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1.
Carbon and nitrogen stable isotope analyses have improved our understanding of food webs and movement patterns of aquatic
organisms. These techniques have recently been applied to diet studies of elasmobranch fishes, but isotope turnover rates
and isotope diet–tissue discrimination are still poorly understood for this group. We performed a diet switch experiment on
captive sandbar sharks (Carcharhinus plumbeus) as a model shark species to determine tissue turnover rates for liver, whole blood, and white muscle. In a second experiment,
we subjected captive coastal skates (Leucoraja spp.) to serial salinity reductions to measure possible impacts of tissue urea content on nitrogen stable isotope values.
We extracted urea from spiny dogfish (Squalus acanthias) white muscle to test for effects on nitrogen stable isotopes. Isotope turnover was slow for shark tissues and similar to
previously published estimates for stingrays and teleost fishes with low growth rates. Muscle isotope data would likely fail
to capture seasonal migrations or diet switches in sharks, while liver and whole blood would more closely reflect shorter
term movement or shifts in diet. Nitrogen stable isotope values of skate blood and skate and dogfish white muscle were not
affected by tissue urea content, suggesting that available diet–tissue discrimination estimates for teleost fishes with similar
physiologies would provide accurate estimates for elasmobranchs. 相似文献
2.
In marine food web studies, stable isotopes of nitrogen (δ15N) and carbon (δ13C) are widely used to estimate organisms’ trophic levels (TL) and carbon sources, respectively. For smaller organisms, whole
specimens are commonly analyzed. However, this “bulk method” involves several pitfalls since different tissues may fractionate
stable isotopes differently. We compared the δ15N and δ13C values of exoskeleton versus soft tissue, in relation to whole specimens, of three common Arctic amphipods in Svalbard waters:
the benthic Anonyx nugax, the sympagic (ice-associated) Gammarus wilkitzkii and the pelagic Themisto libellula. The δ15N values of the exoskeletons were significantly lower than those of the soft tissues for A. nugax (10.5 ± 0.7‰ vs. 15.7 ± 0.7‰), G. wilkitzkii (3.3 ± 0.3‰ vs. 8.3 ± 0.4‰) and T. libellula (8.6 ± 0.3‰ vs.10.8 ± 0.3‰). The differences in δ13C values between exoskeletons and soft tissues were insignificant, except for A. nugax (−21.2 ± 0.2‰ vs. −20.3 ± 0.2‰, respectively). The δ15N values of whole organisms were between those of the exoskeletons and the soft tissues, being similarly enriched in 15N as the exoskeletons (except G. wilkitzkii) and depleted in 15N by 1.2–3.7‰ compared to the soft tissues. The δ15N-derived TLs of the soft tissues agreed best with the known feeding preferences of the three amphipods, which suggest a potential
underestimation of 0.5–1.0 TL when stable isotope analyses are performed on whole crustaceans with thick exoskeletons. The
insignificant or small differences in δ13C values among exoskeletons, soft tissues and whole specimens, however, suggest low probability for misinterpretations of
crustaceans’ primary carbon source in marine ecosystems with distinctly different δ13C-carbon sources. 相似文献
3.
Carbon and nitrogen stable isotopes are frequently used to study energy sources and food web structure in ecosystems, and
more recently, to study the effects of anthropogenic stress on aquatic ecosystems. We investigated the effect of nutrient
enrichment on δ13C and δ15N in fine (FPOM), coarse (CPOM) particulate organic matter, periphyton, invertebrates and fish in nine boreal streams in south-central
Sweden. In addition, we analysed the diet of benthic consumers using stable isotope data. Increases in δ15N of periphyton (R
2 = 0.88), CPOM (0.78), invertebrates (0.92) and fish (0.89) were related to nutrient enrichment. In contrast, δ13C signatures did not change along the nutrient gradient. Our results show that δ15N has potential as a sensitive indicator of nutrient enrichment in boreal streams. Carbon and nitrogen isotopes failed to
elucidate putative diets of selected aquatic consumers. Indeed, comparison of low- and high-impact sites showed that δ13C of many consumers were found outside the ranges of basal resource δ13C. Moreover, ranges of basal resource δ13C and δ15N overlapped at both low and high sites, making discrimination between the importance of allochthonous and autochthonous production
difficult. Our findings show that a fractionation rate of 3.4‰ is not always be appropriate to assess trophic interactions,
suggesting that more studies are needed on fractionation rates along gradients of impairment.
Handling editor: M. Power 相似文献
4.
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. 相似文献
5.
Using stable isotopes to study resource acquisition and allocation in procellariiform seabirds 总被引:1,自引:0,他引:1
Some procellariiform seabirds use a dual strategy for provisioning their chicks by alternating short (ST) and long (LT) foraging
trips. Parent birds gain mass during LT but they lose mass while increasing the chick feeding frequency during ST. Self-feeding
during LT is crucial for the success of ST because firstly most of the energy used during ST is likely to be derived from
the energy stored during LT and secondly self-feeding during ST is presumed to be negligible. Self-feeding by adult procellariiforms
is thus a key issue to understand allocation processes but it is still poorly known. We tested these predictions by using
the stable isotope (δ15N and δ13C) technique on birds’ plasma and prey with the short-tailed shearwater Puffinus tenuirostris breeding at Tasmania as a model. Parent shearwaters returning to the colony after a LT have an Antarctic/subantarctic δ13C signature in their plasma (−23.8‰), thus indicating that they fed in cold waters, far away from their breeding colony, for
their own maintenance. Parent birds returning to the colony after a ST also have a distant Antarctic/subantarctic δ13C signature in their plasma (−24.3‰), thus verifying that self-feeding is negligible during ST and that birds fast at that
time, using energy stores built up in cold waters. Plasma δ15N values of adults (8.8‰) indicates they mainly prey upon zooplankton-eating organisms, probably mesopelagic myctophid fishes.
A simple isotopic mixing model estimates that they consume by mass 87% myctophids and 13% subantarctic krill when self-feeding.
Finally and as expected, the carbon isotopic signature of chick plasma (−22.2‰) was intermediate between those of high- and
low-latitude marine organisms and is thus in agreement with chicks being fed with a large diversity of prey species caught
by adult birds from Antarctic to Tasmanian waters. One main consequence of this system is that reproduction of a Tasmanian
species is controlled by resources available at great distances from the breeding colony that drive allocation decisions of
parent birds. 相似文献
6.
Effects of nutritional restriction on nitrogen and carbon stable isotopes in growing seabirds 总被引:4,自引:0,他引:4
When using stable isotopes as dietary tracers it is essential to consider effects of nutritional state on isotopic fractionation.
While starvation is known to induce enrichment of 15N in body tissues, effects of moderate food restriction on isotope signatures have rarely been tested. We conducted two experiments
to investigate effects of a 50–55% reduction in food intake on δ15N and δ13C values in blood cells and whole blood of tufted puffin chicks, a species that exhibits a variety of adaptive responses to
nutritional deficits. We found that blood from puffin chicks fed ad libitum became enriched in 15N and 13C compared to food-restricted chicks. Our results show that 15N enrichment is not always associated with food deprivation and argue effects of growth on diet–tissue fractionation of nitrogen
stable isotopes (Δ15N) need to be considered in stable isotope studies. The decrease in δ13C of whole blood and blood cells in restricted birds is likely due to incorporation of carbon from 13C-depleted lipids into proteins. Effects of nutritional restriction on δ15N and δ13C values were relatively small in both experiments (δ15N: 0.77 and 0.41‰, δ13C: 0.20 and 0.25‰) compared to effects of ecological processes, indicating physiological effects do not preclude the use of
carbon and nitrogen stable isotopes in studies of seabird ecology. Nevertheless, our results demonstrate that physiological
processes affect nitrogen and carbon stable isotopes in growing birds and we caution isotope ecologists to consider these
effects to avoid drawing spurious conclusions. 相似文献
7.
Establishing the ecological role of predators within an ecosystem is central to understanding community dynamics and is useful
in designing effective management and conservation strategies. We analysed differences in the trophic ecology of four species
of reef sharks (Carcharhinus melanopterus, Carcharhinus amblyrhynchos, Triaenodon obesus and Negaprion acutidens) at Ningaloo Reef, Western Australia, by analysing tissue stable isotopes (δ15N and δ13C). We also monitored animals using acoustic telemetry to determine long-term residency patterns in a bay at the southern
end of the reef, Coral Bay. Overall, mean δ13C was similar among species, ranging between −10.9 and −11.8‰, suggesting a food-web dependency on coastal producers. Classification
and regression tree analysis identified an effect of species on δ15N that separated C. amblyrhynchos and C. melanopterus from N. acutidens and T. obesus. For C. amblyrhynchos and C. melanopterus, animals were also divided by size classes, with smaller sharks having lower average δ15N than larger animals; this suggests that δ15N increases with size for these two species. Juvenile C. melanopterus, juvenile N. acutidens and adult T. obesus had trophic levels of 3.7, for juvenile C. amblyrhynchos and adult C. melanopterus it was 4, and adult C. amblyrhynchos had a value of 4.3. Trophic-level estimates for C. melanopterus and C. amblyrhynchos corroborate previous conclusions based on diet studies. We found no evidence for a difference in isotopic composition between
resident and non-resident sharks. The lack of variation in isotopic composition was consistent with high mean residency of
these species recorded using acoustic telemetry, which was 79% (±0.09 SE) of days monitored for T. obesus, followed by N. acutidens (57 ± 19.55%), C. amblyrhynchos (54 ± 13%) and C. melanopterus (33 ± 8.28%). High δ13C composition in reef sharks and long-term residency behaviour suggest that coastal marine reserves might provide effective
conservation refuges for some species. 相似文献
8.
S. I. Kiyashko T. A. Velivetskaya A. V. Ignatiev 《Russian Journal of Marine Biology》2011,37(4):297-302
Stable isotope ratios of sulfur (34S/32S), carbon (13C/12C), and nitrogen (15N/14N) were analyzed in the soft tissues of 12 common species of fish from the near-shore waters of the Peter the Great Bay in
the Sea of Japan. The average δ13C values of individual species varied from −20.7‰ for planktivorous fish to −16.8‰ for benthivorous fish, reflecting the growing
relative contribution of benthic primary producers to fish nutrition. The majority of the various species representatives
studied can be assigned to one trophic level, as indicated by their narrow range of δ15N values (9.9 to 12.6‰). Large interspecific variations were found in the sulfur stable isotope ratios of fish (the mean δ34S values ranged from 11.2 to 19.5‰). This is the result of the different contributions to fish nutrition of infaunal invertebrates
that are depleted in 34S due to the microbial food chain of the bottom sediments. 相似文献
9.
We provide preliminary carbon (δ13C) and nitrogen (δ15N) stable isotope assessment of the Greenland halibut (Reinhardtius hippoglossoides) diet in Cumberland Sound, with focus on two possible prey sources: pelagic represented by capelin (Mallotus villosus) and epibenthic represented by shrimp (Lebbeus polaris). The δ13C for the Greenland halibut stock indicated a pelagic carbon source in Cumberland Sound while stable isotope mixing models,
IsoSource and MixSIR, indicated a 99% dietary composition of capelin relative to the shrimp. The δ15N did not vary across Greenland halibut size ranges and placed them at a fourth trophic position relative to a primary herbivore.
This study provides the starting point for more elaborate Cumberland Sound research on the local Greenland halibut feeding
ecology by confirming pelagic feeding and establishing relative trophic position as well as identifying stable isotopes as
a useful tool for the study of diet in cold water fish species. 相似文献
10.
As apex predators, sharks play an important role shaping their respective marine communities through predation and associated risk effects. Understanding the predatory dynamics of sharks within communities is, therefore, necessary to establish effective ecologically based conservation strategies. We employed non-lethal sampling methods to investigate the feeding ecology of bull sharks (Carcharhinus leucas) using stable isotope analysis within a subtropical marine community in the southwest Indian Ocean. The main objectives of this study were to investigate and compare the predatory role that sub-adult and adult bull sharks play within a top predatory teleost fish community. Bull sharks had significantly broader niche widths compared to top predatory teleost assemblages with a wide and relatively enriched range of δ13C values relative to the local marine community. This suggests that bull sharks forage from a more diverse range of δ13C sources over a wider geographical range than the predatory teleost community. Adult bull sharks appeared to exhibit a shift towards consistently higher trophic level prey from an expanded foraging range compared to sub-adults, possibly due to increased mobility linked with size. Although predatory teleost fish are also capable of substantial migrations, bull sharks may have the ability to exploit a more diverse range of habitats and appeared to prey on a wider diversity of larger prey. This suggests that bull sharks play an important predatory role within their respective marine communities and adult sharks in particular may shape and link ecological processes of a variety of marine communities over a broad range. 相似文献
11.
Asunción Borrell Alex Aguilar Manel Gazo R. P. Kumarran Luis Cardona 《Environmental Biology of Fishes》2011,92(4):559-567
We investigated the sex- and size-related differences in the diet of whale sharks from the Arabian Sea (north-western Indian
Ocean) using carbon and nitrogen stable-isotope analyses in white muscle. The samples were collected during the commercial
fishing season between April and May of 2001 in Veraval (Gujarat, India). The overall isotope signature was similar to that
of the pelagic-neritic zooplanktivore Ilisha melastoma, which suggests that both species are feeding on similar prey. In whale sharks, a positive relationship was found between
δ15N and δ13C. This, together with a significant enrichment of both heavy stable isotopes with total length indicates that the contribution
to the diet of small fish and/or larger zooplankton of higher trophic level increases with the movement from offshore areas
to coastal areas as they grow. Gender differences in the isotopic ratios were not statistically significant, but small sample
size cannot rule out completely the existence of some degree of spatial or dietary segregation between sexes. 相似文献
12.
Contributions of stable-isotope data to elucidating food webs of Mediterranean rocky littoral fishes 总被引:18,自引:0,他引:18
The food webs of rocky infra-littoral ecosystems in the Mediterranean have been little studied. In this investigation stable
isotopes and dietary data were compared in an attempt to describe features of the food webs concerned. δ13C and δ15N were determined for plants, invertebrates and fishes from the Bay of Calvi, Corsica. Dietary data were derived from the
literature. δ13C of plants ranged from –8.59‰ to –33.74‰, of benthic invertebrates from –17.0‰ to –20.52‰, of planktonic invertebrates from
–20.08‰ to –22.34‰ and of fishes from –16.27‰ to –19.59‰. δ15N was generally greater at higher trophic levels. δ15N of plants was 0.95–2.92‰, of benthic invertebrates 1.69–6.54‰, of planktonic invertebrates 3.51–6.82‰ and of fishes 4.63–9.77‰.
13C enrichment tended to be associated with benthic food chains and 13C depletion with planktonic chains. Stable-isotope data suggested more varied diets for many species than implied by gut-contents
data. Omnivory and trophic plasticity were widespread, and many consumers fed lower down the food chain than previous studies
had suggested. Both stable-isotope and gut-contents analysis resolved differences between fishes feeding on planktonic and
benthic prey and indicated that the herbivorous fish Sarpa salpa fed on a diet substantially different from that of other fishes. Zooplankton were important in the diets of several consumers
(both primary and secondary), as was plankton derived detritus. One species of fish previously identified as planktivorous
was shown to feed largely on benthic organisms, whilst several species of benthic invertebrates may feed on plankton-derived
detritus. Although herbivores seemed to obtain most of their C from macroalgae, δ15N data suggested that many of these animals supplemented their intake of N, although gut-contents analysis did not provide
evidence for such uptake. The isotopic data have elucidated several features of the food web which we would not otherwise
have detected.
Received: 26 April 1999 / Accepted: 24 September 1999 相似文献
13.
Edna De la Llata Quiroga Randall Arauz Arturo Tripp Valdez Laura Porras Murillo Manuel Spinola Parallada Ricardo Sánchez-Murillo Elpis J. Chávez 《Journal of fish biology》2023,102(3):669-679
Bull shark (Carcharhinus leucas) is a near-threatened elasmobranch species capable of moving between the fresh and salty waters of tropical and subtropical coastal areas, for which we still lack important ecological information. During their first years of life, bull sharks use estuarine systems as nursery areas, making them highly susceptible to environmental and anthropogenic pressures. We studied the trophic ecology of juveniles found in the Coyote estuary, a potential nursery area in Costa Rica, to understand the potential impact of further bull shark declines and gain knowledge that could aid in their conservation. We analysed the trophic ecology of juvenile bull sharks [81–103 cm total length (TL)] in the Coyote estuary, Costa Rica, using stable isotopes of δ15N and δ13C. Since one problem using this technique in juveniles is the confounding effect of the maternal signature, we sampled different tissues (muscle and plasma), verified the status of the shark's umbilical scar and identified the size at which the isotope signature is a result of the animal's current diet. The isotopic values of the muscle tissue reflected the maternal isotopic signature. In contrast, plasma values reflected the diet of juvenile bull sharks >95 cm TL and with a closed umbilical scar. Juvenile bull sharks fed primarily on teleost fishes of the order Anguilliformes and Siluriformes, and have a high trophic position (≥4.0) in the Coyote estuary. Our findings suggest that this estuary is an important feeding site for juvenile bull sharks of the Pacific of Costa Rica. Thus, the protection of essential habitats such as the Coyote estuary will benefit not only bull shark conservation, but also the conservation of an array of fish species that also use this habitat as a rookery, many of which are of commercial interest. 相似文献
14.
Feeding ecology of phocid seals and some walrus in the Alaskan and Canadian Arctic as determined by stomach contents and stable isotope analysis 总被引:1,自引:0,他引:1
Larissa-A. Dehn Gay G. Sheffield Erich H. Follmann Lawrence K. Duffy Dana L. Thomas Todd M. O’Hara 《Polar Biology》2007,30(2):167-181
Feeding habits of ringed (Phoca hispida), bearded (Erignathus barbatus), spotted (Phoca largha) and ribbon (Phoca fasciata) seals and walrus (Odobenus rosmarus) were studied using stomach contents and stable carbon and nitrogen isotopes. Bearded seals fed benthically, primarily crustaceans and mollusks. Both zooplankton and fish were significant prey for ringed seals, while fish was principal spotted seal prey. Few gastric contents were available from ribbon seals. δ15N was positively correlated with age in ribbon seals and δ13C was positively correlated with age in ringed and ribbon seals. δ15N was highest in spotted seals, in agreement with their fish-dominated diet. δ15N was not different between Alaskan-harvested ringed and bearded seals, while δ15N was lowest in ribbon seals and walrus. Carbon-13 was most enriched in bearded seals and walrus reflecting benthic ecosystem use. Canadian ringed seals were depleted in 13C compared to Alaskan pinnipeds, likely because of Beaufort Sea versus Chukchi and Bering seas influence. 相似文献
15.
Jari Syv?ranta Aurélia Martino Dorothée Kopp Régis Céréghino Frédéric Santoul 《Hydrobiologia》2011,658(1):383-388
We tested the impacts of most common sample preservation methods used for aquatic sample materials on the stable isotope ratios
of carbon and nitrogen in clams, a typical baseline indicator organism for many aquatic food web studies utilising stable
isotope analysis (SIA). In addition to common chemical preservatives ethanol and formalin, we also assessed the potential
impacts of freezing on δ13C and δ15N values and compared the preserved samples against freshly dried and analysed samples. All preservation methods, including
freezing, had significant impacts on δ13C and δ15N values and the effects in general were greater on the carbon isotope values (1.3–2.2‰ difference) than on the nitrogen isotope
values (0.9–1.0‰ difference). However, the impacts produced by the preservation were rather consistent within each method
during the whole 1 year experiment allowing these to be accounted for, if clams are intended for use in retrospective stable
isotope studies. 相似文献
16.
K. M. Gorbatenko S. I. Kiyashko A. Ye. Lazhentsev V. A. Nadtochii A. B. Savin 《Russian Journal of Marine Biology》2008,34(7):497-506
The composition, abundance, diet and trophic status of zooplankton, bottom invertebrates, fish and nekton were analyzed based
on the data collected by the staff of the TINRO-Center during complex bottom trawl catches on the Bering Sea shelf in the
fall of 2004. The stomach contents of mass fish species were analyzed and the nitrogen and carbon isotopic composition of
36 mass species of plankton, benthos, nekton and nektobenthos, which together make up the basis of pelagic and bottom communities,
was determined. It was found that zooplankton noticeably differ from benthic invertebrates in carbon isotopic composition:
δ13C values in zooplankton varied from −20.3‰ to −17.9‰; in benthos—from −17.5‰to −13.0‰; and in fish—from −19.2‰ (juvenile walleye
pollock) to −15.3‰ (saffron cod). The levels of 13C isotope in the tissues of fish depended mostly on the share of pelagic or benthic animals in their diet. δ15N values in the studied species ranged from 8.6‰ (in sea urchins) to 17.2‰ (in large Pacific cods), which corresponds to a
trophic level of 2.8. Obviously the δ15N values reflect the degree of predation and generally show the ratio of primary, secondary and tertiary consumers in a fish’s
diet. Trophic interactions manifest a high degree of interdependence between benthic and pelagic communities (even without
taking into account such lower components of the food web as phytoplankton, bacteria, and protozoa) occurring in most nektonic
species that depend on both bottom and pelagic food. 相似文献
17.
Sediment organic matter (OM) and its stable carbon and nitrogen isotopes were studied in 12 Slovenian mountain lakes in the
Julian Alps. The lakes have different catchment areas and display a range of trophic states. Surface sediment atomic C/N ratios
ranged from 8.4 to 13.2. Based on these C/N ratios, we concluded that autochthonous OM dominates in these lakes and constitutes
approximately 65–92% of the total OM. Higher contributions of autochthonous OM sources were observed in lakes above the tree
line. Relatively constant C/N ratios in the deeper sediments suggest that degradation processes are most intense in the upper
few centimetres of the sediments and/or that remaining OM is relatively resistant to further degradation. Surface sediment
δ13C and δ15N values ranged from −36.1 to −14.1‰ and from −5.2 to +1.1‰, respectively. In sediment cores from seven lakes, higher δ13C and lower δ15N values characterize oligotrophic lakes situated above the tree line, whereas the reverse is true for eutrophic lakes below
the tree line that are also exposed to more anthropogenic impact. Carbon and nitrogen biogeochemical cycling differs considerably
among the lakes. Stratigraphic shifts in carbon, total nitrogen, C/N ratios and stable C and N isotopes in cores record changes
in inputs, and hence water column processes, as well as alterations in loading to the lakes. The stratigraphic variations
are also the result of post-depositional diagenetic changes in the upper few centimetres of sediment. All the lakes show impacts
from recent increases in atmospheric deposition of dissolved inorganic nitrogen. Application of sediment OM analysis thus
proved to be useful to reconstruct paleoecological changes in sensitive mountain lake ecosystems that are either natural and/or
anthropogenically derived. 相似文献
18.
Benthic biofilms have been identified using stable isotope analysis (SIA) as an important resource supporting many freshwater
food webs. However, biofilm δ13C signatures are highly variable in freshwaters, which may hamper our understanding of energy flow through food webs in these
systems. There has been little consideration of the influence that substratum may have on biofilm δ13C signature variability and energy flows to primary consumers. We investigated the effect of organic and inorganic substrata
on biofilm dynamics by examining: (1) temporal variability of biofilm stable isotope (δ13C, δ15N) signatures on allochthonous leaf-litter (Eucalyptus camaldulensis) and cobble substrata over 12 months in a lowland river in south-eastern Australia; and (2) the effect of substrata on biofilm
energy flows to a grazer snail, Physa acuta (Gastropoda: Physidae), using SIA and ecological stoichiometry in a laboratory experiment. The temporal study indicated that
cobble biofilm varied significantly in δ13C signature during the 12 months (up to 11‰), whereas the δ13C signature of leaf biofilm was less variable (less than 2‰). In contrast, biofilm δ15N signatures varied temporally on both cobble (2.6‰) and leaf (1‰) substrata. This suggests that leaf biofilm was more reliant
on leaf tissue for carbon and therefore less limited by carbon supply than cobble biofilm whereas for nitrogen biofilm on
both substrata was reliant on external sources. In the laboratory experiment, snails fed leaf biofilm reflected more of an
allochthonous δ13C signature than cobble biofilm fed snails, suggesting assimilation of leaf carbon via the heterotrophic microbial community
within the biofilm. Snails grew largest on cobble biofilm, which had lower C:N ratios than leaf biofilm. Our results demonstrate
that the type of substratum can influence the temporal variability of biofilm δ13C signatures and energy flow to primary consumers. 相似文献
19.
Quantifying pathways of energy transfer between plants, pests, and beneficial insects is a necessary step toward maintaining
pest stable agroecosystems in the absence of chemical subsidies. A diet switching experiment utilizing a predatory ladybird
beetle, Hippodamia variegata (Goeze), evaluated the use of naturally occurring stable C and N isotopes as an economically feasible and safe method for
quantifying pathways of energy flow within agroecosystems. Stable isotope values of the ladybird beetle Coleomegilla maculata lengi (Timberlake) collected from an agroecosystem were used to estimate the relative amount of C and N derived from agricultural
plants and incorporated by ladybird beetles based on mass balance equations. At the beginning of the diet-switching experiment
δ13C and δ15N values of H. variegata (–12.0‰ and 6.3‰, respectively) differed by –0.2‰ and 2.9‰ from the aphids that were provided exclusively as their diet. These
data are consistent with previous estimates of trophic level isotope effects. After switching the diet of H.
variegata to an alternative food, isotope values of H. variegata gradually shifted toward expected values for individuals fed this diet (–22.9‰ and 8.8‰ for δ13C and δ15N values, respectively). Isotope values of another ladybird beetle, C. maculata, collected from the field indicated that in May, alfalfa and maize (pollen) obtained in the previous year contributed 32%
and 68% of the C or N to the diets of these individuals and in August, 52%, 6%, and 42% of the C or N assimilated by these
insects was derived from alfalfa, wheat, and maize, respectively. These data are consistent with expectations based on the
relative abundance of C. maculata in various crops during the season. The field and laboratory data are a clear indication that isotope values are sensitive
to dietary changes on a relatively short time scale (days) and provide a strong basis for the use stable C and N isotope to
trace energy flow patterns of these beneficial organisms within agroecosystems.
Received: 17 November 1995 / Accepted: 20 June 1996 相似文献
20.
Thorsten E. E. Grams Herbert Werner Daniel Kuptz Wilma Ritter Frank Fleischmann Christian P. Andersen Rainer Matyssek 《Trees - Structure and Function》2011,25(2):187-198
Stable carbon (C) isotopes, in particular employed in labeling experiments, are an ideal tool to broaden our understanding
of C dynamics in trees and forest ecosystems. Here, we present a free-air exposure system, named isoFACE, designed for long-term
stable C isotope labeling in the canopy of 25 m tall forest trees. Labeling of canopy air was achieved by continuous release
of CO2 with a δ13C of −46.9‰. To this end, micro-porous tubes were suspended at c. 1 m distance vertically through the canopy, minimizing CO2 gradients from the exterior to the interior and allowing for C labeling exposure during periods of low wind speed. Target
for CO2 concentration ([CO2]) increase was ambient +100 μmol mol−1. Canopy [CO2] stayed within 10% of the target during more than 57% of the time and resulted in a drop of δ13C in canopy air by 7.8‰. After 19 labeling days about 50% of C in phloem sugars and stem CO2 efflux were turned over and 20–30% in coarse root CO2 efflux and soil CO2. The isoFACE system successfully altered δ13C of canopy air for studying turn-over of C pools in forest trees and soils, highlighting their slow turn-over rates. 相似文献