Intrapopulation isotopic niche structure in mammalian carnivores and herbivores across contrasting habitats

Quantifying the niche of contemporary and fossil organisms is key to identifying the primary factors driving species and community dynamics through time, in particular teasing apart abiotic and biotic drivers of change. However, niche quantification can be difficult due to short time spans (for contemporary systems), time averaging (for fossil systems), and incomplete information on different aspects of ecology and environment (for both contemporary and fossil systems). Here, we use stable isotope analyses coupled with specimen-level radiocarbon dating from the Rancho La Brea Tar Pits in Los Angeles, California to examine niche dynamics over the last >55,000 years. We sampled over 100 specimens of small and mid-sized mammals, mostly sciurids (squirrels) and leporids (rabbits), from Rancho La Brea to quantify their isotopic niche, track niche changes through time, and identify probable cause(s) of those changes. Individual specimens were radiocarbon dated and niches were quantified from stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of fossil collagen to track individual isotopic niches at precise points in time. Overall, sciurids and leporids exhibit different isotopic signals, suggesting niche variation among taxa. Comparison of animals during the Pleistocene versus the Holocene reveals overall greater δ13C values and greater δ13C and δ15N isotopic niche breadth among Holocene individuals, suggesting that small mammal resource use changed from the last glacial to current interglacial period. Evaluating the isotopic data continuously through time against a high-resolution regional paleoclimate record shows that climate contributed to small mammal niche variation over the last 55,000 years in the Los Angeles Basin. These findings reveal the complexity of long-term abiotic and biotic forcings on organismal niches and emphasize the importance of scale and data resolution when quantifying and interpreting (paleo)ecological patterns and processes.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 565:113-129 (2017) - DOI: https://doi.org/10.3354/meps12023 Trophic niche of the invasive red king crab Paralithodes camtschaticus in a benthic food web Mona M. Fuhrmann*, Torstein Pedersen, Einar M. Nilssen Department of Arctic and Marine Biology, UiT–The Arctic University of Norway, 9037 Tromsø, Norway *Corresponding author: mona.m.fuhrmann@uit.no ABSTRACT: Understanding the trophic ecology of an invasive species is important for risk assessment. The red king crab Paralithodes camtschaticus is both a valuable fishery resource and a potential threat to native biota in the Barents Sea. We combined gut content analysis and stable carbon and nitrogen isotope analysis to study feeding strategy, variation in resource use and niche overlap within the benthic food web of Porsangerfjord (70.1° to 70.9°N, 25° to 26.5°E) on the northern Norwegian coast. This fjord has experienced recent invasion by the red king crab. Sediment-dwelling bivalves and polychaetes dominated gut contents of the red king crab with respect to occurrence, and the wide range of prey from multiple trophic levels revealed a generalist, opportunistic feeding strategy. There were differences in diet related to crab size and foraging location, reflecting habitat choice and depth distribution of crabs during their life cycle. Small crabs, feeding in shallow water, relied to a larger extent on littoral species such as sea urchins and gastropods. The estimated mean trophic level for red king crab in Porsangerfjord was 3.1 (range 2.7-3.5). There was no evidence of a pronounced ontogenetic niche shift in stable isotopes, with local effects concealing possible overall size effects. Competition may arise with native anomuran species (e.g. Lithodes maja), large predatory asteroids and gastropods, all of which overlapped with red king crab in isotopic niche. A low overlap in isotopic niche between red king crab and fish suggests that they exploit different major food resources and that predatory fish occupy a higher trophic position than the red king crab in Porsangerfjord. KEY WORDS: Decapod · Diet · Stable isotopes · Trophic ecology · Trophic level · Introduced species · North Atlantic Full text in pdf format Supplementary material PreviousNextCite this article as: Fuhrmann MM, Pedersen T, Nilssen EM (2017) Trophic niche of the invasive red king crab Paralithodes camtschaticus in a benthic food web. Mar Ecol Prog Ser 565:113-129. https://doi.org/10.3354/meps12023 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 565. Online publication date: February 17, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Trophic redundancy within a diverse community of sympatric delphinids in the oligotrophic Caribbean Sea.

Temporal variation in food web structure is widespread among highly seasonal environments, such as the Arctic, and is driven by changes in resource availability. Variation in resource availability can lead to species differences in diet composition, isotopic niche width, and trophic position (TP) across seasons. Here, we used tissue samples that represent two distinct turnover rates for diet (liver = shorter term, muscle = longer term) from 18 fish and three marine mammal species to investigate seasonal (i) variation in TPs within the Southampton Island marine ecosystem of Hudson Bay, (ii) variation in consumer isotopic niche width within this part of the food web, and (iii) variation in community niche dynamics among a fish and marine mammal community using stable carbon (δ13C) and nitrogen (δ15N) isotope analyses. Many zooplanktivores and piscivores increased in TP in summer (i.e., shorter-term turnover period), whereas benthic feeders dependent on ice-obligate prey decreased in TP. Most isotopic niche widths and community metrics (δ15N range, total ellipse area, mean centroid distance) were higher in liver than muscle. Our findings demonstrate seasonal changes in TPs, which suggests that Arctic communities may be differentially affected by longer ice-free periods and earlier onset of primary production due to accelerated climate change.

Stable isotope analysis has been utilized in archaeology since the 1970s, yet standardized protocols for terminology, sampling, pretreatment evaluation, calibration, quality assurance and control, data presentation, and graphical or statistical treatment still remain lacking in archaeological applications. Here, we present recommendations and requirements for each of these in the archaeological context of: bulk stable carbon and nitrogen isotope analysis of organics; bulk stable carbon and oxygen isotope analysis of carbonates; single compound stable carbon and nitrogen isotope analysis on amino acids in collagen and keratin; and single compound stable carbon and hydrogen isotope analysis on fatty acids. The protocols are based on recommendations from the Commission on Isotopic Abundances and Atomic Weights of the International Union of Pure and Applied Chemistry (IUPAC) as well as an expanding geochemical and archaeological science experimental literature. We hope that this will provide a useful future reference for authors and reviewers engaging with the growing number of stable isotope applications and datasets in archaeology.

The Balearic Islands occupy a central space in the western Mediterranean, at the maritime crossroads between North Africa, the Iberian Peninsula and the rest of southwestern Europe. As such, it is well placed to investigate changes in subsistence practices associated with the major cultural transitions following the arrival of Islamic rule. Stable carbon and nitrogen isotope analysis was carried out on bone collagen from the Islamic cemetery (ca. AD 950–1150) population excavated at 33 Bartomeu Vicent Ramon, Ibiza, including human (n = 42) and faunal remains (n = 3). Stable oxygen and carbon isotope analysis was also undertaken on human tooth enamel carbonate (n = 6), and six humans were directly radiocarbon dated, confirming the presence of two distinct burial phases. The collagen results emphasise a C3-based diet, with variable but generally minor contributions from marine and/or C4 foods. However, the enamel carbonate results indicate a far greater importance of C4 crops than suggested by the collagen results, contributing up to 40% of energy intake. In keeping with previous studies of the region and period, the dietary contribution of marine protein is probably limited. A small number of outliers in both collagen and carbonate isotope results are identified, suggesting the presence of individuals originating elsewhere. The results are compared with those from previous investigations on the Balearics and the Spanish mainland, highlighting the complexity of factors—both cultural and methodological—affecting inter-regional dietary investigation.

"Late Holocene Climatic Changes Recorded In Macropod Bone Collagen Stable Carbon And Nitrogen Isotopes At Fromms Landing, South Australia." Australian Archaeology, 49(1), pp. 48–49

Classic and contemporary trophic ecology-based studies have shown that most non-native freshwater fish species (NNS) that integrate into novel environments have the potential to influence the recipient ecosystems’ structure and function. However, the interspecific trophic interactions amongst co-occurring NNS within invaded systems remain poorly studied. Here, we used carbon (δ13C) and nitrogen (δ15N) stable isotope analyses to examine general fish trophic diversity patterns (native and non-native fishes) and to explore trophic niche patterns amongst co-occurring NNS within a flow-modified river system, the Great Fish River (South Africa). The system was characterised by isotopic variation, which revealed spatial differences in trophic complexity from uninvaded headwater tributaries to invaded mainstem and downstream sections. Two of the invaded sections, the upper mainstem of the Great Fish River (UGFR) and the Koonap River, had low isotopic overlaps between NNS and the native fish assemblages. Furthermore, co-occurring NNS in these two invaded sections had variable isotopic niche sizes and low interspecific isotopic niche overlaps, suggesting the potential for trophic differentiation. By comparison, there was evidence of high resource use patterns among NNS within the lower mainstem section of the Great Fish River (LGFR), which likely reflected trophic plasticity. Overall, results of this study provided evidence of both trophic niche differentiation (UGFR and Koonap River) and niche overlap (LGFR) as probable mechanisms of co-occurrences of the non-native fishes within different invaded sections of the Great Fish River system, and underscores the difficulties associated with predicting their trophic impacts.

Sablefish (Anoplopoma fimbria, Anoplopomatidae) and shortraker rockfish (Sebastes borealis, Sebastidae) co-occur in deepwater marine habitats in the northeast Pacific. Both species are economically valuable, but their ecologies are not well known. We used stable isotope analysis of carbon and nitrogen to explore isotopic niches of A. fimbria and S. borealis in two distinct locations—a deep strait in the inside passage area and an open coastal area of the continental shelf, both in southeast Alaska, USA. Anoplopoma fimbria and S. borealis exhibited similar positions of isotopic niches based on nitrogen and carbon isotopic ratios, suggesting potential interspecific competition, especially in the inside location. In addition, S. borealis had a smaller niche breadth compared to A. fimbria in the coastal location. Both species had enriched nitrogen and carbon isotopic ratios in the inside location compared to the coastal location. Differences in isotopic niches between these two locations suggest the possibility of location-specific variation in isotopic niches of these two species of widespread, abundant deepwater fishes.

Background: Theories of density-dependent habitat selection provide two solutions for co-existence of competing species. The niche compression hypothesis predicts that species reduce their respective niche breadths in response to inter-specific competition. Alternatively, if the species have similar resource preferences, the subordinate species may be forced to expand its niche to incorporate secondary resources. Aim: Determine whether grazing ungulate species partition the resource by compression or expansion of dietary niches. Organisms: Black wildebeest (Connochaetes gnou) and blue wildebeest (C. taurinus). Methods: Stable carbon and nitrogen isotope analysis of faeces. Isotopic niche breadths are compared across allopatric and sympatric wildebeest populations in South African grasslands. Results: Stable carbon and nitrogen isotope niche breadths of the two wildebeest species were virtually identical. In sympatry, however, black wildebeest had a narrower δ13C niche breadth (indicating almost exclusive use of C4 grass), whereas blue wildebeest had a wider δ13C niche breadth (indicating significant contributions from C3 sources). Blue wildebeest also had a wider δ15N niche breadth than sympatric black wildebeest. Moreover, the δ13C niche breadths of sympatric black wildebeest and blue wildebeest were narrower and wider, respectively, than those of allopatric populations of either species. Conclusions: Isotope niche dynamics across allopatric and sympatric populations arise due to the combined effects of competition and habitat heterogeneity on resource use. Although results for black wildebeest resemble niche compression, this hypothesis cannot explain patterns observed in blue wildebeest. Expansion of the blue wildebeest niche, and restricted niche breadth of black wildebeest, is consistent with predictions of a shared preference model in which black wildebeest are the dominant competitor. When competition is operating, differences in the way species use secondary resources can have an important role in structuring grazer assemblages.

Diet, Body Size, and Landscape Use among Holocene People in the Southern Cape, South Africa

Diet, Body Size, and Landscape Use among Holocene People in the Southern Cape, South Africa

Species’ partitioning of resources remains one of the most integral components for understanding community assembly. Analysis of stable carbon and nitrogen isotopes in animal tissues has the potential to help resolve patterns of partitioning because these proxies represent the individual’s diet and trophic niche, respectively. Using free-ranging rodents in a southern African savanna as a model community, we find that syntopic species within habitats occupy distinct isotope niches. Moreover, species with strongly overlapping isotope niches did not overlap in their spatial distribution patterns, suggesting an underlying effect of competitive exclusion. Niche conservatism appears to characterize the behaviour of most species in our sample - with little or no observed changes across habitats - with the exception of one species, Mastomys coucha. This species displayed a generalist distribution, being found in similar abundances across a variety of habitats. This spatial pattern was coupled with a generalist isotope niche that shifted across habitats, likely in response to changes in species composition over the same spatial gradient. The case for M. coucha supports contentions that past competition effects played a significant evolutionary role in shaping community structures of today, including the absence of strong interspecific niche overlaps within particular habitats. Our study highlights the value of stable isotope approaches to help resolve key questions in community ecology, and moreover introduces novel analytical approaches to quantifying isotope niche breadths and niche overlaps that are easily comparable with traditional metrices.

Foxtail and broomcorn millets are the most important crops in northern China since the early Neolithic. However, little evidence is available on how people managed these two crops in the past, especially in prehistory. Previous research on major C3 crops in western Eurasia demonstrated the potential of stable carbon and nitrogen isotope analysis of charred archaeobotanical remains to reveal the management of water and manure, respectively. Here, we evaluate the feasibility of a similar approach to C4 millets. Foxtail and broomcorn millet plants grown in pots in a greenhouse under different manuring and watering regimes were analysed to test the effects of management on stable carbon and nitrogen isotope values of grains. Stable nitrogen isotope values of both millets increased as manuring level increased, ranging from 1.7 ‰ to 5.8 ‰ in different conditions; hence, it appears a feasible tool to identify manuring practices, in agreement with results from recent field studies. However, the two millets exhibit opposing trends in stable carbon isotope values as watering level increased. The shift in stable carbon isotope values of millets is also smaller than that observed in wheat grown in the same experimental environment, making it difficult to identify millet water status archaeologically. In addition, we charred millet grains at different temperatures and for varying durations to replicate macro-botanical remains recovered archaeologically, and to evaluate the offsets in carbon and nitrogen isotope values induced by charring. We found that the stable nitrogen isotope values of foxtail millet and broomcorn millet can shift up to 1-2 ‰ when charred, while the stable carbon isotope values change less than 0.3 ‰. Overall, we demonstrate that stable nitrogen isotope values of charred foxtail and broomcorn millet seeds could provide insight into past field management practices, and both carbon and nitrogen isotope values can together inform palaeodietary reconstruction.

New home, new diet? Reconstruction of diet at the 10th century CE Hungarian Conquest period site of Kenézlő-Fazekaszug from stable carbon and nitrogen isotope analyses