Temporal and intrapopulation variation in prey choice of wintering geese determined by stable isotope analysis

1. Individual variability in prey preferences can have marked effects on many demographic parameters from individual survival and fecundity to the vital rates of entire populations. A population level response is ultimately determined by individual prey choices; however, the effect of individual dietary choice is often overlooked. 2. We determined prey choice by individual consumers, light-bellied Brent geese Branta bernicla, during the overwintering period. Two hundred and eighty-one individuals were sampled at distinct temporal points over two winters. Stable isotopic ratios of carbon and nitrogen for blood cells and blood plasma, from each sampled individual were measured. Isotopic ratios for potential prey items were also measured. 3. Delta15N and delta13C for blood samples were both significantly different between sample months. Generally we found a decrease in both isotopic ratios during the course of the winter. All potential prey items were also isotopically distinct. Multisource mixing models (isosource) were used to determine the range of possible contribution to the diet of individuals. 4. During early winter, diet consisted almost exclusively of sea grass Zostera spp. The level of Zostera spp. in the diet dropped until mid-winter, and was supplemented by the utilization of green algae Ulva lactuca, and Enteromorpha spp., and terrestrial grasses. Terrestrial grass comprised an increasing proportion of the diet in late winter, representing virtually the exclusive food source by April. 5. By examining intrapopulation variability in resource utilization we highlight a number of ecologically important factors not addressed by previous population level studies.     

Using Bayesian stable isotope mixing models to estimate wolf diet in a multi-prey ecosystem

Stable isotope analysis (SIA) of wolf (Canis lupus) tissues can be used to estimate diet and intra-population diet variability when potential prey have distinct δ¹³C and δ¹⁵N values. We tested this technique using guard hairs collected from 44 wolves in 12 northwestern Montana packs, summer 2009. We used hierarchical Bayesian stable isotope mixing models to determine diet and scales of diet variation from δ¹³C and δ¹⁵N of wolves and potential prey, white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemionus), elk (Cervus canadensis), moose (Alces alces), snowshoe hare (Lepus americanus), and other prey. As a check on SIA results, we conducted a separate diet analysis with temporally matched scats (i.e., collected in summer 2008) from 4 of the same packs. Wolves were centered on the ungulate prey in the isotope mixing space. Both methods revealed differences among pack diets and that wolves may consume moose in greater proportions than predicted by available biomass. Stable isotope analysis, and scat results were not entirely concordant; assumptions related to tissues of use in SIA, hair growth period in wolves, and scat sampling may have contributed to a mismatch between methods. Incorrect fractionation values, insufficient separation of prey in the isotope mixing space, choice of prior information in the Bayesian mixing models, and unexplained factors may have distorted diet estimates. However, the consistently high proportion of moose in pack diets suggests that increased population monitoring would benefit management of moose and wolves. Our results also support suggestions of other researchers that species-specific fractionation values should be used whenever possible, and that SIA may sometimes only provide indices of use for general groups of prey (e.g., large ungulates). © 2012 The Wildlife Society.     

Using stable isotope biogeochemistry to study marine mammal ecology

Stable isotope analysis (SIA) has emerged as a common tool in ecology and has proven especially useful in the study of animal diet, habitat use, movement, and physiology. SIA has been vigorously applied to the study of marine mammals, because most species live in habitats or undergo large migrations/movements that make them difficult to observe. Our review supplies a complete list of published SIA contributions to marine mammal science and highlights informative case examples in four general research areas: (1) physiology and fractionation, (2) foraging ecology and habitat use, (3) ecotoxicology, and (4) historic ecology and paleoecology. We also provide a condensed background of isotopic nomenclature, highlight several physiological considerations important for accurate interpretation of isotopic data, and identify research areas ripe for future growth. Because it is impossible to conduct controlled laboratory experiments on most marine mammal species, future studies in marine mammal ecology must draw on isotopic data collected from other organisms and be cognizant of key assumptions often made in the application of SIA to the study of animal ecology. The review is designed to be accessible to all audiences, from students unfamiliar with SIA to those who have utilized it in published studies.     

Changes in feeding niche widths of perch and roach following biomanipulation, revealed by stable isotope analysis

1. We made an empirical test of a recent proposal that feeding niche widths might be determined as variance of stable isotope values. We determined δ ¹³C and δ ¹⁵N values of perch ( Perca fluviatilis ), roach ( Rutilus rutilus ) and their prey from a biomanipulated lake, when the mass removal of fish led to reduced inter- and intra-specific competition and increases in zooplankton abundance and body size.
2. After the first fish removals, both perch and roach mean δ ¹³C values decreased and mean δ ¹⁵N values increased, indicating a greater diet contribution from pelagic sources.
3. Variances of both δ ¹³C and δ ¹⁵N values first increased in both fish populations, indicating a wider food spectrum and expanded feeding niche width following reduced fish abundances. Observed changes were greater for the perch population than for roach.
4. In 2006, the perch population abruptly changed its diet so that most individuals were primarily consuming the abundant young-of-the-year fish, and this was reflected in significantly reduced variances of both δ ¹³C and δ ¹⁵N values.
5. We conclude that isotopic variance can indeed reflect changes in feeding niche width and offers a promising way to study such general ecological concepts.     

Trophic relationships in a tropical stream food web assessed by stable isotope analysis

1. Stable isotope analysis, coupled with dietary data from the literature, was used to investigate trophic patterns of freshwater fauna in a tropical stream food web (Guadeloupe, French West Indies).
2. Primary producers (biofilm, algae and plant detritus of terrestrial origin) showed distinct δ¹³C signatures, which allowed for a powerful discrimination of carbon sources. Both autochthonous (¹³C-enriched signatures) and allochthonous (¹³C-depleted signatures) resources enter the food web. The migrating behaviour of fishes and shrimps between marine and freshwater during their life cycles can be followed by carbon isotopes. Here, shrimp δ¹³C signatures were shown to shift from −16‰ (for juveniles under marine influence) to −24.7‰ (for adults in freshwater habitats). For resident species, δ¹³C values partly reflected the species' habitat preferences along the river continuum : species living in river mouths were ¹³C-enriched in comparison with those collected upstream.
3. Nitrogen isotopic ratios were also discriminating and defined three main trophic guilds among consumers. The δ¹⁵N values of herbivores/detritivores were 5.0–8.4‰, omnivores 8.8–10.2‰ and carnivores 11–12.7‰.
4. Mixing model equations were employed to calculate the possible range of contribution made by respective food sources to the diet of each species. The results revealed the importance of omnivorous species and the dependence of riverine biota on terrestrial subsidies, such as leaf detritus and fruits. Finally, the abundance of shrimps and their feeding habits placed in relief their key role in tropical freshwater food webs. Isotopic analysis provides a useful tool for assessing animal feeding patterns.     

North Atlantic minke whale (Balaenoptera acutorostrata) feeding habits and migrations evaluated by stable isotope analysis of baleen

Isotopic analyses of the incrementally growing baleen in Mysticeti have been used to learn about their feeding and movement patterns. Using methods previously applied to Pacific minke whales, stable δ¹⁵N and δ¹³C isotope values were measured along the baleen plates of male and female minke whales from two locations in the Northeast Atlantic. The sample sizes used in this study are comparable to those previously used in the literature, and, although limited in size, the evidence suggests differences in isotopic signatures between whales caught at different locations. Both the δ¹⁵N and δ¹³C data suggest whales at the higher latitude site of Svalbard have a narrower diet than the whales from Lofoten/Vesterålen in Norway. Across all whales, the δ¹⁵N data indicate the whales primarily prey on fish for much of the year, only switching to zooplankton during the spring bloom. The δ¹³C data fail to confirm whether the whales migrate over long distances.     

Using stable isotopes to trace long-distance dispersal in birds and other taxa

The study of long‐distance dispersal (LDD) in animals may be advanced by recent applications of stable isotope analyses designed to track migratory organisms and to link populations throughout their annual cycle. This approach depends on there being enough isotopic difference in tissues among potential source populations such that individuals can be unequivocally assigned to their source. The isotopic mapping of such populations will be feasible only for species occurring in relatively few disjunct populations. However, the identification of isotopic outliers within known populations will be an extremely useful first step in the forensic application of stable isotopes to identify dispersal in general, and LDD in particular. The use of deuterium isotope analysis (δD) of tissues that can be assigned to its source (e.g. feather moult or its hair growth location) has provided a recent breakthrough in our ability to associate individuals with geographical origins at continental scales. The combination of this stable isotope with others and the ultimate combination of a variety of techniques, including the measurement of trace elements and molecular genetics markers, will undoubtedly improve resolution. The isotopic cataloguing of known history (i.e. philopatric) individuals within populations will be an important step in applying isotope techniques to evaluating LDD in any species. For aquatic insects, the isotopic marking of large numbers of individuals is possible through isotopic enrichment of local food webs using labelled compounds.     

The role of alien fish (the centrarchid Micropterus salmoides) in lake food webs highlighted by stable isotope analysis

相似文献   

Trophic position and seasonal changes in the diet of the red wood ant Formica aquilonia as indicated by stable isotope analysis

1. Red wood ants are among the most numerous generalist predators and strongly affect the composition of arthropod communities in forest ecosystems. However, their trophic position remains poorly understood. Stable isotope analysis was applied to study the trophic position of Formica aquilonia and reveal seasonal changes in its trophic links with both myrmecophilous aphids and other invertebrates in a mixed forest of western Siberia. 2. The δ¹⁵N values of F. aquilonia exceeded those of herbivores and aphids by approximately 3.5‰. Despite obligate trophobiotic relationships with aphids, F. aquilonia occupied the trophic position of first‐order predator. The higher content of ¹³C in the worker ants, compared with members of grazing food chains, was explained by their consumption of ¹³C‐enriched aphid honeydew. 3. Myrmecophilous tree‐dwelling aphids were enriched in ¹³C and ¹⁵N relative to grass‐inhabiting species, and the honeydew of tree‐dwelling aphids had higher δ¹³C values than those of the honeydew of grass‐inhabiting aphids. 4. The decrease in δ¹³C values of the worker ants from spring and summer to autumn apparently reflected the transition from the collection of tree sap and feeding on the aphid honeydew from trees with high ¹³C content in the spring and early summer to a more diverse liquid diet in late summer, which included ¹³C‐depleted honeydew of aphids from herbs. 5. The prevalence of the ¹⁵N‐depleted aphid honeydew in the ants' diet in the second half of the summer is discussed as one possible explanation for the seasonal decline in δ¹⁵N values of the worker ants.     

Stock delineation of pink snapper and tailor from Western Australia by analysis of stable isotope and strontium/calcium ratios in otolith carbonate

The ¹⁸O/¹⁶O and ¹³C/¹²C ratios in the otolith carbonate of pink snapper Pagrus auratus and tailor (bluefish) Pomatomus saltatrix, from several locations along the Western Australian coast, indicated that pink snapper stocks are location specific but that tailor stocks are less so. The hypersaline Shark Bay, on the coast of Western Australia, generated strongly characteristic isotopic signatures which serve as natural tags. Otolith carbonate from pink snapper from normal oceanic waters just north of Shark Bay showed no evidence that the fish had been in hypersaline water. Similarly, pink snapper from the hypersaline bay showed no evidence of having spent time at normal oceanic salinity. By contrast, some tailor from oceanic waters showed evidence of having spent considerable time in the bay, and some fish from the bay had oceanic signatures. This suggested that tailor were more migratory than snapper. The similarity in the distribution of the isotopic signatures (from oceanic to hypersaline) in otolith carbonate from tailor from oceanic waters north of Shark Bay (Koks Island), and from those within Shark Bay, indicated a single stock in this region (in contrast to pink snapper). Moreover, tailor from coastal south-western Australia and from the Shark Bay area could be considered seperately for some management purposes. For pink snapper stocks from oceanic waters, oxygen isotope signatures were clearly related to water temperature although the temperature relationship was obscured for fish within Shark Bay because of the strength of the signal generated by the hypersaline water. For tailor the temperature relationship was not obvious, probably because migrations of tailor smeared the temperature effect, and the hypersaline Shark Bay waters dominated, and, possibly, at the southern extemity of the range, the freshwater in some estuaries influenced the isotopic signatures of the otolith carbonate. Strontium/calcium ratios in pink snapper otoliths also indicated a separation of stocks, but for tailor overlap of signatures again suggested migratory behaviour.     

Combined study of daily growth variability and nitrogen-carbon isotopic signature analysis of schooling Sardina pilchardus larvae

A combined study of Alborán Sea Sardina pilchardus larval daily growth and isotopic signature was carried out to elucidate the cause of morphometric differences observed in a single larval school whereby the standard length (L(S)) v. dry mass (M(D)) relationship differentiated a heavier-by-size larval group from a lighter larval group. The daily growth analysis revealed that this difference originated from two larval growth patterns, where a fast growing population (F) in contrast to a slow-growing larval population (S) was distinguished. The S-growing larval cohort had a significantly higher nitrogen (N) content as a result of greater somatic mass build up with time in the form of structural proteins. Alternatively, the F-growing population showed a significantly greater amount of carbon (C) content with age, indicating faster metabolic rates of C accretion compared to the S-growing group. In consequence, the C:N ratios of the F-growing larvae were significantly higher than the S-group. C:N ratios of both larval populations showed significant linear decrease with age (and size), while K showed an inverse relationship. The stable isotopes of N did not show significant differences between the S and F-growing larvae. In F-growing larvae, however, a significant linear increase in δ(15)N (by age class) was observed, indicating that as larvae undergo ontogenetic development, trophic level tends to increase. This was also made evident by the significant decrease in age of δ(15)N coefficients of variation (by age class). The higher δ(13)C values in the S-growing larvae were related to the lower growth rates observed in this group. These results suggest a broader trophic flexibility in younger larvae, but moving towards a trophic specialization and more selective diets with age. This trophic specialization shows a tendency of a greater prey size with age. These findings suggest that S-growing larvae have a more omnivorous diet than the F-growing ones.     

Sources of organic carbon in the littoral of Lake Gooimeer as indicated by stable carbon isotope and carbohydrate compositions

The relative importance of potential carbon sources in the littoral of Lake Gooimeer, a lake in the centre of the Netherlands, was studied using a combination of ¹³C/¹²C-ratio analysis and carbohydrate composition analysis. The littoral is covered on the land side by a 80 m wide Phragmites australis bed. Potential carbon sources were macrophyte litter, seston and benthic algae. Samples of potential carbon sources, sediments and benthic macrofauna from inside and outside the bed were analyzed for their¹³C/¹²C-ratio and some for their carbohydrate composition. Results indicate that inside the bed, macrophyte litter was the main source of carbon for both the sediment organic matter and the benthic macrofauna, and that algal material was of minor importance. Outside the bed, production by benthic algae was the main carbon source, with seston as a second source. No macrophyte derived material could be detected outside the reed bed.Abbreviations DOC (Dissolved Organic Carbon) - SOM (Sediment Organic Matter)     

Using stable isotope analysis to examine the effect of economic change on breastfeeding practices in Spitalfields, London, UK

Breastfeeding patterns were subject to a number of fads in 18th and 19th century Britain. Feeding infants by hand, rather than maternal breastfeeding or wet-nursing, became more prevalent among both the wealthy and poor. Substitute foods may have been a convenient alternative for mothers employed away from the household. This study used stable isotope ratio analysis to examine the weaning schedule in the 18th and 19th century skeletal assemblage from Spitalfields, London, UK. Analysis of 72 juvenile ribs revealed δ(15) N elevations of 2-3‰ above the adult mean for individuals up to the age of two, while elevations of 1-2‰ were observed in δ(13) C for the first year of life. This suggests that the introduction of solid foods took place before the end of the first year, and that breastfeeding had entirely ceased by 2 years of age. The age at death of many of these infants is known from historical records, and can be used to pinpoint the amount of time required for the breast milk signal to be observed in the stable isotope ratios of rib collagen. Results show that a δ(15) N elevation can be detected in the ribs of individuals who died as young as 5-6 weeks. Not all individuals at Spitalfields were breastfed, and there may not have been a single uniformly practiced weaning scheme. There is, however, more evidence for prolonged breastfeeding during the 19th century than the 18th century.     

Analysis of stable isotope ratios to investigate stock structure of red emperor and Rankin cod in northern Western Australia

The ratios of stable isotopes ¹⁸O/¹⁶O and ¹³C/¹²C, in sagittal otolith carbonate from two tropical demersal teleosts, red emperor Lutjanus sebae and Rankin cod Epinephelis multinotatus , from several locations in northern Western Australia, differed between sites. On a broad scale, fish from the four locations, Shark Bay, Ningaloo, Pilbara, and Broome had stable isotope values that were sufficiently different to indicate separate stocks, and it is appropriate to manage these populations of the two species independently in these areas. On a smaller scale, there may be limited mixing of these species between the Pilbara trawl fishery and the trap and line fisheries operating out of Onslow and Broome. Values of stable oxygen isotopes were strongly related to sea surface temperature, although there were some sites in shallow water where low values of stable oxygen isotopes indicated that fish were living in warm water. The use of stable oxygen and carbon isotope values is a valuable, cost effective method of determining the degree of mixing of fish stocks.     

Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition

We investigated the seasonal and geographical variation in the stable carbon isotope ratios of total dissolved inorganic carbon (¹³C_POC) and suspended matter (¹³C_POC) in the freshwater part of the River Scheldt. Two major sources of particulate organic matter (POM) occur in this riverine system: riverine phytoplankton and terrestrial detritus. In winter the lowest ¹³C_DIC values are observed due to enhanced input of CO₂ from decomposition of ¹³C-depleted terrestrial plant detritus (average ¹³C_DIC = –/14.3). During summer, when litter input from terrestrial flora is the lowest, water column respiration on POM of terrestrial origin is also the lowest as evidenced by less negative ¹³C_DIC values (average ¹³C_DIC = –9.9). In winter the phytoplankton biomass is low, as indicated by low chlorophyll a concentrations (Chl a < 4.5 gl^–1), compared to summer when chlorophyll a concentrations can rise to a maximum of 54 gl^–1. Furthermore, in winter the very narrow range of ¹³C_POC (from –26.5 to –27.6) is associated with relatively high C/N ratios (C/N > 9) suggesting that in winter a major fraction of POC is derived from allochthonous matter. In summer ¹³C_POC exhibits a very wide range of values, with the most negative values coinciding with high Chl a concentrations and low C/N ratios (C/N < 8). This suggests predominance of phytoplankton carbon in the total particulate carbon pool, utilising a dissolved inorganic carbon reservoir, which is already significantly depleted in ¹³C. Using a simple two source mixing approach a reconstruction of the relative importance of phytoplankton to the total POC pool and of ¹³C/¹²C fractionation by phytoplankton is attempted.     

利用稳定氢氧同位素定量区分白刺水分来源的方法比较

水是影响植物分布的重要生态因子之一,对植物水源的研究有助于在全球变化背景下了解植物的时空分布格局.根据同位素质量守恒,利用稳定氢氧同位素可以确定植物水分来源,相关的方法也不断改进.利用三源线性混合模型、多源线性混合模型、吸水深度模型以及动态模型分别对格尔木白刺(Nitraria Tangutorum)的水分来源进行了对比研究,发现格尔木白刺主要吸收利用50-100 cm处的土壤水及地下水.在研究方法上,各模型都有自己的应用范围和局限:三源线性混合模型一般只能在植物吸收的水分来源不超过3个的情况下运行;多源线性混合模型弥补了三源线性混合模型的不足,可以同时比较多种来源水各自对白刺的贡献率及贡献范围;吸水深度模型弥补了混合模型中不能计算白刺对土壤水的平均吸水深度的缺陷;动态模型则会为未来降水格局变化对植物的时空分布的影响研究起很大作用.针对不同的适用范围,模型的选择及综合应用会更广泛.但是,该技术还存在一些不足,需要结合测定土水势,富氘水的示踪等方法来弥补.     

Investigation of diachronic dietary patterns on the islands of Ibiza and formentera, Spain: Evidence from carbon and nitrogen stable isotope ratio analysis

To examine how dietary patterns may have changed in the western Mediterranean through time, stable carbon and nitrogen isotope ratios were measured on extracted bone collagen from fauna (n = 75) and humans (n = 135) spanning four distinct chronological periods: Chalcolithic (c.2100–1600 BC), Punic (6th–2nd/1st century BC), Late Antiquity‐Early Byzantine (4th–7th century AD), and Islamic (c.10th–13th century AD) on the islands of Ibiza and Formentera, Spain. The Chalcolithic, Punic, and Late Antiquity‐Byzantine societies all showed evidence of a predominately C₃ terrestrial‐based diet with a possible input of a small amount of marine and/or C₄ dietary resources. In contrast, the Islamic population on Ibiza had a subsistence strategy that was reliant on a significant amount of C₄ plants and/or animals fed a C₄ diet, likely millet. These results indicate a fairly constant C₃ terrestrial‐based diet on the islands of Ibiza and Formentera through time, with a shift to C₄ dietary resources during the Islamic Period. Further research is needed from other Islamic populations in and around the Mediterranean to better understand this unique dietary adaptation. Am J Phys Anthropol 143:512–522, 2010. © 2010 Wiley‐Liss, Inc.