indicator of gull trophic position. Temporal trends in egg 15 N values were related to egg FA proWles. In years when egg 15 N values were greater, egg FA patterns reXected the consumption of more aquatic prey. Egg 15 N values were also correlated with annual estimates of prey Wsh abundance. These results indicated that temporal changes in aquatic prey availability were reXected in the gull diet (as inferred from ecological tracer proWles in gull eggs). Analysis of individual eggs within years conWrmed that birds consuming more aquatic prey occupied higher trophic positions. Furthermore, increases in trophic position were associated with increased concentrations of most persistent organic contaminants in eggs. However, levels of highly brominated polybrominated diphenyl ether congeners, e.g, 2,2Ј,3,3Ј,4,4Ј,5,5Ј,6,6Ј-decabromoDE (BDE-209), showed a negative relationship with trophic position. These contrasting Wndings reXected diVerences among contaminant groups/homologs in terms of their predominant routes of transfer, i.e., aquatic versus terrestrial food webs. High trophic level omnivores, e.g., herring gulls, are common in food webs. By characterizing ecological tracer proWles in such species we can better understand spatial, temporal, and individual diVerences in pathways of contaminant, energy, and nutrient Xow.

Trophic relationships of breeding Red-necked Grebes (Podiceps grisegena) on wetlands with and without fish in the Aspen Parkland

“…We chose to pool tissue samples from multiple individuals prior to SIA because our goal was to represent ''typical'' values for isotopic signals from each taxon and to focus on trophic relationships relative to the Red-necked Grebe, not to document wetland food webs in detail. Pooling tissue from multiple individuals of a taxon has been a common practice in studies using SIA (e.g., Hobson and Welch 1992; Hebert et al 2000Hebert et al , 2009bGoodale et al 2008;Logan et al 2008;Nilsen et al 2008;Matthews and Mazumder 2008), but it can mask individual variation in feeding and foraging patterns and ecological information may be lost (Hebert et al 1999(Hebert et al , 2009a.…”

Trace me if you can: the use of intrinsic biogeochemical markers in marine top predators

“…In addition, recent analytical improvements allow for the analysis of virtually all tracers via minimally invasive procedures, such as blood sampling (Henriksen et al 1998;; Williams and Buck 2010). As the distribution and integration of tracers in ecosystems and within tissues, respectively, are being clarified, the next aim for ecological research is the simultaneous use of multiple tracers (eg Hebert et al 2009). However, by continuing to rely on more traditional methods, many researchers focus only on part of the entire biogeochemical spectrum.…”

Survey of four essential nutrients and thiaminase activity in five Lake Ontario prey fish species

“…They have several biological roles and have been used as tracers in food webs (Budge et al, 2006;Hebert et al, 2009;Napolitano, 1998). Two long-chain unsaturated fatty acids (EPA and ARA) are precursors of eicosanoids which function as signaling molecules.…”