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1.
The use of stable isotopes to investigate animal diets, habitat use, and trophic level requires understanding the rate at
which animals incorporate the 13C and 15N from their diets and the factors that determine the magnitude of the difference in isotopic composition between the animal’s
diet and that of its tissues. We determined the contribution of growth and catabolic turnover to the rate of 13C and 15N incorporation into several tissues that can be sampled non-invasively (skin, scute, whole blood, red blood cells, and plasma
solutes) in two age classes of a rapidly growing ectotherm (loggerhead turtles, Caretta caretta). We found significant differences in C and N incorporation rates and isotopic discrimination factors (Δ13C = δ13Ctissues − δ13Cdiet and Δ15N = δ15Ntissues − δ15Ndiet) among tissues and between age classes. Growth explained from 26 to 100% of the total rate of incorporation in hatchling
turtles and from 15 to 52% of the total rate of incorporation in juvenile turtles. Because growth contributed significantly
to the rate of isotopic incorporation, variation in rates among tissues was lower than reported in previous studies. The contribution
of growth can homogenize the rate of isotopic incorporation and limit the application of stable isotopes to identify dietary
changes at contrasting time scales and to determine the timing of diet shifts. The isotopic discrimination factor of nitrogen
ranged from −0.64 to 1.77‰ in the turtles’ tissues. These values are lower than the commonly assumed average 3.4‰ discrimination
factors reported for whole body and muscle isotopic analyses. The increasing reliance on non-invasive and non-destructive
sampling in animal isotopic ecology requires that we recognize and understand why different tissues differ in isotopic discrimination
factors. 相似文献
2.
Linking isotopic and migratory patterns in a pelagic seabird 总被引:1,自引:0,他引:1
The value of stable isotope analysis in tracking animal migrations in marine environments is poorly understood, mainly due
to insufficient knowledge of isotopic integration into animal tissues within distinct water masses. We investigated isotopic
and moult patterns in Cory’s shearwaters to assess the integration of different stable isotopes into feathers in relation
to the birds’ transoceanic movements. Specimens of Mediterranean Cory’s shearwater Calonectris diomedea diomedea caught accidentally by Catalan longliners were collected and the signatures of stable isotopes of C (δ13C), N (δ15N) and S (δ34S) were analysed in 11 wing and two tail feathers from 20 birds, and in some breast feathers. Based on isotopic signatures
and moult patterns, the feathers segregated into two groups (breeding and wintering), corresponding to those grown in the
Mediterranean or Atlantic regions, respectively. In addition, feathers grown during winter, i.e. moulted in Atlantic waters,
were grouped into two isotopically distinct profiles, presumably corresponding to the two main wintering areas previously
identified for Mediterranean Cory’s shearwater in tracking studies. N signatures mainly indicated the Mediterranean-to-Atlantic
migration, whereas C and S signatures differed according to the Atlantic wintering area. Our results indicate that isotopic
signatures from distant oceanic regions can integrate the feathers of a given bird and can indicate the region in which each
feather was grown. This study thus underscores how stable isotope analysis can link marine animals to specific breeding and
wintering areas, and thereby shed new light on studies involving assignment, migratory connectivity and carry-over effects
in the marine environment.
Xavier Ruiz deceased 27 April 2008. 相似文献
3.
Summary Stable carbon isotope ratios in bone collagen have been used in a variety of dietary studies in modern and fossil animals,
including humans. Inherent in the stable isotope technique is the assumption that the isotopic signature is a reflection of
the diet and is persistent in collagen because this is a relatively inert protein. Carbon isotope analyses of bones from a
southern Indian population of Asian elephant (Elephas maximus), a long-lived mammal that alternates seasonally between a predominantly C3 (browse) and C4 (grass) plant diet, showed two patterns that have important implications for dietary interpretation based on isotopic studies.
Relative to the quantity of the two plant types consumed on average, the δ13C signal in collagen indicated that more carbon was incorporated from C3 plants, possibly due to their higher protein contribution. There was a much greater variance in δ13C values of collagen in sub-adult (range -10.5‰ to-22.7‰, variance=14.51) compared to adult animals (range -16.0‰ to -20.3‰,
variance=1.85) pointing to high collagen turnover rates and non-persistent isotopic signatures in younger, growing animals.
It thus seems important to correct for any significant relative differences in nutritive value of food types and also consider
the age of an animal before drawing definite conclusions about its diet from isotope ratios. 相似文献
4.
Stephan Unger Cristina Máguas João S. Pereira Luis M. Aires Teresa S. David Christiane Werner 《Oecologia》2010,163(4):1043-1057
Combining C flux measurements with information on their isotopic composition can yield a process-based understanding of ecosystem
C dynamics. We studied the variations in both respiratory fluxes and their stable C isotopic compositions (δ13C) for all major components (trees, understory, roots and soil microorganisms) in a Mediterranean oak savannah during a period
with increasing drought. We found large drought-induced and diurnal dynamics in isotopic compositions of soil, root and foliage
respiration (δ13Cres). Soil respiration was the largest contributor to ecosystem respiration (R
eco), exhibiting a depleted isotopic signature and no marked variations with increasing drought, similar to ecosystem respired
δ13CO2, providing evidence for a stable C-source and minor influence of recent photosynthate from plants. Short-term and diurnal
variations in δ13Cres of foliage and roots (up to 8 and 4‰, respectively) were in agreement with: (1) recent hypotheses on post-photosynthetic
fractionation processes, (2) substrate changes with decreasing assimilation rates in combination with increased respiratory
demand, and (3) decreased phosphoenolpyruvate carboxylase activity in drying roots, while altered photosynthetic discrimination
was not responsible for the observed changes in δ13Cres. We applied a flux-based and an isotopic flux-based mass balance, yielding good agreement at the soil scale, while the isotopic
mass balance at the ecosystem scale was not conserved. This was mainly caused by uncertainties in Keeling plot intercepts
at the ecosystem scale due to small CO2 gradients and large differences in δ13Cres of the different component fluxes. Overall, stable isotopes provided valuable new insights into the drought-related variations
of ecosystem C dynamics, encouraging future studies but also highlighting the need of improved methodology to disentangle
short-term dynamics of isotopic composition of R
eco. 相似文献
5.
Understanding what governs patterns of soil δ15N and δ13C is limited by the absence of these data assembled throughout the development of individual ecosystems. These patterns are important because stable isotopes of soil organic N and C are integrative indicators of biogeochemical processing of soil organic matter. We examined δ15N of soil organic matter (δ15NSOM) and δ13CSOM of archived soil samples across four decades from four depths of an aggrading forest in southeastern USA. The site supports an old-field pine forest in which the N cycle is affected by former agricultural fertilization, massive accumulation of soil N by aggrading trees over four decades, and small to insignificant fluxes of N via NH3 volatilization, nitrification, and denitrification. We examine isotopic data and the N and C dynamics of this ecosystem to evaluate mechanisms driving isotopic shifts over time. With forest development, δ13CSOM became depth-dependent. This trend resulted from a decline of ~2‰ in the surficial 15 cm of mineral soil to −26.0‰, due to organic matter inputs from forest vegetation. Deeper layers exhibited relatively little trend in δ13CSOM with time. In contrast, δ15NSOM was most dynamic in deeper layers. During the four decades of forest development, the deepest layer (35–60 cm) reached a maximum δ15N value of 9.1‰, increasing by 7.6‰. The transfer of >800 kg ha−1 of soil organic N into aggrading vegetation and the forest floor and the apparent large proportion of ectomycorrhizal (ECM) fungi in these soils suggest that fractionation via microbial transformations must be the major process changing δ15N in these soils. Accretion of isotopically enriched compounds derived from microbial cells (i.e., ECM fungi) likely promote isotopic enrichment of soils over time. The work indicates the rapid rate at which ecosystem development can impart δ15NSOM and δ13CSOM signatures associated with undisturbed soil profiles. 相似文献
6.
Effects of nutritional restriction on nitrogen and carbon stable isotopes in growing seabirds 总被引:4,自引:0,他引:4
When using stable isotopes as dietary tracers it is essential to consider effects of nutritional state on isotopic fractionation.
While starvation is known to induce enrichment of 15N in body tissues, effects of moderate food restriction on isotope signatures have rarely been tested. We conducted two experiments
to investigate effects of a 50–55% reduction in food intake on δ15N and δ13C values in blood cells and whole blood of tufted puffin chicks, a species that exhibits a variety of adaptive responses to
nutritional deficits. We found that blood from puffin chicks fed ad libitum became enriched in 15N and 13C compared to food-restricted chicks. Our results show that 15N enrichment is not always associated with food deprivation and argue effects of growth on diet–tissue fractionation of nitrogen
stable isotopes (Δ15N) need to be considered in stable isotope studies. The decrease in δ13C of whole blood and blood cells in restricted birds is likely due to incorporation of carbon from 13C-depleted lipids into proteins. Effects of nutritional restriction on δ15N and δ13C values were relatively small in both experiments (δ15N: 0.77 and 0.41‰, δ13C: 0.20 and 0.25‰) compared to effects of ecological processes, indicating physiological effects do not preclude the use of
carbon and nitrogen stable isotopes in studies of seabird ecology. Nevertheless, our results demonstrate that physiological
processes affect nitrogen and carbon stable isotopes in growing birds and we caution isotope ecologists to consider these
effects to avoid drawing spurious conclusions. 相似文献
7.
It is widely accepted that stable isotope ratios in inert tissues such as feather keratin reflect the dietary isotopic signature
at the time of the tissue synthesis. However, some elements such as stable nitrogen isotopes can be affected by individual
physiological state and nutritional stress. Using malaria infection experiment protocols, we estimated the possible effect
of malaria parasite infections on feather carbon (δ13C) and nitrogen (δ15N) isotope signatures in juvenile common crossbills Loxia curvirostra. The birds were experimentally infected with Plasmodium relictum (lineage SGS1) and P. ashfordi (GRW2), two widespread parasites of passerines. Experimental birds developed heavy parasitemia of both parasites and maintained
high levels throughout the experiment (33 days). We found no significant difference between experimental and control birds
in both δ13C and δ15N values of feathers re-grown. The study shows that even heavy primary infections of malaria parasites do not affect feather
δ13C and δ15N isotopic signatures. The results of this experiment demonstrate that feather isotope values of wild-caught birds accurately
reflect the dietary isotopic sources at the time of tissue synthesis even when the animal’s immune system might be challenged
due to parasitic infection. 相似文献
8.
Patterns and controls of seasonal variability of carbon stable isotopes of particulate organic matter in lakes 总被引:2,自引:0,他引:2
Carbon stable isotopes (δ13C) of particulate organic matter (POM) have been used as indicators for energy flow, primary productivity and carbon dioxide
concentration in individual lakes. Here, we provide a synthesis of literature data from 32 freshwater lakes around the world
to assess the variability of δ13CPOM along latitudinal, morphometric and biogeochemical gradients. Seasonal mean δ13CPOM, a temporally integrated measure of the δ13CPOM, displayed weak relationships with all trophic state indices [total phosphorus (TP), total nitrogen (TN), and chlorophyll
a (Chl a)], but decreased significantly with the increase in latitude, presumably in response to the corresponding decrease
in water temperature and increase in CO2 concentration. The seasonal minimum δ13CPOM also correlated negatively with latitude while seasonal maximum δ13CPOM correlated positively with all trophic state indices, pH, and δ13C of dissolved inorganic carbon (DIC). Seasonal amplitude of δ13CPOM (the difference between seasonal maximum and minimum values) correlated significantly with pH, TP and Chl a concentrations
and displayed small variations in oligotrophic, mesotrophic and low latitude eutrophic lakes, which is attributed to low primary
productivity and abundant non-living POM in the low trophic state lakes and relatively stable environmental conditions in
the subtropics. Seasonal amplitude of δ13CPOM was the greatest in high latitude eutrophic lakes. Greater seasonal changes in solar energy and light regime may be responsible
for the large seasonal variability in high latitude productive lakes. This synthesis provides new insights on the factors
controlling variations in stable carbon isotopes of POM among lakes on the global scale. 相似文献
9.
Nitrogen cycling in forest soils has been intensively studied for many years because nitrogen is often the limiting nutrient
for forest growth. Complex interactions between soil, microbes, and plants and the consequent inability to correlate δ15N changes with biologic processes have limited the use of natural abundances of nitrogen isotopes to study nitrogen (N) dynamics.
During an investigation of N dynamics along the 250-year-old successional sequence in Glacier Bay, Alaska, United States,
we observed several puzzling isotopic patterns, including a consistent decline in δ15N of the late successional dominant Picea at older sites, a lack of agreement between mineral N δ15N and foliar δ15N, and high isotopic signatures for mycorrhizal fungi. In order to understand the mechanisms creating these patterns, we developed
a model of N dynamics and N isotopes (Nitrogen Isotope Fluxes in Terrestrial Ecosystems, NIFTE), which simulated the major
transformations of the N cycle and predicted isotopic signatures of different plant species and soil pools. Comparisons with
field data from five sites along the successional sequence indicated that NIFTE can duplicate observed patterns in δ15N of soil, foliage, and mineral N over time. Different scenarios that could account for the observed isotopic patterns were
tested in model simulations. Possible mechanisms included increased isotopic fractionation on mineralization, fractionation
during the transfer of nitrogen from mycorrhizal fungi to plants, variable fractionation on uptake by mycorrhizal fungi compared
to plants, no fractionation on mycorrhizal transfer, and elimination of mycorrhizal fungi as a pool in the model. The model
results suggest that fractionation during mineralization must be small (˜2‰), and that no fractionation occurs during plant
or mycorrhizal uptake. A net fractionation during mycorrhizal transfer of nitrogen to vegetation provided the best fit to
isotopic data on mineral N, plants, soils, and mycorrhizal fungi. The model and field results indicate that the importance
of mycorrhizal fungi to N uptake is probably less under conditions of high N availability. Use of this model should encourage
a more rigorous assessment of isotopic signatures in ecosystem studies and provide insights into the biologic transformations
which affect those signatures. This should lead to an enhanced understanding of some of the fundamental controls on nitrogen
dynamics.
Received: 1 July 1998 / Accepted: 23 December 1998 相似文献
10.
Investigations into trophic ecology and aquatic food web resolution are increasingly accomplished through stable isotope analysis.
The incorporation of dietary and metabolic changes over time results in variations in isotope signatures and turnover rates
of producers and consumers at tissue, individual, population and species levels. Consequently, the elucidation of trophic
relationships in aquatic systems depends on establishing standard isotope values and tissue turnover rates for the level in
question. This study investigated the effect of diet and food quality on isotopic signatures of four mussel tissues: adductor
muscle, gonad, gill and mantle tissue from the brown mussel Perna perna. In the laboratory, mussels were fed one of the two isotopically distinct diets for 3 months. Although not all results were
significant, overall δ13C ratios in adductor, mantle and gill tissues gradually approached food source signatures in both diets. PERMANOVA analyses
revealed significant changes over time in tissue δ13C (mantle and gill) with both diets and in δ15N (all tissues) and C:N ratios (mantle and gill) for one diet only. The percentage of replaced carbon isotopes were calculated
for the 3 month period and differed among tissues and between diets. The tissue with the highest and lowest amount of replaced
isotopes over 81 days were mantle tissue on the kelp diet (33.89%) and adductor tissue on the fish food diet (4.14%), respectively.
Percentages could not be calculated for any tissue in either diet for δ15N due to the lack of significant change in tissue nitrogen. Fractionation patterns in tissues for both diets can be linked
to nutritional stress, suggesting that consumer isotopic signatures are strongly dependent on food quality, which can significantly
affect the degree of isotopic enrichment within a trophic level. 相似文献