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1.
Contributions of stable-isotope data to elucidating food webs of Mediterranean rocky littoral fishes 总被引:18,自引:0,他引:18
The food webs of rocky infra-littoral ecosystems in the Mediterranean have been little studied. In this investigation stable
isotopes and dietary data were compared in an attempt to describe features of the food webs concerned. δ13C and δ15N were determined for plants, invertebrates and fishes from the Bay of Calvi, Corsica. Dietary data were derived from the
literature. δ13C of plants ranged from –8.59‰ to –33.74‰, of benthic invertebrates from –17.0‰ to –20.52‰, of planktonic invertebrates from
–20.08‰ to –22.34‰ and of fishes from –16.27‰ to –19.59‰. δ15N was generally greater at higher trophic levels. δ15N of plants was 0.95–2.92‰, of benthic invertebrates 1.69–6.54‰, of planktonic invertebrates 3.51–6.82‰ and of fishes 4.63–9.77‰.
13C enrichment tended to be associated with benthic food chains and 13C depletion with planktonic chains. Stable-isotope data suggested more varied diets for many species than implied by gut-contents
data. Omnivory and trophic plasticity were widespread, and many consumers fed lower down the food chain than previous studies
had suggested. Both stable-isotope and gut-contents analysis resolved differences between fishes feeding on planktonic and
benthic prey and indicated that the herbivorous fish Sarpa salpa fed on a diet substantially different from that of other fishes. Zooplankton were important in the diets of several consumers
(both primary and secondary), as was plankton derived detritus. One species of fish previously identified as planktivorous
was shown to feed largely on benthic organisms, whilst several species of benthic invertebrates may feed on plankton-derived
detritus. Although herbivores seemed to obtain most of their C from macroalgae, δ15N data suggested that many of these animals supplemented their intake of N, although gut-contents analysis did not provide
evidence for such uptake. The isotopic data have elucidated several features of the food web which we would not otherwise
have detected.
Received: 26 April 1999 / Accepted: 24 September 1999 相似文献
2.
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
3.
Isotopic analysis of three food web theories in constricted and floodplain regions of a large river 总被引:10,自引:0,他引:10
Analyses of stable isotope (δ13C and δ15N) and C:N ratios of food webs within a floodplain and a constricted-channel region of the Ohio River during October 1993
and July 1994 indicate that the increasingly influential flood pulse concept (FPC) does not, for either location, adequately
address food web structure for this very large river. Furthermore, results of this study suggest that the riverine productivity
model (RPM) is more appropriate than the widely known river continuum concept (RCC) for the constricted region of this river.
These␣conclusions are based on stable isotope analyses of potential sources of organic matter (riparian C3 trees, riparian C4 grasses and agricultural crops, submerged macrophytes, benthic filamentous algae, benthic particulate organic matter, and
transported organic matter containing detritus and phytoplankton) and various functional feeding groups of invertebrate and
fish consumers. The FPC, which stresses the key contribution of organic matter, particularly terrestrial organic matter, originating
from the floodplain to riverine food webs, was judged inappropriate for the floodplain region of the Ohio River for hydrodynamic
and biotic reasons. The rising limb and peak period of discharge typically occur in November through March when temperatures
are low (generally much less than 10°C) and greater than bank-full conditions are relatively unpredictable and short-lived.
The major food potentially available to riverine organisms migrating into the floodplain would be decaying vegetation because
autotrophic production is temperature and light limited and terrestrial insect production is minimal at that time. It is clear
from our data that terrestrial C4 plants contribute little, if anything, to the consumer food web (based on δ13C values), and δ15N values for C3 plants, coarse benthic organic matter, and fine benthic organic matter were too depleted (∼7–12‰ lower than most invertebrate
consumer values) for this organic matter to be supporting the food web. The RPM, which emphasizes the primary role of autotrophic
production in large rivers, is the most viable of the remaining two ecosystem models for the constricted-channel region of
the Ohio based on stable isotope linkage between sources and consumers of organic matter in the food web. The most important
form of food web organic matter is apparently transported (suspended) fine (FTOM) and ultra-fine particulate organic matter.
We propose that phytoplankton and detritus of an autochthonous origin in the seston would represent a more usable energy source
for benthic (bivalve molluscs, hydropsychid caddisflies) and planktonic (microcrustaceans) suspension feeders than the more
refractory allochthonous materials derived from upstream processing of terrestrial organic matter. Benthic grazers depend
heavily on nonfilamentous benthic algae (based on gut analysis from a separate study), but filamentous benthic algae have
no apparent connection to invertebrate consumers (based on δ13C values). Amphipod and crayfish show a strong relationship to aquatic macrophytes (possibly through detrital organic matter
rather than living plant tissue). These observations contrast with the prediction of the RCC that food webs in large rivers
are based principally on refractory FTOM and dissolved organic matter from upstream inefficiencies in organic-matter processing
and the bacteria growing upon these suspended or dissolved detrital compounds. The conclusions drawn here for the Ohio River
cannot yet be extended to other floodplain and constricted-channel rivers in temperate and tropical latitudes until more comparable
data are available on relatively pristine and moderately regulated rivers.
Received: 3 January 1997 / Accepted: 28 August 1998 相似文献
4.
Plant invasions can fundamentally alter detrital inputs and the structure of detritus-based food webs. We examined the detrital
pathways in mangrove food webs in native (Puerto Rican) and introduced (Hawaiian) Rhizophora mangle forests using a dual isotope approach and a mixing model. Based on trophic-level fractionation of 0–1‰ for δ
13C and 2–3‰ for δ
15N, among the invertebrates, only nematodes, oligochaetes, and nereid polychaetes from native mangroves exhibited stable isotopes
consistent with a mangrove-derived diet. Certain fauna, in particular tubificid oligochaetes, had δ
13C values consistent with the consumption of mangrove leaves, but they were depleted in 15N, suggesting their primary nitrogen source was low in 15N, and was possibly N2-fixing bacteria. In introduced mangroves, all feeding groups appeared to rely heavily on non-mangrove sources, especially
phytoplankton inputs. Mixing model results and discriminant analysis showed clear separation of introduced and native mangrove
sites based on differential food source utilization within feeding groups, with stronger and more diverse use of benthic foods
observed in native forests. Observed differences between native and invasive mangrove food webs may be due to Hawaiian detritivores
being poorly adapted to utilizing the tannin-rich, nitrogen-poor mangrove detritus. In addition, differential utilization
of mangrove detritus between native and introduced mangroves may be a consequence of forest age. We postulate that increasing
mangrove forest age may promote diversification of bacterial food webs important in N and S cycling. Our results also suggest
a potentially important role for sulfur bacteria in supporting the most abundant infaunal consumers, nematodes, in the most
mature systems.
Electronic supplementary material The online version of this article (doi:) contains supplementary material that is available to authorized users. 相似文献
5.
W. Thimdee G. Deein N. Nakayama Y. Suzuki K. Matsunaga 《Wetlands Ecology and Management》2008,16(6):463-470
Stable carbon and nitrogen isotope ratios were used to elucidate primary carbon sources and trophic relationships of the fish
and shrimp community in the Klong Ngao mangrove ecosystem, southern Thailand. There were no significant differences in isotopic
compositions of biota between mangrove and offshore sites (Welch–Aspin test). The δ15N values of eight fish species and two shrimp species at both sites were also not significantly different by the test, meaning
that at both sites they feed on the same diets due to the discharge of large quantities of mangrove sediments. The δ15N isotopic enrichment of consumers suggested that there are four trophic levels in the Klong Ngao food web, with at least
two fish species capable of switching feeding strategies and thus altering their apparent trophic positions. Phytoplankton
culture experiments indicated that mangrove-derived sediments could play an important role in stimulating phytoplankton growth
for low turbidity offshore areas, thus providing an alternate food source. The isotopic associations among sources and consumers
indicated that mangroves were the major carbon source supporting aquatic food webs in the Klong Ngao ecosystem. 相似文献
6.
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
7.
Significance of instream autotrophs in trophic dynamics of the Upper Mississippi River 总被引:1,自引:0,他引:1
Trophic dynamics of large river–floodplain ecosystems are still not well understood despite development of several conceptual
models over the last 25 years. To help resolve questions about the relative contribution of algal and detrital organic matter
to food webs in the Upper Mississippi River, we (1) separated living and detrital components of ultrafine and fine transported
organic matter (UTOM and FTOM, respectively) by colloidal silica centrifugation; (2) identified stable isotope signatures
(δ13C and δ15N) for these two portions of transported organic matter and other potential organic matter sources; and (3) employed a multiple
source, dual-isotope mixing model to determine the relative contribution of major energy sources to primary consumers and
the potential contribution of basal sources to the biomass of secondary consumers. The δ13C and δ15N of living and detrital fractions of UTOM and FTOM were distinct, indicating clear differences in isotopic composition of
the algal and detrital fractions of transported organic matter. Living and detrital transported organic matter also differed
from other potential organic matter sources by either δ13C or δ15N. A six-source mixing model using both δ13C and δ15N indicated that algal transported organic matter was the major resource assimilated by primary consumers. The contribution
of detrital transported organic matter was small in most cases, but there were a small number of taxa for which it could potentially
contribute to more than half the assimilated diet. Colloidal dissolved organic matter, which includes heterotrophic bacteria,
accounted for only a small fraction of the organic matter assimilated by most primary consumers, indicating that coupling
between microbial processes and metazoan production is minimal. Terrestrial C3 litter from the floodplain forest floor and aquatic macrophytes were also relatively unimportant to the assimilated diet
of primary consumers. Application of the mixing model to compare basal source isotopic ratios to secondary consumers revealed
that most organic matter moving from primary to secondary consumers originated from algal TOM. Our findings indicate that
autochthonous organic matter is the major energy source supporting metazoan production in the main channel of this large river,
at least during the summer. This study joins a number of other investigations performed globally that indicate organic matter
originating from instream production of sestonic and benthic microalgae is a major driver in the trophic dynamics of large
river ecosystems. 相似文献
8.
Rivers link oceans with the land, creating global hot spots of carbon processing in coastal seas. Coastlines around the world
are dominated by sandy beaches, but beaches are unusual in that they are thought to rely almost exclusively on marine imports
for food. No significant connections to terrestrial production having been demonstrated. By contrast, we isotopically traced
carbon and nitrogen pathways leading to clams (Donax deltoides) on beaches. Clams from areas influenced by river plumes had significantly different isotope signatures (δ13C: −18.5 to −20.2‰; δ15N: 8.3–10.0‰) compared with clams remote from plumes (δ13C: −17.5 to −19.5‰; δ15N: 7.6–8.7‰), showing that terrestrial carbon and sewage, both delivered in river plumes, penetrate beach food webs. This
is a novel mechanism of trophic subsidy in marine intertidal systems, linking the world’s largest shore ecosystem to continental
watersheds. The same clams also carry pollution signatures of sewage discharged into rivers, demonstrating that coastal rivers
connect ecosystems in unexpected ways and transfer contaminants across the land–ocean boundary. The links we demonstrate between
terrigenous matter and the largest of all marine intertidal ecosystems are significant given the immense social, cultural,
and economic values of beaches to humans and the predicted consequences of altered river discharge to coastal seas caused
by global climate change. 相似文献
9.
Decreased trophic position as a function of increasing body size of a benthic omnivorous fish from the largest freshwater lake in China 总被引:1,自引:0,他引:1
Potential body size-trophic position relationships of the Darkbarbel catfish Pelteobagrus vachelli (Richardson 1846) were examined using stable isotope analysis. Pelteobagrus vachelli is a benthic feeding fish from Lake Poyang, the largest freshwater lake in China. Two-source mixing model with mussel (Corbicula fluminea) and snail (Bellamya aeruginosa) as baseline primary consumers of planktonic and benthic food webs, respectively, was used to estimate contribution of carbon
derived from planktonic vs. benthic food web. Results showed that as an indicator of trophic position, δ15N was negatively correlated with the body length and weight of the fish; on the other hand, as an indicator of the end-member
food sources, δ13C was not correlated with fish size. The mixing model results showed that the averaged trophic position of our sampled 3.3–12.7 cm
Pelteobagrus vachelli was 3.1 ± 0.2 and derived 68 ± 27% of their food from the benthic food web, confirming that the feeding behavior of the catfish
favors benthic food sources. 相似文献
10.
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
11.
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
12.
Sean B. Menke Andy V. Suarez Chadwick V. Tillberg Cheng T. Chou David A. Holway 《Oecologia》2010,164(3):763-771
Studies of food webs often employ stable isotopic approaches to infer trophic position and interaction strength without consideration
of spatio-temporal variation in resource assimilation by constituent species. Using results from laboratory diet manipulations
and monthly sampling of field populations, we illustrate how nitrogen isotopes may be used to quantify spatio-temporal variation
in resource assimilation in ants. First, we determined nitrogen enrichment using a controlled laboratory experiment with the
invasive Argentine ant (Linepithema humile). After 12 weeks, worker δ15N values from colonies fed an animal-based diet had δ15N values that were 5.51% greater compared to colonies fed a plant-based diet. The shift in δ15N values in response to the experimental diet occurred within 10 weeks. We next reared Argentine ant colonies with or without
access to honeydew-producing aphids and found that after 8 weeks workers from colonies without access to aphids had δ15N values that were 6.31% larger compared to colonies with access to honeydew. Second, we sampled field populations over a
1-year period to quantify spatio-temporal variability in isotopic ratios of L. humile and those of a common native ant (Solenopsis xyloni). Samples from free-living colonies revealed that fluctuations in δ15N were 1.6–2.4‰ for L. humile and 1.8–2.9‰ for S. xyloni. Variation was also detected among L. humile castes: time averaged means of δ15N varied from 1.2 to 2.5‰ depending on the site, with δ15N values for queens ≥ workers > brood. The estimated trophic positions of L. humile and S. xyloni were similar within a site; however, trophic position for each species differed significantly at larger spatial scales. While
stable isotopes are clearly useful for examining the trophic ecology of arthropod communities, our results suggest that caution
is warranted when making ecological interpretations when stable isotope collections come from single time periods or life
stages. 相似文献
13.
Despite the recognition of the functional role of Hymenoptera (ants, bees and wasps) and Isoptera (termites) in tropical ecosystems,
their detailed feeding habits are not well known. To examine the feeding habits of these groups, we measured nitrogen (N)
and carbon (C) stable isotope ratios (δ15N and δ13C) of hymenopterans (12 families, ≥16 genera and ≥32 species) and isopterans (one family and 10 species) collected in a tropical
rain forest, Sarawak, Malaysia. We compared the isotopic signatures of these insects to those previously reported for other
consumers collected in the same forest. The δ15N and δ13C values of these insects overlapped with those of the other consumers, indicating that they have access to diverse C and
N sources in the forest. The δ15N values of ants and termites indicated that their feeding habits range along a continuum from herbivory (i.e. dependent on
honeydew and nectar) to predation and from wood-feeders to soil-feeders, respectively. In addition, the δ15N values of wasps varied greatly from −0.1‰ (Braconidae sp.) to 8.6‰ (Bembix sp.), suggesting that their feeding habits also range from omnivory to predation. The ant species Camponotus gigas had δ13C values similar to those of invertebrate detritivores and omnivores rather than to those of invertebrate herbivores, although
the diet of this species consists mostly of honeydew. This discrepancy suggests that the ant uses carbohydrates as an energy
source, the isotopic signatures of which are not well retained in the body tissues. Values of both δ15N and δ13C of the predatory army ant Leptogenys diminuta and the soil-feeding termite Dicuspiditermes nemorosus did not differ significantly, indicating that both trophic level and the humification of feeding substrates can increase
the isotopic signatures of terrestrial consumers. 相似文献
14.
Carbon and nitrogen stable isotopes are frequently used to study energy sources and food web structure in ecosystems, and
more recently, to study the effects of anthropogenic stress on aquatic ecosystems. We investigated the effect of nutrient
enrichment on δ13C and δ15N in fine (FPOM), coarse (CPOM) particulate organic matter, periphyton, invertebrates and fish in nine boreal streams in south-central
Sweden. In addition, we analysed the diet of benthic consumers using stable isotope data. Increases in δ15N of periphyton (R
2 = 0.88), CPOM (0.78), invertebrates (0.92) and fish (0.89) were related to nutrient enrichment. In contrast, δ13C signatures did not change along the nutrient gradient. Our results show that δ15N has potential as a sensitive indicator of nutrient enrichment in boreal streams. Carbon and nitrogen isotopes failed to
elucidate putative diets of selected aquatic consumers. Indeed, comparison of low- and high-impact sites showed that δ13C of many consumers were found outside the ranges of basal resource δ13C. Moreover, ranges of basal resource δ13C and δ15N overlapped at both low and high sites, making discrimination between the importance of allochthonous and autochthonous production
difficult. Our findings show that a fractionation rate of 3.4‰ is not always be appropriate to assess trophic interactions,
suggesting that more studies are needed on fractionation rates along gradients of impairment.
Handling editor: M. Power 相似文献
15.
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
16.
The Breton Sound estuary in southern Louisiana receives large amounts of Mississippi River water via a controlled diversion
structure at the upstream end of the estuary. We used stable isotopes to trace spatial and seasonal responses of the downstream
food web to winter and spring introductions of river water. Analysis of δ13C, δ15N, and δ34S in the common local consumers such as grass shrimp (Palaemonetes sp.), barnacles (Balanus sp.), and small plankton-feeding fish (bay anchovies, Anchoa mitchilli) showed that the diversion was associated with two of the five major source regimes that were supporting food webs: a river
regime near the diversion and a river-influenced productive marsh regime farther away from the diversion. Mixing models identified
a third river-influenced source regime at the marine end of the estuary where major natural discharge from the Bird’s Foot
Delta wraps around into estuarine waters. The remaining two source regimes represented typical estuarine conditions: local
freshwater sources especially from precipitation and a brackish source regime representing higher salinity marine influences.
Overall, the Mississippi River diversion accounted for 75% of food web support in the upper estuary and 25% in the middle
estuary, with influence strongest along known flow pathways and closest to the diversion. Isotopes also traced seasonal changes
in river contributions, and indicated increased plant community productivity along the major flow path of diversion water.
In the Breton Sound estuary, bottom–up forcing of food webs is strongly linked to river introductions and discharge, occurring
in spatial and temporal patterns predictable from known river input regimes and known hydrologic circulation patterns. 相似文献
17.
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
18.
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
19.
Nitrogen isotopes have been widely used to investigate trophic levels in ecological systems. Isotopic enrichment of 2–5‰ occurs with trophic level increases in food webs. Host–parasite relationships deviate from traditional food webs in that parasites are minimally enriched relative to their hosts. Although this host–parasite enrichment pattern has been shown in multiple systems, few studies have used isotopic relationships to examine other potential symbioses. We examined the relationship between two gut-nematodes and their lizard hosts. One species, Physaloptera retusa, is a documented parasite in the stomach, whereas the relationship of the other species, Parapharyngodon riojensis (pinworms), to the host is putatively commensalistic or mutualistic. Based on the established trophic enrichments, we predicted that, relative to host tissue, parasitic nematodes would be minimally enriched (0–1‰), whereas pinworms, either as commensals or mutualists, would be significantly enriched by 2–5‰. We measured the 15N values of food, digesta, gut tissue, and nematodes of eight lizard species in the family Liolaemidae. Parasitic worms were enriched 1±0.2‰ relative to host tissue, while the average enrichment value for pinworms relative to gut tissue was 6.7±0.2‰. The results support previous findings that isotopic fractionation in a host–parasite system is lower than traditional food webs. Additionally, the larger enrichment of pinworms relative to known parasites suggests that they are not parasitic and may be several trophic levels beyond the host. 相似文献
20.
δ13C and δ15N measurements are still poorly conducted in benthic invertebrate larvae. To assess the δ13C and δ15N changes occurring after a dietary shift, experiments were conducted on veliger larvae of Crepidula fornicata fed with two cultured microalgae (Isochrysis galbana and Pavlova lutheri) of known isotopic composition, 13C-enriched and 15N-depleted compared to the initial values of the larvae. Rapid changes in larval δ13C and δ15N were observed after the dietary shift, with an increase in δ13C and a decrease in δ15N. After 19 days of feeding, isotopic equilibrium was still not reached, a period which is close to the duration of the pelagic life of the larvae. This implies that the isotopic composition measured in field-collected larvae might only partly reflect actual larval feeding but also the parental isotopic signature, especially during the early developmental stages. Isotopic measurements in marine invertebrate larvae should thus be interpreted cautiously. In planktonic food web investigations, the study of field-collected larvae of different size/developmental stage may reduce potential misinterpretations. 相似文献