Kangaroo tooth enamel oxygen and carbon isotope variation on a latitudinal transect in southern Australia: implications for palaeoenvironmental reconstruction

Tooth enamel apatite carbonate carbon and oxygen isotope ratios of modern kangaroos (Macropus spp.) collected on a 900-km latitudinal transect spanning a C₃–C₄ transition zone were analysed to create a reference set for palaeoenvironmental reconstruction in southern Australia. The carbon isotope composition of enamel carbonate reflects the proportional intake of C₃ and C₄ vegetation, and its oxygen isotope composition reflects that of ingested water. Tooth enamel forms incrementally, recording dietary and environmental changes during mineralisation. Analyses show only weak correlations between climate records and latitudinal changes in δ¹³C and δ¹⁸O. No species achieved the δ¹³C values (~?1.0 ‰) expected for 100 % C₄ grazing diets; kangaroos at low latitudes that are classified as feeding primarily on C₄ grasses (grazers) have δ¹³C of up to ?3.5 ‰. In these areas, δ¹³C below ?12 ‰ suggests a 100 % C₃ grass and/or leafy plant (browse) diet while animals from higher latitude have lower δ¹³C. Animals from semi-arid areas have δ¹⁸O of 34–40 ‰, while grazers from temperate areas have lower values (~28–30 ‰). Three patterns with implications for palaeoenvironmental reconstruction emerge: (1) all species in semi-arid areas regularly browse to supplement limited grass resources; (2) all species within an environmental zone have similar carbon and oxygen isotope compositions, meaning data from different kangaroo species can be pooled for palaeoenvironmental investigations; (3) relatively small regional environmental differences can be distinguished when δ¹³C and δ¹⁸O data are used together. These data demonstrate that diet–isotope and climate–isotope relationships should be evaluated in modern ecosystems before application to the regional fossil record.     

Annual variability in dentin δ15N and δ13C reveal sex differences in weaning age and feeding habits in Risso's dolphins (Grampus griseus)

Teeth of odontocetes accumulate annual dentinal growth layer groups (GLGs) that record isotope ratios, which reflect the time of their synthesis. Collectively, they provide lifetime records of individual feeding patterns from which life history traits can be inferred. We subsampled the prenatal dentin and postnatal GLGs in Risso's dolphins (Grampus griseus) (n = 65) that stranded or were collected as bycatch in Taiwan (1994–2014) and analyzed them for δ¹⁵N and δ¹³C. Age‐specific δ¹⁵N and δ¹³C values were corrected for effects of calendar year, stranding site, C/N, and sex. δ¹⁵N values were higher in prenatal layers (14.94‰ ± 0.74‰) than in adult female GLGs (12.58‰ ± 0.20‰), suggesting fetal enrichment during gestation. Decreasing δ¹⁵N values in early GLGs suggested changes in dietary protein sources during transition to complete weaning. Weaning age was earlier in males (1.09 yr) than in females (1.81 yr). Significant differences in δ¹⁵N values between weaned males and females suggest potential sexual segregation in feeding habits. δ¹³C values increased from the prenatal to the 4th GLG by ~1.0‰, indicative of a diet shift from ¹³C‐depleted milk to prey items. Our results provide novel insights into the sex‐specific ontogenetic changes in feeding patterns and some life history traits of Risso's dolphins.     

Altitudinal gradients of grassland carbon and nitrogen isotope composition are recorded in the hair of grazers

Aim The hair of grazers provides an isotopic record of environmental and nutritional signals. Here, we assess the effect of altitude on the carbon and nitrogen isotope composition of the hair of ruminant grazers and its relation to grassland vegetation, to evaluate the use of hair isotope data for ecosystem reconstruction, animal nutritional ecology and biogeochemical studies in montane environments. Location European Alps. Methods We sampled grassland vegetation (pure C₃) and the hair of ruminants along an altitudinal gradient (400–2500 m), and analysed their isotope composition (δ¹³C and δ¹⁵N). Results were compared with published effects of altitude on ¹³C in C₃ plants at the species level and on ¹⁵N at the community level. The study was complemented with a comparison of diet and hair isotope composition in ruminants held in confinement. Results δ¹³C of hair increased (c. 1.1‰ km⁻¹) and δ¹⁵N decreased (c. 1.1‰ km⁻¹) with altitude. The same changes occurred in local grassland vegetation, and in regional to global grassland data sets. Offsets between hair and vegetation ¹³C or ¹⁵N (‘diet–hair shift’) were independent of altitude. Sheep (Ovis aries) and cattle (Bos taurus) exhibited a ¹³C shift near +3‰, but that of goats (Capra hircus) was larger (+4.2‰) in alpine environments and in confinement. The diet–hair shift for ¹⁵N was more variable (+2.1 to +3.6‰). Main conclusions Grazer hair provides a faithful spatially and temporally integrated record of grassland isotope composition, useful for ecosystem and environment reconstruction. The effect of altitude on hair ¹⁵N is important for studies of trophic relationships: an altitude shift of 2000 m produced the same effect in hair ¹⁵N as would a shift from an animal tissue‐based to a plant‐based diet. The similarity of altitude effects on δ¹³C of individual plant species, vegetation and hair indicates that the effect of altitude on species‐level ‘intrinsic water use efficiency’ scales up linearly to the community and landscape level.     

Fueling phocids: Divergent exploitation of primary energy sources and parallel ontogenetic diet switches among three species of subarctic seals

Determining how marine predators partition resources is hindered by the difficulty in obtaining information on diet and distribution. Stable isotopes (SI) of carbon (¹³C/¹²C, δ¹³C) and nitrogen (¹⁵N/¹⁴N, δ¹⁵N) provide a two‐dimensional estimate of the dietary space of consumers; an animal's isotopic composition is directly influenced by what they consume and where they feed. Harp (Pagophilus groenlandicus) and hooded (Cystophora cristata) seals are abundant phocid species found in the North Atlantic. We measured and contrasted SI values between seals sampled at nearshore and offshore sites to test for effects of sampling location, sex, age‐class, and body size to gain insight into how these species partition space and prey resources. In addition we contrasted previously published results for gray seals (Halichoerus grypus). Isotope values differed significantly by age class and location in harp and hooded seals. We found significant differences in SI values (mean δ¹³C and δ¹⁵N ± SE) between all species. Hooded seals, a continental shelf‐edge, deep‐diving species, exhibited low SI values (juveniles: ?20.9‰ ± 0.03‰, 13.36‰ ± 0.05‰; adults: ?20.41‰ ± 0.03‰, 14.81‰ ± 0.04‰) characteristic of feeding on meso‐ to bathypelagic prey. Harp seals, which dive to moderate depths primarily on the shelf had intermediate SI values (juveniles: ?20.53‰ ± 0.01‰, 13.91‰ ± 0.01‰; adults: ?20.13‰ ± 0.01‰, 14.96‰ ± 0.01‰) characteristic of feeding on epipelagic prey, whereas gray seals, which feed on or near the sea floor in shallow shelf waters, had high SI values (juveniles: ?19.74‰ ± 0.04‰, 17.51‰ ± 0.05‰; adults: ?18.86‰ ± 0.01‰, 17.23‰ ± 0.02‰) characteristic of feeding on demersal prey. In all species, δ¹³C values increased with body size and age in the same manner, indicating that seals exploit or forage in deeper habitats as they get larger and older. We hypothesize that the consistent ontogenetic shift in foraging niche, despite large differences between species in their diving behavior, geographic range and habitat use, not only reflects increased access to different prey due to increased diving capacity, but a progressive adjustment to balance energy budgets by reducing foraging costs.     

INVESTIGATING TROPHIC RELATIONSHIPS OF PINNIPEDS IN ALASKA AND WASHINGTON USING STABLE ISOTOPE RATIOS OF NITROGEN AND CARBON

We measured stable-nitrogen (δ¹⁵N) and stable-carbon (δ¹³C) isotope ratios in muscle and hair from 7 northern fur seals (Callorhinus ursinus) from the Pribilof Islands, Alaska, and 27 Steller sea lions (Eumetopias jubatus), and 14 harbor seals (Phoca vitulina) from the Gulf of Alaska and coast of Washington State, in order to contrast dietary information derived from isotopic vs. available conventional dietary studies. Stable-nitrogen-isotope analysis of muscle revealed that harbor seals were enriched over sea lions (mean δ¹⁵N = 18.6‰vs. 17.5‰) which were in turn enriched over northern fur seals (mean δ¹⁵N = 16.6‰). Trophic segregation among these species likely results primarily from differential reliance on herring (Clupea harengus), Atka mackerel (Pleurogrammus monopterygius), and large vs. small walleye pollock (Theregra chalcogramma). According to their δ¹⁵N values, adult male Steller sea lions showed a higher trophic position than adult females (mean δ¹⁵N: 18.0‰vs. 17.2‰), whereas adult female northern fur seals were trophically higher than juvenile male fur seals (mean δ¹⁵N: 16.5‰vs. 15.0‰). Each of these observed differences likely resulted from differential reliance on squid or differences in the size range of pollock consumed. Three northern fur seal pups showed higher δ¹⁵N enrichment over adults (mean 17.7‰vs. 15.8‰) due to their reliance on their mother's milk. Stable-carbon isotope measurements of hair revealed a cline toward more negative values with latitude. Segregation in hair δ¹³C between Steller sea lions and harbor seals off the coast of Washington (mean δ¹³C: ?13.6‰vs.?15.0‰) reflected the greater association of harbor seals with freshwater input from the Columbia River. Our study demonstrates the utility of the stable isotope approach to augment conventional dietary analyses of pinnipeds and other marine mammals.     

Stable isotope composition and parasitic infections of harbor seal young‐of‐the‐year used as prey‐based diet indicators

The stable isotope composition (δ¹³C and δ¹⁵N values) of harbor seals (Phoca vitulina) is influenced by their diet. Young‐of‐the‐year during lactation and postweaning fast are expected be enriched in ¹⁵N compared to foraging seals. We studied the temporal variation of stable isotope composition of young‐of‐the‐year and adults to determine from which point in time the young‐of‐the‐year tissues (i.e., muscles and vibrissae) are influenced by independent foraging only. These results were compared with the development of trophically transmitted parasitic infections. The δ¹⁵N values in young‐of‐the‐year muscles decreased from June (20.3‰ ± 0.5‰) to October (18.5‰ ± 0.4‰), while those of foraging seals were all year long below 19.2‰. This decrease coincides with the increase of parasitic infections in young‐of‐the‐year, reflecting a shift to fish diet. Together these results suggest that the muscles of the young‐of‐the‐year older than 5–6 mo reflect independent foraging and that they can therefore be used in community diet studies. The nursing signal in vibrissae was unclear, as the δ¹⁵N values of young‐of‐the‐year were stable over time, whereas those of adults varied seasonally. However, δ¹⁵N values of nursing pups were significantly higher than those of adults in May and June, maybe due to their reliance on milk.     

Tracing dietary origins of aphids and the predatory beetle Propylea japonica in agricultural systems using stable isotope analyses

Tracing dietary origins of the predatory beetle Propylea japonica (Thunberg) (Coleoptera: Coccinellidae) aids understanding their roles in the food web and provides information to develop strategies for effective conservation in agroecosystems comprised of wheat [Triticum aestivum L. (Poaceae)], cotton [Hirsutum spp. (Malvaceae)], and maize [Zea mays L. (Poaceae)]. Intrinsic markers of carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) in P. japonica need to be developed to ascertain the source(s) of diet. Experiments were carried out to examine the changes of δ¹³C and δ¹⁵N among the three crops, pests (wheat, cotton, and maize aphids; all Hemiptera: Aphididae), and P. japonica fed on aphids of each of the three crops. Results indicated that δ¹³C values in P. japonica fed on wheat, cotton, and maize aphids were ?27.2 to ?26.5‰, ?24.2 to ?23.9‰, and ?11.0 to ?10.7‰, respectively, whereas their δ¹⁵N values were 1.1 to 2.9‰, 6.0 to 7.4‰, and ?0.6 to 0.1‰, respectively. δ¹³C and δ¹⁵N plots clearly identify the three crops, the dietary origins of the aphids, and the host origins of the aphid prey consumed by the ladybird beetles, as each pathway displays a non‐overlapping pattern. Based on the values of δ¹³C and δ¹⁵N of the three food webs, dietary origins can be traced in the predatory beetle P. japonica derived from wheat, cotton, and maize crops.     

An assessment of the reproductive biology of the Marico barb Barbus motebensis from the upper Groot Marico catchment,South Africa

Temporal changes in fatty acid composition and δ¹⁵N, δ¹³C stable isotope values of the phytobenthos growing on artificial clay substrates under natural conditions over a 28-day period at an upstream and a downstream site in the Kowie River near Grahamstown were investigated in 2012. High concentrations of diatom markers 16:1ω7 and 20:5ω3 fatty acids were recorded, especially at the downstream site, reflecting the importance of diatoms in contributing to the phytobenthos communities at that station. After day 7 at the downstream site the average δ¹⁵N value of the phytobenthos was lighter, gradually increasing by ～2‰ and ～5‰ overall to heavier values on day 28. At the upstream site there were no significant changes (<1‰ increase) in δ¹⁵N values of the phytobenthos over time. Stable nitrogen (δ¹⁵N) and carbon (δ¹³C) signatures in the phytobenthos communities were significantly different between sites (one-way ANOVA; p < 0.001). The stable isotope values and fatty acid concentrations of phytobenthos at the downstream site were different to those of the phytobenthos at the upstream site, and they changed concurrently with changes in the phytobenthos community structure. At the downstream site there was a strong correlation of the δ¹⁵N of phytobenthos with nitrates (R = 0.56) and time (weeks; R = 0.81). However, the fatty acids were not specific enough to characterise the composition of phytobenthos communities. Other biomarker methods, such as stable isotopes and microscopic examination of the communities, were found to be useful. The results from this relatively small-scale tile experiment indicate the complexity of changes in fatty acid composition and δ¹⁵N, δ¹³C stable isotope values of a phytobenthos community. Stable isotope and fatty acid composition can be successfully used to map changes in phytobenthos composition and carbon and nitrogen flow patterns along a river continuum.     

Dietary analysis of the herbivorous hemiramphid Hyporhamphus regularis ardelio: an isotopic approach

The stable isotope values for a range of size classes of Hyporhamphus regularis ardelio from Moreton Bay, south‐east Australia were determined. There was a positive linear relationship between δ¹³C and standard length (L_S)(δ¹³C = 0·034 L_S ? 16·23; r² = 0·78). δ¹³C ranged from ?8·48 to ?17·29‰ with the smallest size class (50 mm L_S) being on average 1·04‰ enriched with respect to that of zooplankton (Temora turbinata) and 7·97‰ depleted compared to Zostera capricorni. δ¹³C was positively correlated with L_S(P < 0·01)(more enriched with increasing L_S) with those fish of the largest size class (225 mm L_S) being 9·86 and 0·84‰ enriched than T. turbinata and Z. capricorni, respectively. There was no detectable trend in δ¹⁵N values with L_S(P > 0·01) with δ¹⁵N, ranging from 9·18 to 11·00‰. Fish of all size classes were on average 2·32 and 7·63‰ more enriched than zooplankton and seagrass, respectively. Carbon isotope data indicate that H. r. ardelio commence life as carnivores and change to a diet in which seagrass is the primary carbon source. The dependence on animal matter, however, is always present. Due to the low percentage of nitrogen in Z. capricorni(2·5%) compared to zooplankton (9·1%) it appears that nitrogen from zooplankton is necessary throughout their life history with the carbon requirements for these fish coming chiefly from Z. capricorni.     

Stable carbon isotope composition of bone hydroxylapatite: significance in paleodietary analysis

The stable carbon isotope composition of the structural carbonate derived from animal bone hydroxylapatite (δ¹³C_B-HA) could record an animal’s diet. These records provide critical evidence for different paleontological disciplines, e.g., paleodiet analyses, and paleoclimate reconstructions. Compared to those of other body tissues, such as bone collagen or teeth enamel hydroxylapatite, δ¹³C_B-HA values record information on the whole diet of an animal in its last years. δ¹³C_B-HA can be applied to fossil animals of various body sizes. The δ¹³C analytical instruments available only require that prepared bone samples be approximately 2–5 mg for precise measurement, allowing δ¹³C_B-HA analysis to be feasible on most vertebrate fossils without destructive sampling, especially on small mammals or birds whose teeth are not large enough for sampling or are lost. Moreover, δ¹³C_B-HA can be used from different times or under less than ideal burial environments. For fossils dating back to Devonian or buried in hot and humid regions, dietary information has been completely lost in bone collagen during post-depositional processes but still remained in the δ¹³C_B-HA values because hydroxylapatite is less influenced by diagenetic effects after deposition. In addition, systematic methods such as X-ray diffraction and Fourier transform infrared spectroscopy have been developed to qualitatively or semiquantitatively assess the influence of diagenesis on bone hydroxylapatite to ensure the credibility of the δ¹³C_B-HA values. With the above merits, δ¹³C_B-HA analysis is therefore becoming an increasingly important method in paleodiet-related research. Currently, applications of the δ¹³C_B-HA method on fossil animals are primarily focused on two aspects, namely, paleodietary reconstruction of fossil animals with uncertain diets and paleoenvironmental reconstruction based on the δ¹³C_B-HA values of fossil herbivores. The published researches, combined with our new results from early birds, demonstrate the considerable significance of the δ¹³C_B-HA method in paleontological and paleoenvironmental research. Notably, the δ¹³C_B-HA-based paleodietary analysis of early vertebrates, especially the large number of small birds or mammals discovered in the past decades would be an important work in the near future.     

Isotopic biosignatures in carbonate‐rich,cyanobacteria‐dominated microbial mats of the Cariboo Plateau,B.C.

Photosynthetic activity in carbonate‐rich benthic microbial mats located in saline, alkaline lakes on the Cariboo Plateau, B.C. resulted in pCO₂ below equilibrium and δ¹³C_DIC values up to +6.0‰ above predicted carbon dioxide (CO₂) equilibrium values, representing a biosignature of photosynthesis. Mat‐associated δ¹³C_carb values ranged from ~4 to 8‰ within any individual lake, with observations of both enrichments (up to 3.8‰) and depletions (up to 11.6‰) relative to the concurrent dissolved inorganic carbon (DIC). Seasonal and annual variations in δ¹³C values reflected the balance between photosynthetic ¹³C‐enrichment and heterotrophic inputs of ¹³C‐depleted DIC. Mat microelectrode profiles identified oxic zones where δ¹³C_carb was within 0.2‰ of surface DIC overlying anoxic zones associated with sulphate reduction where δ¹³C_carb was depleted by up to 5‰ relative to surface DIC reflecting inputs of ¹³C‐depleted DIC. δ¹³C values of sulphate reducing bacteria biomarker phospholipid fatty acids (PLFA) were depleted relative to the bulk organic matter by ~4‰, consistent with heterotrophic synthesis, while the majority of PLFA had larger offsets consistent with autotrophy. Mean δ¹³C_org values ranged from ?18.7 ± 0.1 to ?25.3 ± 1.0‰ with mean Δ¹³C_inorg‐org values ranging from 21.1 to 24.2‰, consistent with non‐CO₂‐limited photosynthesis, suggesting that Precambrian δ¹³C_org values of ~?26‰ do not necessitate higher atmospheric CO₂ concentrations. Rather, it is likely that the high DIC and carbonate content of these systems provide a non‐limiting carbon source allowing for expression of large photosynthetic offsets, in contrast to the smaller offsets observed in saline, organic‐rich and hot spring microbial mats.     

Nitrogen outputs from fecal and urine deposition of small mammals: implications for nitrogen cycling

The contribution of small mammals to nitrogen cycling could have repercussions for the producer community in the maintaining or perhaps magnifying of nitrogen availability. Our objective was to model nitrogen outputs (deposition of feces and urine) of small mammals in an old-field ecosystem and estimate the amount of fecal and urinary nitrogen deposited annually. To address this objective, we used models from laboratory studies and combined these with data from field studies to estimate dietary nitrogen and monthly and annual nitrogen outputs from fecal and urine deposition of five rodent species. The models accounted for monthly fluctuations in density and biomass of small-mammal populations. We estimated that the minimal amount of nitrogen deposited by rodents was 1.0 (0.9–1.1) and 2.7 (2.6–2.9) kg Nha⁻¹ year⁻¹ from feces and urine, respectively, for a total contribution of 3.7 (3.5–4.0) kg Nha⁻¹ year⁻¹. Hispid cotton rats (Sigmodon hispidus) accounted for >75% of the total nitrogen output by small mammals. Our estimates of annual fecal and urinary nitrogen deposited by rodents were comparable to nitrogen deposits by larger herbivores and other nitrogen fluxes in grassland ecosystems and should be considered when assessing the potential effects of herbivory on terrestrial nitrogen cycles.     

Spatial,temporal, age,and sex related variation in the diet of South American sea lions in southern Chile

We analyzed spatial, temporal, and age/sex variation in the diet of the South American sea lions (SASL, Otaria byronia) in southern Chile via δ¹³C and δ¹⁵N isotope analysis, with emphasis on exotic farmed and feral salmonids as a source of prey for this generalist predator. Isotope mixing models show that the primary prey consumed by SASL were demersal and benthopelagic fishes. Individuals sampled in summer and in the outer coast had higher δ¹⁵N values than those from winter or from the inner coast due to consumption of high trophic level demersal fish. We also found evidence of an ontogenetic shift in isotopic niche width as measured by δ¹³C and δ¹⁵N standard ellipse areas, with juveniles showing a restricted isotopic niche width (1.0‰²) in comparison to subadult (2.2‰²) and adult males (1.9‰²). The proportion of salmonids in the diet of the SASL was negligible and lower than reported in previous studies, which may be related to a recent drop in the production of salmon aquaculture in the region. Our study suggests that the SASL are able to adapt to shifts in spatiotemporal variations in the abundance of potential prey, including feral and farmed salmonids.     

Size-Dependent Variation of Carbon and Nitrogen Isotope Abundances in Epiphytic Bromeliads

Abstract: While atmospheric species of bromeliads have narrow leaves, densely covered with water‐absorbing trichomes throughout their life cycles, many tank bromeliads with broad leaves, forming phytotelmata, go through an atmospheric juvenile phase. The effect of the different habits and the phase change in tank‐forming bromeliads on water and nutrient relations was investigated by analysing the relationship between plant size, C/N ratios and the natural abundance of ¹³C and ¹⁵N in five epiphytic bromeliad species or morphospecies of a humid montane forest in Xalapa, Mexico. The atmospheric species Tillandsia juncea and T. butzii exhibited full crassulacean acid metabolism, with δ¹³C values (mean ‐ 15.3 ‰ and ‐ 14.7 ‰, respectively) independent of size. In Tillandsia species with C₃ photosynthesis, δ¹³C decreased with increasing plant size, indicating stronger drought stress in juveniles. The increase of the C/N ratio with size suggests that, at least in heteroblastic bromeliads, the availability of water is more limiting during early growth, and that limitations of nitrogen supply become more important later on, when water stored in the tank helps to bridge dry periods, reducing water shortage. δ¹⁵N values of the two atmospheric species were very negative (‐ 12.6 ‰ and ‐ 12.2 ‰, respectively) and did not change with plant size. Tank‐forming bromeliads had less negative δ¹⁵N values (c ‐ 6 ‰), and, in species with atmospheric juveniles and tank‐forming adults, δ¹⁵N values increased significantly with plant size. These differences do not appear to be an effect of the isotopic composition of N sources, but rather reflect N availability and limitation and stress‐induced changes in ¹⁵N discrimination.     

Linking aboveground and belowground food webs through carbon and nitrogen stable isotope analyses

Carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) have been used for more than two decades in analyses of food web structure. The utility of isotope ratio measurements is based on the observation that consumer δ¹³C values are similar (<1‰ difference) to those of their diet, while consumer δ¹⁵N values are about 3‰ higher than those of their diet. The technique has been applied most often to aquatic and aboveground terrestrial food webs. However, few isotope studies have examined terrestrial food web structure that includes both above- and belowground (detrital) components. Here, we review factors that may influence isotopic signatures of terrestrial consumers in above- and belowground systems. In particular, we emphasize variations in δ¹³C and δ¹⁵N in belowground systems, e.g., enrichment of ¹³C and ¹⁵N in soil organic matter (likely related to soil microbial metabolism). These enrichments should be associated with the high ¹³C (~3‰) enrichment in belowground consumers relative to litter and soil organic matter and with the large variation in δ¹⁵N (~6‰) of the consumers. Because such enrichment and variation are much greater than the trophic enrichment generally used to estimate consumer trophic positions, and because many general predators are considered dependent on energy and material flows from belowground, the isotopic variation in belowground systems should be taken into account in δ¹³C and δ¹⁵N analyses of terrestrial food webs. Meanwhile, by measuring the δ¹³C of key predators, the linkage between above- and belowground systems could be estimated based on observed differences in δ¹³C of primary producers, detritivores and predators. Furthermore, radiocarbon (¹⁴C) measurements will allow the direct estimation of the dependence of predators on the belowground systems.     

DIFFERENCES IN FORAGING LOCATION OF MEXICAN AND CALIFORNIA ELEPHANT SEALS: EVIDENCE FROM STABLE ISOTOPES IN PUPS

Female northern elephant seals, Mirounga angustirostris, from Año Nuevo (AN) in central California feed offshore in mid‐latitude waters (40°–55°N). Migratory patterns and foraging locations of seals from Mexico are unknown. Rookeries on San Benitos (SB) islands in Baja California Sur, Mexico, are ～1,170 km south of AN. Although the colonies are similar in size, seals from SB begin breeding earlier and have an earlier breeding birthing peak than seals from AN. To determine if the foraging location of seals from Mexico was similar to that of seals from California, we measured δ¹³C and δ¹⁵N values in the hair of 48 suckling pups at SB and 37 from AN, assuming that their isotopic signatures reflected those of mothers' milk, their exclusive diet. The mean δ¹³C and δ¹⁵N values for SB pups (?16.1‰± 0.9‰ and 17.7‰± 0.9‰, respectively) were significantly higher than those for AN pups (?17.6‰± 0.4‰ and 15.6‰± 1.0‰, respectively). From data on environmental isotope gradients and known behavior of SB and AN populations, we hypothesize that the isotope differences are due to females in the SB colony foraging ～8° south of seals from AN. This hypothesis can be tested by deployment of satellite tags on adult females from the SB colony.     

Characteristics of stable isotope signature of diet in tissues of captive Japanese macaques as revealed by controlled feeding

We determined the magnitude of isotopic fractionation of carbon and nitrogen stable isotope ratios (as enrichment factors, Δδ¹³C and Δδ¹⁵N, respectively) between the tissues and diets of captive Japanese macaques (Macaca fuscata) using a controlled feeding experiment, to provide basic data for reconstructing their feeding habits. The Δδ¹³C and Δδ¹⁵N values, respectively, were 0.9 ± 0.2 ‰ (mean ± standard deviation, SD) and 3.0 ± 0.3 ‰ for whole blood, 1.3 ± 0.2 ‰ and 4.3 ± 0.3 ‰ for plasma, and 0.8 ± 0.2 ‰ and 3.0 ± 0.2 ‰ for red blood cells. However, the Δδ¹³C and Δδ¹⁵N values for hair were 2.8 ± 0.3 ‰ and 3.4 ± 0.2 ‰, respectively. No difference was detected in the δ¹³C and δ¹⁵N values of hair sampled from different parts of the body. We investigated the effects of diet on δ¹³C in growing hair by alternating the diet of the macaques each month between two diets that differed markedly in δ¹³C. Hair regrown after shaving repeatedly recorded the δ¹³C of the diet consumed during the time of hair growth. On the other hand, hair naturally grown during the diet-change experiment did not show a clear pattern. One possible reason is that the hair had grown abnormally under unnatural indoor conditions and showed complicated isotope signatures. To reconstruct the long-term feeding history of Japanese macaques, we need to further clarify the relationships between the stable isotope signature of diet and various body tissues.     

Role of body size and temporal hydrology in the dietary shifts of shortjaw tapertail anchovy Coilia brachygnathus (Actinopterygii, Engraulidae) in a large floodplain lake

Seasonal water-level changes in floodplain lakes can induce variations in primary and secondary production, thus affecting trophic interactions. In this study, we tested the latter by studying size- and temporal hydrology-related shifts in the diet of shortjaw tapertail anchovy Coilia brachygnathus (Actinopterygii, Engraulidae) from Lake Poyang. During the wet season, δ¹³C values ranged from ?28.2‰ for small anchovies to ?24.6‰ for larger individuals, but δ¹⁵N ranged from 18.9‰ for smaller fish to 12.4‰ for larger fish. Significant ¹³C-enrichment and ¹⁵N-depletion occurred with increasing size, revealing that different carbon sources were used as the fish grew. Given the high hydrologic fluctuation levels, significant differences in δ¹³C values were observed among larger anchovies between seasons, indicating a temporal dietary shift. Anchovies fed primarily on shrimp and fish during the low-water season despite the predominance of zooplankton during the two seasons studied, which indicated increased piscivorous reliance. C. brachygnathus exhibited higher δ¹⁵N values during the wet season because the food items were ¹⁵N-enriched. Human waste brought by floods could be another possible interpretation. Considering C. brachygnathus is an important link between plankton production and higher piscivorous trophic levels, changes in the species are expected to affect the functioning of lake food webs along the trophic pathway.     

Spatial,ontogenetic and interspecific variability in stable isotope ratios of nitrogen and carbon of Merluccius capensis and Merluccius paradoxus off South Africa

General linear models (GLMs) were used to determine the relative importance of interspecific, ontogenetic and spatial effects in explaining variability in stable isotope ratios of nitrogen (δ¹⁵N) and carbon (δ¹³C) of the co‐occurring Cape hakes Merluccius capensis and Merluccius paradoxus off South Africa. Significant GLMs were derived for both isotopes, explaining 74 and 56% of observed variance in Merluccius spp. δ¹⁵N and δ¹³C, respectively. Spatial effects (west or south coast) contributed most towards explaining variability in the δ¹⁵N model, with Merluccius spp. off the west coast having higher (by c. 1·4‰) δ¹⁵N levels than Merluccius spp. off the south coast. Fish size and species were also significant in explaining variability in δ¹⁵N, with both species showing significant linear increases in δ¹⁵N with size and M. capensis having higher (by c. 0·7‰) δ¹⁵N values than M. paradoxus. Species and coast explained most and similar amounts of variability in the δ¹³C model, with M. capensis having higher (by c. 0·8‰) δ¹³C values than M. paradoxus, and values being lower (by c. 0·7‰) for fishes off the west coast compared with the south coast. These results not only corroborate the knowledge of Merluccius spp. feeding ecology gained from dietary studies, in particular the ontogenetic change in trophic level corresponding to a changing diet, but also that M. capensis feeds at a slightly higher trophic level than M. paradoxus. The spatial difference in Merluccius spp. δ¹⁵N appears due to a difference in isotopic baseline, and not as a result of Merluccius spp. feeding higher in the food web off the west than the south coast, and provides new evidence that corroborates previous observations of biogeographic differences in isotopic baselines around the South African coast. This study also provides quantitative data on the relative trophic level and trophic width of Cape hakes over a large size range that can be used in ecosystem models of the southern Benguela.     

Did central Australian megafaunal extinction coincide with abrupt ecosystem collapse or gradual climate change?

Aim In central Australia, the giant flightless bird Genyornis newtoni disappeared about 45–50 thousand years ago (ka). It has been reported that coincident with this extinction the carbon isotopic composition of preserved eggshells of the extant emu (Dromaius novaehollandiae) shows an abrupt dietary shift from tropical grasses (C₄ photosynthesis) to temperate grasses and/or woody browse (C₃ photosynthesis). This abrupt shift has been interpreted as signalling ‘ecosystem collapse’ due to landscape burning by humans. We evaluate an alternative interpretation, that the shift in diet was not abrupt, but gradual, and caused by the weakening of the Australian monsoon. Location Lake Eyre, central Australia. Methods We re‐analysed a large, published dataset of emu diet δ¹³C (inferred from δ¹³C of preserved eggshells) spanning the last 140,000 years, using time‐series analysis. Using Akaike's information criterion, we compared two contrasting models: (1) there was an abrupt shift in δ¹³C coincident with the extinction of Genyornis, assumed 47.5 ka; and (2) there was a gradual shift in δ¹³C, correlated with reconstructed water level in Lake Eyre, a proxy for monsoon intensity. Results There was little evidence of an abrupt shift in emu diet δ¹³C about 45–50 ka, but δ¹³C appeared to steadily decrease between about 80 and 30 ka. Indeed, the model representing a correlation between δ¹³C and lake level was more than seven times more likely than the model representing an abrupt shift at 47.5 ka. Main conclusions The emu eggshell isotopic record from Lake Eyre does not support the hypothesis that landscape burning by humans transformed a savanna?grassland mosaic into the modern desert scrub, contributing to the extinction of Genyornis. While our findings cast strong doubt on the foremost line of evidence that landscape burning by humans caused the megafaunal extinctions, and suggest that central Australia was becoming increasingly arid in the Late Pleistocene, the relative roles of hunting by humans and climate change in the megafaunal extinctions remain unresolved.