Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals
01 Jan 1980-
TL;DR: In this article, 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 and found that the variability of the relationship between the δ^(15)N values of animals and their diets is greater for different individuals raised on the same diet than for the same species raised on different diets.
Abstract: 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.
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TL;DR: In this article, the authors developed and discussed methods for generating an isotopic baseline and evaluate the assump- tions required to estimate the trophic position of consumers using stable isotopes in multiple ecosystem studies.
Abstract: The stable isotopes of nitrogen (8'5N) and carbon (8'3C) provide powerful tools for estimating the trophic positions of and carbon flow to consumers in food webs; however, the isotopic signature of a consumer alone is not generally sufficient to infer trophic position or carbon source without an appropriate isotopic baseline. In this paper, I develop and discuss methods for generating an isotopic baseline and evaluate the assump- tions required to estimate the trophic position of consumers using stable isotopes in multiple ecosystem studies. I test the ability of two primary consumers, surface-grazing snails and filter-feeding mussels, to capture the spatial and temporal variation at the base of aquatic food webs. I find that snails reflect the isotopic signature of the base of the littoral food web, mussels reflect the isotopic signature of the pelagic food web, and together they provide a good isotopic baseline for estimating trophic position of secondary or higher trophic level consumers in lake ecosystems. Then, using data from 25 north temperate lakes, I evaluate how 815N and 8'3C of the base of aquatic food webs varies both among lakes and between the littoral and pelagic food webs within lakes. Using data from the literature, I show that the mean trophic fractionation of b'5N is 3.4%o (1 SD = 1%M) and of 8'3C is 0.4%o (1 SD = 1.3%o), and that both, even though variable, are widely applicable. A sen- sitivity analysis reveals that estimates of trophic position are very sensitive to assumptions about the trophic fractionation of '5 N, moderately sensitive to different methods for gen- erating an isotopic baseline, and not sensitive to assumptions about the trophic fractionation of 8'3C when 8'3C is used to estimate the proportion of nitrogen in a consumer derived from two sources. Finally, I compare my recommendations for generating an isotopic baseline to an alternative model proposed by M. J. Vander Zanden and J. B. Rasmussen. With an appropriate isotopic baseline and an appreciation of the underlying assumptions and model sensitivity, stable isotopes can help answer some of the most difficult questions in food web ecology.
5,648 citations
Cites background or methods from "Influence of Diet On the Distribtio..."
...I used data from both individual laboratory trials (e.g., DeNiro and Epstein 1978, Adams and Sterner 2000) and whole ecosystem studies (e.g., Hansson et al. 1997)....
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...Fractionation estimates for carbon were drawn from DeNiro and Epstein (1978), Fry et al. (1978), Haines and Montague (1979), Petelle et al. (1979), Teeri and Schoeller (1979), Rau and Anderson (1981), Fry and Arnold (1982), Macko et al. (1982), Gu et al. (1996), Focken and Becker (1998)....
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TL;DR: The use of stable isotopes to solve biogeochemical problems in ecosystem analysis is increasing rapidly because stable isotope data can contribute both source-sink (tracer) and process information: the elements C, N, S, H, and all have more than one isotope, and isotopic compositions of natural materials can be measured with great precision with a mass spectrometer as mentioned in this paper.
Abstract: The use of stable isotopes to solve biogeochemical problems in ecosystem analysis is increasing rapidly because stable isotope data can contribute both source-sink (tracer) and process information: The elements C, N, S, H, and all have more than one isotope, and isotopic compositions of natural materials can be measured with great precision with a mass spectrometer. Isotopic compositions change in predictable ways as elements cycle through the biosphere. These changes have been exploited by geochemists to understand the global elemental cycles. Ecologists have not until quite recently employed these techniques. The reasons for this are, first, that most ecologists do not have the background in chemistry and geochemistry to be fully aware of the possibilities for exploiting the natural variations in stable isotopic compositions, and second, that stable isotope ratio measurements require equipment not normally available to ecologists. This is unfortunate because some of the more intractable problems in ecology can be profitably addressed using stable isotope measurements. Stable isotopes are ideally suited to increase our understanding of element cycles in ecosystems. This review is written for ecologists who would like to learn more about how stable isotope analyses have been and can be used in ecosystem studies. We begin with an explanation of isotope terminology and fractionation, then summarize isotopic distributions in the C, N, and S biogeochemical cycles, and conclude with five case studies that show how stable isotope measurements can provide crucial information for ecosystem analysis. We restrict this review to studies of natural variations in C, N, and S isotopic abundances, cxcluding from consideration ~5N enrichment studies and hydrogen and oxygen isotope studies. Our focus on C, N, and S derives in part from our
5,234 citations
TL;DR: The isotopic composition of nitrogen was measured in marine and fresh-water animals from the East China Sea, The Bering Sea, Lake Ashinoko and Usujiri intertidal zone as mentioned in this paper.
4,020 citations
TL;DR: For example, this article found that the trophic shift for C was lower for consumers acidified prior to analysis than for unacidified samples ( +0.5 + 0.13%o rather than 0.0%o, as commonly assumed).
Abstract: Use of stable isotope ratios to trace pathways of organic matter among consumers requires knowledge of the isotopic shift between diet and consumer. Variation in trophic shift among consumers can be substantial. For data from the published literature and supplementary original data (excluding fluid-feeding consumers), the mean isotopic shift for C was + 0.5 + 0.13%o rather than 0.0%o, as commonly assumed. The shift for C was higher for consumers analyzed as muscle (+ 1.3 + 0.30%o) than for consumers analyzed whole (+ 0.3 +0.14%o). Among consumers analyzed whole, the trophic shift for C was lower for consumers acidified prior to analysis (-0.2 + 0.21%o) than for unacidified samples ( +0.5 + 0.17%o). For N, trophic shift was lower for consumers raised on invertebrate diets (+ 1.4 + 0.21%o) than for consumers raised on other high-protein diets (+3.3 +0.26%o) and was intermediate for consumers raised on plant and algal diets (+2.2 +0.30%o). The trophic shift for S differed between high-protein (+ 2.0 + 0.65%o) and low-protein diets (-0.5 + 0.56%o). Thus, methods of analysis and dietary differences can affect trophic shift for consumers; the utility of stable isotope methods can be improved if this information is incorporated into studies of trophic relationships. Although few studies of stable isotope ratios have considered variation in the trophic shift, such variation is important because small errors in estimates of trophic shift can result in large errors in estimates of the contribution of sources to consumers or in estimates of trophic position.
2,477 citations
Cites background from "Influence of Diet On the Distribtio..."
...Although the shift in H isotope ratio between diet and consumer is small relative to variation in the environment (Estep and Dabrowski 1980, Macko et al. 1983), H isotope ratios of consumers are affected by factors other than diet (DeNiro and Epstein 1981b)....
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...Metabolic fractionation also may cause isotope ratios of different tissues to vary substantially within individual consumers (DeNiro and Epstein 1981a, Hobson and Clark 1992)....
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...20‰ (mean SE); one estimate of (15)N for Artemia (DeNiro and Epstein 1981a) was...
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...For the early studies by DeNiro and Epstein (1978, 1981a), the mean trophic shift for C ( 13C; denotes the change in isotope ratio between diet and consumer) was about +1‰, and the mean 15N was about +3‰....
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...Nitrogen – Excreted nitrogen typically is depleted in (15)N relative to a consumer’s diet (DeNiro and Epstein 1981a) or tissues (Checkley and Miller 1989)....
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TL;DR: The results indicate that lipid extraction or normalization is most important when lipid content is variable among consumers of interest or between consumers and end members, and when differences in δ13C between end members is <10–12‰.
Abstract: Within an organism, lipids are depleted in (13)C relative to proteins and carbohydrates (more negative delta(13)C), and variation in lipid content among organisms or among tissue types has the potential to introduce considerable bias into stable isotope analyses that use delta(13)C. Despite the potential for introduced error, there is no consensus on the need to account for lipids in stable isotope analyses. Here we address two questions: (1) If and when is it important to account for the effects of variation in lipid content on delta(13)C? (2) If it is important, which method(s) are reliable and robust for dealing with lipid variation? We evaluated the reliability of direct chemical extraction, which physically removes lipids from samples, and mathematical normalization, which uses the carbon-to-nitrogen (C:N) ratio of a sample to normalize delta(13)C after analysis by measuring the lipid content, the C:N ratio, and the effect of lipid content on delta(13)C (Deltadelta(13)C) of plants and animals with a wide range of lipid contents. For animals, we found strong relationships between C:N and lipid content, between lipid content and Deltadelta(13)C, and between C:N and Deltadelta(13)C. For plants, C:N was not a good predictor of lipid content or Deltadelta(13)C, but we found a strong relationship between carbon content and lipid content, lipid content and Deltadelta(13)C, and between and carbon content and Deltadelta(13)C. Our results indicate that lipid extraction or normalization is most important when lipid content is variable among consumers of interest or between consumers and end members, and when differences in delta(13)C between end members is <10-12 per thousand. The vast majority of studies using natural variation in delta(13)C fall within these criteria. Both direct lipid extraction and mathematical normalization reduce biases in delta(13)C, but mathematical normalization simplifies sample preparation and better preserves the integrity of samples for delta(15)N analysis.
2,103 citations
Cites background from "Influence of Diet On the Distribtio..."
...animal movement patterns, and establishing baselines to estimate trophic position (Peterson and Fry 1987; Hobson 1999; Post 2002) because it expresses little trophic fractionation (DeNiro and Epstein 1978; Peterson and Fry 1987; Post 2002; McCutchan et al. 2003)....
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...…diet sources, identifying animal movement patterns, and establishing baselines to estimate trophic position (Peterson and Fry 1987; Hobson 1999; Post 2002) because it expresses little trophic fractionation (DeNiro and Epstein 1978; Peterson and Fry 1987; Post 2002; McCutchan et al. 2003)....
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...While trophic fractionation has received considerable recent attention (DeNiro and Epstein 1978; Peterson and Fry 1987; Post 2002; McCutchan et al. 2003), the synthesis and accumulation of lipids, which are depleted in 13C and typically have d13C values that are more negative than those for…...
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References
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TL;DR: The lipid decomposition studies in frozen fish have led to the development of a simple and rapid method for the extraction and purification of lipids from biological materials that has been applied to fish muscle and may easily be adapted to use with other tissues.
Abstract: Lipid decomposition studies in frozen fish have led to the development of a simple and rapid method for the extraction and purification of lipids from biological materials. The entire procedure can...
46,099 citations
TL;DR: In this article, the authors developed and discussed methods for generating an isotopic baseline and evaluate the assump- tions required to estimate the trophic position of consumers using stable isotopes in multiple ecosystem studies.
Abstract: The stable isotopes of nitrogen (8'5N) and carbon (8'3C) provide powerful tools for estimating the trophic positions of and carbon flow to consumers in food webs; however, the isotopic signature of a consumer alone is not generally sufficient to infer trophic position or carbon source without an appropriate isotopic baseline. In this paper, I develop and discuss methods for generating an isotopic baseline and evaluate the assump- tions required to estimate the trophic position of consumers using stable isotopes in multiple ecosystem studies. I test the ability of two primary consumers, surface-grazing snails and filter-feeding mussels, to capture the spatial and temporal variation at the base of aquatic food webs. I find that snails reflect the isotopic signature of the base of the littoral food web, mussels reflect the isotopic signature of the pelagic food web, and together they provide a good isotopic baseline for estimating trophic position of secondary or higher trophic level consumers in lake ecosystems. Then, using data from 25 north temperate lakes, I evaluate how 815N and 8'3C of the base of aquatic food webs varies both among lakes and between the littoral and pelagic food webs within lakes. Using data from the literature, I show that the mean trophic fractionation of b'5N is 3.4%o (1 SD = 1%M) and of 8'3C is 0.4%o (1 SD = 1.3%o), and that both, even though variable, are widely applicable. A sen- sitivity analysis reveals that estimates of trophic position are very sensitive to assumptions about the trophic fractionation of '5 N, moderately sensitive to different methods for gen- erating an isotopic baseline, and not sensitive to assumptions about the trophic fractionation of 8'3C when 8'3C is used to estimate the proportion of nitrogen in a consumer derived from two sources. Finally, I compare my recommendations for generating an isotopic baseline to an alternative model proposed by M. J. Vander Zanden and J. B. Rasmussen. With an appropriate isotopic baseline and an appreciation of the underlying assumptions and model sensitivity, stable isotopes can help answer some of the most difficult questions in food web ecology.
5,648 citations
TL;DR: The use of stable isotopes to solve biogeochemical problems in ecosystem analysis is increasing rapidly because stable isotope data can contribute both source-sink (tracer) and process information: the elements C, N, S, H, and all have more than one isotope, and isotopic compositions of natural materials can be measured with great precision with a mass spectrometer as mentioned in this paper.
Abstract: The use of stable isotopes to solve biogeochemical problems in ecosystem analysis is increasing rapidly because stable isotope data can contribute both source-sink (tracer) and process information: The elements C, N, S, H, and all have more than one isotope, and isotopic compositions of natural materials can be measured with great precision with a mass spectrometer. Isotopic compositions change in predictable ways as elements cycle through the biosphere. These changes have been exploited by geochemists to understand the global elemental cycles. Ecologists have not until quite recently employed these techniques. The reasons for this are, first, that most ecologists do not have the background in chemistry and geochemistry to be fully aware of the possibilities for exploiting the natural variations in stable isotopic compositions, and second, that stable isotope ratio measurements require equipment not normally available to ecologists. This is unfortunate because some of the more intractable problems in ecology can be profitably addressed using stable isotope measurements. Stable isotopes are ideally suited to increase our understanding of element cycles in ecosystems. This review is written for ecologists who would like to learn more about how stable isotope analyses have been and can be used in ecosystem studies. We begin with an explanation of isotope terminology and fractionation, then summarize isotopic distributions in the C, N, and S biogeochemical cycles, and conclude with five case studies that show how stable isotope measurements can provide crucial information for ecosystem analysis. We restrict this review to studies of natural variations in C, N, and S isotopic abundances, cxcluding from consideration ~5N enrichment studies and hydrogen and oxygen isotope studies. Our focus on C, N, and S derives in part from our
5,234 citations
TL;DR: The isotopic composition of nitrogen was measured in marine and fresh-water animals from the East China Sea, The Bering Sea, Lake Ashinoko and Usujiri intertidal zone as mentioned in this paper.
4,020 citations