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PRIMARY CONSUMER δ 13 C AND δ 15 N AND THE TROPHIC POSITION OF AQUATIC CONSUMERS
Author(s) -
Zanden M. Jake Vander,
Rasmussen Joseph B.
Publication year - 1999
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(1999)080[1395:pccana]2.0.co;2
Subject(s) - trophic level , food web , littoral zone , δ15n , δ13c , primary producers , ecology , pelagic zone , baseline (sea) , isotope analysis , profundal zone , stable isotope ratio , environmental science , biology , fishery , physics , phytoplankton , nutrient , quantum mechanics
Stable nitrogen isotope signatures (δ 15 N) are increasingly used to infer the trophic position of consumers in food web studies. Interpreting the δ 15 N of consumers relative to the δ 15 N characterizing the base of the food web provides a time‐integrated measure of trophic position. We use primary consumers (trophic level 2) as baseline indicator organisms and investigate the variation in baseline δ 15 N values in 14 lakes in Ontario and Quebec. Values of δ 15 N ranged from −2 to +9‰ and varied significantly as a function of lake habitat (mean littoral = 1.6‰, pelagic = 3.1‰, profundal = 5.2 ‰). Stable carbon isotopic signatures (δ 13 C) of primary consumers decreased along this same habitat gradient (mean littoral = −23.8‰, pelagic = −28.4‰, profundal = −30.5‰). Primary consumer δ 13 C and a categorical lake variable explained 72% of the variability in primary consumer δ 15 N. This relationship was corroborated by primary consumer δ 15 N and δ 13 C data from the literature, indicating that habitat‐specific variation in baseline δ 15 N and δ 13 C is a widespread phenomenon in freshwater systems. We present a method that uses the presented baseline δ 15 N–δ 13 C relationship and the δ 15 N and δ 13 C values of the consumer to estimate trophic position; it is a method that corrects for the described variation in baseline δ 15 N. These results emphasize the general importance of accounting for patterns in isotopic signatures characterizing the base of the food web when inferring trophic structure using stable isotopes.