Large 13C/12C and small 15N/14N isotope fractionation in an experimental detrital foodweb (litter–fungi–collembolans)

Correctly estimating the trophic fractionation factors (Δ¹⁵N and Δ¹³C) in controlled laboratory conditions is essential for the application of stable isotope analysis in studies on the trophic structure of soil communities. Laboratory experiments usually suggest large ¹⁵N/¹⁴N and small ¹³C/¹²C trophic fractionation, but in field studies litter-dwelling microarthropods and other invertebrates are consistently enriched in ¹³C relative to plant litter. In the present study, we report data from two laboratory experiments investigating both fungi–collembolans and litter–fungi–collembolans systems. In the fungi–collembolans system, Δ¹⁵N and Δ¹³C averaged 1.4 ± 0.1 and 1.0 ± 0.2 ‰, respectively. In microcosms with fungi-inoculated litter, the difference in δ¹⁵N between collembolans and plant litter averaged 1.5 ± 0.2 ‰, confirming the relatively small ¹⁵N/¹⁴N trophic fractionation at the basal level of detrital foodwebs reported in numerous field studies. In full agreement with field observations, the difference in δ¹³C between bulk litter and collembolans in laboratory microcosms averaged 3.6 ± 0.1 ‰ and only little depended on collembolan species identities or the presence of water-soluble compounds in the litter. We conclude that increased δ¹³C values typical of litter-dwelling decomposers are largely determined by an increased ¹³C content in saprotrophic microorganisms.     

The death of birds on the sea coast of northeastern Sakhalin Island

The taxonomical composition of dead birds found on the northeastern coast of Sakhalin Island and the causes of their death were studied. Sites with high, average, and low concentration of dead birds were identified. The period of highest mortality of birds (July–August) coincided with the beginning of massive migrations of birds and large numbers of young birds after termination of the nesting season. Collection of bird remains in periods of bird migrations and breeding, in addition to other methods of ornithological research (visual observations, fowling, shooting), can provide useful information on the avifauna and ecological state of the investigated region.     

Origin of carbon in organic matter in the Neva estuary

Analysis of the isotopic composition of tissues of representatives of zoobenthos and organic matter of seston have shown that the major part of carbon participating in the biological turnover in the ecosystem of the upper part of the Neva estuary is of terrestrial origin. Obviously, it is discharged from the lake drainage area to the Lake Ladoga–Neva–Neva estuary system. The results have revealed an important role in aquatic ecosystems of the humid zone of allochthonous humic substances creating a supplementary stock of nutrients and enhancing the productivity of ecosystems. Detailed investigations of the role of various forms of allochthonous organic compounds of terrestrial origin are necessary for elaboration of efficient measures for alleviation of eutrophication of the Neva estuary.     

A new species of cestode, Vampirolepis muraiae n. sp. (Cyclophyllidea: Hymenolepididae), from a Chinese bat

Vampirolepis muraiae n. sp. (Cestoda: Cyclophyllidea: Hymenolepididae) is described on the basis of a single specimen from a mouse-eared bat, Myotis sp., from Yunnan Province, China. It is distinguished from its congeners on the basis of the size and shape of the rostellar hooks, which have a blade shorter than the guard, the tubular structure of the initial stage of the developing uterus and eggs with a thick outer coat.     

Changes in elemental and isotopic composition accompanying larval growth and metamorphosis of the moor frog

A variety of early ontogenetic events of anuran species (growth, structural and biochemical diversification, metamorphosis) offers a unique opportunity to evaluate the effectiveness and application limits of mass spectrometry method for the analysis of metabolic and transformation events in developing organisms. The dynamics of relative carbon and nitrogen contents and stable isotopes of these elements during larval development in the period of metamorphosis climax and after its conclusion in moor frog specimens developing in their natural habitat and in vitro on a referent diet are traced. A decrease in C/N ratio and enrichment of the tissues with heavy stable isotopes of carbon and nitrogen during embryonal and larval development (prior to the beginning of independent feeding) indicates the increase in the portion and variety of proteins, accompanied by consumption of yolk lipids. The relative nitrogen content increase and C/N ratio decreases with the growth and development of independently feeding tadpoles, which indicates surpassing increase of the portion of proteins in tissues. In growing tadpoles, the rates of tissue renewal in general and rates of protein metabolism in particular affect the kinetics of changes of tissue isotope composition, which approaches isotope composition of the consumed food. A decrease in С/N ratio in the bodies of metamorphs during mass tissue decomposition is indicative of continuing reconstruction of larval organs and growth of anlage of definitive organs. Significant increase of C/N ratio and depletion of liver samples by heavy carbon isotopes are associated with intensive synthesis and reservation of lipids within the organ. Strong enrichment of metamorphs’ tissues with heavy nitrogen isotope indicates the substitution of ammoniotelic type of nitrogen metabolism by urotelic type. Decrease in C/N ratio and enrichment of tissues by heavy carbon isotope may be connected to intensive oxidation of lipids, which supports the growing energy costs of terrestrial underyearlings. Relative contents of heavy nitrogen isotope in the tissues of underyearlings does not change compared to the tissues of metamorphs.     

Ecotype and geographical variation in carbon and nitrogen stable isotope values in western North Pacific killer whales (Orcinus orca)

Killer whales are top predators in marine trophic chains, and therefore their feeding preferences can substantially affect the abundance of species on the lower trophic levels. Killer whales are known to feed on many different types of prey from small fish to large whales, but a given killer whale population usually focuses on a specific type of prey. Stable isotope analysis is widely used to study whale diets, because direct observations are often impossible. Killer whale feeding habits in the western North Pacific are poorly studied, and the large-scale stable isotope analysis provides a unique opportunity to gain insights into the trophic links of this top predator. In this study, we compare the δ¹³C and δ¹⁵N stable isotope values from killer whale skin samples obtained in different areas of the western North Pacific from fish-eating (R-type) and mammal-eating (T-type) killer whale ecotypes. The effect of ecotype was highly significant: both carbon and nitrogen stable isotope values were lower in R-type whales than in T-type whales. The geographical variation also affected killer whale stable isotope values due to both the differences in killer whale diet and the variation in baseline stable isotope values across the study areas.     

Short-term incorporation of freshly fixed plant carbon into the soil animal food web: field study in a spruce forest

We analyzed the dynamics of the short-term incorporation of recently fixed carbon into the below-ground food web in a boreal forest. Five young spruce trees (Picea abies) were pulse-labeled with ¹³CO₂ and the isotopic label was traced in soil invertebrates during 5 weeks. The freshly fixed plant carbon quickly entered both litter-located and soil-located compartments of the detrital food web. Among invertebrates inhabiting the mineral soil layers, a trophic link to the root-derived C was most pronounced in species with higher δ ¹⁵N values, suggesting this energy source to be more important in deeper mineral soil horizons. The label appeared faster in saprophagous animals than in predators (the median time lag after labeling was 6 and 12 days, respectively), but the difference was not significant. The label was recovered in 15 of 38 species of saprophagous animals and in 20 of 63 species of predators. Among saprophages, the frequency and intensity of the label was relatively high in endogeic collembolans and in bibionid larvae, but earthworms and enchytraeids were not labeled. Several groups of predators, lithobiid centipedes in particular, quickly acquired the root-derived carbon, possibly indicating the feeding on live roots or mycorrhizal mycelium. In total, only 35 % of species or genera examined acquired the label. This suggests that majority of invertebrate taxa in the decomposer food web are unlikely to depend heavily on freshly fixed plant carbon provided by roots and root-associated microorganisms.     

Stable isotopes of carbon and nitrogen in soil ecological studies

The development of stable isotope techniques is one of the main methodological advances in ecology of the last decades of the 20th century. Many biogeochemical processes are accompanied by changes in the ratio between stable isotopes of carbon and nitrogen (¹²C/¹³C and ¹⁴N/¹⁵N), which allows different ecosystem components and different ecosystems to be distinguished by their isotopic composition. Analysis of isotopic composition makes it possible to trace matter and energy flows through biological systems and to evaluate the rate of many ecological processes. The main concepts and methods of stable isotope ecology and patterns of stable isotope fractionation during organic matter decomposition are considered with special emphasis on the fractionation of isotopes in food chains and the use of stable isotope studies of trophic relationships between soil animals in the field.