Determining trophic niche width: a novel approach using stable isotope analysis

Abstract

Summary1. Although conceptually robust, it has proven difficult to find practical measures of niche width that are simple to obtain, yet provide an adequate descriptor of the ecological position of the population examined. 2. Trophic niche has proven more tractable than other niche dimensions. However, indices used as a proxy for trophic niche width often suffer from the following difficulties. Such indices rarely lie along a single scale making comparisons between populations or species difficult; have difficulty in combining dietary prey diversity and evenness in an ecologically meaningful way; and fail to integrate diet over ecological time-scales thus usually only comprise single snapshots of niche width. 3. We propose an alternative novel method for the comparison of trophic niche width: the use of variance of tissue stable isotope ratios, especially those of nitrogen and carbon. 4. This approach is a potentially powerful method of measuring trophic niche width, particularly if combined with conventional approaches, because: it provides a single measure on a continuous axis that is common to all species; it integrates information on only assimilated prey over time; the integration period changes with choice of tissue sampled; and data production is theoretically fast and testing among populations simple. 5. Empirical studies are now required to test the benefits of using isotopic variance as a measure of niche width, and in doing so help refine this approach.

Trophic niches of thirteen damselfishes (Pomacentridae) at the Grand Récif of Toliara, Madagascar

“…Although stable isotope analysis does not provide a detailed picture of dietary preferences, it gives an average estimate of an organism's preferred diet that is much less subject to temporal bias (Pinnegar and Polunin 1999). Moreover, stable isotope analysis was recently revealed to be a powerful tool for assessing the trophic niche widths of species (Bearhop et al 2004).…”

Isotopic niches of sympatric native and exotic fish species in a Neotropical floodplain

“…JULIANA S. PHILIPPSEN, MARÍLIA HAUSER and EVANILDE BENEDITO niche space (Bearhop et al 2004) and is of essential importance to understanding food web structure, resource use and trophic interactions in aquatic ecosystems (Chen et al 2011). Moreover, these studies have practical applications when assessing possible impacts of exotic species on native species (Clarke et al 2005, Pound et al 2011.…”

“…Stable isotope analysis is becoming a very useful tool in studies that investigate the trophic ecology of native and exotic species (Cucherousset et al 2012, Jackson et al 2012. Recently, it has been argued that the isotopic ratios ( 13 C: 12 C and 15 N: 14 N) of the tissues of consumers could be used to represent the trophic niche of a particular species (Bearhop et al 2004, Grey 2006, formalizing the isotopic niche concept (Newsome et al 2007). These isotopic ratios can be used because it is known that these values reflect those of the species's diet (Jackson et al 2011).…”

“…Isotopic data are routinely presented in biplots (δ 13 C on the x-axis and δ 15 N on the y-axis), where isotopic values of the tissue of these animals can be represented on the isotopic space (δ), thus delineating the isotopic niche of a species (Newsome et al 2007, Quevedo et al 2009, Jackson et al 2011. Individual variations in the δ 13 C and δ 15 N values within a population can provide useful information on its trophic ecology (Bearhop et al 2004, Layman et al 2007.…”

The High Cost of Motherhood: End-Lactation Syndrome in Southern Sea Otters (Enhydra Lutris Nereis) on the Central California Coast, Usa

“…Briefly, the analysis of ratios of stable isotopes of carbon (13C) and nitrogen (15N) stored in inert tissues such as bone or vibrissae can be used to evaluate the diet of D R A F T 119 predators, assuming that the stable isotope ratios of potential prey species are also known and are sufficiently distinct (Bearhop et al 2004). The distribution of stable isotope ratio values on individual predators on the Cartesian axes of 13C vs. 15N provides a characterization of dietary niche of the predator population, the so-called "isotopic niche space" (Newsome et al 2012).…”