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1.
Stable carbon- (δ13C), nitrogen- (δ15N) and hydrogen (δD) isotope profiles in feathers of migratory Great Reed Warblers Acrocephalus
arundinaceus recaptured for 2 or more years in 6 successive years were examined to test whether the isotope profiles of individual warblers
appeared to be consistent between years. Similar isotopic signatures in successive years suggested that individual birds tended
to return and grow their feathers in Afro-tropical wintering habitats that generate similar δ13C, δ15N and δD signatures. Previous studies have shown that Great Reed Warblers exhibit strong natal and breeding philopatry, with
most of the surviving birds returning to the breeding site. The present study of feather δ13C, δ15N and δD isotopic values demonstrate the year-to-year fidelity might also include the African moulting sites in this migratory
species. 相似文献
2.
It is widely accepted that stable isotope ratios in inert tissues such as feather keratin reflect the dietary isotopic signature
at the time of the tissue synthesis. However, some elements such as stable nitrogen isotopes can be affected by individual
physiological state and nutritional stress. Using malaria infection experiment protocols, we estimated the possible effect
of malaria parasite infections on feather carbon (δ13C) and nitrogen (δ15N) isotope signatures in juvenile common crossbills Loxia curvirostra. The birds were experimentally infected with Plasmodium relictum (lineage SGS1) and P. ashfordi (GRW2), two widespread parasites of passerines. Experimental birds developed heavy parasitemia of both parasites and maintained
high levels throughout the experiment (33 days). We found no significant difference between experimental and control birds
in both δ13C and δ15N values of feathers re-grown. The study shows that even heavy primary infections of malaria parasites do not affect feather
δ13C and δ15N isotopic signatures. The results of this experiment demonstrate that feather isotope values of wild-caught birds accurately
reflect the dietary isotopic sources at the time of tissue synthesis even when the animal’s immune system might be challenged
due to parasitic infection. 相似文献
3.
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
4.
Using the aquatic macrophyte <Emphasis Type="Italic">Vallisneria americana</Emphasis> (wild celery) as a nutrient bioindicator 总被引:1,自引:0,他引:1
Human sewage and septic waste are significant sources of nutrient loading to many aquatic ecosystems. Ecologically relevant
nitrogen sources can be traced by analyzing nitrogen stable isotope ratios (δ15N signatures) in aquatic plants. Elevated δ15N signatures can suggest increased uptake of nitrogen derived from human and/or animal waste. In the current study, Vallisneria americana, a freshwater angiosperm, was collected from several locations in Upper Saranac Lake, NY, USA. Samples were also collected
from Lake George, NY and the Sassafras River, MD, USA. Plant material was analyzed for δ15N and % N; some samples were also analyzed for δ13C, % C, and % P. Results suggest that there is variation in septic inputs to Upper Saranac Lake, with some areas of the lake
receiving more input than others. Results also show that increased watershed population density is correlated with elevated
δ15N signatures of Vallisneria americana. Taken together, these results suggest that nitrogen stable isotope analysis of aquatic plant tissue is an effective method
for assessing and monitoring septic inputs to freshwater ecosystems. 相似文献
5.
Since 2006, the known distribution of Hemimysis anomala has greatly expanded in the Great Lakes ecosystem, with, to date, 45 sites of occurrence among 91 monitored sites, located
in four of the Great Lakes and the upper St. Lawrence River. By means of carbon and nitrogen stable isotopes, a first assessment
of the feeding ecology of Hemimysis was completed. The δ13C values of 18 individuals collected in Lake Erie (Port Mainland) on a single date (Sept. 23, 2008) ranged from −30.2 to −24.5‰,
indicating that Hemimysis could feed on multiple carbon sources including pelagic and littoral autochthonous and terrestrial carbon. In Lake Erie,
variation in δ13C was related to δ15N, indicating the importance of food source for determining the trophic position of Hemimysis. The δ15N signatures of individuals were strongly related to their C/N ratios, suggesting that variations in the nutritional value
of Hemimysis may depend on trophic position. Isotopic variation among individuals in Lake Erie was complemented by temporal variation
in Lake Ontario. Monthly changes (from June to December 2008) in carbon isotope signatures were observed and related to changes
in water temperature, highlighting the variations in the baseline prey signatures that fuel Hemimysis diets. The observed variation in stable isotope signatures occurring among individuals within a localized Hemimysis assemblage and temporally should be considered as a key design feature in further studies attempting to identify the possible
effects of Hemimysis on nearshore food webs in the Great Lakes. 相似文献
6.
Stable isotope signatures of freshwater snails and mussels have been established as a convenient baseline measurement at the
primary consumer level for food-web coupling studies. We measured δ15N and δ13C of primary consumers, including mussels (Anodonta woodiana, Cristaria plicata, and Unio douglasiae), snails (Bellamya aeruginosa and Hippeutis sp.), and zooplankton from the same habitat within a shallow eutrophic lake. Primary consumers showed positive relationship
between δ15N and δ13C, indicating a linkage between planktonic and benthic habitats in this system. The variation in isotope ratios was higher
in short-lived primary consumers (zooplankton) compared with the long-lived primary consumers (mussels and snails), suggesting
limited availability of short-lived primary consumers as isotopic baselines in aquatic food-web assessment. Significant differences
in isotope ratios were also found among three species of mussels, and when using these mussels separately as pelagic baselines
to calculate trophic position and contribution of planktonic and benthic sources of fishes, bias and even misestimates were
observed. This finding suggests that caution is needed when multiple primary consumers coexist in the same habitat, and it
is important to assess potential effects of different baselines used. 相似文献
7.
Stable isotope signatures of primary producers display high inter- and intraspecific variation. This is assigned to species-specific
differences in isotope fractionation and variable abiotic conditions, e.g., temperature, and nutrient and light availability.
As consumers reflect the isotopic signature of their food source, such variations have direct impacts on the ecological interpretation
of stable isotope data. To elucidate the variability of isotope fractionation at the primary producer level and the transfer
of the signal through food webs, we used a standardised marine tri-trophic system in which the primary producers were manipulated
while the two consumer levels were kept constant. These manipulations were (1) different algal species grown under identical
conditions to address interspecific variability and (2) a single algal species cultivated under different nutrient regimes
to address nutrient-dependent variability. Our experiments resulted in strong interspecific variation between different algal
species (Thalassiosira weissflogii, Dunaliella salina, and Rhodomonas salina) and nutrient-dependent shifts in stable isotope signatures in response to nutrient limitation of R. salina. The trophic enrichment in 15N and 13C of primary and secondary consumers (nauplii of Acartia tonsa and larval herring) showed strong deviations from the postulated degree of 1.0‰ enrichment in δ13C and 3.4‰ enrichment in δ15N. Surprisingly, nauplii of A. tonsa tended to keep “isotopic homeostasis” in terms of δ15N, a pattern not described in the literature so far. Our results suggest that the diets’ nutritional composition and food
quality as well as the stoichiometric needs of consumers significantly affect the degree of trophic enrichment and that these
mechanisms must be considered in ecological studies, especially when lower trophic levels, where variability is highest, are
concerned. 相似文献
8.
The aim of the present study was to identify food sources of bark-living oribatid mites to investigate if trophic niche differentiation
contributes to the diversity of bark living Oribatida. We measured the natural variation in stable isotope ratios (15N/14N, 13C/12C) in oribatid mites from the bark of oak (Quercus robur), beech (Fagus sylvatica), spruce (Picea abies) and pine (Pinus sylvestris) trees and their potential food sources, i.e., the covering vegetation of the bark (bryophytes, lichens, algae, fungi). As
a baseline for calibration the stable isotope signatures of the bark of the four tree species were measured and set to zero.
Oribatid mite stable isotope ratios spanned over a range of about 13 δ units for 15N and about 7 δ units for 13C suggesting that they span over about three trophic levels. Different stable isotope signatures indicate that bark living
oribatid mites feed on different food sources, i.e., occupy distinct trophic niches. After calibration stable isotope signatures
of respective oribatid mite species of the four tree species were similar indicating close association of oribatid mites with
the corticolous cover as food source. Overall, the results support the hypothesis that trophic niche differentiation of bark
living oribatid mites contributes to the high diversity of the group. 相似文献
9.
Despite the recognition of the functional role of Hymenoptera (ants, bees and wasps) and Isoptera (termites) in tropical ecosystems,
their detailed feeding habits are not well known. To examine the feeding habits of these groups, we measured nitrogen (N)
and carbon (C) stable isotope ratios (δ15N and δ13C) of hymenopterans (12 families, ≥16 genera and ≥32 species) and isopterans (one family and 10 species) collected in a tropical
rain forest, Sarawak, Malaysia. We compared the isotopic signatures of these insects to those previously reported for other
consumers collected in the same forest. The δ15N and δ13C values of these insects overlapped with those of the other consumers, indicating that they have access to diverse C and
N sources in the forest. The δ15N values of ants and termites indicated that their feeding habits range along a continuum from herbivory (i.e. dependent on
honeydew and nectar) to predation and from wood-feeders to soil-feeders, respectively. In addition, the δ15N values of wasps varied greatly from −0.1‰ (Braconidae sp.) to 8.6‰ (Bembix sp.), suggesting that their feeding habits also range from omnivory to predation. The ant species Camponotus gigas had δ13C values similar to those of invertebrate detritivores and omnivores rather than to those of invertebrate herbivores, although
the diet of this species consists mostly of honeydew. This discrepancy suggests that the ant uses carbohydrates as an energy
source, the isotopic signatures of which are not well retained in the body tissues. Values of both δ15N and δ13C of the predatory army ant Leptogenys diminuta and the soil-feeding termite Dicuspiditermes nemorosus did not differ significantly, indicating that both trophic level and the humification of feeding substrates can increase
the isotopic signatures of terrestrial consumers. 相似文献
10.
Investigations into trophic ecology and aquatic food web resolution are increasingly accomplished through stable isotope analysis.
The incorporation of dietary and metabolic changes over time results in variations in isotope signatures and turnover rates
of producers and consumers at tissue, individual, population and species levels. Consequently, the elucidation of trophic
relationships in aquatic systems depends on establishing standard isotope values and tissue turnover rates for the level in
question. This study investigated the effect of diet and food quality on isotopic signatures of four mussel tissues: adductor
muscle, gonad, gill and mantle tissue from the brown mussel Perna perna. In the laboratory, mussels were fed one of the two isotopically distinct diets for 3 months. Although not all results were
significant, overall δ13C ratios in adductor, mantle and gill tissues gradually approached food source signatures in both diets. PERMANOVA analyses
revealed significant changes over time in tissue δ13C (mantle and gill) with both diets and in δ15N (all tissues) and C:N ratios (mantle and gill) for one diet only. The percentage of replaced carbon isotopes were calculated
for the 3 month period and differed among tissues and between diets. The tissue with the highest and lowest amount of replaced
isotopes over 81 days were mantle tissue on the kelp diet (33.89%) and adductor tissue on the fish food diet (4.14%), respectively.
Percentages could not be calculated for any tissue in either diet for δ15N due to the lack of significant change in tissue nitrogen. Fractionation patterns in tissues for both diets can be linked
to nutritional stress, suggesting that consumer isotopic signatures are strongly dependent on food quality, which can significantly
affect the degree of isotopic enrichment within a trophic level. 相似文献
11.
Seasonal oscillations in the carbon (δ13C) and nitrogen (δ15N) isotope signatures of aquatic algae can cause seasonal enrichment–depletion cycles in the isotopic composition of planktonic
invertebrates (e.g., copepods). Yet, there is growing evidence that seasonal enrichment–depletion cycles also occur in the
isotope signatures of larger invertebrate consumers, taxa used to define reference points in isotope-based trophic models
(e.g., trophic baselines). To evaluate the general assumption of temporal stability in non-zooplankton aquatic invertebrates,
δ13C and δ15N time series data from the literature were analyzed for seasonality and the influence of biotic (feeding group) and abiotic
(trophic state, climate regime) factors on isotope temporal patterns. The amplitude of δ13C and δ15N enrichment–depletion cycles was negatively related to body size, although all size-classes of invertebrates displayed a
winter-to-summer enrichment in δ13C and depletion in δ15N. Among feeding groups, periphytic grazers were more variable and displayed larger temporal changes in δ13C than detritivores. For nitrogen, temporal variability and magnitude of directional change of δ15N was most strongly related to ecosystem trophic state (eutrophic > mesotrophic, oligotrophic). This study provides evidence
of seasonality in the isotopic composition of aquatic invertebrates across very broad geographical and ecological gradients
as well as identifying factors that are likely to modulate the strength and variability of seasonality. These results emphasize
the need for researchers to recognize the likelihood of temporal changes in non-zooplankton aquatic invertebrate consumers
at time scales relevant to seasonal studies and, if present, to account for temporal dynamics in isotope trophic models. 相似文献
12.
K. Fiedler F. Kuhlmann B. C. Schlick-Steiner F. M. Steiner G. Gebauer 《Insectes Sociaux》2007,54(4):393-402
Studies employing stable isotope technology have greatly contributed to understanding trophic relationships of tropical ants,
but temperate-zone ants remain under-explored. We studied δ15N values of 43 ant species from three subfamilies sampled across central Europe. After statistically accounting for the effects
of elevation and geographical location of habitats, which alter the isotopic composition of nitrogen in ecosystems, significant
patterns in N-isotope signatures were detected. These signatures hint at differences across ants in the contribution of plant-derived
nitrogen obtained via trophobiosis and nectarivory relative to nitrogen obtained via predation and scavenging. In general,
Myrmicinae had higher δ15N values than Formicinae, in line with a greater relative importance of trophobiosis in the latter. The genus Myrmica scored especially high, indicating predominantly predacious nitrogen sources. Remarkably, also the granivore Messor cf. structor had high δ15N values. This suggests that, despite the major portion of food uptake being made up by plant seeds, this ant could derive
substantial fractions of its nitrogen budget from feeding on arthropod corpses or vertebrate faeces. Moreover, this highlights
that deductions from observed quantities of ingested food on its relative contribution to ants’ matter balance should be accompanied
by isotope analyses. At the other end of the spectrum, Camponotus and Plagiolepis had low δ15N values. In line with multiple field observations, this suggests a contribution of trophobiosis not only to their energy,
but also to their nitrogen budget. Formica and Lasius had intermediate 15N values, which is in agreement with the current view that these ants have mixed diets with a balance between trophobiosis
and predation. A possible influence of endosymbiotic bacteria on the isotope signatures of several genera is discussed. This
study provides a first application of stable isotope technology to estimate the role of plant-derived nutrients to the nitrogen
budget of a larger range of central European ants. Furthermore, it shows that N-isotope analysis is applicable across extended
ecological and geographical gradients. Future studies along this line are promising to complement our current understanding
of the nutritional ecology of temperate-zone ants.
Received 20 March 2007; revised 17 June and 24 August; accepted 11 September 2007. 相似文献
13.
Variations in crop grain and soil N isotope composition (δ15N) in relation to liquid hog manure (δ15N of total N was +5.1‰), solid cattle manure (+7.9‰) and chemical fertilizer (+0.7‰ for urea and −1.9‰ for ammonium phosphate)
applications, and control (no fertilizer application) were examined through a 4-year crop rotation under field conditions.
Canola (Brassica napus), hull-less barley (Hordeum vulgare), wheat (Triticum aestivum), and canola were grown sequentially from 2000 (year 1) to 2003 (year 4). From year 2, hog manure or chemical fertilizers,
but not cattle manure, treatments increased grain N concentrations over the control. Grain δ15N (+0.3 to +2.5‰) of crops applied with chemical fertilizers was lower than those in the other treatments, reflecting the
effects of the N source with a lower δ15N, while the manure treatments tended to increase grain δ15N. The higher grain δ15N of crops applied with hog manure (+5.6 to +8.4‰) than those applied with cattle manure (+2.2 to +4.1‰) reflected the higher
N availability of liquid hog manure (up to 70% as NH
4
+
) than solid cattle manure (99% organic N) and higher potentials for ammonia volatilization loss in hog manure rather than
differences in manure δ15N signatures. Soil total- and extractable-N concentrations and δ15N tended to vary with the application of N sources with different N isotope composition and availability. Our study expanded
the application of the δ15N technique for detecting N source (organic vs chemical) effects on N isotopic composition to field conditions and across
a 4-year rotation, and revealed that N availability played a greater role than the δ15N signature of N sources in determining crop δ15N under the studied conditions.
Section Editor: H. Lambers 相似文献
14.
Correlations between foliar δ15N and nitrogen concentrations may indicate plant-mycorrhizal interactions 总被引:1,自引:0,他引:1
Nitrogen isotope measurements may provide insights into changing interactions among plants, mycorrhizal fungi, and soil processes
across environmental gradients. Here, we report changes in δ15N signatures due to shifts in species composition and nitrogen (N) dynamics. These changes were assessed by measuring fine
root biomass, net N mineralization, and N concentrations and δ15N of foliage, fine roots, soil, and mineral N across six sites representing different post-deglaciation ages at Glacier Bay,
Alaska. Foliar δ15N varied widely, between 0 and –2‰ for nitrogen-fixing species, between 0 and –7‰ for deciduous non-fixing species, and between
0 and –11‰ for coniferous species. Relatively constant δ15N values for ammonium and generally low levels of soil nitrate suggested that differences in ammonium or nitrate use were
not important influences on plant δ15N differences among species at individual sites. In fact, the largest variation among plant δ15N values were observed at the youngest and oldest sites, where soil nitrate concentrations were low. Low mineral N concentrations
and low N mineralization at these sites indicated low N availability. The most plausible mechanism to explain low δ15N values in plant foliage was a large isotopic fractionation during transfer of nitrogen from mycorrhizal fungi to plants.
Except for N-fixing plants, the foliar δ15N signatures of individual species were generally lower at sites of low N availability, suggesting either an increased fraction
of N obtained from mycorrhizal uptake (f), or a reduced proportion of mycorrhizal N transferred to vegetation (T
r). Foliar and fine root nitrogen concentrations were also lower at these sites. Foliar N concentrations were significantly
correlated with δ15N in foliage of Populus, Salix, Picea, and Tsuga heterophylla, and also in fine roots. The correlation between δ15N and N concentration may reflect strong underlying relationships among N availability, the relative allocation of carbon
to mycorrhizal fungi, and shifts in either f or T
r.
Received: 14 December 1998 / Accepted: 16 August 1999 相似文献
15.
Linking isotopic and migratory patterns in a pelagic seabird 总被引:1,自引:0,他引:1
The value of stable isotope analysis in tracking animal migrations in marine environments is poorly understood, mainly due
to insufficient knowledge of isotopic integration into animal tissues within distinct water masses. We investigated isotopic
and moult patterns in Cory’s shearwaters to assess the integration of different stable isotopes into feathers in relation
to the birds’ transoceanic movements. Specimens of Mediterranean Cory’s shearwater Calonectris diomedea diomedea caught accidentally by Catalan longliners were collected and the signatures of stable isotopes of C (δ13C), N (δ15N) and S (δ34S) were analysed in 11 wing and two tail feathers from 20 birds, and in some breast feathers. Based on isotopic signatures
and moult patterns, the feathers segregated into two groups (breeding and wintering), corresponding to those grown in the
Mediterranean or Atlantic regions, respectively. In addition, feathers grown during winter, i.e. moulted in Atlantic waters,
were grouped into two isotopically distinct profiles, presumably corresponding to the two main wintering areas previously
identified for Mediterranean Cory’s shearwater in tracking studies. N signatures mainly indicated the Mediterranean-to-Atlantic
migration, whereas C and S signatures differed according to the Atlantic wintering area. Our results indicate that isotopic
signatures from distant oceanic regions can integrate the feathers of a given bird and can indicate the region in which each
feather was grown. This study thus underscores how stable isotope analysis can link marine animals to specific breeding and
wintering areas, and thereby shed new light on studies involving assignment, migratory connectivity and carry-over effects
in the marine environment.
Xavier Ruiz deceased 27 April 2008. 相似文献
16.
Disentangling effects of growth and nutritional status on seabird stable isotope ratios 总被引:1,自引:0,他引:1
A growing number of studies suggest that an individual’s physiology affects its carbon and nitrogen stable isotope signatures,
obscuring a signal often assumed to be only a reflection of diet and foraging location. We examined effects of growth and
moderate food restriction on red blood cell (RBC) and feather δ15N and δ13C in rhinoceros auklet chicks (Cerorhinca monocerata), a piscivorous seabird. Chicks were reared in captivity and fed either control (75 g/day; n = 7) or ~40% restricted (40 g/day; n = 6) amounts of high quality forage fish. We quantified effects of growth on isotopic fractionation by comparing δ15N and δ13C in control chicks to those of captive, non-growing subadult auklets (n = 11) fed the same diet. To estimate natural levels of isotopic variation, we also collected blood from a random sample of
free-living rhinoceros auklet adults and chicks in the Gulf of Alaska (n = 15 for each), as well as adult feather samples (n = 13). In the captive experiment, moderate food restriction caused significant depletion in δ15N of both RBCs and feathers in treatment chicks compared to control chicks. Growth also induced depletion in RBC δ15N, with chicks exhibiting lower δ15N when they were growing the fastest. As growth slowed, δ15N increased, resulting in an overall pattern of enrichment over the course of the nestling period. Combined effects of growth
and restriction depleted δ15N in chick RBCs by 0.92‰. We propose that increased nitrogen-use efficiency is responsible for 15N depletion in both growing and food-restricted chicks. δ15N values in RBCs of free-ranging auklets fell within a range of only 1.03‰, while feather δ15N varied widely. Together, our captive and field results suggest that both growth and moderate food restriction can affect
stable isotope ratios in an ecologically meaningful way in RBCs although not feathers due to greater natural variability in
this tissue. 相似文献
17.
Trophic patterns of omnivorous freshwater shrimps, Exopalaemon modestus and Macrobrachium nipponensis, were investigated in two shallow eutrophic lakes by using stable isotope analysis. δ15N and δ13C of M. nipponensis and E. modestus increased with increasing body weight, which might be attributed to larger individuals ingesting organisms that feed higher
up the food chain and/or increased assimilation of benthic food items with enriched isotopic signatures. Of the freshwater
shrimps occurring in the studied lakes, those from Lake Taihu had significantly elevated δ15N and δ13C values (4.3‰ and 1.8‰, respectively) compared with those from the less eutrophic Lake Chaohu, indicating that the isotopic
signature might partially reflect the trophic states of their habitats. Mixing model results suggested that the benthic food
web provides the primary carbon source for both shrimp species, and that E. modestus assimilated relatively more pelagic food sources than M. nipponensis in these lakes.
Handling editor: S. Wellekens 相似文献
18.
Natural variability in stable isotope ratios and element concentrations in calcified structures of fish (e.g. scales and otoliths) has provided biogeochemical ‘tags’ for studying origins and movements of marine species, but has been little used in freshwater studies. We examine whether variability in scale δ15N and δ13C values of Salmo trutta L., could provide a tag of fish over small spatial scales in a small river catchment (River Dee, U.K.) and compared their performance as tags with that of scale/otolith element concentrations. Whole scale δ15N and δ13C values differed among six study sites and fish could be classified to their site of origin with a high degree of accuracy. Classifying fish to their site of capture was marginally superior using scale δ15N and δ13C values compared to that achieved using Sr, Mn, Ba and Mg in scale hydroxyapatite or otolith aragonite. Scale δ15N and δ13C values could therefore provide non-lethally collectable biogeochemical tags superior in performance to element concentrations in otoliths and scales. A comprehensive study of δ15N and δ13C values within freshwater systems would develop our understanding of factors influencing geographical variability in baseline δ15N and δ13C signatures. 相似文献
19.
Facultative hyperparasitism is likely to be the most common form of intraguild predation among parasitoids. However, difficulties associated with studying facultative hyperparasitoids in the field have hampered a thorough understanding of their trophic ecology. In this study, we used a combination of stable isotope analysis and published natural history information to infer trophic interactions in a guild of field-collected primary parasitoids and facultative hyperparasitoids that attack a gall-making midge on Baccharis pilularis. Our three a priori hypotheses were: (1) stable isotope values should increase incrementally from the host plant to higher trophic levels; (2) the two species of ectoparasitoids should exhibit higher stable isotope signatures than the two endoparasitoids, and; (3) the two facultative hyperparasitoids should exhibit stable isotope signatures that fall between zero and one trophic level steps above that observed for the primary parasitoids. Food webs inferred from stable isotope data generally agreed with previously published accounts of community structure. As expected, both δ13C and δ15N were progressively enriched in the heavy isotope from the host plant to the herbivorous midge to the parasitic wasps. Multivariate analysis of stable isotope data revealed that the two primary ectoparasitoids occupied a similar trophic niche, but were significantly different from the primary endoparasitoids. We attribute this result to “coincidental intraguild predation” by ectoparasitoids that develop on already-parasitized midge larvae. One of the facultative hyperparasitoids, Zatropis capitis, exhibited a stable isotope signature approximately one trophic step above the primary parasitoids. Unexpectedly, the second facultative hyperparasitoid, Mesopolobus sp., appeared to be developing as a primary parasitoid at all sites. Coupled with independent assessments of community structure, stable isotope analysis validated trophic links constructed by previous researchers and identified potential taxon-specific differences in trophic interactions for two facultative hyperparasitoids in the B. pilularis gall community.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at . 相似文献
20.
Stable isotopes (δD and δ13C) are geographic indicators of natal origins of monarch butterflies in eastern North America 总被引:1,自引:0,他引:1
Wing membranes of laboratory and field-reared monarch butterflies (Danaus plexippus) were analyzed for their stable-hydrogen (δD) and carbon (δ13C) isotope ratios to determine whether this technique could be used to identify their natal origins. We hypothesized that
the hydrogen isotopic composition of monarch butterfly wing keratin would reflect the hydrogen isotope patterns of rainfall
in areas of natal origin where wings were formed. Monarchs were reared in the laboratory on milkweed plants (Asclepias sp.) grown with water of known deuterium content, and, with the assistance of volunteers, on native milkweeds throughout
eastern North America. The results show that the stable hydrogen isotopic composition of monarch butterflies is highly correlated
with the isotopic composition of the milkweed host plants, which in turn corresponds closely with the long-term geographic
patterns of deuterium in rainfall. Stable-carbon isotope values in milkweed host plants were similarly correlated with those
values in monarch butterflies and showed a general pattern of enrichment along a southwest to northeast gradient bisecting
the Great Lakes. These findings indicate that natal origins of migratory and wintering monarchs in Mexico can be inferred
from the combined δD and δ13C isotopic signatures in their wings. This relationship establishes that analysis of hydrogen and carbon isotopes can be used
to answer questions concerning the biology of migratory monarch butterflies and provides a new approach to tracking similar
migratory movements of other organisms.
Received: 1 July 1998 / Accepted: 11 November 1998 相似文献