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1.
Organic Matter Stable Isotope (δ13C, δ15N) Response to Historical Eutrophication of Lake Taihu, China 总被引:1,自引:0,他引:1
We explored the use of carbon and nitrogen isotope ratios (δ13C, δ15N) in sediment organic matter as proxy indicators of historical changes in the trophic state of Lake Taihu, the third largest
freshwater lake in China. Stable isotope signatures in four sediment cores spanning the 20th century were compared with instrumental
records of lake-water trophic state. The comparative study shows that, between ∼
∼1950 and 1990 AD, the δ13C and δ15N of sediment organic matter throughout Lake Taihu increased along the trophic gradient from oligotrophy to eutrophy due to
biological isotopic fractionation. However, in the 1990s, the trophic state of Lake Taihu diverged into two different trophic
systems, a hypereutrophic western Lake Taihu dominated by blue-green algae and a mesoeutrophic eastern Lake Taihu dominated
by vascular aquatic plants. During the post-1990 AD shift from mesoeutrophic to hypereutrophic state in western Lake Taihu,
organic matter δ13C and δ15N decreased sharply in response to pronounced shifts in the aquatic ecosystem. The results indicate that 13C-depleted phytoplankton replaced macrophytes in western Lake Taihu. δ15N values in western Lake Taihu also decreased because of N2 fixation by cyanobacteria in this highly productive ecosystem. By contrast, in eastern Lake Taihu, organic matter δ13C and δ15N values show a post-1990 AD trend towards slightly lower values, but they remain higher than the long-term average. This
recent 13C–enrichment of organic matter indicates that periods of high productivity in the restricted eastern sub-basin of Lake Taihu
limited aqueous CO2 availability, causing a decrease in isotopic discrimination during photosynthesis. After ∼
∼1990 AD, organic matter δ15N values for eastern Lake Taihu only dropped slightly, suggesting that the contribution of phytoplankton to the sediment organic
matter increased slightly. Taken together, the results indicate that nitrogen-fixing cyanobacteria probably played a much
smaller role in primary productivity in this part of eastern Lake Taihu, compared with western Lake Taihu. Despite the complexity
of carbon and nitrogen cycles in lakes, the agreement between the stable isotope signatures and instrumental records for Lake
Taihu suggests that δ13C and δ15N in sediment organic matter are capable of recording important shifts in the spatial and temporal evolution of lake-water
trophic state. 相似文献
2.
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
3.
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
4.
Matthew M. Guzzo G. Douglas Haffner Stuart Sorge Scott A. Rush Aaron T. Fisk 《Hydrobiologia》2011,675(1):41-53
Stable isotopes of carbon (δ13C) and nitrogen (δ15N) often have unique values among lake habitats (e.g. benthic, littoral, pelagic), providing a widely used tool for measuring
the structure and energy flow in aquatic food webs. However, there has been little recognition of the spatial and temporal
variabilities of these isotopes within habitats of aquatic ecosystems. To address this, δ13C and δ15N were measured in seston, zebra mussels (Dreissena polymorpha) and young-of-year (YOY) yellow (Perca flavescens), and white perch (Morone americana) collected from four sites across the offshore habitat of the western basin of Lake Erie during June–September 2009. Values
of δ13C and δ15N showed significant spatial and temporal variations, with month accounting for >50% of the variation, for both stable isotopes
and all the species except seston. Such variation in isotope values has the potential to significantly influence or confound
interpretation of stable isotopes in measures, such as trophic position (TP) which use lower trophic level organisms as their
baseline. For example, TP was found to vary up to 0.7 for yellow and white perch (TP = δ15Nfish − δ15Nzebra mussel/diet-tissue fractionation factor) depending on the zebra mussel data used (e.g., from a different location or a different
collection month). As the use of stable isotopes continues to move from qualitative to more quantitative measures of trophic
structure, food web research must recognize the importance of stable isotopes' variability in lower trophic level organisms,
especially in large lake systems. 相似文献
5.
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
6.
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
7.
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
8.
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
9.
Stable isotope data are often used to assess diet, trophic level, trophic niche width and the extent of omnivory. Notwithstanding
ongoing discussions about the value of these approaches, variations in isotopic signatures among individuals depend on inherent
variability as well as differences in feeding habitats. Remarkably, the relative contributions of diet variation and inherent
variability to differences in δ15N and δ13C among individuals have not been quantified for the same species at the same life history stages, and inherent variability
has been ignored or assumed. We quantified inherent variability in δ13C and δ15N among individuals of a marine fish (the European sea bass, Dicentrarchus labrax) reared in a controlled environment on a diet of constant isotopic composition and compared it with variability in δ13C and δ15N among individuals from wild bass populations. The analysis showed that inherent variability among reared individuals on
a controlled diet was equivalent to a large proportion of the observed variability among wild individuals and, therefore,
that inherent variability should be measured to establish baseline variability in wild populations before any assumptions
are made about the influence of diet. Given that inherent variability is known to be dependent on species, life history stage
and the environment, our results show that it should be quantified on a case-by-case basis if diet studies are intended to
provide absolute assessments of dietary habits. 相似文献
10.
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
11.
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
12.
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
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.
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
15.
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
16.
Kimiko Uchii Noboru Okuda Ryuji Yonekura Zin’ichi Karube Kazuaki Matsui Zen’ichiro Kawabata 《Limnology》2007,8(1):59-63
Trophic polymorphism was recently reported in introduced bluegill (Lepomis macrochirus) in Lake Biwa, Japan, where three morphs are specialized in benthic invertebrates (benthivorous type), submerged aquatic
plants (herbivorous type), and zooplankton (planktivorous type). We evaluated the long-term effects of food resource utilization
by these trophic morphs using stable isotope ratios, δ15N and δ13C. A significant difference in δ15N was found between the benthivorous and planktivorous types. The planktivorous type had the higher δ15N value, which corresponded with the value expected from its prey, zooplankton. The lower δ15N value of the benthivorous type would be derived from the lower δ15N values of benthic prey organisms compared to zooplankton. These results support previous findings that the benthivorous
and planktivorous types have different food resource utilization. In contrast, the δ15N and δ13C values of the herbivorous type were distinctly different from the expected values, indicating that this type was unlikely
to utilize aquatic plants substantially, contradicting the results of the dietary analysis. 相似文献
17.
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
18.
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
19.
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
20.
The frequency of individuals with empty stomachs (FES) can vary greatly among northern pike populations. However, the FES
has only seldom been analyzed in this species and its meaning is still not fully understood. It has been suggested that a
high FES may reflect a strongly piscivorous behaviour while low FES could reflect a higher utilization of invertebrates. We
compared the stomach contents and the trophic position of northern pike in 16 populations of individuals feeding mainly on
fish or benthic invertebrates. We tested the hypothesis that northern pike with empty stomachs or with fish in their stomachs
have a higher trophic position than individuals feeding on invertebrates. Carbon (δ13C) and nitrogen (δ15N) stable isotope signatures were used to estimate the trophic position of individuals. We found no significant difference
in the trophic position among piscivores, invertebrate feeders, and northern pike with empty stomachs. The average trophic
position of northern pike was high (mean ± SD = 4.3 ± 0.4, n = 66) and was correlated with total length. These results indicate that, although invertebrates could be an important part
of the diet of northern pike in Canadian Shield lakes, fish are still the dominant prey. Hence, feeding on invertebrates in
our study lakes would reflect an opportunistic rather than a specialized feeding strategy. 相似文献