Beyond carbon and nitrogen: guidelines for estimating three‐dimensional isotopic niche space

Abstract

Isotopic niche has typically been characterized through carbon and nitrogen ratios and most modeling approaches are limited to two dimensions. Yet, other stable isotopes can provide additional power to resolve questions associated with foraging, migration, dispersal and variations in resource use. The ellipse niche model was recently generalized to n‐dimensions. We present an analogous methodology which incorporates variation across three stable dimensions to estimate the significant features of a population's isotopic niche space including: 1) niche volume (referred to as standard ellipsoid volume, SEV), 2) relative centroid location (CL), 3) shape and 4) area of overlap between multiple ellipsoids and 5) distance between two CLs. We conducted a simulation study showing the accuracy and precision of three dimensional niche models across a range of values. Importantly, the model correctly identifies differences in SEV and CL among populations, even with small sample sizes and in cases where the absolute values cannot precisely be recovered. We use these results to provide guidelines for sample size in conducting multivariate isotopic niche modeling. We demonstrate the utility of our approach with a case study of three bottlenose dolphin populations which appear to possess largely overlapping niches when analyzed with only carbon and nitrogen isotopes. Upon inclusion of sulfur, we see that the three dolphin ecotypes are in fact segregated on the basis of salinity and find the stable isotope niche of inshore bottlenose dolphins significantly larger than coastal and offshore populations.

Re-examining trophic dead ends: stable isotope values link gelatinous zooplankton to leatherback turtles in the California Current

“…Stable isotope values can also provide information about animal resource use and therefore may provide insight into their ecological niche space (Newsome et al 2007, Jackson et al 2011, Rossman et al 2016. We compared the isotopic niche widths of leatherbacks and gelatinous zooplankton, using the package SIBER (Stable Isotope Bayesian Ellipses in R) in R (R Core Team 2016).…”

“…We used the δ 15 N and δ 13 C data to estimate the isotopic niches of leatherbacks and gelatinous zooplankton. Calculating standard ellipse areas can provide information about resource use and diet (δ 15 N) as well as primary production and environment (δ 13 C) (Newsome et al 2007, Rossman et al 2016.…”

Individual growth as a non‐dietary determinant of the isotopic niche metrics

“…Although quantitative analytical approaches for applying isotopic niche concept in the trophic diversity analysis are proliferating rapidly (Cucherousset & Villéger, ; Rossman, Ostrom, Gordon, & Zipkin, ; Swanson et al., ), the assumptions behind the isotopic niche applications are rarely tested (but see Brind'Amour & Dubois, ). Of particular concern are physiological drivers of isotope fractionation and related effects on the niche metrics.…”

Multidimensional stable isotope analysis illuminates resource partitioning in a sub‐Antarctic island bird community

“…Although captive and field Figure 3. Standard ellipse volume (2.5th, 50.0th and 97.5th percentiles) estimated with a Bayesian framework (Rossman et al 2016) using carbon membrane , nitrogen and oxygen stable isotope data from 12 bird species breeding on Marion Island. See Table 1 for species abbreviations.…”

“…Three-dimensional isotopic niche space was analysed following Rossman et al (2016) to investigate whether the isotopic niches of the 12 species were better discriminated in a three dimensional space rather than using a standard twodimensional approach. This uses a Bayesian framework to estimate a relative centroid location, a niche volume (referred to as standard ellipsoid volume [‰ 3 ]), and a volume of overlap between multiple ellipsoids among various parameters.…”