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1.
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
2.
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
3.
A basic understanding of current food web dynamics and baseline data from which to measure future change is necessary to understand
species re-distribution and altered competition for food with climate change. We use mercury (Hg) and carbon (δ13C) and nitrogen (δ15N) stable isotope ratios as biomarkers to understand species diet differences and age class differences among ringed (Phoca hispida), bearded (Erignathus barbatus), and harbour (P. vitulina) seals in a subarctic marine ecosystem. Adult bearded seals had significantly lower δ15N and muscle Hg than bearded seal pups, whereas the opposite was observed in ringed seals where pups had lower δ15N than adults, suggesting age specific foraging differences in trophic food level for both species. For harbour seals, δ15N did not differ significantly among ages while Hg and δ13C did. The δ13C in muscle supports that bearded seals in this study are benthic feeders and are part of a separate food web from ringed
seals and harbour seals. Harbour seals had the highest levels of mercury and δ15N, indicating they feed at a higher trophic level relative to the other two seal species. Carbon and nitrogen isotopic ratios
and Hg levels illustrate how resources are partitioned among three seal species and offer evidence for separation based on
life stages within species. 相似文献
4.
Stable carbon and nitrogen isotope ratio profiling of sperm whale teeth reveals ontogenetic movements and trophic ecology 总被引:1,自引:0,他引:1
Teeth from male sperm whales (Physeter macrocephalus) stranded in the North-eastern Atlantic were used to determine whether chronological profiles of stable isotope ratios of
C (δ13C) and N (δ15N) across dentine growth layers could be used to detect known ontogenetic benchmarks in movements and trophic ecology. Profiles
showed a general decrease in δ13C (median = 1.91‰) and an increase in δ15N (median = 2.42‰) with age. A marked decline in δ13C occurred for all 11 teeth around 9–10 years and again for six individuals around 20 years. After the early twenties the
δ13C continued to decline with age for all teeth. These results are consistent with males segregating from natal groups in low
latitudes with the onset of puberty between 4 and 15 years and gradually dispersing pole-ward into 13C-depleted temperate waters. Penetration into further depleted, productive high latitudes after the age of 20 might facilitate
the spurt of accelerated growth rate observed around this age. Breeding migrations back to lower latitudes were not reflected
in the δ13C profiles possibly due to being short compared to the time spent feeding in high latitudes. The timings of marked isotopic
change in the δ15N profiles reflect those of the δ13C profiles, suggesting a link between dietary changes and movements. The observed increase in δ15N with age is likely to be caused by a trophic level increase as males grow in size, probably feeding on larger prey. An additional
explanation could be that, in the higher latitudes of the North Atlantic, the main prey source is the high trophic level squid
Gonatus fabricii. Also, the lower latitudes from where males disperse are depleted in basal 15N. Profiles of δ13C and δ15N in sperm whale teeth gathered from different regions, sexes, and periods in time, could provide a unique way to understand
the ecology of this species across different oceans. 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.
Rune Knudsen Anna Siwertsson Colin E. Adams Monica Garduño-Paz Jason Newton Per-Arne Amundsen 《Evolutionary ecology》2011,25(3):589-604
There is now strong evidence that foraging niche specialisation plays a critical role in the very early stages of resource
driven speciation. Here we test critical elements of models defining this process using a known polymorphic population of
Arctic charr from subarctic Norway. We test the long-term stability of niche specialisation amongst foraging predators and
discuss the possibility that contrasting foraging specialists are exposed to differing selection regimes. Inter-individual
foraging niche stability was measured by combining two time-integrated ecological tracers of the foraging niche (each individual’s
δ13C and δ15N stable isotope (SI) signatures and their food borne parasite fauna) with a short-term measure of foraging niche use (stomach
contents composition). Three dietary subgroups of predators were identified, including zooplankton, gammarid and benthivore
specialists foragers. Zooplanktivorous specialists had muscle low in δ 13C, a high abundance of parasites transmitted from pelagic copepods, a smaller head, longer snout and a more slender body-form
than gammaridivorous specialist individuals which had muscle more enriched in δ 13C and high abundance of parasites transmitted from benthic Gammarus. Benthivorous individuals were intermediate between the other two foraging groups according to muscle SI-signals (δ13C) and loadings of parasites transmitted from both copepods and Gammarus. The close relationship between subgroups identified by stomach contents, time-integrated tracers of niche use (SI and parasites)
and functional trophic morphology (niche adaptations) demonstrate a long-term temporally stable niche use of each individual
predator. Differential habitat use and contrasting parasite communities and loadings, show differential exposure to different
suites of selection pressures for different foraging specialists. Results also show that individual specialisation in trophic
behaviour and thus exposure to different suites of selection pressures are stable over time, and thus provide a platform for
disruptive selection to operate within this sympatric system. 相似文献
7.
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
8.
Size-related diet shifts are important characteristics of fish trophodynamics. Here, body size–related changes in muscle δ15N and δ13C of four coral reef fishes, Acanthurus nigrofuscus (herbivore), Chaetodon lunulatus (corallivore), Chromis xanthura (planktivore) and Plectropomus leopardus (piscivore) were investigated at two locations in the Solomon Islands. All four species occupied distinct isotopic niches
and the concurrent δ13C′ values of C. xanthura and P. leopardus suggested a common planktonic production source. Size-related shifts in δ15N, and thus trophic level, were observed in C. xanthura, C. lunulatus and P. leopardus, and these trends varied between location, indicating spatial differences in trophic ecology. A literature review of tropical
fishes revealed that positive δ15N-size trends are common while negative δ15N-size trends are rare. Size-δ15N trends fall into approximately equal groups representing size-based feeding within a food chain, and that associated with
a basal resource shift and occurs in conjunction with changes in production source, indicated by δ13C. The review also revealed large scale differences in isotope-size trends and this, combined with small scale location differences
noted earlier, highlights a high degree of plasticity in the reef fishes studied. This suggests that trophic size analysis
of reef fishes would provide a productive avenue to identify species potentially vulnerable to reef impacts as a result of
constrained trophic behaviour. 相似文献
9.
We provide preliminary carbon (δ13C) and nitrogen (δ15N) stable isotope assessment of the Greenland halibut (Reinhardtius hippoglossoides) diet in Cumberland Sound, with focus on two possible prey sources: pelagic represented by capelin (Mallotus villosus) and epibenthic represented by shrimp (Lebbeus polaris). The δ13C for the Greenland halibut stock indicated a pelagic carbon source in Cumberland Sound while stable isotope mixing models,
IsoSource and MixSIR, indicated a 99% dietary composition of capelin relative to the shrimp. The δ15N did not vary across Greenland halibut size ranges and placed them at a fourth trophic position relative to a primary herbivore.
This study provides the starting point for more elaborate Cumberland Sound research on the local Greenland halibut feeding
ecology by confirming pelagic feeding and establishing relative trophic position as well as identifying stable isotopes as
a useful tool for the study of diet in cold water fish species. 相似文献
10.
Aurore Aubail Jonas Teilmann Rune Dietz Frank Rig��t Tero Harkonen Olle Karlsson Aqqalu Rosing-Asvid Florence Caurant 《Polar Biology》2011,34(9):1411-1420
Recent studies have shown that the complementary analysis of mercury (Hg) concentrations and stable isotopic ratios of nitrogen
(δ15N) and carbon (δ13C) can be useful for investigating the trophic influence on the Hg exposure and accumulation in marine top predators. In this
study, we propose to evaluate the interspecies variability of Hg concentrations in phocids from polar areas and to compare
Hg bioaccumulation between both hemispheres. Mercury concentrations, δ15N and δ13C were measured in fur from 85 individuals representing 7 phocidae species, a Ross seal (Ommatophoca rossii), Weddell seals (Leptonychotes weddellii), crabeater seals (Lobodon carcinophagus), harbour seals (Phoca vitulina), grey seals (Halichoerus grypus), ringed seals (Pusa hispida) and a bearded seal (Erignathus barbatus), from Greenland, Denmark and Antarctica. Our results showed a positive correlation between Hg concentrations and δ15N values among all individuals. Seals from the Northern ecosystems displayed greater Hg concentrations, δ15N and δ13C values than those from the Southern waters. Those geographical differences in Hg and stable isotopes values were likely
due to higher environmental Hg concentrations and somewhat greater number of steps in Arctic food webs. Moreover, dissimilarities
in feeding habits among species were shown through δ15N and δ13C analysis, resulting in an important interspecific variation in fur Hg concentrations. A trophic segregation was observed
between crabeater seals and the other species, resulting from the very specific diet of krill of this species and leading
to the lowest observed Hg concentrations. 相似文献
11.
Nitrogen and carbon isotope responses of Chinese cabbage and chrysanthemum to the application of liquid pig manure 总被引:2,自引:0,他引:2
Sang-Sun Lim Woo-Jung Choi Jin-Hyeob Kwak Jae-Woon Jung Scott X. Chang Han-Yong Kim Kwang-Sik Yoon Soo-Myung Choi 《Plant and Soil》2007,295(1-2):67-77
The effects of the liquid pig manure (LM) used in organic farming on the natural abundance of 15N and 13C signatures in plant tissues have not been studied. We hypothesized that application of LM will (1) increase δ15N of plant tissues due to the high δ15N of N in LM as compared with soil N or inorganic fertilizer N, and (2) increase δ13C of plant tissues as a result of high salt concentration in LM that decreases stomatal conductance of plants. To test these
hypotheses, variations in the δ15N and δ13C of Chinese cabbage (Brassica campestris L.) and chrysanthemum (Chrysanthemum morifolium Ramatuelle) with two different LMs (with δ15N of +15.6 and +18.2‰) applied at two rates (323 and 646 kg N ha-1 for cabbage and 150 and 300 kg N ha-1 for chrysanthemum), or urea (δ15N = -2.7‰) applied at the lower rate above for the respective species, in addition to the control (no N input) were investigated
through a 60-day pot experiment. Application of LM significantly increased plant tissue δ15N (range +9.4 to +14.9‰) over the urea (+3.2 to +3.3‰) or control (+6.8 to 7.7‰) treatments regardless of plant species, strongly
reflecting the δ15N of the N source. Plant tissue δ13C were not affected by the treatments for cabbage (range −30.8 to −30.2‰) or chrysanthemum (−27.3 to −26.8‰). However, cabbage
dry matter production decreased while its δ13C increased with increasing rate of LM application or increasing soil salinity (P < 0.05), suggesting that salinity stress caused by high rate of LM application likely decreased stomatal conductance and
limited growth of cabbage. Our study expanded the use of the δ15N technique in N source (organic vs. synthetic fertilizer) identification and suggested that plant tissue δ13C maybe a sensitive indicator of plant response to salinity stress caused by high LM application rates. 相似文献
12.
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
13.
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
14.
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
15.
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
16.
In two laboratory experiments using tilapia (Oreochromis niloticus) and common carp (Cyprinus carpio), we investigated the effect of lipid content in the fish carcass on the stable carbon isotope ratio (δ13C). In both experiments, a significant negative correlation was found between lipid content in the carcass dry matter and
δ13C of total dry matter, but there was no influence on the δ13C of fat-free dry matter or lipids. As the lipid content of fish is known to vary with reproductive stage, season or nutritional
state, separate analysis of fractions of the proximate composition of dry matter will lead to more reliable results than analysing
the whole body. The differences in δ13C between diet and fish carcass (trophic shift) were different for the two species, calling for feeding trials under controlled
conditions using the species and the feeds in question before applying the stable isotope tracer technique in the analysis
of food webs.
Received: 1 December 1997 / Accepted: 1 March 1998 相似文献
17.
Regional food web studies that fail to account for small-scale isotopic variability can lead to a mismatch between an organism’s
inferred and true trophic position. Misinterpretation of trophic status may result, substantially limiting spatial and temporal
comparability of food web studies. We sampled several carbon sources and consumers in a nested design to assess the variability
of food web members across small spatial scales (100 s of m to several km) in regions around the Windmill Islands and Vestfold
Hills in East Antarctica. For carbon sources, δ13C in sea ice POM was particularly variable between locations (km apart) and between sites (100 s of m apart) with replicate
samples varying by up to 16‰. Macroalgae δ13C was less variable (replicate samples ranging up to 6.9‰ for the red alga Iridaea cordata), yet still differed between locations. Sediment POM and pelagic POM were the least variable, displaying minimal differences
between locations or sites for δ13C and δ15N. Three out of eight consumers were significantly different between locations for δ13C, and five out of eight for δ15N, with the fish Trematomus bernacchii the most variable for both δ13C and δ15N. At smaller scales, the amphipod Paramorea walkeri showed significant variation between sites in δ13C but not in δ15N. We attribute small-scale variability to the dynamic physical environment for carbon sources in coastal systems and a close
coupling of diet to habitat for consumers. We highlight the need to account for small-scale spatial variation in sampling
designs for regional food web studies. 相似文献
18.
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
19.
Categorizing animal populations by diet can mask important intrapopulation variation, which is crucial to understanding a
species’ trophic niche width. To test hypotheses related to intrapopulation variation in foraging or the presence of diet
specialization, we conducted stable isotope analysis (δ13C, δ15N) on hair and claw samples from 51 grizzly bears (Ursus arctos) collected from 2003 to 2006 in the Mackenzie Delta region of the Canadian Arctic. We examined within-population differences
in the foraging patterns of males and females and the relationship between trophic position (derived from δ15N measurements) and individual movement. The range of δ15N values in hair and claw (2.0–11.0‰) suggested a wide niche width and cluster analyses indicated the presence of three foraging
groups within the population, ranging from near-complete herbivory to near-complete carnivory. We found no linear relationship
between home range size and trophic position when the data were continuous or when grouped by foraging behavior. However,
the movement rate of females increased linearly with trophic position. We used multisource dual-isotope mixing models to determine
the relative contributions of seven prey sources within each foraging group for both males and females. The mean bear dietary
endpoint across all foraging groups for each sex fell toward the center of the mixing polygon, which suggested relatively
well-mixed diets. The primary dietary difference across foraging groups was the proportional contribution of herbaceous foods,
which decreased for both males and females from 42–76 to 0–27% and 62–81 to 0–44%, respectively. Grizzlies of the Mackenzie
Delta live in extremely harsh conditions and identifying within-population diet specialization has improved our understanding
of varying habitat requirements within the population. 相似文献
20.
J. M. Guehl A. M. Domenach M. Bereau T. S. Barigah H. Casabianca A. Ferhi J. Garbaye 《Oecologia》1998,116(3):316-330
Functional aspects of biodiversity were investigated in a lowland tropical rainforest in French Guyana (5°2′N, annual precipitation
2200 mm). We assessed leaf δ15N as a presumptive indicator of symbiotic N2 fixation, and leaf and wood cellulose δ13C as an indicator of leaf intrinsic water-use efficiency (CO2 assimilation rate/leaf conductance for water vapour) in dominant trees of 21 species selected for their representativeness
in the forest cover, their ecological strategy (pioneers or late successional stage species, shade tolerance) or their potential
ability for N2 fixation. Similar measurements were made in trees of native species growing in a nearby plantation after severe perturbation
(clear cutting, mechanical soil disturbance). Bulk soil δ15N was spatially quite uniform in the forest (range 3–5‰), whereas average leaf δ15N ranged from −0.3‰ to 3.5‰ in the different species. Three species only, Diplotropis purpurea, Recordoxylon speciosum (Fabaceae), and Sclerolobium melinonii (Caesalpiniaceae), had root bacterial nodules, which was also associated with leaf N concentrations higher than 20 mg g−1. Although nodulated trees displayed significantly lower leaf δ15N values than non-nodulated trees, leaf δ15N did not prove a straightforward indicator of symbiotic fixation, since there was a clear overlap of δ15N values for nodulated and non-nodulated species at the lower end of the δ15N range. Perturbation did not markedly affect the difference δ15Nsoil − δ15Nleaf, and thus the isotopic data provide no evidence of an alteration in the different N acquisition patterns. Extremely large
interspecific differences in sunlit leaf δ13C were observed in the forest (average values from −31.4 to −26.7‰), corresponding to intrinsic water-use efficiencies (ratio
CO2 assimilation rate/leaf conductance for water vapour) varying over a threefold range. Wood cellulose δ13C was positively related to total leaf δ13C, the former values being 2–3‰ higher than the latter ones. Leaf δ13C was not related to leaf δ15N at either intraspecific or interspecific levels. δ13C of sunlit leaves was highest in shade hemitolerant emergent species and was lower in heliophilic, but also in shade-tolerant
species. For a given species, leaf δ13C did not differ between the pristine forest and the disturbed plantation conditions. Our results are not in accord with the
concept of existence of functional types of species characterized by common suites of traits underlying niche differentiation;
rather, they support the hypothesis that each trait leads to a separate grouping of species.
Received: 18 August 1997 / Accepted: 14 April 1998 相似文献