Differences In δ15N Research Articles

Stable isotope analysis of well-preserved 120,000-year-old herbivore bone collagen from the Middle Palaeolithic site of Neumark-Nord 2, Germany reveals niche separation between bovids and equids

Herbivores from the Neumark-Nord 2 archaeological site, Germany, were analysed for bone collagen stable carbon (δ13C) and nitrogen (δ15N) isotope ratios in order to investigate feeding ecology at this early Last Interglacial (Eemian) shallow-lake site. Of 42 faunal samples selected, 23 yielded collagen, demonstrating remarkable preservation for material of this age. The results indicate clear inter-specific differences in δ15N and δ13C values, notably between equids (Equus) and bovids (Bos/Bison), with mean difference Δ15N of +2‰ measured in the bovids compared to the equids. The potential reasons for these differences are explored, including physiology, herbivore feeding ecology, biogeography and resource partitioning within the local environment. The data are compared to previously published archaeological data, and modern experimental and ecological data, suggesting that these inter-specific differences are not consistent and therefore unlikely to be solely the product of physiology or habitual forage preference. Data from this study are compared to the local vegetation (as reconstructed from pollen profiles), and it is suggested that these trends are likely the result of niche partitioning at the shallow lake site, reflecting the local diversity in vegetational zones. The evidence for resource partitioning amongst Pleistocene herbivore communities at Neumark-Nord 2 and elsewhere is discussed. This study represents one of the largest data sets for collagen of this age, and the implications for our understanding of Late Pleistocene herbivore ecology, local herbivore community behaviour and hominin palaeodietary studies are explored.

Carbon sequestration in soil in a semi‐natural Miscanthus sinensis grassland and Cryptomeria japonica forest plantation in Aso, Kumamoto, Japan

AbstractAlthough Miscanthus sinensis grasslands (Misc‐GL) and Cryptomeria japonica forest plantations (Cryp‐FP) are proposed bioenergy feedstock systems, their relative capacity to sequester C may be an important factor in determining their potential for sustainable bioenergy production. Therefore, our objective was to quantify changes in soil C sequestration 47 years after a Misc‐GL was converted to a Cryp‐FP. The study was conducted on adjacent Misc‐GL and Cryp‐FP located on Mt. Aso, Kumamoto, Japan. After Cryp‐FP establishment, only the Misc‐GL continued to be managed by annual burning every March. Mass C and N, δ13C, and δ15N at 0–30 cm depth were measured in 5 cm increments. Carbon and N concentrations, C:N ratio, δ13C, and δ15N were measured in litter and/or ash, and rhizomes or roots. Although C input in Misc‐GL by M. sinensis was approximately 36% of that in Cryp‐FP by C. japonica, mean annual soil C sequestration in Misc‐GL (503 kg C ha−1 yr−1) was higher than that in Cryp‐FP (284 kg C ha−1 yr−1). This was likely the result of larger C input from aboveground litter to soil, C‐quality (C:N ratio and lignin concentration in aboveground litter) and possibly more recalcitrant C (charcoal) inputs by annual burning. The difference in soil δ15N between sites indicated that organic C with N had greater cycling between heterotrophic microbes and soil and produces more recalcitrant humus in Misc‐GL than in Cryp‐FP. Our data indicate that in terms of soil C sequestration, maintenance of Misc‐GL may be more advantageous than conversion to Cryp‐FP in Aso, Japan.

Isotopic fractionation in wild and captive European spiny lobsters (Palinurus elephas)

Differences in tissue specific fractionation have important practical implications for ecological studies. We have examined isotopic fractionation δ13C and δ15N among four different tissues in the spiny lobster Palinurus elephas (Fabricius, 1787). Two sets of individuals differing on diet-quality (captive animals with monospecific diet and wild lobsters) were studied to determine the best tissue to be used as a proxy of feeding ecology: muscles of the pleon, muscles of the legs, telson, and hemolymph.We observed significant differences in isotopic fractionation δ13C and δ15N among the analyzed tissues. In both captive and wild specimens leg muscle was the most δ15N enriched tissue, followed by pleonal muscle, hemolymph, and telson. For δ13C the sequence in isotopic discrimination was pleonal muscle > leg muscle > hemolymph ≈ telson. Lower intra-individual variability was observed in captives compared to wild individuals, as expected from a constant diet. Finally, we conclude that leg muscle is the best tissue for studying P. elephas trophism since it presents the lowest variability at isotopic level for N. The sampling of leg muscle, a regenerating tissue, is therefore suitable as a non lethal technique for trophic assessment at lobsters.

Comparing isotope signatures of prey fish: does gut removal affect δ13C or δ15N?

Stable isotope analysis is a quick and inexpensive method to monitor the effects of food web changes on aquatic communities. Traditionally, whole specimens have been used when determining isotope composition of prey fish or age-0 recreational fishes. However, gut contents of prey fish could potentially alter isotope composition of the specimen, especially when recent foraging has taken place or when the gut contains non-assimilated material that would normally pass through fishes undigested. To assess the impacts of gut content on prey fish isotope signatures, we examined the differences in isotopic variation of five prey fish species using whole fish, whole fish with the gut contents removed, and dorsal muscle only. We found significant differences in both δ15N and δ13C between the three tissue treatments. In most cases, muscle tissue was enriched compared to whole specimens or gut-removed specimens. Moreover, differences in mean δ15N within a species were up to 2‰ among treatments. This would result in a change of over half a trophic position (TP) based on a 3.4‰ increase per trophic level. However, there were no apparent relationships between tissue isotope values in fish with increased gut fullness (more prey tissue present). We suggest that muscle tissue should be used as the standard tissue for determining isotope composition of prey fish or age-0 recreational fishes, especially when determining enrichment for mixing models, calculating TP, or constructing aquatic food webs.

Tracking the fate of digesta 13C and 15N compositions along the ruminant gastrointestinal tract: Does digestion influence the relationship between diet and faeces?

Faecal stable isotope compositions reflect wildlife diets, if digestive processes along the gastrointestinal tract (GIT) do not alter diet–faeces isotopic relationships in an unpredictable way. We investigated 13C and 15N compositions of digesta along the ruminant GIT, using Saanen dairy goats kept on pure grass hay or browse for >20 days. Isotopic changes occurred in the ventral rumen, and in the small intestine, where digesta had significantly higher δ13C and δ15N (associated with lower C or higher N content, respectively) values relative to other GIT sites. However, effects on isotope fractionation were small (∼1.0‰ for δ13C and ∼ 2.0‰ for δ15N), and were reversed in the hindgut such that faecal isotope compositions did not differ from the foregut. No other substantial isotopic changes occurred across GIT sites, despite the morphophysiological complexity of the ruminant GIT. We found similarly small differences across GIT components of rheem gazelles (Gazella leptoceros) fed a mixture of C3 lucerne and C4 grass, although in this case faeces were 15N-depleted relative to other GIT components. Along with differences in δ15N between goats fed browse or grass, this result implies a systematic difference in diet–faeces δ15N relationships, contingent on the botanical composition of ruminant diets. Thus, while our results support faecal δ13C as a reliable proxy for wildlife diets, further work on factors influencing faecal 15N abundance is needed. Finally, we note high levels of isotopic variability between individuals fed the same diets, even accounting for the relatively short duration of the experiments, suggesting an important influence of stochasticity on isotope fractionation.

Evaluation of surface runoff and road dust as sources of nitrogen using nitrate isotopic composition

Stable nitrogen and oxygen isotope ratios of nitrate (δ15N–NO3 and δ18O–NO3) have recently been used to identify nitrogen sources in water environments. However, there have been no investigations designed to determine nitrate isotopes in non-point sources in urban areas for evaluating the impact of surface deposits on nitrogen in surface runoff. In this study, we collected rainwater, surface runoff and surface deposits (road dust, roof dust and soil) to evaluate the nitrogen sources in surface runoff using nitrate isotopes. There were no large differences in δ15N–NO3 among rainwater (−0.3‰ to 1.5‰), surface runoff (−2.7‰ to 0.4‰), leachates from road dust (−5.8‰ to 6.2‰) and soil (−11.5‰ to 0.6‰). In contrast, the δ18O–NO3 in surface runoff (28.5–47.9‰) was lower than that in rainwater (62.7–78.6‰), and higher than that in leachates from road dust (6.1–27.6‰) and soil (−1.1‰ to 6.6‰). δ18O–NO3 is a useful indicator for evaluating the NO3–N sources in surface runoff. Using this indicator, NO3–N from road dust was estimated to account for more than half of the NO3–N in surface runoff. This is consistent with a result based on a comparison of their loads per unit surface between rainwater and surface runoff, which also showed that most of the nitrogen in surface runoff was derived from surface deposits.

Unique seasonal forage bases within a local population of bottlenose dolphin (Tursiops truncatus)

AbstractUsing photo‐identification data, bottlenose dolphin (Tursiops truncatus) populations can be differentiated based on their use of particular estuaries or coastal habitats. Questions remain, however, about the validity of such fine‐scale population partitioning and whether the resulting assemblages utilize unique forage bases. To address the issue of forage base use, stable isotopes of carbon (δ13C), nitrogen (δ15N) and sulfur (δ34S) were analyzed from skin tissues (n= 74) of bottlenose dolphins sampled seasonally along the coast and in three estuaries near Charleston, South Carolina. Autumn values of δ34S, δ15N, and δ13C and summer values of δ34S indicated that dolphins sampled from these four assemblages utilized unique forage bases, despite limited sample sizes. Likewise, autumn and spring differences in δ15N and δ13C values were evident in the North Edisto River, and in δ34S from dolphins sampled from all three estuarine assemblages; no seasonal differences were identified in the coastal assemblage. Results demonstrate the importance of considering spatial and temporal variation in forage base when developing local management plans for bottlenose dolphin and highlight the discriminatory power of δ34S for estuarine and coastal marine mammals. These results also suggest that stable isotopes could be developed as a complementary tool for photo‐identification based partitioning of bottlenose dolphin populations.

Natural 15N abundance of paddy rice (Oryza sativa L.) grown with synthetic fertilizer, livestock manure compost, and hairy vetch

Nitrogen isotope abundance (δ15N) of paddy rice (Oryza sativa L.) grown for 110 days after transplanting (DAT) under field conditions with ammonium sulfate (AS with −0.4‰ as a synthetic fertilizer), pig manure compost (PMC with 15.3‰ as a livestock manure compost), and hairy vetch (HV with −0.5‰ as a green manure) was investigated to test the possible use of δ15N technique in discriminating organically grown from conventionally grown rice. At 15 DAT, the δ15N of whole rice decreased (P 5.5‰ for control (without N input) > 4.0‰ for HV > 1.8‰ for AS. This difference seemed to reflect primarily the δ15N signal of N sources. Although differences in δ15N of rice grown with isotopically distinct N inputs (i.e. PMC vs. AS and PMC vs. HV) became smaller over time, the difference (2.8 and 3.0‰ difference at harvest on 110 DAT, respectively) was still significant (P < 0.05). However, there was no distinguishable difference between AS and HV treatment after 42 DAT. Such effect of N inputs on δ15N of whole rice was also observed for root, shoot, and grain at harvest. Therefore, our study suggests that it is possible to distinguish rice grown with manure composts from that grown with synthetic fertilizers. However, if green manure of preceding N2-fixing plants is used as the N source, δ15N of rice may not be a good surrogate of N sources.

Trophic relationships between a native and a nonnative predator in a system of natural lakes

Abstract – Bull trout, a species of char listed as threatened under the US Endangered Species Act, have been displaced from portions of their historic range following the introduction of nonnative lake trout. It has been suggested that competitive exclusion as a result of trophic overlap between bull trout and lake trout may be the causal mechanism associated with displacement of bull trout. This study used stable isotope data to evaluate trophic relationships among native bull trout, nonnative lake trout and other fishes in seven lakes in Glacier National Park (GNP), Montana. Bull trout and lake trout had greater δ15N values relative to other fishes among lakes (δ15N ≥ 3.0‰). Lake trout had greater δ15N values relative to bull trout (δ15N = +1.0‰). Bull trout had greater δ13C values relative to lake trout in six of the seven lakes examined. Although both bull trout and lake trout had greater δ15N values relative to other fishes within lakes in GNP, differences in δ15N and δ13C between bull trout and lake trout suggest that they are consuming different prey species or similar prey species in different proportions. Therefore, displacement of bull trout as a direct result of complete overlap in food resource use is not anticipated unless diet shifts occur or food resources become limiting. Additionally, future studies should evaluate food habits to identify important prey species and sources of partial dietary overlap between bull trout and lake trout.

Variation in nitrogen use strategies and photosynthetic pathways among vascular epiphytes in the Brazilian Central Amazon

The variation in nitrogen use strategies and photosynthetic pathways among vascular epiphyte families was addressed in a white-sand vegetation in the Brazilian Central Amazon. Foliar nitrogen and carbon concentrations and their isotopic composition (δ15N and δ13C, respectively) were measured in epiphytes (Araceae, Bromeliaceae and Orchidaceae) and their host trees. The host tree Aldina heterophylla had higher foliar N concentration and lower C:N ratio (2.1 ± 0.06% and 23.6 ± 0.8) than its dwellers. Tree foliar δ15N differed only from that of the orchids. Comparing the epiphyte families, the aroids had the highest foliar N concentration and lowest C:N ratios (1.4 ± 0.1% and 34.9 ± 4.2, respectively). The orchids had more negative foliar δ15N values (-3.5 ± 0.2‰) than the aroids (-1.9 ± 0.7‰) and the bromeliads (-1.1 ± 0.6‰). Within each family, aroid and orchid taxa differed in relation to foliar N concentrations and C:N ratios, whereas no internal variation was detected within bromeliads. The differences in foliar δ15N observed herein seem to be related to the differential reliance on the available N sources for epiphytes, as well as to the microhabitat quality within the canopy. In relation to epiphyte foliar δ13C, the majority of epiphytes use the water-conserving CAM-pathway (δ13C values around -17‰), commonly associated with plants that live under limited and intermittent water supply. Only the aroids and one orchid taxon indicated the use of C3-pathway (δ13C values around -30‰).

Functional differences between woodland savannas and seasonally dry forests from south-eastern Brazil: Evidence from 15N natural abundance studies

Nitrogen availability and N-cycling dynamics across ecosystems play a critical role in plant functioning and species distribution. Measurements of 15N natural abundance provides a way to assess ecosystem N dynamics, and the range of nitrogen stable isotope values (δ15N) for plants in an ecosystem can indicate divergent strategies for N uptake. We tested the hypotheses that the N-rich seasonally dry forest would have higher soil and leaf δ15N and a smaller range of leaf δ15N values compared to the N-poor cerradao (savanna woodland). We measured N concentration and δ15N in two soil depths and leaves of 27 woody species in cerradao and 26 in seasonally dry forest. As expected, total soil N concentration decreased while soil δ15N value increased with soil depth. Regardless of soil depth, seasonally dry forest soils had higher δ15N and total N concentration compared to cerradao soils. Foliar δ15N values varied from −6.4‰ to 5.9‰ in cerradao and from −2.3‰ to 8.4‰ in seasonally dry forest plants. Phylogenetically independent contrasts analysis and comparisons of δ15N mean values of the most abundant species and species co-occurring in both sites confirmed the hypothesis of higher δ15N for seasonally dry forest in comparison to cerradao. These results corroborate the expectation of higher soil and leaf δ15N values in sites with higher soil N availability. However, except for the most abundant species, no across-site leaf–soil (δ15N leaf –δ15N soil) differences (Δδ15N) were found suggesting that differences in leaf δ15N between cerradao and seasonally dry forest are driven by differences in soil δ15N. Variation of leaf δ15N was large in both sites and only slightly higher in cerradao, suggesting high diversity of N use strategies for both cerradao and seasonally dry forest communities.

Role of mixotrophy and light for growth and survival of the toxic haptophyte Prymnesium parvum

Mixotrophy in Prymnesium parvum was investigated using carbon (δ13C) and nitrogen (δ15N) stable isotopes. The experiment was performed in light and dark. In the dark treatment we expected that the mixotrophic P. parvum would rely solely on its prey and therefore reflect the prey isotopic signatures. In the light treatment P. parvum can perform photosynthesis as well as utilize its prey, thus we expect the isotopic signatures to be between the dark mixed cultures and the monocultures, depending on how much prey was utilized. In the light treatment, the addition of the ciliate Myrionecta rubra resulted in higher P. parvum cell numbers compared to monocultures. During the experiment, cell numbers in the dark monocultures and the mixed dark cultures did not increase. P. parvum had 2.5–3 times higher cellular phosphorus and nitrogen content in the dark compared to the cultures in the light whereas no difference in carbon content between treatments could be observed. This suggests that P. parvum can utilize nitrogen and phosphorus but not carbon in the dark. It thus seems as if P. parvum relies on photosynthesis to meet the carbon and energy demand required for growth. The expected isotopic signatures “become what you eat…plus a few per mil” were not observed. In the dark treatment, the δ13C did not differ between monocultures and mixed cultures. In the light treatments P. parvum δ13C became less negative then the corresponding dark treatments indicating that P. parvum used CO2 rather than carbon from the added prey. No difference in δ15N between monocultures and mixed cultures could be observed during the experiment. We argue that light is necessary for P. parvum growth and that the ability to utilize nutrients originating from their prey may be important in bloom formation.

Niche differentiation of bottlenose dolphin species in South Australia revealed by stable isotopes and stomach contents

Context Animal species with overlapping ranges are common worldwide, but how these species coexist is less obvious. Dolphins are protected in Australia and yet little information is available on their resource use which is essential for successful management and conservation. Aim The aim of this study was to determine the degree of overlap in diet and feeding ecology of the two Tursiops spp. that have overlapping ranges in South Australia. Methods Stomach content (91 Tursiops sp. and 14 T. truncatus) and stable isotope (δ13C, δ15N) analyses (39 Tursiops sp. and 14 T. truncatus) were conducted. Carcasses of dolphins were opportunistically collected between 1974 and 2005. Diet was quantified by frequency of occurrence (FOO) and numerical abundance (NA) of prey. Key results Delta13C from teeth revealed distinct differences in primary source of carbon, corresponding to coastal (Tursiops sp. n = 39, = –12.24, s.d. = 1.32) and offshore habitats (T. truncatus n = 14, = –14.21, s.d. = 0.55). Differences in δ15N revealed Tursiops sp. ( = 11.66, s.d. = 0.58) feeds at a lower trophic level than T. truncatus ( = 14.29, s.d. = 0.88). Stomach content analyses for Tursiops sp. corroborated stable isotope results. There was a significant difference between the diets of Tursiops sp. from north Spencer Gulf and south Spencer Gulf (ANOSIM R = 0.249, P = 0.001). Prey were generally demersal in habit with the most important from the cephalopod families Octopodidae, Sepiidae and Loliginidae and fish families Carangidae, Clupeidae, Terapontidae and Apogonidae. For T. truncatus there were insufficient stomach contents for assessment. Conclusions South Australian bottlenose dolphin species exhibit distinct niche differentiation with clear evidence of regional variation in the diet of Tursiops sp. Implications The between and within species diet differentiation demonstrated, highlights the importance of regional management. Such results are internationally significant as coastal and offshore forms of Tursiops spp. occur worldwide.

Functional diversity in amphipods revealed by stable isotopes in an eelgrass ecosystem

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 420:277-281 (2010) - DOI: https://doi.org/10.3354/meps08873 NOTE Functional diversity in amphipods revealed by stable isotopes in an eelgrass ecosystem J. P. Farlin1,*, L. S. Lewis1,2, T. W. Anderson1, C. T. Lai1 1 Department of Biology and Coastal & Marine Institute, San Diego State University, 5500 Campanile Drive, San Diego, California 92182-4614, USA 2Present address: Center for Marine Biodiversity and Conservation, Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, California 92083-0202, USA *Email: nilraf@gmail.com ABSTRACT: Amphipods are often dominant components of benthic marine communities and may exhibit taxon-specific differences in feeding behavior. As a result, variation in the composition of amphipod communities is an important metric for the interpretation of trophic dynamics in benthic marine ecosystems. Though previous studies of amphipod diets indicate functional diversity among taxa, few studies have examined whether these differences are detectible using time-integrated natural tracers of in situ feeding habits. We used stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) to examine trophic structure among amphipod taxa belonging to 5 families in an eelgrass (Zostera marina) ecosystem in San Diego Bay, California. The relative contribution of sources of primary production to amphipod diets was further analyzed using a mixing model bracketed by 2 dominant sources of primary production in the system: eelgrass and algae. We detected significant differences in both δ13C and δ15N among amphipod taxa, indicating family-specific differences in feeding habits that generally agree with previous studies of amphipod diets. Hyalids fed almost exclusively on eelgrass, ischyrocerids and ampithoids tended to feed more on algae and eelgrass, respectively, and caprellids exhibited heterogeneous feeding on both algae and eelgrass. The relatively high δ15N value of oedicerotids suggested that this group was likely carnivorous. Our findings are in general agreement with previous descriptions of family-specific amphipod feeding behaviors, suggesting that stable isotopes are a useful tool for describing the functional roles of mesograzers in eelgrass ecosystems. KEY WORDS: Functional diversity · Stable isotopes · Eelgrass food web · Amphipods · Amphipod feeding Full text in pdf format PreviousNextCite this article as: Farlin JP, Lewis LS, Anderson TW, Lai CT (2010) Functional diversity in amphipods revealed by stable isotopes in an eelgrass ecosystem. Mar Ecol Prog Ser 420:277-281. https://doi.org/10.3354/meps08873 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 420. Online publication date: December 16, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Evidence for discrete subpopulations of sea perch (Helicolenus ercoides) across four fjords in Fiordland, New Zealand

In coastal populations of invertebrates and fishes, the distribution of discrete subpopulations is influenced by adult and larval dispersal, as well as by the effects of habitat heterogeneity on site fidelity or connectivity. Here, we examine evidence for spatial structure of sea perch, Helicolenus percoides, populations among four fjords in the Fiordland region of southwestern New Zealand. We examine patterns in adult morphology, length-at-age, δ13C and δ15N of muscle tissue, and trace elemental composition of whole otoliths as proxies for population isolation among the four inner fjord regions. A multivariate analysis of morphometrics reveals significant differences among populations from each of the four sites, suggesting existence of four distinct subpopulations. These patterns are consistent with observed differences in δ13C and δ15N, and length-at-age estimates among the four subpopulations. Differences in whole otolith concentrations of Sr, Ba, Mg and Li, and high classification scores based on the whole otolith elemental fingerprint are also consistent with significant subdivision among areas. Patterns across all four markers are consistent with discrete subpopulation structure of adult sea perch among the four study sites. These data indicate that the newly implemented network of marine protected areas in Fiordland is likely to contain discrete populations of sea perch.

Trophic fractionation (Δ15N) in Collembola depends on nutritional status: A laboratory experiment and mini-review

Abstract Isotopic studies in temperate forest soils suggested that collembolans occupy a broad range of trophic niches. This notion is mainly based on the wide (up to 8–9‰) range of δ15N signatures of different species. The interpretation of these data depends strongly on the correct estimation of nitrogen isotope fractionation per trophic level. It is usually assumed that a consumer is on average enriched in 15N by about 3.4‰ relative to its diet. However, trophic fractionation is not uniform across different animal taxa and different tissues, and varies with a range of factors, including quality of the diet and the nutritional status of animals. We performed a laboratory experiment aiming to compare the trophic fractionation of nitrogen isotopes (Δ15N) in different Collembola species fed with three fungi of different palatability. Collembolans were fed with a single-species fungal diet for 75 days. There was a positive correlation between the whole body C:N ratio and reproduction rates of collembolans. We therefore used the C:N ratio as a proxy of nutritional status. In all species of collembolans, the trophic fractionation decreased with increased whole body C:N ratio, and this factor explained most of the within-species variation in Δ15N. The analysis of published data on the trophic fractionation of collembolans in laboratory experiments confirmed this conclusion. However, the mean trophic fractionation in most collembolan species studied in the laboratory was fairly similar. In contrast, field studies have documented a consistent difference in δ15N among different families of collembolans. In particular, in nearly all published cases Onychiuridae had δ15N higher than Isotomidae or Entomobryidae. A sharp contrast between laboratory-based estimates of the trophic fractionation (generally uniform in different species and families) and field data (which show a consistent difference in δ15N among different species and even families of collembolans) confirms that δ15N values of field-collected animals bear important information on the trophic position occupied by a particular species, and are not heavily affected by the species-specific differences in trophic fractionation. As the Δ15N in collembolans depends on their nutritional status, we suggest that the C:N values should be reported along with isotopic data to allow cross-study comparisons.

Stable isotope analysis to examine possible diet-morphology relationships among Red-whiskered Bulbuls introduced on Réunion Island

A recent study on the introduced Red-whiskered Bulbul Pycnonotus jocosus on Réunion Island has highlighted the existence of rapid morphological divergence in bill size between the leeward and windward sides of the island. The hypothesis that diet could explain such geographical variation was explored by means of stable isotope analysis (C and N) on bird tissues. We found no evidence of geographical differences in δ15N and δ13C in muscle and feather tissues of birds collected on both sides of the island, despite morphological differences. Correlations between wing length, tail length and δ15N in tissues suggested that bigger birds could benefit from greater feeding opportunities on insects. However, stable isotope ratios in bird tissues marginally explained variation in bill size, indicating that diet specialisation may not be the major cause for morphological divergence among Red-whiskered Bulbuls on Réunion Island.

Dietary protein quality influences the pattern of natural isotopic composition of nitrogen in rats

The natural 15N enrichment (δ15N) in some specific tissues (blood, hair) has been shown to vary with diet quality. In this work, we investigated the influence of two dietary protein sources of different quality (milk and soy) on the δ15N values in various tissues. Male Wistar rats (n=18) were fed for 3 weeks experimental diets differing only in their protein source (soy or milk). δ15N values were determined in both protein and non‐protein fractions of blood and peripheral (muscle, kidney, skin) and splanchnic (liver, intestine) organs. Results were expressed as diet‐tissue discrimination (Δ15N = δ15Ntissue − δ15Ndiet). Regardless of the diet, the protein fraction of tissues was always enriched in 15N relative to the non‐protein fraction and relative to the diets (Δ15N&gt;0). Δ15N of protein fractions differed among tissues and were also influenced by the protein source. They were indeed higher in rats fed with soy (vs. milk) diet, in all tissues but the intestine (see Fig.). We conclude that Δ15N is lower when dietary protein quality is higher. Furthermore, the amplitude of Δ15N differences between diets varied among tissues (being for instance 3‐fold higher in skin than in liver), indicating that the nature of the dietary protein source differentially impacts the metabolism of splanchnic and peripheral tissues. We propose that Δ15N is a sensitive marker of protein biological value and regional protein metabolism.image

Effects of climate, tree age, dominance and growth on δ15N in young pinewoods

Needles, annual rings from basal stem discs and bark of three dominant and three suppressed Pinus pinaster from a 12-year-old pine stand (naturally regenerated after a wildfire) were analysed to study the effects of climate, tree age, dominance, and growth on tree δ15N. Foliar-N concentration in dominant pines (0.780–1.474% N) suggested that soil N availability was sufficient, a circumstance that allowed isotopic discrimination by plants and (greater) differences in δ15N among trees. The δ15N decreases in the order wood (−0.20 to +6.12‰), bark (−1.84 to +1.85‰) and needles (−2.13 to +0.77‰). In all trees, before dominance establishment (years 1–8), the N stored in each ring displayed a decreasing δ15N tendency as the tree grows, which is mainly due to a more “closed” N cycle or an increasing importance of N sources with lower δ15N. After dominance establishment (years 9–12), wood δ15N values were higher in suppressed than in dominant trees (2.62 and 1.46‰, respectively; P < 0.01) while the reverse was true for needles and bark; simultaneously, the absolute amount of N stored by suppressed pines in successive rings decreased, suggesting a lower soil N assimilation. These results could be explained by lignification acting as major N source for needles in suppressed pines because products released and reallocated during lignification are 15N-depleted compared with the source. According to principal component analysis, wood δ15N appears associated with wood N concentration and precipitation during the growing season, but clearly opposed to age, basal area increment and mean temperature in spring and summer.

Regional differences in bone collagen δ13C and δ15N of Pleistocene mammoths: Implications for paleoecology of the mammoth steppe

In this study, we present bone collagen δ 13C and δ 15N values from a large set of Pleistocene woolly mammoths ( Mammuthus primigenius) from Siberia, Alaska and Yukon. Overall, results for mammoth specimens from eastern Beringia (Alaska and Yukon) significantly differ, for both δ 13C and δ 15N values, from those from western Beringia (northeastern Siberia). In agreement with palynological, entomological, and physiographic data from the same regions, these isotopic differences strongly imply that the ‘mammoth steppe,’ the extensive ice-free region spanning northern Eurasia and northwestern North America, was ecologically variable along its east–west axis to a significant degree. Prior to the Last Glacial Maximum (LGM), the high-latitude portions of Siberia and the Russian Far East appear to have been colder and more arid than central Alaska and Yukon, which were ecologically more diverse. During the LGM itself, however, isotopic signatures of mammoths from eastern Beringia support the argument that this region also experienced an extremely cold and arid climate. In terms of overall temporal trend, Beringia thus went from a condition prior to the LGM of greater ecological variability in the east to one of uniformly cold and dry conditions during the LGM.