Stable isotope ecology

Stable isotope analysis of Late Upper Palaeolithic human and faunal remains from Grotta del Romito (Cosenza), Italy

by Andre Carlo Colonese

Stable isotope composition of Late Pleistocene-Holocene Eobania vermiculata (Müller, 1774) (Pulmonata, Stylommatophora) shells from the Central Mediterranean basin: Data from Grotta d’Oriente (Favignana, Sicily)

by Andre Carlo Colonese

Stable isotope composition of Helix ligata (Müller, 1774) from Late Pleistocene–Holocene archaeological record from Grotta della Serratura (Southern Italy): Palaeoclimatic implications

by Andre Carlo Colonese

A feather hydrogen isoscape for Mexico

by Keith Larson

Hobson, K. A., S. L. Van Wilgenburg, K. W. Larson, and L. I. Wassenaar. 2009. A feather hydrogen isoscape for Mexico. Journal of Geochemical Exploration 102:167–174. doi: 10.1016/j.gexplo.2009.02.007.

Developing useful biological isoscapes for areas of the world is a priority. This is the case for Mexico that hosts a... more Developing useful biological isoscapes for areas of the world is a priority. This is the case for Mexico that hosts a large percentage of North America's Neotropical migrant birds. Here we investigated the use of House Sparrow (Passer domesticus) feathers to create a spatially explicit feather deuterium isoscape for that country using samples (n=461) that were collected across Mexico. Considerable and useful spatial hydrogen isotopic structure was observed, suggesting that isotopes may be a potential forensic tool for evaluating origins of Mexican derived fauna and flora. The most positive feather δD values occurred in the northeast and most negative in the south-central part of the country, roughly matching δD patterns observed in groundwater. A weak negative isotopic relationship was found with altitude in both the Pacific and Atlantic drainage systems. The most parsimonious model describing isotopic spatial variation in feathers between 300 and 3000 m a.s.l. included groundwater δD (δDgw; precipitation proxy), sex, amount of precipitation, and the coefficient of variation in amount of precipitation. Overall, δDgw was a poor predictor of sparrow δDf values for all of Mexico. However, this relationship was considerably strengthened when we considered sex separately, removed the Baja peninsula from our sample, and considered the Atlantic and Pacific drainage basins separately. The strongest relationship between δDgw and δDf was found for female sparrows in the Atlantic drainage basin (r2=0.464). We recommend that researchers interested in inferring origins of migratory birds and other animals in Mexico create species specific isotopic basemaps that may be guided by the isotopic patterns we have observed for House Sparrows and groundwater.

Stable Isotope Biogeochemistry of Seabird Guano Fertilization: Results from Growth Chamber Studies with Maize (Zea mays)

by Paul Szpak

Szpak P., F. J. Longstaffe, J.-F. Millaire, C. D. White. 2012. Stable Isotope Biogeochemistry of Seabird Guano Fertilization: Results from Growth Chamber Studies with Maize (Zea mays). PLoS One 7: e33741.

Background
Stable isotope analysis is being utilized with increasing regularity to examine a wide range of issues... more Background
Stable isotope analysis is being utilized with increasing regularity to examine a wide range of issues (diet, habitat use, migration) in ecology, geology, archaeology, and related disciplines. A crucial component to these studies is a thorough understanding of the range and causes of baseline isotopic variation, which is relatively poorly understood for nitrogen (δ15N). Animal excrement is known to impact plant δ15N values, but the effects of seabird guano have not been systematically studied from an agricultural or horticultural standpoint.


Methodology/Principal Findings
This paper presents isotopic (δ13C and δ15N) and vital data for maize (Zea mays) fertilized with Peruvian seabird guano under controlled conditions. The level of 15N enrichment in fertilized plants is very large, with δ15N values ranging between 25.5 and 44.7‰ depending on the tissue and amount of fertilizer applied; comparatively, control plant δ15N values ranged between −0.3 and 5.7‰. Intraplant and temporal variability in δ15N values were large, particularly for the guano-fertilized plants, which can be attributed to changes in the availability of guano-derived N over time, and the reliance of stored vs. absorbed N. Plant δ13C values were not significantly impacted by guano fertilization. High concentrations of seabird guano inhibited maize germination and maize growth. Moreover, high levels of seabird guano greatly impacted the N metabolism of the plants, resulting in significantly higher tissue N content, particularly in the stalk.

Conclusions/Significance
The results presented in this study demonstrate the very large impact of seabird guano on maize δ15N values. The use of seabird guano as a fertilizer can thus be traced using stable isotope analysis in food chemistry applications (certification of organic inputs). Furthermore, the fertilization of maize with seabird guano creates an isotopic signature very similar to a high-trophic level marine resource, which must be considered when interpreting isotopic data from archaeological material.

Isotopic fractionation in a large herbivorous insect, the Auckland tree weta

by Priscilla (McAllum) Wehi

Foraging Strategy and Longevity in Male Southern Elephant Seals

by Matthieu Authier

Dietary Heterogeneity among Western Industrialized Countries Reflected in the Stable Isotope Ratios of Human Hair

by Luciano Valenzuela

PLoS ONE

Although the globalization of food production is often assumed to result in a homogenization of consumption patterns... more Although the globalization of food production is often assumed to result in a homogenization of consumption patterns with a convergence towards a Western style diet, the resources used to make global food products may still be locally produced (glocalization). Stable isotope ratios of human hair can quantify the extent to which residents of industrialized nations have converged on a standardized diet or whether there is persistent heterogeneity and glocalization among countries as a result of different dietary patterns and the use of local food products. Here we report isotopic differences among carbon, nitrogen and sulfur isotope ratios of human hair collected in thirteen Western European countries and in the USA. European hair samples had significantly lower δ13C values (-22.7 to -18.3 ‰), and significantly higher δ15N (7.8 to 10.3 ‰) and δ34S (4.8 to 8.3 ‰) values than samples from the USA (δ13C: -21.9 to -15.0 ‰, δ15N: 6.7 to 9.9 ‰, δ34S: -1.2 to 9.9 ‰). Within Europe, we detected differences in hair δ13C and δ34S values among countries and covariation of isotope ratios with latitude and longitude. This geographic structuring of isotopic data suggests heterogeneity in the food resources used by citizens of industrialized nations and supports the presence of different dietary patterns within Western Europe despite globalization trends. Here we showed the potential of stable isotope analysis as a population-wide tool for dietary screening, particularly as a complement of dietary surveys, that can provide additional information on assimilated macronutrients and independent verification of data obtained by those self-reporting instruments.

Key words: Hair protein, stable isotopes, Western Europe, dietary heterogeneity, glocalization, globalization.

A hierarchical change-point model for estimating ontogenetic shifts with stable isotope data

by Matthieu Authier

Maternal strategies in the southern elephant seal a stable isotope investigation

by Matthieu Authier

Unveiling the At-Sea Ecology of Southern Elephant Seals from Indirect Evidence

by Matthieu Authier

Population-Level Metrics of Trophic Structure Based on Stable Isotopes and Their Application to Invasion Ecology

by Jonathan Grey

PLoS One 2012

Biological invasions are a significant driver of human-induced global change and many ecosystems sustain sympatric... more Biological invasions are a significant driver of human-induced global change and many ecosystems sustain sympatric invaders. Interactions occurring among these invaders have important implications for ecosystem structure and functioning, yet they are poorly understood. Here we apply newly developed metrics derived from stable isotope data to provide quantitative measures of trophic diversity within populations or species. We then use these to test the hypothesis that sympatric invaders belonging to the same functional feeding group occupy a smaller isotopic niche than their allopatric counterparts. Two introduced, globally important, benthic omnivores, Louisiana swamp crayfish (Procambarus clarkii) and carp (Cyprinus carpio), are sympatric in Lake Naivasha, Kenya. We applied our metrics to an 8-year data set encompassing the establishment of carp in the lake. We found a strong asymmetric interaction between the two invasive populations, as indicated by inverse correlations between carp abundance and measures of crayfish trophic diversity. Lack of isotopic niche overlap between carp and crayfish in the majority of years indicated a predominantly indirect interaction. We suggest that carp-induced habitat alteration reduced the diversity of crayfish prey, resulting in a reduction in the dietary niche of crayfish. Stable isotopes provide an integrated signal of diet over space and time, offering an appropriate scale for the study of population niches, but few isotope studies have retained the often insightful information revealed by variability among individuals in isotope values. Our population metrics incorporate such variation, are robust to the vagaries of sample size and are a useful additional tool to reveal subtle dietary interactions among species. Although we have demonstrated their applicability specifically using a detailed temporal dataset of species invasion in a lake, they have a wide array of potential ecological applications.

The use of stable isotopes to trace small scale movements by small fish species

by Jonathan Grey

Hydrobiologia 2010

Valuable biological information can be obtained by monitoring the movement of organisms. However, the choice of... more Valuable biological information can be obtained by monitoring the movement of organisms. However, the choice of monitoring method becomes highly restricted when following small organisms (<100 mm), especially in aquatic ecosystems. Stable isotopes are being increasingly used in this respect but rarely at the local spatial scale, i.e. 10–1000 s of metres. We sought to identify movement of small fishes between a main river channel and its tributary. Little overlap in isotope baseline was detected between the two channels despite some temporal variability in δ15N of baseline indicator organisms in the main river. The individuals of two small cyprinid fish species (Leuciscus souffia and Alburnoides bipunctatus) of all the size classes (40–100 mm) caught within the tributary showed considerable heterogeneity in δ15N values. Classification and discriminant analysis on isotope-derived data distinguished two significantly different groups. Moreover, this result was supported by further sampling of fish caught in the main river (in May and December 2006). Alternative hypotheses, such as dietary differences, biological factors, temporal shifts and spatial differences in diet, did not explain δ15N variability. This application of stable isotopes at a relatively small spatial and temporal scales further demonstrates its potential as a tool for ecologists.

Ferox Trout (Salmo trutta) as ‘Russian dolls’: complementary gut content and stable isotope analyses of the Loch Ness foodweb

by Jonathan Grey

Freshwater Biology 2002

1. Conventional collection methods for pelagic fish species (netting, trawling) are impractical or prohibited in Loch... more 1. Conventional collection methods for pelagic fish species (netting, trawling) are impractical or prohibited in Loch Ness, U.K. To investigate trophic relationships at the top
of the Loch Ness food web, an alternative strategy, angling, provided samples of the top predator, the purely piscivorous ferox trout (Salmo trutta).
2. The gut contents of these fish provided further samples of prey-fish, and subsequent examination of prey-fish guts revealed their dietary intake, analogous to the famous nested
‘Russian dolls’. Each trophic level separated by gut content analysis provided further complementary samples for stable isotope analysis and thus information on the longer
term, assimilated diet.
3. Ferox trout exhibited considerable cannibalism to supplement a diet of Arctic charr (Salvelinus alpinus). However, conspecifics stemmed from a lower isotopic baseline in relation to charr, so ferox trout exhibited a lower trophic level than predicted (4.3) by using the d15N values. Charr displayed dietary specialisation with increasing length, and isotopic values supported by the gut data placed the charr at a trophic level of 3.5. The isotope data
also indicated that charr carbon was primarily autochthonous in origin.

The use of stable isotope analyses in freshwater ecology: current awareness

by Jonathan Grey

Symposium for European Freshwater Sciences 2005 Plenary Talk published in the Polish Journal of Ecology 2006

Ecological research using stable isotopes has progressed rapidly during the last 20 years and although more studies... more Ecological research using stable isotopes has progressed rapidly during the last 20 years and although more studies are including the addition of isotopically labelled compounds
at tracer levels, the overwhelming majority rely on measurements of natural abundance ratios. Access to isotope ratio mass spectrometry has increased, spurred on by awareness of the techniques and increasing demand, and consequently cost of sample analysis has dropped. Today stable isotopes of carbon (13C/12C), nitrogen (15N/14N), sulphur (34S/32S), oxygen (18O/16O), and hydrogen (2H/1H) can be determined routinely. Perhaps one of the most appealing attributes of isotopic signatures is their potential use to find patterns and determine mechanisms across a range of scales
from the molecular level through to characterising whole food webs, reconstructing palaeoenvironments, tracing nutrient fluxes between ecosystems and identifying subsidies, or migrations of organisms.
Ecologists from every discipline who are unlikely to have been trained as isotope chemists have added stable isotope analysis (SIA) to their “toolbox”, but often increasing use leads to increasing abuse. The usefulness of SIA arises from predictable physical and enzymatic-based discrimination between biological and non-biological materials leading to different isotopic compositions. Without some ecological understanding
of these, interpretation of isotope-derived data can often be flawed.
Here, I explore how SIA recently has been used for research in aquatic ecology, reviewing how some of these techniques have
allowed elucidation of key processes in aquatic systems such as the contribution of allochthony to lake food webs, and discuss the “state of the art”. Included are some thoughts on where our knowledge in aquatic ecology remains deficient
and how continued development and future application of SIA and interdisciplinary methodologies may be applied.

Laboratory measures of isotope discrimination factors: comments on Caut, Angulo & Courchamp (2008, 2009)

by Jonathan Grey

Journal of Applied Ecology 2010

1. In a recent paper, Caut, Angulo & Courchamp (2008,Functional Ecology, 22, 255) experimentally measured isotope... more 1. In a recent paper, Caut, Angulo & Courchamp (2008,Functional Ecology, 22, 255) experimentally measured isotope discrimination factors for rats Rattus rattus. In their study, values for their discrimination factors spanned a much larger range than previously reported in the literature and were found to be negatively related to the stable isotope composition of the diet that the rats were fed.
2. In a subsequent meta-analysis, Caut, Angulo & Courchamp (2009, Journal of Applied Ecology, 46, 443) confirmed the trends they had found in their previous study and pointed to a method for obtaining adequate values for discrimination factors when they could not be measured experimentally.
3. Synthesis and applications. We argue that the discrimination factors determined by Caut et al. (2008) were an artefact of experimental design. We also argue that the reported linear relationships between the stable isotope composition of the diet and isotope discrimination factors in their follow-up meta-analyses (Caut et al. 2009) do not reflect relevant trends that can be extrapolated to the field and that the method they proposed for obtaining adequate values for discrimination factors should be used with considerable care.

High site fidelity and low site connectivity in temperate salt marsh fish populations: a stable isotope approach

by Jonathan Grey

Oecologia 2012

Adult and juvenile fish utilise salt marshes for food and shelter at high tide, moving into adjacent sublittoral... more Adult and juvenile fish utilise salt marshes for food and shelter at high tide, moving into adjacent sublittoral regions during low tide. Understanding whether there are high levels of site fidelity for different species of coastal fish has important implications for habitat conservation and the design of marine protected areas. We hypothesised that common salt marsh fish species would demonstrate a high site fidelity, resulting in minimal inter-marsh connectivity. Carbon (13C) and nitrogen (15N) stable isotope ratios of larvae and juveniles of five common salt marsh fish (Atherina presbyter, Chelon labrosus, Clupea harengus, Dicentrarchus labrax, Pomatoschistus microps), seven types of primary producer and seven secondary consumer food sources were sampled in five salt marshes within two estuary complexes along the coast of south-east England. Significant differences in 13C and 15N signatures between salt marshes indicated distinct sub-populations utilising the area of estuary around each salt marsh, and limited connectivity, even within the same estuary complex. 15N ratios were responsible for the majority of inter-marsh differences for each species and showed similar site-specific patterns in ratios in primary producers, secondary consumers and fish. Fish diets (derived from isotope mixing models) varied between species but were mostly consistent between marsh sites, indicating that dietary shifts were not the source of variability of the inter-marsh isotopic signatures within species. These results demonstrate that for some common coastal fish species, high levels of site fidelity result in individual salt marshes operating as discrete habitats for fish assemblages.

Endangered species, archaeology, and stable isotopes: huemul (Hippocamelus bisulcus) isotopic ecology in central-western Patagonia (South America)

by Ramiro Barberena

R. BARBERENA, C. MÉNDEZ, F. MENA, O. REYES
(J. Arc. Sc. 2011)

The management and conservation of animal species should be based upon a long-term analysis that considers its... more The management and conservation of animal species should be based upon a long-term analysis that considers its geographical distribution and feeding patterns. The study of carbon and nitrogen stable isotopes on skeletal remains provides a quantitative approach to the paleodietary reconstructions and constitutes a potent tool for comparing behavioral aspects of the fauna. In this paper we present the first set of isotopic values for modern and archaeological samples of Huemul (Hippocamelus bisulcus) from the forests of Central-western Patagonia, Chile. Contrary to initial expectations, our analysis indicates that there is no evidence of an important incidence of the canopy effect on the δ13Ccollagen values, which we suggest is due to an ecological selection that drives the huemul to focus its predation on open sectors within the forest. On the other hand, a wide range of δ15Ncollagen values for huemul was verified. This could reflect the N impoverishment of the forest soils and provide an interesting ecological indicator. The long-term information offered by the archaeological record provides the necessary context for decision-making conducive towards the preservation of Hippocamelus bisulcus in Patagonia.

A comparison of methods to determine carbon algal signatures

by Jérôme Marty

Evaluation of carbon pathways supporting the diet of invasive Hemimysis anomala in a large river

by Jérôme Marty

Published in Journal of Great Lakes Research

This study is providing the first insight on the food sources supporting Hemimysis anomala in a lotic ecosystem where... more This study is providing the first insight on the food sources supporting Hemimysis anomala in a lotic ecosystem where food webs differ from those of lentic ecosystems. Using carbon and nitrogen stable isotopes, the diet of Hemimysis was evaluated in multiple sites of the St Lawrence River where higher density swarms have been recently reported. We found that Hemimysis may feed on multiple food sources, including benthic and pelagic production, and from multiple trophic levels. Results from a mixing model applied to evaluate the importance of benthic versus pelagic food sources revealed site specific variations in diet. At the low flow sites located in the Montréal Harbour, Hemimysis fed primarily on pelagic production compared to the more open sites exposed to higher flow located outside of the harbor. This study indicates that Hemimysis may adapt its feeding behavior to environmental conditions and/or food source availability, potentially increasing its impacts on food web structure.