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1.
The use of stable isotopes to investigate animal diets, habitat use, and trophic level requires understanding the rate at
which animals incorporate the 13C and 15N from their diets and the factors that determine the magnitude of the difference in isotopic composition between the animal’s
diet and that of its tissues. We determined the contribution of growth and catabolic turnover to the rate of 13C and 15N incorporation into several tissues that can be sampled non-invasively (skin, scute, whole blood, red blood cells, and plasma
solutes) in two age classes of a rapidly growing ectotherm (loggerhead turtles, Caretta caretta). We found significant differences in C and N incorporation rates and isotopic discrimination factors (Δ13C = δ13Ctissues − δ13Cdiet and Δ15N = δ15Ntissues − δ15Ndiet) among tissues and between age classes. Growth explained from 26 to 100% of the total rate of incorporation in hatchling
turtles and from 15 to 52% of the total rate of incorporation in juvenile turtles. Because growth contributed significantly
to the rate of isotopic incorporation, variation in rates among tissues was lower than reported in previous studies. The contribution
of growth can homogenize the rate of isotopic incorporation and limit the application of stable isotopes to identify dietary
changes at contrasting time scales and to determine the timing of diet shifts. The isotopic discrimination factor of nitrogen
ranged from −0.64 to 1.77‰ in the turtles’ tissues. These values are lower than the commonly assumed average 3.4‰ discrimination
factors reported for whole body and muscle isotopic analyses. The increasing reliance on non-invasive and non-destructive
sampling in animal isotopic ecology requires that we recognize and understand why different tissues differ in isotopic discrimination
factors. 相似文献
2.
Foliar δ15N, %N and %P in the dominant woody and herbaceous species across nutrient gradients in New Zealand restiad (family Restionaceae)
raised bogs revealed marked differences in plant δ15N correlations with P. The two heath shrubs, Leptospermum scoparium (Myrtaceae) and Dracophyllum scoparium (Epacridaceae), showed considerable isotopic variation (−2.03 to −15.55‰, and −0.39 to −12.06‰, respectively) across the
bogs, with foliar δ15N strongly and positively correlated with P concentrations in foliage and peat, and negatively correlated with foliar N:P
ratios. For L. scoparium, the isotopic gradient was not linked to ectomycorrhizal (ECM) fractionation as ECMs occurred only on higher nutrient marginal
peats where 15N depletion was least. In strong contrast, restiad species (Empodisma minus Sporadanthus ferrugineus, S. traversii) showed little isotopic variation across the same nutrient gradients. Empodisma minus and S. traversii had δ15N levels consistently around 0‰ (means of −0.12‰ and +0.15‰ respectively), and S. ferrugineus, which co-habited with E. minus, was more depleted (mean −4.97‰). The isotopic differences between heath shrubs and restiads were similar in floristically
dissimilar bogs and may be linked to contrasting nutrient demands, acquisition mechanisms, and root morphology. Leptospermum scoparium shrubs on low nutrient peats were stunted, with low tissue P concentrations, and high N:P ratios, suggesting they were P-limited,
which was probably exacerbated by markedly reduced mycorrhizal colonisations. The coupling of δ15N depletion and %P in heath shrubs suggests that N fractionation is promoted by P limitation. In contrast, the constancy in
δ15N of the restiad species through the N and P gradients suggests that these are not suffering from P limitation. 相似文献
3.
Yoshito Chikaraishi Nanako O. Ogawa Hideyuki Doi Naohiko Ohkouchi 《Ecological Research》2011,26(4):835-844
Compound-specific stable isotope analysis (CSIA) of amino acids is a new method that enables estimates of trophic position
for consumers in food webs. We examined the nitrogen isotopic composition (δ15N) of amino acids of Japanese social insects (three bee, three wasp, and four hornet species) to evaluate the potential of
CSIA of amino acids in studies of terrestrial food webs. For wasps, we also examined samples at different growth stages (ranging
from egg to adult) to assess the effect of metamorphosis on CSIA estimates of trophic position. The δ15N values of bulk tissues for Japanese social insects are only weakly correlated with the biologically expected trophic positions.
In contrast, the trophic positions estimated from the δ15N values of amino acids (yielding values of between 2.0 and 2.3 for bees, between 2.8 and 3.3 for wasps, and between 3.5 and
4.1 for hornets) are consistent with the biologically expected trophic positions for these insects (i.e., 2.0 for bees, 3.0
for wasps, and 3.0–4.0 for hornets). Although large variability is observed among the δ15N values of individual amino acids (e.g., ranging from 3.0 to 14.9‰ for phenylalanine), no significant change is observed
in the trophic position during wasp metamorphosis. Thus, the CSIA of amino acids is a powerful tool for investigating not
only aquatic food webs but also terrestrial food webs with predatory insects. 相似文献
4.
Food web structure of a shallow eutrophic lake (Lake Taihu,China) assessed by stable isotope analysis 总被引:1,自引:0,他引:1
Lake Taihu is a large, shallow, and eutrophic lake in China. It has provided local communities with valuable fisheries for
centuries, but little is known of the trophodynamics, or of its faunal communities. Carbon and nitrogen isotopic composition
was used to assess its trophic pathways and the food web structure [food sources and trophic levels (TL)]. Basal food sources
were distinguishable based on their δ13C values, ranging from −27.2 to −15.2‰. Consumers were also well separated in δ13C (−26.9 to −17.9‰ for invertebrates and −25.7 to −18.1‰ for fishes), which allowed for an effective discrimination of carbon
sources between these fauna. An average trophic enrichment factor of 3.4‰ was used to calculate the TLs based on δ15N of zooplankton, with results indicating a food web having four TLs. Although δ15N values overlap and cover a large range within trophic compartments, the isotopic signatures of the species assessed revealed
a general trend of 15N enrichment with increasing TL. Stable isotope signatures were also used to establish a general food web scheme in which
five main trophic pathways were analyzed. 相似文献
5.
A total of 23 genotypes belonging to seven tropical food yams and two wild relative species of different origin and coming
from two sampling ecological zones (the Republic of Benin in Africa and Guadeloupe in the Caribbean) was analysed for their
13C content. The δ13C values for all yam samples (from −25.39 and −30.07 ‰) indicated that all species had a C3 photosynthetic type. 相似文献
6.
A feeding trial was performed in the laboratory with the catfish species Pterygoplichthys disjunctivus to determine stable carbon (13C) and nitrogen (15 N) turnover rates and discrimination factors in non-lethally sampled tissues (red blood cells, plasma solutes, and fin).
A second feeding trial was conducted to determine what P. disjunctivus could assimilate from low-quality wood-detritus—refractory polysaccharides (e.g., cellulose), or soluble wood-degradation products inherent in wood-detritus. This was performed
by feeding the fish an artificial wood-detritus diet with fibrous (δ13C = −26.36‰; δ15
N = 2.13‰) and soluble portions (δ13C = −11.82‰; δ15
N = 3.39‰) that had different isotopic signatures and monitoring the dynamics of isotopic incorporation in the different tissues
over time. Plasma solutes turned over more quickly than red blood cells for 13C and 15 N. However, in contrast to previous studies of juvenile fishes, C and N incorporation was primarily driven by catabolic tissue
turnover as opposed to growth rate. Tissue-diet discrimination factors for 15 N varied from 4.08 to 5.17‰, whereas they were <2‰ for 13C (and less than 0.3‰ for plasma and red blood cells). The results of trial two suggested that P. disjunctivus could not assimilate refractory polysaccharides. Moreover, the δ13C and δ15 N signatures of wild-caught P. disjunctivus from Florida confirmed their detrital trophic standing in Floridian aquatic ecosystems. 相似文献
7.
We studied the nutritional modes of the orchid Serapias strictiflora and its mycorrhizal fungus Epulorhiza sp. using the differences in carbon isotopic composition (δ13C) of C3 orchid and C4 maize tissues. We found that if cultivated in substrate lacking any organic compounds, the mycorrhizal extraradical mycelia
(δ13C = −26.3 ± 0.2 ‰) developed well, despite being fully dependent on nutrition from orchid roots (δ13C = −28.6 ± 0.1 ‰). If the mycorrhizal fungus had additional access to and colonized decaying maize roots (δ13C = −14.6 ± 0.1 ‰), its isotopic composition (δ13C = −21.6 ± 0.4 ‰) reflected a mixture of biotrophy and saprotrophy. No statistically significant differences in δ13C of new storage tubers were found between Epulorhiza-associated orchids with (δ13C = -28.2 ± 0.1 ‰) and without access to maize roots (δ13C = −28.6 ± 0.2 ‰). We conclude that autotrophy is the predominant nutritional mode of mature S. strictiflora plants and that they supply their mycorrhizal fungus with substantial amount of carbon (69 ± 3 % of the fungus demand), even
if the fungus feeds saprotrophically. 相似文献
8.
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
9.
Nitrogen isotopes (15N/14N ratios, expressed as δ15N values) are useful markers of the mycorrhizal role in plant nitrogen supply because discrimination against 15N during creation of transfer compounds within mycorrhizal fungi decreases the 15N/14N in plants (low δ15N) and increases the 15N/14N of the fungi (high δ15N). Analytical models of 15N distribution would be helpful in interpreting δ15N patterns in fungi and plants. To compare different analytical models, we measured nitrogen isotope patterns in soils, saprotrophic fungi, ectomycorrhizal fungi, and plants with different mycorrhizal habits on a glacier foreland exposed during the last 100 years of glacial retreat and on adjacent non-glaciated terrain. Since plants during early primary succession may have only limited access to propagules of mycorrhizal fungi, we hypothesized that mycorrhizal plants would initially be similar to nonmycorrhizal plants in δ15N and then decrease, if mycorrhizal colonization were an important factor influencing plant δ15N. As hypothesized, plants with different mycorrhizal habits initially showed similar δ15N values (−4 to −6‰ relative to the standard of atmospheric N2 at 0‰), corresponding to low mycorrhizal colonization in all plant species and an absence of ectomycorrhizal sporocarps. In later successional stages where ectomycorrhizal sporocarps were present, most ectomycorrhizal and ericoid mycorrhizal plants declined by 5–6‰ in δ15N, suggesting transfer of 15N-depleted N from fungi to plants. The values recorded (−8 to −11‰) are among the lowest yet observed in vascular plants. In contrast, the δ15N of nonmycorrhizal plants and arbuscular mycorrhizal plants declined only slightly or not at all. On the forefront, most ectomycorrhizal and saprotrophic fungi were similar in δ15N (−1 to −3‰), but the host-specific ectomycorrhizal fungus Cortinarius tenebricus had values of up to 7‰. Plants, fungi and soil were at least 4‰ higher in δ15N from the mature site than in recently exposed sites. On both the forefront and the mature site, host-specific ectomycorrhizal fungi had higher δ15N values than ectomycorrhizal fungi with a broad host range. From these isotopic patterns, we conclude:(1) large enrichments in 15N of many ectomycorrhizal fungi relative to co-occurring ectomycorrhizal plants are best explained by treating the plant-fungal-soil system as a closed system with a discrimination against 15N of 8–10‰ during transfer from fungi to plants, (2) based on models of 15N mass balance, ericoid and ectomycorrhizal fungi retain up to two-thirds of the N in the plant-mycorrhizal system under the N-limited conditions at forefront sites, (3) sporocarps are probably enriched in 15N by an additional 3‰ relative to available nitrogen, and (4) host-specific ectomycorrhizal fungi may transfer more N to plant hosts than non-host-specific ectomycorrhizal fungi. Our study confirms that nitrogen isotopes are a powerful tool for probing nitrogen dynamics between mycorrhizal fungi and associated plants. 相似文献
10.
Spatial patterns of foliar stable carbon isotope compositions of C<Subscript>3</Subscript> plant species in the Loess Plateau of China 总被引:1,自引:0,他引:1
The spatial pattern of foliar stable carbon isotope compositions (δ13C) of dominant species and their relationships with environmental factors in seven sites, Yangling, Yongshou, Tongchuan, Fuxian,
Ansai, Mizhi and Shenmu, standing from south to north in the Loess Plateau of China, was studied. The results showed that
in the 121 C3 plant samples collected from the Loess Plateau, the foliar δ13C value ranged from −22.66‰ to −30.70‰, averaging −27.04‰. The foliar δ13C value varied significantly (P<0.01) among the seven sites, and the average δ13C value increased by about 1.69‰ from Yangling in the south to Shenmu in the north as climatic drought increased. There was
a significant difference in foliar δ13C value among three life-forms categorized from all the plant samples in the Loess Plateau (P<0.001). The trees (−26.74‰) and shrubs (−26.68‰) had similar mean δ13C values, both significantly (P<0.05) higher than the mean δ13C value of herbages (−27.69‰). It was shown that the trees and shrubs had higher WUEs and employed more conservative water-use
patterns to survive drier habitats in the Loess Plateau. Of all the C3 species in the Loess Plateau, the foliar δ13C values were significantly and negatively correlated with the mean annual rainfall (P<0.001) and mean annual temperature (P<0.05), while being significantly and positively correlated with the latitude (P<0.001) and the annual solar radiation (P<0.01). In general, the foliar δ13C values increased as the latitude and solar radiation increased and the rainfall and temperature decreased. The annual rainfall
as the main influencing factor could explain 13.3% of the spatial variations in foliar δ13C value. A 100 mm increment in annual rainfall would result in a decrease by 0.88‰ in foliar δ13C values. 相似文献
11.
Abstract
Freshwater ecosystems derive organic carbon from both allochthonous and autochthonous sources. We studied the relative contributions
of different carbon sources to zooplankton in a small, polyhumic, steeply stratified lake, using six replicate surface-to-sediment
enclosures established during summer and autumn 2004. We added 13C-enriched bicarbonate to the epilimnion of half the enclosures for three weeks during each season and monitored carbon stable
isotope ratios of DIC, DOC, POC and Daphnia, along with physical, chemical and biological variables. During summer, 13C-enriched DIC (δ13C up to 44 ± 7.2‰) was soon taken up by phytoplankton (δ13C up to −5.1 ± 13.6‰) and was transmitted to Daphnia (δ13C up to −1.7 ± 7.2‰), demonstrating consumption of phytoplankton. In contrast, during autumn, 13C-enriched DIC (δ13C up to 56.3 ± 9.8‰) was not transmitted to Daphnia, whose δ13C became progressively lower (δ13C down to −45.6 ± 3.3‰) concomitant with decreasing methane concentration. Outputs from a model suggested phytoplankton contributed
64–84% of Daphnia diet during summer, whereas a calculated pelagic carbon mass balance indicated only 30–40% could have come from phytoplankton.
Although autumn primary production was negligible, zooplankton biomass persisted at the summer level. The model suggested
methanotrophic bacteria contributed 64–87% of Daphnia diet during autumn, although the calculated carbon mass balance indicated a contribution of 37–112%. Thus methanotrophic
bacteria could supply virtually all the carbon requirement of Daphnia during autumn in this lake. The strongly 13C-depleted Daphnia values, together with the outputs from the models and the calculated carbon mass balance showed that methanotrophic bacteria
can be a greater carbon source for Daphnia in lakes than previously suspected. 相似文献
12.
The relationships between 13C isotopic discrimination and water stress are well documented for C3 and C4 plants. However, the application in the field is hampered by complex interaction patterns with other common stress factors,
such as nutrient deficiency. In addition, questions arise if temporal reductions in water availability during crop growth
can be traced back using δ13C data in the field. The objective of this study therefore is to assess the potential use of δ13C observations to quantify water stress and its dynamics in maize (Zea mays L.) grown under low to high nitrogen availability, and to develop tools based on δ13C values for its diagnosis in the field. In a pot experiment, carried out in a screen house in Ibadan, Nigeria, we grew maize
for 60 days under four watering regimes, (i) optimum (at field capacity) during 60 days, (ii) optimum from 0 to 30 days and
stressed (50% field capacity) from 30 to 60 days, (iii) stressed from 0 to 30 days and optimum from 30 to 60 days, and (iv)
stressed throughout the 60 days. Nitrogen was applied at three rates (none, moderate (45 kg N ha−1) and high (120 kg N ha−1)). Plants were sampled after 30 and 60 days. At 60 days, leaves developed during the first 30 days were sampled separately
from those developed between 30 and 60 days. Shoot production showed a clear water–nitrogen interaction. Nitrogen response
increased with decreasing water stress, in particular from 30 to 60 days. δ13C values ranged from −12.42‰ to −10.80‰. Overall, a clear and significant water and nitrogen effect (P<0.0001) on the isotopic discrimination in maize was observed, opposite in direction from C3 plants. δ13C values decreased with increasing water stress, but increased with decreasing nitrogen availability, particularly when combined
with limited water supply. In addition, isotopic discrimination was observed to be variable within plant, and could be related
to a water stress in that growth period, in which the plant parts were developed. This shows that δ13C values measured in different plant parts at harvest can be used as a historical account on how water availability varied
during the entire cropping cycle. 相似文献
13.
The δ15N trophic enrichment in littoral food webs is not well known despite the importance of macroinvertebrates in lacustrine energy
fluxes. We wanted to assess the influence of functional feeding group (grazer, collector, shredder, predator, predator–hematophagous,
predator–sucker) and spatiotemporal variables (year, month, station of sampling) on littoral macroinvertebrate δ15N signatures. For 2 years, during the plant growth period phytophilous littoral macroinvertebrates were sampled in Lake St.
Pierre, a large fluvial lake of the St. Lawrence River, Québec, Canada. The δ15N analyses showed that station was the most important factor for explaining δ15N variation, followed by sampling month and functional feeding group. The organisms sampled in the stations of the south shore,
which experienced greater macrophyte abundance, slower currents, and stronger NO3 depletion exhibited higher δ15N values than those sampled on the north shore. Grazer-to-predator δ15N enrichment valued 1.6‰, which is inferior to the 3.4‰ generally admitted in food-web research. Shredders exhibited the lowest
δ15N values and predators–hematophagous the highest. δ15N signature of invertebrates increased 3‰ through the summer between May and September. Only samples collected within a short
period should be pooled to avoid an error value equivalent to one trophic level (1.6) enrichment. Furthermore, it is recommended
not to pool macroinvertebrate samples collected at stations with differing watershed land uses. 相似文献
14.
The degree of trophic differentiation of millipedes in taxocenes of temperate and tropical forests was estimated by isotopic
analysis. The isotope ratio variation among species was notably wider in a tropical forest (23 millipede species, δ15N ranges within 10‰) than in a temperate broad-leaved forest (9 species, δ15N range less than 3‰). It is suggested that partitioning of food resources among species contributes significantly to the
maintenance of high diversity of soil saprotrophic animals in tropical ecosystems. 相似文献
15.
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
16.
The genus Ramaria is composed of several subgenera that often correspond to specific trophic strategies. Because carbon and nitrogen isotopes
can be used to assess fungal trophic status and nitrogen sources, we accordingly carried out an extensive survey of isotopic
patterns in archived specimens of Ramaria from Germany and other locations. Isotopic patterns in species generally corresponded to subgeneric affiliations and to the
range of different potential substrates, with fungi fruiting on wood and litter (subgenera Asteroramaria and Lentoramaria) much lower in δ15N (≈−3‰) than ectomycorrhizal taxa (≈12‰) (subgenus Ramaria) or taxa fruiting on soil (≈13‰) (subgenus Echinoramaria). Conversely, fungi fruiting on wood and litter were higher in δ13C (−23‰) than those fruiting on soil (≈−27‰), with ectomycorrhizal fungi intermediate (≈−24.5‰). Fungi colonizing mineral
soil horizons were about 3‰ enriched in 15N relative to those colonizing both mineral and organic horizons. The high δ15N and low δ13C signatures of taxa fruiting on soil remains unexplained. The high degree of fidelity of isotopic signatures with subgeneric
classifications and life history traits suggests that sporocarps are good integrators of patterns of carbon and nitrogen cycling
for specific taxa. Archived specimens represent a useful trove of life history information that could be mined without requiring
extensive supporting isotopic data from other ecosystem pools. 相似文献
17.
D. R. Bowling W. J. Massman S. M. Schaeffer S. P. Burns R. K. Monson M. W. Williams 《Biogeochemistry》2009,95(1):37-59
Considerable research has recently been devoted to understanding biogeochemical processes under winter snow cover, leading
to enhanced appreciation of the importance of many winter ecological processes. In this study, a comprehensive investigation
of the stable carbon isotope composition (δ13C) of CO2 within a high-elevation subalpine forest snowpack was conducted. Our goals were to study the δ13C of biological soil respiration under snow in winter, and to assess the relative importance of diffusion and advection (ventilation
by wind) for gas transport within snow. In agreement with other studies, we found evidence of an active microbial community
under a roughly 1-m deep snowpack during winter and into spring as it melted. Under-snow CO2 mole fractions were observed up to 3,500 μmol mol−1, and δ13C of CO2 varied from ~−22 to ~−8‰. The δ13C of soil respiration calculated from mixing relationships was −26 to −24‰, and although it varied in time, it was generally
close to that of the bulk organic horizon (−26.0‰). Subnivean CO2 and δ13C were quite dynamic in response to changes in soil temperature, liquid water availability, and wind events. No clear biologically-induced
isotopic changes were observed during periods when microbial activity and root/rhizosphere activity were expected to vary,
although such changes cannot be eliminated. There was clear evidence of isotopic enrichment associated with diffusive transport
as predicted by theory, but simple diffusive enrichment (4.4‰) was not observed. Instead, ventilation of the snowpack by sustained
wind events in the forest canopy led to changes in the diffusively-enriched gas profile. The isotopic influence of diffusion
on gases in the snowpack and litter was greatest at greater depths, due to the decreased relative contribution of advection
at depth. There were highly significant correlations between the apparent isotopic content of respiration from the soil with
wind speed and pressure. In summary, physical factors influencing gas transport substantially modified and potentially obscured
biological factors in their effects on δ13C of CO2 within this subalpine forest snowpack. 相似文献
18.
Stable isotopes and trophic positions of littoral fishes from a Mediterranean marine protected area 总被引:1,自引:0,他引:1
Stable isotope analyses were employed to explore feeding and foraging habitats and trophic levels of littoral fishes in a
western Mediterranean Marine Protected Area (Egadi Islands, Sicily, Italy). Carbon and nitrogen stable isotope ratios were
measured in primary producers, invertebrates and fishes collected in December 2001 and January 2002. Fishes of the littoral
region of the Egadi Islands had isotopic signatures that fell into a wider range for δ
13C (about 6‰) than for δ
15N (about 3‰). Carbon isotope ratios were consistent with a food web based on mixed sources and two trophic pathways leading
to different fish species. Differences in the isotopic composition between islands were higher for benthivorous than for planktivorous
fishes. The overall picture gained from this study is of a isotopic distinction between planktivorous and benthivorous fishes,
resource partitioning facilitating the coexistence of similar species within the same ecosystem, and spatial variability in
the isotopic signatures and trophic level of fishes. Asymmetrical analysis of variance showed that estimated trophic levels
were lower in the area with the highest level of protection (Zone A) for only two out of the nine fishes analysed. As a consequence,
overall spatial differences do not seem to be a consequence of protection, since in most cases trophic levels did not change
significantly between zone A and zones C where professional fishing (trawling apart) is permitted, but of natural sources
of variation (e.g. variability in food availability and site-specific food preferences of fishes). However, the results of
this study suggest a different response at the species compared to the community level. 相似文献
19.
Lake Ellesmere (Te Waihora) is a nationally important coastal brackish lake in New Zealand, however degradation in water quality
and loss of submerged macrophytes over past decades have raised concerns in regards to the declining status of the lake’s
commercial and customary fisheries, predominantly targeted at shortfin eels (Anguilla australis). We investigated foodweb dynamics and trophic linkages to shortfin eels in Lake Ellesmere using a combination of abundance
assessments, dietary studies, and stable isotope analyses. Data from our study are compared with historical data sets on benthic
invertebrate community composition and shortfin eel diets to trace changes in the trophic linkages to top predators that have
occurred since the late 1960s. Stable isotope analyses indicate that the foodweb is predominantly driven by epipelic and phytoplankton
derived carbon sources, although it was difficult to discriminate between these two carbon pools because of wind-driven resuspension
of lake sediments. Comparison of our survey results with historical data sets indicates a clear shift in benthic biota from
being dominated by phytofaunal species such as Potamopyrgus antipodarum (comprising 90% of total invertebrate biomass) during the 1960s, to now being almost entirely comprised of subterranean species
such as Chironomus zealandicus and oligochaetes (together comprising 82% of total invertebrate biomass). This shift in benthic communities has resulted
in significant changes in the size-specific diet of juvenile shortfin eels (<400 mm) from those reported for Lake Ellesmere
during the mid 1970s, with Chironomus larvae now comprising 65% of the diets of juvenile eels, whereas historically P. antipodarum was the dominant food item (>30% of total biomass). This shift towards foraging on smaller sediment-dwelling species could
have implications for juvenile eel bioenergetics, and may help explain why juvenile shortfin growth rates have significantly
decreased in past decades. Juvenile shortfins now appear to switch to foraging on preyfish (mainly common bullies, Gobiomorphus cotidianus) at a smaller size (≈400 mm) than historically recorded (>500 mm). Dietary and stable isotope signatures indicated that small
shortfins (100–299 mm) have considerable overlap in trophic position (δ13C = −20.4‰, δ15N = 13.6‰) with common bullies (δ13C = −20.5‰, δ15N = 13.7‰), the dominant fish in Lake Ellesmere (92% of total abundance CPUE), potentially indicating that these two species
may directly compete for food resources. These findings again highlighted the importance of C. zealandicus in sustaining the fish populations of the lake.
Handling editor: S. Declerck 相似文献
20.
The cardinal tetra (Paracheirodon axelrodi) is the most abundant species of the Brazilian ornamental fish trade, constituting more than 80% of the ornamental fish collected
in the middle Negro River basin. Stable isotope analyses were used to identify the autotrophic carbon sources and trophic
position for the cardinal in relation to the plant groups at the base of its foodchain. Filamentous algae, tree and plant
leaves and cardinals were collected in stream habitats, flooded forest and interfluvial swamps (campos) during peak flood,
falling water and low water periods. δ15N values of the cardinal in relation to the plants at the base of the food chain indicated a trophic position of omnivore.
Values of δ13C for the plants ranged from −43.1 to −26.4‰, with averages of −37.6, −30.4, and −29.4‰ for filamentous algae, flooded forest
leaves, and campo leaves, respectively. The δ13C values for the cardinal ranged from −35.0 to −27.9‰, with an average of −31.4‰. Relative contributions of plants to fish
carbon were estimated in a two end-member mixing model which determined that the leaves (flooded forest and campo leaves combined)
and filamentous algae had average relative contributions to cardinal carbon of 71% and 29%, respectively. However, seasonal
variation in the relative contributions was encountered throughout the hydrological cycle. The cardinals least enriched in
13C were encountered in November during the falling water period, indicating that they had perhaps recently migrated down from
interfluvial campos where filamentous algae production is significant. Considering that algal production has been reported
to be less than 1% of total primary production in the Negro River, these results could suggest some evidence of selective
herbivory in the cardinal’s food chain.
Handling editor: J. M. Melack 相似文献