Local isotopic ecologies matter in the Pacific: an example from Waya Island, Fiji

Chlorinated ethenes are among the most frequently detected groundwater contaminants in industrially developed countries. Although their degradation pathways have been understood, assessing the progress of natural attenuation of chlorinated ethenes still remains a challenge. This thesis explored the possibilities and limits of the use of compound-specific stable isotope analysis as a field investigation tool to document and to quantify the progress of natural attenuation of chlorinated ethenes. The thesis focused particularly on the fate of reductive dechlorination intermediates such as cis-dichloroethene (cDCE) and vinyl chloride (VC) as the success of natural attenuation of chlorinated ethenes depends principally on the fate of these compounds. Two field investigations were carried out to demonstrate the use of stable isotope analysis to characterize the progress of natural attenuation of chlorinated ethenes. One site was characterized as a complex hydrological and geochemical system at the groundwater-surface water interface where a tetrachloroethene- (PCE) plume discharged through the streambed. Another site was located under relatively stable hydrological conditions and characterized by a 2-km long plume of chlorinated ethenes. Laboratory studies evaluated the use of combined carbon and chlorine isotope analysis to distinguish different degradation pathways of cDCE and VC, and the same approach was employed at a field site to determine the fate of cDCE. Numerical studies evaluated the field applicability of isotope-based quantification, according to the Rayleigh isotope fractionation model, to estimate the extent of degradation and the first-order reaction rate under various flow conditions. In addition, a scheme to quantify the reductive dechlorination rates of chlorinated ethenes based on field concentration and isotope data at one of the field sites was proposed and evaluated with a series of 3D analytical solutions to accommodate sequential reactions.The studies demonstrated that stable carbon analysis is a robust and sensitive tool to identify the progress of reductive dechlorination of chlorinated ethenes as well as the possibility of other degradation pathways of intermediate compounds even under geochemically and hydrologically complex conditions and even if only a small level of degradation occurs. Although carbon isotope analysis alone can not conclusively determine the fate of degradation intermediates such as cDCE and VC, the use of combined chlorine and carbon isotope analysis can assist in elucidating their fate at field scales. Furthermore, based on the field isotope data, it is possible to estimate the degradation rate even for a complex reaction series such as sequential reductive dechlorination of chlorinated ethenes. And the accuracy of the rate quantification increases with increased knowledge of local flow conditions.

Archaeodiet in the Greek World: Dietary Reconstruction from Stable Isotope Analysis

To understand the ecology of migratory animals it is important to link geographic regions used by individuals including breeding, wintering, and intermediate stopover sites. Previous conventional approaches used to track animal movements have relied on extrinsic markers and typically the subsequent recovery of individuals. This approach has generally been inappropriate for most small, or non-game animals. The use of intrinsic markers such as fatty acid profiles, molecular DNA analyses, and the measurement of naturally occurring stable isotopes in animal tissues offer alternative approaches. This paper reviews the use of stable isotope analyses (primarily δ13C, δ15N, δ34S, δD, δ87Sr) to trace nutritional origin and migration in animals. This approach relies on the fact that foodweb isotopic signatures are reflected in the tissues of organisms and that such signatures can vary spatially based on a variety of biogeochemical processes. Organisms moving between isotopically distinct foodwebs can carry with them information on the location of previous feeding. Such an approach has been used to track animal use of inshore versus offshore, marine versus freshwater, terrestrial C3 versus marine, terrestrial mesic versus xeric, and C3 versus C4 or Crassulacean acid metabolism foodwebs. More recently, the use of stable hydrogen isotope analyses (δD) to link organisms to broad geographic origin in North America is based on large-scale isotopic contours of growing-season average δD values in precipitation. This technique, especially when combined with the assay of other stable isotopes, will be extremely useful in helping to track migration and movement of a wide range of animals from insects to birds and mammals. Future research to refine our understanding of natural and anthropogenic-induced isotopic gradients in nature, and to explore the use of stable isotopes of other elements, is recommended.

The investigation of wildlife trade and crime has benefitted from advances in technology and scientific development in a variety of fields. Stable isotope analysis (SIA) represents one rapidly developing approach that has considerable potential to contribute to wildlife trade investigation, especially in complementing other methods including morphological, genetic, and elemental approaches. Here, we review recent progress in the application of SIA in wildlife trade research to highlight strengths, shortcomings, and areas for development in the future. SIA has shown success in species identification, determination of geographic provenance, and differentiating between captive-bred and wild individuals. There are also emerging applications of SIA in wildlife trade research including the use of labelling for traceability, more in-depth analyses such as compound specific isotope analysis (CSIA), the use of trace metal isotopes, and monitoring the health of individuals (e.g. dietary history and nutritional status). While these applications have shown the utility of SIA in wildlife trade investigations, there are a number of limitations and issues where standardisation of analytical procedures would improve the comparability and interpretation of results. First, there is high variation within many stable isotopes geographically and within tissues - this variation presents opportunities for tracking and monitoring but can also challenge detection of patterns when variation is high. Second, the choice of isotopes and tissues within an organism (and ideally, multiple isotopes and tissues) should be considered carefully as different isotopes and tissue types have variable strengths and weaknesses depending on the research question. Third, validation of SIA methods remains underutilised in the field but is critical for applying SIA broadly to wildlife trade investigations and, particularly, for applications in forensics and in court. Fourth, standards are essential for comparisons across studies. Fifth, while some reference databases exist for the use of SIA in wildlife trade research (e.g. ivory), there are still few comprehensive reference databases available. Development of robust reference databases should be a priority for advancing the use of SIA in wildlife trade research, and ecological study more broadly. Ultimately, further recognition of these primary challenges (and development of solutions) within wildlife SIA research will improve the potential for this technique in tackling the threat of overexploitation to global biodiversity - particularly in concert with the application of other investigative techniques such as genetics and elemental analysis.

On the basis of a review of current literature, France (1995) questioned the utility of stable isotope analysis (SIA) in describing food webs and understanding the effects of human perturbation in lotic ecosystems. His three main conclusions were (i) “autotrophic pathways within forested headwaters are much more important to lotic food webs than would be suggested by their particulate inputs alone,” (ii) “the great variability in attached algal δC may often preclude use of SIA for identifying carbon pathways in stream ecosystems,” and (iii) “the utility of carbon SIA in understanding anthropogenic alterations to the carbon budget of streams is presently minimal.” The first of these conclusions may well be correct, but points ii and iii appear to be based on a fundamental misunderstanding of the use of SIA. We have examined the same reports considered by France, as well as the wider literature concerning SIA, and feel that SIA can be a powerful technique for deciphering food webs and identifying impacts of alterations in land use. France’s attempt “to search for general patterns that transcend individual studies” by pooling δC data on carbon sources and animal consumers from freshwaters throughout the world is fundamentally flawed. While allochthonous organic matter is remarkably uniform in its isotopic signature, δC values of aquatic plants are widely recognized to be extremely variable between sites (Deines 1980; Osmond et al. 1981; Boutton 1991). It would be very surprising if there were any consistent pattern of C depletion or enrichment in the δC values of aquatic algae on a global scale. The fact that allochthonous δC values (≈–28‰) fall within the global range of reported autochthonous δC values (–46 to –22‰) in no way invalidates SIA as a means of assessing the importance of the two potential sources of energy. Rather, it means that such evaluations must be site specific (Rosenfeld and Roff 1992), and they are easily interpreted only when the potential carbon sources are isotopically distinct (Bunn et al. 1989). Since France bases his conclusions on pooled data, and not on site-specific algal and leaf litter δC values, no conclusions regarding the utility of SIA and the carbon dependencies of stream animals are possible. In addition, France fails to mention the importance of trophic fractionation in the interpretation of faunal δC values. Animals are usually enriched by ≈+1‰ relative to their diets (DeNiro and Epstein 1978), so that primary consumers are expected to be enriched by ≈+1‰, secondary consumers by ≈+2‰, and top predators by ≈+3‰ compared with their primary food sources (Rau et al. 1983). If one does not consider the trophic position of the organisms that are analyzed (France apparently expected the δC values of invertebrates and fish to be exactly the same as that of the primary carbon sources), no statement can be accurately made as to which animals are outside (or inside) the range of allochthonous dependence. There are similar problems with France’s critique of SIA in understanding anthropogenic alterations to the carbon flow of streams. After pooling data on “similar” species from forested and open sites, he found that (i) faunal δC could increase, decrease, or remain unchanged, and (ii) in almost 80% of the cases there was little or no change in faunal δC with landscape modification. The only surprising aspect of this is France’s expectation of consistent decreases in faunal δC values as evidence of increased utilization of autochthonous carbon following riparian deforestation. We agree that there have been too few analyses of autochthonous carbon sources, but it is precisely the “confounding by environmental co-determinants” that disallows France’s direct comparison between the δC values of similar species at forested and open sites: “although there is strong temptation to compare absolute

Freshwater fish ecology has greatly benefited from the use of innovative tools such as stable isotope analysis to determine the ecological effects of non‐native fishes. Stable isotope analyses are based on the predictable relationship between the isotope composition of a consumer and its prey, and have become increasingly popular amongst aquatic ecologists. In parallel, they have been implemented as a sensitive, cost‐effective and temporally integrative tool to analyse the trophic interactions between native and non‐native species, and to detect some subtle ecological effects of human activities, such as the introduction of non‐native freshwater fish species. This review aimed to understand how stable isotope analyses have been used and how they have provided new insights into the ecological impacts of non‐native freshwater fishes. Specifically, the published literature (45 articles) was reviewed to establish the current state‐of‐the‐art. The use of stable isotope analyses in the field is still an emerging approach. The majority of studies were conducted on lentic ecosystems in North America targeting three main families of non‐native fish species. Measurements were most commonly made with carbon and nitrogen stable isotopes using muscle samples. The most recent theoretical and methodological advances were illustrated by selecting some case studies conducted with different non‐native species and biotic interactions. Finally, several recommendations for an optimised use of stable isotope analyses for freshwater ecological studies related to trophic interactions of non‐native freshwater fish species were established.

The fish of Lake Titicaca: implications for archaeology and changing ecology through stable isotope analysis

Within the complex world of disaster victim identification, or DVI, forensic science practitioners use a variety of investigative techniques to work toward a common goal: identification of the decedents, bringing closure to the affected communities. Identification is a complex undertaking; the event (disaster) also can be extraordinarily complex, as it may be an acute event, or one that spans months or years. Compounding this time issue, remains may be heavily fragmented, dispersed, commingled, or otherwise disrupted by either the perpetrators or the disaster itself. To help solve these complexities, we explore the use of stable isotope analysis (SIA) in DVI events. SIA can be used with a variety of body tissues (hair, nail, bone, and teeth), and each represents different time depths in a decedent's life. Bone collagen and tooth enamel carbonate are useful to reconstruct an individual's diet and source water intakes, respectively, leading to likely population or geographic origin determinations. Additionally, the carbon and nitrogen isotopic signatures of bone collagen have calculated intraperson ranges. These facts allow investigators to determine likely origin of remains using isotopic data and can be used to link skeletal elements (to an individual), or perhaps more importantly, show that remains are not linked. Application of SIA can thus speed remains identification by eliminating individuals from short lists for identification, linking or decoupling remains, and reducing the need for some DNA testing. These strategies and hypothesis tests should commence early in the DVI process to achieve maximum effectiveness.

Previous studies have demonstrated the potential of carbon and nitrogen stable isotope analysis (SIA) of feces for use in understanding dietary components and sources. These studies suggest that SIA is useful because it is noninvasive and provides more recent dietary information integrated over a shorter time period than SIA of tissues. We sought to determine whether SIA could be employed in the analysis of feces of American black bears (Ursus americanus) in Utah. Using archived feces, we compared SIA with gross fecal analyses (GFA) to determine if a relationship existed. The percent volume of grass and pine nuts were the only significant indicators of the δ13C of feces. The amount of animal matter was the sole significant indicator of the δ15N value of feces. Although these measures were only weakly indicative (R2 ≤ 0.21), it is interesting that even in an environment that is isotopically homogenous, δ15N and δ13C provided information on the contribution of dietary components. The comparatively tight distribution of fecal δ13C values, essentially ranging −24 to −28‰, clearly indicated a diet of C3 plants. However, this study did not examine the effect of differential digestibility or intestinal slough on δ13C and δ15N values of feces. This needs to be examined. We also encourage additional studies on the usefulness of SIA of feces of omnivores and carnivores. Very few studies exist for these species, and since many of these species are particularly difficult to handle, SIA of feces may provide crucial knowledge of their short-term dietary habits.

Stable carbon isotope palaeodietary research at the Roonka Flat archaeological site, lower Murray River, South Australia (Pate and Schoeninger 1993; Pate 1995a, 1995b) suggested that there was minimal movement of people and/or food between the inland riverine area and the southeastern coastal and arid interior regions of South Australia during the late Holocene. Other archaeological and physical anthropological data, for example, cemetery and site distributions and numbers and cranial non-metric traits (see Pardoe 1995) also provide evidence for increased sedentism and territoriality in the lower Murray region during the late Holocene. Thus, in some cases, bone chemistry analyses can provide archaeologists with an independent method to assess past human dietary composition, landscape use, sedentism and territoriality. Along with similar bone collagen  I´ 13 C  studies at Broadbeach, Queensland and Swanport, South Australia (Hobson and Collier 1984; Collier and Hobson 1987), the Roonka Flat programme has established stable isotope palaeodietary analyses as a productive research area within Australian archaeology (Pate 1997a). The present paper reports the results of the first application of dual isotope (carbon and nitrogen) palaeodietary analysis to precontact human bone collagen in Australia. The use of stable nitrogen isotopes in addition to carbon isotopes in palaeodietary research via plots of I´ 13 C versus I´ 15 N values for past human diet and potential food sources (cf. Walker and DeNiro 1986; Keegan and DeNiro 1988; Little and Schoeninger 1995) provides better discrimination regarding dietary inferences than single isotope analyses. Stable carbon and nitrogen isotope values for human bone from the Roonka Flat site are compared with isotopic values for a variety of marine, riverine and terrestrial foods in order to provide additional information regarding the dietary composition of this inland riverine population during the late Holocene.

Stable isotope analysis (SIA) has become a powerful tool for ecotoxicologists to study dietary exposure and biomagnification of contaminants in wild animal populations. The use of SIA in ecotoxicology continues to expand and, while much more is known about the mechanisms driving patterns of isotopic ratios in consumers, there remain several considerations or sources of uncertainty that can influence interpretation of data from field studies. We outline current uses of SIA in ecotoxicology, including estimating the importance of dietary sources of carbon and their application in biomagnification studies, and we present six main considerations or sources of uncertainty associated with the approach: (1) unequal diet-tissue stable isotope fractionation among species, (2) variable diet-tissue stable isotope fractionation within a given species, (3) different stable isotope ratios in different tissues of the animal, (4) fluctuating baseline stable isotope ratios across systems, (5) the presence of true omnivores, and (6) movement of animals and nutrients between food webs. Since these considerations or sources of uncertainty are difficult to assess in field studies, we advocate that researchers consider the following in designing ecotoxicological research and interpreting results: assess and utilize variation in stable isotope diet-tissue fractionation among animal groups available in the literature; determine stable isotope ratios in multiple tissues to provide a temporal assessment of feeding; adequately characterize baseline isotope ratios; utilize stomach contents when possible; and assess and integrate life history of study animals in a system.

Until relatively recently, stable sulphur isotope analysis of bone collagen was seldom undertaken in bioarchaeological research. With increasing frequency, its application has proven useful in reconstructing palaeodiets and palaeoecologies, as well as identifying potential migration and mobility patterns. Here, sulphur (δ34S) isotope analysis, together with carbon (δ13C) and nitrogen (δ15N), was performed on six fish and 34 mammal bone collagen samples from 14 prehistoric sites in Lithuania dating from the Late Mesolithic (ca. 7000–5000 cal BC) to the Late Bronze Age (ca. 1100–500 cal BC). We present the first δ34S data from Lithuania, including coupled δ13C and δ15N data, offering a crucial dataset for future research to explore spatial and temporal variability in the region and beyond.

Stable isotope analyses are a powerful tool in understanding diets, defining trophic networks, inferring geographical origins of animals and in forensic tracing of the origins of deceased humans or illegally traded animal and plant material. African grey parrots Psittacus erithacus are one of the most traded animal species in the world, and the origin of confiscated illegal or deceased specimens are often unknown. We measured stable isotope values (δ13C, δ15N and δ2H) in different African grey parrots (n = 32) and determined feather type (i.e. primary, tail, breast) standardization values for comparing individuals. δ13C and δ2H values differed between known wild (n = 42) and captive (n = 50) birds when standardized for feather type, but not for δ15N. δ13C and δ2H values in feathers from a consignment of African grey parrots (n = 100), all of which were deceased, aligned significantly with that of known wild birds. We suggest that further analyses of feathers, across a range of spatial and temporal scales, will enhance stable isotope analyses as a valuable tool in monitoring and combatting the trade of African grey parrots. Furthermore, the use of stable isotope analyses may improve the monitoring of illegally traded bird species, and other wildlife, across the globe.

The question of defining ecosystem boundaries is important in creating management policies, conservation guidelines, and continuing accurate research. In the case of urban ecosystems, boundaries cannot be defined by strictly cultural or physical methods. Approaching boundary definitions in this manner ignores the importance of energy movement through an ecosystem. Part of the energy budget of an urban ecosystem is the anthropogenic food input, which can serve to attract wildlife to the city. It is proposed that this attraction to urban centers due to food resources influences surrounding classically defined natural ecosystems to such an extent that the urban ecosystem should be redefined to include the environment surrounding cities. The research technique that is the most time and cost effective, least invasive, and allows multiple species to be compared at once is stable isotope analysis. Isotope compositions have been commonly used for decades, and among the most important isotopes for deciphering ecosystem functions are carbon and nitrogen. Through the use of stable isotope analysis, urban wildlife can be differentiated from wildlife that is not influenced by human inputs to the ecosystem by the carbon value. The isotope ratio of anthropogenic foods is unique enough from natural sources of food that it can be used as a marker for human influence on the food chain. Previous work supports that species and individuals within a species can be differentiated using stable isotope analysis. It is proposed that stable isotope analysis be used to analyze samples of wildlife for carbon and nitrogen values in an attempt to measure the impact that people are having on urban and non-urban species.

What makes some species successful invaders while others fail, and why some invaders have major impacts in invaded ecosystems are pivotal questions that are attracting major research effort. The increasing availability of high resolution, georeferenced stable isotope landscapes (‘isoscapes’), coupled with the commercialization of stable isotope‐enriched tracer molecules and the development of new analytical approaches, is facilitating novel applications of stable isotope techniques in ecology. We can now address ecological questions that were previously intractable. We review and discuss how stable isotope analysis (SIA) can complement fundamental research themes in the study of biological invasions, especially in answering questions relating to the physiological and ecological mechanisms underlying invasion processes and invader impacts. SIA was first used for simply describing the diet of invaders but, more recently, SIA‐informed metrics of population and community trophic structure have been advanced. These approaches now permit the comparison of diets across space and time and provide quantitative tools to compare food webs across different stages of invasion. SIA has also been pivotal in quantifying competition for resources between native and non‐native species (e.g. competition for food, water, or nutrient use). Specific questions related to modes of dispersal (e.g. origin and distance/direction travelled) and mechanisms of establishment can also be addressed using SIA in diverse taxa. An overarching goal is to highlight examples of recent studies that have used SIA in key areas of invasion ecology and use these to synthesize testable predictions where SIA could be applied to future studies. We conclude by highlighting several paths forward and describing how unresolved challenges in quantifying the rates, impacts, and mechanisms underlying invasions could potentially benefit from the use of SIA.