Estimating niche width using stable isotopes in the face of habitat variability: a modelling case study in the marine environment.

David O Cummings,Stephen J Simpson,Raymond W Lee,Jerome Buhl,Sebastian P Holmes,Simon Thrush

doi:10.1371/journal.pone.0040539

David O Cummings, Stephen J Simpson + Show 4 more

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https://doi.org/10.1371/journal.pone.0040539

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Abstract

Distributions of stable isotopes have been used to infer an organism's trophic niche width, the ‘isotopic niche’, and examine resource partitioning. Spatial variation in the isotopic composition of prey may however confound the interpretation of isotopic signatures especially when foragers exploit resources across numerous locations. In this study the isotopic compositions from marine assemblages are modelled to determine the role of variation in the signature of prey items and the effect of dietary breadth and foraging strategies on predator signatures. Outputs from the models reveal that isotopic niche widths can be greater for populations of dietary specialists rather than for generalists, which contravenes what is generally accepted in the literature. When a range of different mixing models are applied to determine if the conversion from δ to p-space can be used to improve model accuracy, predator signature variation is increased rather than model precision. Furthermore the mixing models applied failed to correctly identify dietary specialists and/or to accurately estimate diet contributions that may identify resource partitioning. The results presented illustrate the need to collect sufficiently large sample sizes, in excess of what is collected under most current studies, across the complete distribution of a species and its prey, before attempts to use stable isotopes to make inferences about niche width can be made.

Highlights

Stable isotope analysis is often used by ecologists to identify trophic interactions [1]
In the majority of cases, higher variances indicated that dietary specialists (DsHg and dietary specialists and habitat specialists (DsHs)) occupied greater bivariate space than dietary generalists (DgHs and dietary generalists and habitat generalists (DgHg))
Pooled results for each model show that the isotopic niche can be greater for dietary specialists (DsHg and DsHs) with variances of 1.7 to 5.6 and 2 – 3 times greater for d13C and d15N, respectively, than dietary generalists (DgHs and DgHg) (Table 3)

Summary

Introduction

Stable isotope analysis is often used by ecologists to identify trophic interactions [1]. This approach can be less problematic than others such as gut analysis, which may have logistical constraints and require regular and large sampling regimes [2,3]. A number of authors have used stable isotopes to estimate trophic niche width [1,3] and to examine resource partitioning [4,5]. There has, been a growing realisation that interpreting patterns of stable isotope relies heavily on a comprehensive understanding of habitat use by predators, and the spatial patterns of isotopic variation among organisms at all trophic levels [6,7,8,9,10]. The challenge for ecologists is to determine where isotopic variation exists and why

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