On the Use of Stable Hydrogen Isotope Measurements (δ2H) to Discern Trophic Level in Avian Terrestrial Food Webs

Rien E Van Wijk,Keith A Hobson,Yahkat Barshep

doi:10.3390/d13050202

Rien E Van Wijk, Keith A Hobson + Show 1 more

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https://doi.org/10.3390/d13050202

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Abstract

The measurement of stable hydrogen isotope ratios (δ2H) in animal tissues is a popular means of inferring spatial origins and migratory connections. However, the use of this isotope to infer diet and potentially trophic position remains poorly understood, especially in non-aquatic terrestrial ecosystems. In many animal communities, tissue δ15N values are strongly associated with trophic position. Correlations between tissue δ2H and δ15N are expected, then, if δ2H is affected by trophic enrichment of 2H. In addition, within sites, we would expect higher tissue δ2H values in insectivorous species compared to granivores or nectarivores. We tested these hypotheses for two resident avian communities in Nigeria consisting of 30 species representing a range of dietary guilds (granivores, frugivores, nectarivores, omnivores, insectivores) by comparing feather δ2H, δ15N and δ13C values. We found considerable isotopic overlap among all guilds except granivores, with no clear pattern of enrichment in 2H with trophic position. However, at one of our sites (open scrubland), feather δ2H was positively correlated with feather δ15N (R2 = 0.30) compared to a closed canopy forest site (R2 = 0.09). Our results indicate weak evidence for predictable trophic enrichment in 2H in terrestrial environments and indicate that controlled studies are now required to definitively elucidate the behavior of H isotopes in terrestrial food webs.

Highlights

The measurement of naturally occurring stable isotope ratios of several elements in food webs has provided a wealth of ecological information over the last decades
Such trophic enrichment in δ2 H can derive from exchange with ambient waters in aquatic food webs, causing a so-called apparent trophic enrichment [12], and processes that can lead to metabolic trophic enrichment in terrestrial food webs per se are by no means clear
We found clear differences in δ2 H among guilds, with insectivores being most enriched while granivores were most depleted (Table 2)

Summary

Introduction

The measurement of naturally occurring stable isotope ratios of several elements in food webs has provided a wealth of ecological information over the last decades. Isotopic applications to date have been used in ecological studies to trace origins of primary production and consumer trophic position. Such approaches, in turn, have largely depended on the use of stable carbon (δ13 C) and nitrogen (δ15 N) isotope measurements based on key isotopic differences in photosynthetic pathways (C3, C4, CAM). Interest in using δ2 H measurements as a trophic indicator stems from studies showing a weak correlation between δ2 H and δ15 N values in food webs [9,10,11]. There seems to be almost no experimental support for metabolic processes as a mechanism for changes in δ2 H values in terrestrial and aquatic consumers once other mechanisms are considered [12,13,14,15,16]

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