Consequences of employing amino acid vs. bulk‐tissue, stable isotope analysis: a laboratory trophic position experiment

Abstract

Citation: Bowes, R. E., and J. H. Thorp. Consequences of employing amino acid vs bulk-tissue, stable isotope analysis: a laboratory trophic position experiment. Ecosphere 6(1):14. http://dx.doi.org/10.1890/ES14-00423.1Abstract. An important metric of environmental health is food web structure because it reflects species richness, natural history diversity, and resource availability. While bulk-tissue stable isotope analysis has proven valuable for food web studies, field conditions may severely restrict its use and data can be quite variable. Amino acid stable isotope analysis potentially reduces this variability, in part by eliminating the need for signatures near the trophic base because a single top consumer contains both the primary producer signature (constant phenylalanine signature) and information reflecting number of trophic transfers (a progressively increasing d 15 N signature of glutamic acid).To evaluate the ecological sensitivity and cost/benefits of the techniques, we conducted a laboratory food chain experiment with four trophic levels. Water fleas (Daphnia magna) were cultured on a diet of powdered algae and then fed daily to guppies (Poecilia reticulata) for three months. These invertivorous fishes were then consumed by piscivororus bluegill sunfishes (Lepomis macrochirus) for a subsequent three months. All members of the food web were analyzed for 15 N values and degree of fractionation using both bulk-tissue and amino acid stable isotope techniques. Our experiment demonstrated that the amino acid technique more accurately identified the true trophic position (TP) and food chain length (FCL ¼ maximum TP) with significantly less variability around mean values for each consumer trophic level. Moreover, use of amino acids requires significantly fewer replicates to identify TP. We discuss here the relative advantages and disadvantages of both approaches for determining TP and FCL and recommend that investigators switch as soon as possible to the amino acid isotope technique for determining FCL.

Quantifying terrestrial carbon in freshwater food webs using amino acid isotope analysis: Case study with an endemic cavefish

“…Strategy 3), our approach to quantifying allochthony addresses two common shortfalls associated with conventional bulk isotope approaches. First, consistent differences in δ 13 C fingerprints between allochthonous and autochthonous carbon sources contrast the unpredictable fluctuations in bulk tissue δ 13 C data (Bowes & Thorp, ). Second, the availability of non‐fractionating tracers (i.e.…”

“…This can differ between taxonomic groups (Vander Zanden & Rasmussen, ) as well as across the spectrum of predator–prey biochemical compatibility (Bastos, Correa, Winemiller, & Garcia, ; Brett et al, ). Consequently, bulk isotope approaches are difficult to up‐scale spatially and temporally because time‐ and location‐specific sampling of primary producers are needed to account for uncertainties in primary producer δ 13 C (Bowes & Thorp, ; Hadwen, Spears, & Kennard, ). Relevant primary producers, however, can be difficult to collect (e.g.…”

Embracing variability in amino acid δ15N fractionation: mechanisms, implications, and applications for trophic ecology

“…Superscripts indicate references: 1 K. Arthur, unpublished data ; 2 Bloomfield et al. (); 3 Bowes and Thorp (); 4 Bradley et al. (); 5 Chikaraishi et al.…”

Reweaving river food webs through time

“…Bowes & Thorp, 2015;Chikaraishi et al, 2014). To determine if the hydrogeomorphic complexity of rivers affected our conclusions, we compared potential historical changes in food webs fish in a formerly unregulated, anastomosing river (UMR) with those from a mostly single-channel river (LOR) of roughly comparable size.…”