Are stable isotope ratios suitable for describing niche partitioning and individual specialization?

Abstract

As concerns about anthropogenic and natural disturbance grow, understanding animal resource use patterns has been increasingly prioritized to predict how changes in environmental conditions, food web structure, and population dynamics will affect biological resilience. Among the tools used to assess resource use, stable isotope analysis has proliferated in ecological studies, particularly in relation to describing intra‐ and interspecific variation in trophic interactions. Despite a growing need to disseminate scientific information, the inherent limitations of stable isotope ratios and inappropriate synonymizing of distinct evolutionary and ecological processes may mislead ecological inferences in natural systems. This situation necessitates a re‐evaluation of the utility of stable isotope ratios to address certain ecological questions. Here, we assess the efficacy of stable isotope ratios to describe two fundamental ecological processes, niche partitioning and individual specialization. Investigation of these processes has increased substantially in accordance with increased access to stable isotope data. This article discusses the circumstances and approaches that are necessary to evaluate niche partitioning and individual specialization, and outlines key considerations for the associated application of stable isotope ratios.

Integrating isotopic and nutritional niches reveals multiple dimensions of individual diet specialisation in a marine apex predator

“…The ecological consequences of individual diet specialisation can depend on the magnitude and specific nature of the trophic interactions that vary between individuals (Araujo et al, 2011;Bolnick et al, 2002;Ingram et al, 2011). However, many isotopic studies assess individual diet specialisation in δ-space alone and thus do not offer specific information on individual differences in food use (Matich et al, 2021;Shipley & Matich, 2020). We addressed this limitation using mixing models, Gallagher & Klimley, 2018;Myers et al, 2007).…”

Improving stable isotope assessments of inter‐ and intra‐species variation in coral reef fish trophic strategies

“…However, within‐species individual specialization and/or overlapping isotope values in dietary sources make reliance on only δ 15 N and δ 13 C for isotopic niche characterization unsuitable in certain scenarios. In these cases, additional information (i.e., ecological processes of resource partitioning) or advanced stable isotope techniques may be needed to accurately determine how individual variation affects a species' wider ecological role (Matich et al, 2021 ).…”

Artificial selection for predatory behaviour results in dietary niche differentiation in an omnivorous mammal

“…The realized dietary niche is thus a combination of the species' fundamental niche (e.g. the hypothetical ideal diet), and the constraints on access to the ideal diet [3,4]. Differences among individuals in dietary niche are generated by environmental and genetic variation as well as phenotypic plasticity [1,2], but the relative effects of these factors have rarely been tested [2,[5][6][7].…”

“…We compared the dietary niche of bank voles from lines artificially selected for an increased predatory tendency [18] with unselected lines by measuring stable isotope ratios of carbon and nitrogen in the hair of field-reared individuals of both types. Stable isotope methods are suited to studying individual dietary niches as they permit an evaluation of the consumed diet based on the isotopic signatures in the animal's tissues, integrating dietary information over longer time periods [4,19]. A higher isotope ratio of nitrogen ( 15 N/ 14 N), relative to other organisms in the same system, indicates consumption of food items from a higher trophic level because 15 N is enriched along the food chain [20].…”