The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

To investigate feeding habits, carbon and nitrogen stable isotope ratios were measured in hair sampled from Asiatic black bears (Ursus thibetanus) inhabiting an alpine area, including the Northern Japanese Alps and the periphery of villages in Nagano Prefecture, in central Japan. Asiatic black bears in the Northern Japanese Alps are subject to little human influence, but in rural areas human encounters with bears seeking food in cornfields and garbage have become an issue that needs to be resolved. We investigated the feeding habits of bears by analyzing the isotopic changes along the entire length of hair samples. Rural bears, including nuisance bears, showed slightly higher δ15N and δ13C values than alpine bears, suggesting that rural nuisance bears may have greater access to anthropogenic food resources than their alpine counterparts. Hair samples were further examined by growth section analysis (GSA), in which sectioned samples from the root to the tip are used for isotopic analysis, to estim...

Estimation of feeding history by measuring carbon and nitrogen stable isotope ratios in hair of Asiatic black bears

Polar bear (Ursus maritimus) diet may become more variable in some Arctic regions due to climate warming and altered sea ice habitat. We surveyed carbon and nitrogen stable isotope profiles of five polar bear tissues sampled from adult females in the Southern Beaufort Sea of Alaska in order to assess inter-tissue isotopic variability and to determine whether any dietary shifts are occurring in this population. We did not detect any significant shifts from historical means in population-level tissue stable isotope values. A number of sectioned hair samples, however, were significantly depleted in 15N relative to the mean. We hypothesized that lower hair δ15N values were due to the consumption of bowhead whale (Balaena mysticetus) tissue. Telemetry data showed that polar bears with 15N-depleted hair sections were located on multiple dates near known subsistence-harvested bowhead whale bone piles and had spent 90 % of the prior year within 50 km of the shore. Bears with hair section δ15N values at or above the mean spent no time near bowhead whale bone piles and less than half of the year nearshore. An isotopic mixing model estimation of diet proportions determined that bowhead whale comprised approximately 50–70 % of fall diet for bears with lower hair δ15N values. We conclude that these results offer emergent evidence of an alternative foraging strategy within this population: ‘coastal’ bears, which remain near to shore for much of the year and use bowhead whale bone piles when they are present. In contrast, ‘pelagic’ bears follow a more typical strategy and forage widely on sea ice for seals.

Diet of female polar bears in the southern Beaufort Sea of Alaska: evidence for an emerging alternative foraging strategy in response to environmental change

We determined the magnitude of isotopic fractionation of carbon and nitrogen stable isotope ratios (as enrichment factors, Δδ13C and Δδ15N, respectively) between the tissues and diets of captive Japanese macaques (Macaca fuscata) using a controlled feeding experiment, to provide basic data for reconstructing their feeding habits. The Δδ13C and Δδ15N values, respectively, were 0.9 ± 0.2 ‰ (mean ± standard deviation, SD) and 3.0 ± 0.3 ‰ for whole blood, 1.3 ± 0.2 ‰ and 4.3 ± 0.3 ‰ for plasma, and 0.8 ± 0.2 ‰ and 3.0 ± 0.2 ‰ for red blood cells. However, the Δδ13C and Δδ15N values for hair were 2.8 ± 0.3 ‰ and 3.4 ± 0.2 ‰, respectively. No difference was detected in the δ13C and δ15N values of hair sampled from different parts of the body. We investigated the effects of diet on δ13C in growing hair by alternating the diet of the macaques each month between two diets that differed markedly in δ13C. Hair regrown after shaving repeatedly recorded the δ13C of the diet consumed during the time of hair growth. On the other hand, hair naturally grown during the diet-change experiment did not show a clear pattern. One possible reason is that the hair had grown abnormally under unnatural indoor conditions and showed complicated isotope signatures. To reconstruct the long-term feeding history of Japanese macaques, we need to further clarify the relationships between the stable isotope signature of diet and various body tissues.

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Characteristics of stable isotope signature of diet in tissues of captive Japanese macaques as revealed by controlled feeding

Grizzly bears (Ursus arctos) cohabit landscapes with a diversity of ungulates, but the degree to which grizzly bears are carnivorous is unclear and likely varies across landscapes. We used stable isotopes of carbon and nitrogen to infer seasonal diets of grizzly bears in northern British Columbia while studying predator–prey dynamics in a largely undisturbed system. We found high seasonal variation in diets among individuals; males consumed more ungulate prey than did females throughout the year. In fall, both sexes increased their consumption of prey; large ungulates constituted 51% and 32% of the fall diets of males and females, respectively. This increase in carnivory appeared to be primarily associated with consumption of elk (Cervus elaphus). Estimates of prey proportions in the diets of grizzly bears were highly sensitive to the range of tissue to diet discrimination values that were incorporated in isotope models. Small changes in discrimination values resulted in estimated prey intakes that varied more than threefold as a percentage of the diet depending on sex and season. We caution against using standard discrimination values, and we recommend that diet reconstructions using stable isotopes be based on tissue-specific values that would be appropriate for the species of interest. © 2012 The Wildlife Society.

Quantifying carnivory by grizzly bears in a multi-ungulate system

Carbon and nitrogen stable isotope ratios were measured in hair samples of the Asiatic black bear (Ursus thibetanus) inhabiting the Northern Japanese Alps (NJA) (n = 20) and the periphery of Nagano City (NC) (n = 6), in Nagano Prefecture, Japan. The hair of NJA bears, which did not have access to anthropogenic foods, showed lower values of δ13C and δ15N than that of NC bears which had access to garbage and corn fields, especially during the summer. These results reflect somewhat differing diets between the NJA and NC bears. We attempted to assess the feeding history during the hair growth cycle using the growth section analysis method. Each hair sample had been cut into 3 mm lengths from root to tip, labeled, and analyzed along the hair growth. We measured the carbon and nitrogen stable isotope ratios of each 3 mm length of hair sample from one NC bear which had been killed while raiding a corn field. The sections showed wide ranges of isotope ratios, from −23.2‰ to −14.6‰ for δ13C, and from 0.3‰ to 4.6‰ ...

M. Goto

Papers

Temporal diet changes recorded by stable isotopes in Asiatic black bear (Ursus thibetanus) hair