Stable isotopes and mtDNA reveal niche segregation but no evidence of intergradation along a habitat gradient in the Lesser Whitethroat complex (Sylvia curruca; Passeriformes; Aves)

Niche segregation plays a critical role in the speciation process, but determining the extent to which taxa are geographically or ecologically isolated is challenging. In this study, we use stable isotopes of carbon (δ13C), nitrogen (δ15N), hydrogen (δ2H) and oxygen (δ18O) to test for ecological differences among taxa in the Lesser Whitethroat Sylvia curruca complex. Analysis of mitochondrial DNA (mtDNA) revealed 6 distinct haplotype groups, which conform to at least 5 distinct taxa. Stable isotopes provided insight into geographical and broad-scale ecological differences among haplotypes. The most striking isotope differences were between the populations inhabiting Siberian boreal forest (S. c. blythi) from the one inhabiting semi-desert in Kazakhstan (S. c. halimodendri). It is generally assumed that these two populations form a morphological cline along a gradient from mesic to xeric habitat. Our sample includes a large proportion of morphologically intermediate individuals that appear to represent a hybrid population. However, in all of these, there is strict correspondence between haplotype and isotope signature, suggesting an ecological division on the breeding grounds between all our samples of these two taxa. The lack of ecologically intermediate individuals among our sample of morphologically intermediate ones thus speaks against the existence of a cline. The two taxa blythi and halimodendri emerge as potential models for the study of the early stages of the speciation process. While differences in stable isotopes may be largely influenced by geography, we also demonstrate how, in specific instances (such as the alleged cline reported here), they may be used to evaluate niche segregation between taxa, providing information of importance for determination of species limits

Estimating stable isotope turnover rates of epidermal mucus and dorsal muscle for an omnivorous fish using a diet-switch experiment

© 2018, The Author(s). Stable isotope (SI) analysis studies rely on knowledge of isotopic turnover rates and trophic-step discrimination factors. Epidermal mucus (‘mucus’) potentially provides an alternative SI ‘tissue’ to dorsal muscle that can be collected non-invasively and non-destructively. Here, a diet-switch experiment using the omnivorous fish Cyprinus carpio and plant- and fish-based formulated feeds compared SI data between mucus and muscle, including their isotopic discrimination factors and turnover rates (as functions of time T and mass G, at isotopic half-life (50) and equilibrium (95)). Mucus isotope data differed significantly and predictively from muscle data. The fastest δ13C turnover rate was for mucus in fish on the plant-based diet (T50: 17 days, T95: 74 days; G50: 1.08(BM), G95: 1.40(BM)). Muscle turnover rates were longer for the same fish (T50: 44 days, T95: 190 days; G50: 1.13(BM), G95: 1.68(BM)). Longer half-lives resulted in both tissues from the fish-based diet. δ13C discrimination factors varied by diet and tissue (plant-based: 3.11–3.28‰; fishmeal: 1.28–2.13‰). Mucus SI data did not differ between live and frozen fish. These results suggest that mucus SI half-lives provide comparable data to muscle, and can be used as a non-destructive alternative tissue in fish-based SI studies

Carbon storage in soils of Southeastern Nigeria under different management practices

<p>Abstract</p> <p>Background</p> <p>Changes in agricultural practices-notably changes in crop varieties, application of fertilizer and manure, rotation and tillage practices-influence how much and at what rate carbon is stored in, or released from, soils. Quantification of the impacts of land use on carbon stocks in sub-Saharan Africa is challenging because of the spatial heterogeneity of soil, climate, management conditions, and due to the lack of data on soil carbon pools of most common agroecosystems. This paper provides data on soil carbon stocks that were collected at 10 sites in southeastern Nigeria to characterize the impact of soil management practices.</p> <p>Results</p> <p>The highest carbon stocks, 7906-9510 gC m^-2, were found at the sites representing natural forest, artificial forest and artificial grassland ecosystems. Continuously cropped and conventionally tilled soils had about 70% lower carbon stock (1978-2822 gC m^-2). Thus, the soil carbon stock in a 45-year old <it>Gmelina </it>forest was 8987 gC m^-2, whereas the parts of this forest, that were cleared and continuously cultivated for 15 years, had 75% lower carbon stock (1978 gC m^-2). The carbon stock of continuously cropped and conventionally tilled soils was also 25% lower than the carbon stock of the soil cultivated by use of conservation tillage.</p> <p>Conclusion</p> <p>Introducing conservation tillage practices may reduce the loss of soil carbon stocks associated with land conversion. However, the positive effect of conservation tillage is not comparable to the negative effect of land conversion, and may not result in significant accumulation of carbon in southeastern Nigeria soils.</p

Stable carbon and nitrogen isotope enrichment in primate tissues

Isotopic studies of wild primates have used a wide range of tissues to infer diet and model the foraging ecologies of extinct species. The use of mismatched tissues for such comparisons can be problematic because differences in amino acid compositions can lead to small isotopic differences between tissues. Additionally, physiological and dietary differences among primate species could lead to variable offsets between apatite carbonate and collagen. To improve our understanding of the isotopic chemistry of primates, we explored the apparent enrichment (ε*) between bone collagen and muscle, collagen and fur or hair keratin, muscle and keratin, and collagen and bone carbonate across the primate order. We found that the mean ε* values of proteinaceous tissues were small (≤1‰), and uncorrelated with body size or phylogenetic relatedness. Additionally, ε* values did not vary by habitat, sex, age, or manner of death. The mean ε* value between bone carbonate and collagen (5.6 ± 1.2‰) was consistent with values reported for omnivorous mammals consuming monoisotopic diets. These primate-specific apparent enrichment values will be a valuable tool for cross-species comparisons. Additionally, they will facilitate dietary comparisons between living and fossil primates

Turnover rates of nitrogen stable isotopes in the salt marsh mummichog, Fundulus heteroclitus, following a laboratory diet switch

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Springer-Verlag GmbH for personal use, not for redistribution. The definitive version was published in Oecologia 147 (2006): 391-395, doi:10.1007/s00442-005-0277-z.Nitrogen stable isotopes are frequently used in ecological studies to estimate trophic position and determine movement patterns. Knowledge of tissue-specific turnover and nitrogen discrimination for the study organisms is important for accurate interpretation of isotopic data. We measured δ15 N turnover in liver and muscle tissue in juvenile mummichogs, Fundulus heteroclitus, following a laboratory diet switch. Liver tissue turned over significantly faster than muscle tissue suggesting the potential for a multiple tissue stable isotope approach to study movement and trophic position over different time scales; metabolism contributed significantly to isotopic turnover for both liver and muscle. Nitrogen diet-tissue discrimination was estimated at between 0.0 and 1.2‰ for liver and –1.0 and 0.2‰ for muscle. This is the first experiment to demonstrate a significant variation in δ15 N turnover between liver and muscle tissues in a fish species.This study was funded by NSF LTER grant OCE-9726921

Bats' Conquest of a Formidable Foraging Niche: The Myriads of Nocturnally Migrating Songbirds

Along food chains, i.e., at different trophic levels, the most abundant taxa often represent exceptional food reservoirs, and are hence the main target of consumers and predators. The capacity of an individual consumer to opportunistically switch towards an abundant food source, for instance, a prey that suddenly becomes available in its environment, may offer such strong selective advantages that ecological innovations may appear and spread rapidly. New predator-prey relationships are likely to evolve even faster when a diet switch involves the exploitation of an unsaturated resource for which few or no other species compete. Using stable isotopes of carbon and nitrogen as dietary tracers, we provide here strong support to the controversial hypothesis that the giant noctule bat Nyctalus lasiopterus feeds on the wing upon the multitude of flying passerines during their nocturnal migratory journeys, a resource which, while showing a predictable distribution in space and time, is only seasonally available. So far, no predator had been reported to exploit this extraordinarily diverse and abundant food reservoir represented by nocturnally migrating passerines

From Food to Offspring Down: Tissue-Specific Discrimination and Turn-Over of Stable Isotopes in Herbivorous Waterbirds and Other Avian Foraging Guilds

Isotopic discrimination and turn-over are fundamental to the application of stable isotope ecology in animals. However, detailed information for specific tissues and species are widely lacking, notably for herbivorous species. We provide details on tissue-specific carbon and nitrogen discrimination and turn-over times from food to blood, feathers, claws, egg tissues and offspring down feathers in four species of herbivorous waterbirds. Source-to-tissue discrimination factors for carbon (δ13C) and nitrogen stable isotope ratios (δ15N) showed little variation across species but varied between tissues. Apparent discrimination factors ranged between −0.5 to 2.5‰ for δ13C and 2.8 to 5.2‰ for δ15N, and were more similar between blood components than between keratinous tissues or egg tissue. Comparing these results with published data from other species we found no effect of foraging guild on discrimination factors for carbon but a significant foraging-guild effect for nitrogen discrimination factors

Intrapopulation Variability Shaping Isotope Discrimination and Turnover: Experimental Evidence in Arctic Foxes

Tissue-specific stable isotope signatures can provide insights into the trophic ecology of consumers and their roles in food webs. Two parameters are central for making valid inferences based on stable isotopes, isotopic discrimination (difference in isotopic ratio between consumer and its diet) and turnover time (renewal process of molecules in a given tissue usually measured when half of the tissue composition has changed). We investigated simultaneously the effects of age, sex, and diet types on the variation of discrimination and half-life in nitrogen and carbon stable isotopes (δ15N and δ13C, respectively) in five tissues (blood cells, plasma, muscle, liver, nail, and hair) of a top predator, the arctic fox Vulpes lagopus. We fed 40 farmed foxes (equal numbers of adults and yearlings of both sexes) with diet capturing the range of resources used by their wild counterparts. We found that, for a single species, six tissues, and three diet types, the range of discrimination values can be almost as large as what is known at the scale of the whole mammalian or avian class. Discrimination varied depending on sex, age, tissue, and diet types, ranging from 0.3‰ to 5.3‰ (mean = 2.6‰) for δ15N and from 0.2‰ to 2.9‰ (mean = 0.9‰) for δ13C. We also found an impact of population structure on δ15N half-life in blood cells. Varying across individuals, δ15N half-life in plasma (6 to 10 days) was also shorter than for δ13C (14 to 22 days), though δ15N and δ13C half-lives are usually considered as equal. Overall, our multi-factorial experiment revealed that at least six levels of isotopic variations could co-occur in the same population. Our experimental analysis provides a framework for quantifying multiple sources of variation in isotopic discrimination and half-life that needs to be taken into account when designing and analysing ecological field studies

Pollen, biomarker and stable isotope evidence of late Quaternary environmental change at Lake McKenzie, southeast Queensland

Unravelling links between climate change and vegetation response during the Quaternary is important if the climate–environment interactions of modern systems are to be fully understood. Using a sediment core from Lake McKenzie, Fraser Island, we reconstruct changes in the lake ecosystem and surrounding vegetation over the last ca. 36.9 cal kyr. Evidence is drawn from multiple sources, including pollen, micro-charcoal, biomarker and stable isotope (C and N) analyses, and is used to gain a better understanding of the nature and timing of past ecological changes that have occurred at the site. The glacial period of the record, from ca. 36.9 to 18.3 cal kyr BP, is characterised by an increased abundance of plants of the aquatic and littoral zone, indicating lower lake water levels. High abundance of biomarkers and microfossils of the colonial green alga Botryococcus occurred at this time and included large variation in individual botryococcene d13C values. A slowing or ceasing of sediment accumulation occurred during the time period from ca. 18.3 to 14.0 cal kyr BP. By around 14.0 cal kyr BP fire activity in the area was reduced, as was abundance of littoral plants and terrestrial herbs, suggesting wetter conditions from that time. The Lake McKenzie pollen record conforms to existing records from Fraser Island by containing evidence of a period of reduced effective precipitation that commenced in the mid-Holocene