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1.
This study aimed at establishing the trophic significance of the kelp Laminaria digitata for consumers inhabiting two rocky shores of Northern Brittany (France), displaying contrasted ecological conditions. The general trophic structure did not vary between these two sites, with a wide diversity of filter-feeders and predators, and only 14% of the species sampled belonging to the grazers' trophic group. The diversity of food sources fueling the food web appeared also similar. The food webs comprised four trophic levels and the prevalence of omnivory appeared relatively low compared to previous studies in the same area. Conversely, to the food web structure, which did not differ, the biochemical composition of L. digitata differed between the two sites, and was correlated to a larger diversity of grazers feeding on this kelp in sheltered conditions. This indicated that the spatial variability occurring in the nutritive value of L. digitata is likely to deeply affect the functioning of kelp-associated food webs. The contribution of L. digitata-derived organic matter to the diet of filter-feeders inhabiting these two environments was assessed using the mixing model Isosource, which showed the higher contribution of kelp matter in sheltered conditions. These results highlight the spatial variability that may occur in the functioning of kelp-associated food webs. Moreover, this suggests that hydrodynamics is likely to control the availability of kelp-derived organic matter to local filter-feeders, probably through an increase of detritus export in exposed areas.  相似文献   

2.
The internal organization of plankton communities plays a key role in biogeochemical cycles and in the functioning of aquatic ecosystems. In this study, the structure of a marine plankton community (including both unicellular and multicellular organisms) was inferred by applying an ecological network approach to species abundances observed weekly at the long‐term ecological research station MareChiara (LTER‐MC) in the Gulf of Naples (Tyrrhenian Sea, Mediterranean Sea) in the summers of 2002–2009. Two distinct conditions, characterized by different combination of salinity and chlorophyll values, alternated at the site: one influenced by coastal waters, herein named ‘green’, and the other reflecting more offshore conditions, named ‘blue’. The green and blue ‘phases’ showed different keystone biological elements: namely, large diatoms and small‐sized flagellates, respectively. Several correlations amongst species belonging to different trophic groups were found in both phases (connectance ~0.30). In the green phase, several links between phytoplankton and mesozooplankton and within the latter were detected, suggesting matter flow from microbes up to carnivorous zooplankton. A microbial‐loop‐like sub‐web, including mixo‐ and heterotrophic dinoflagellates and ciliates, was present in the green phase, but it was relatively more important in the blue phase. The latter observation suggests a more intense cycling of matter at the microbial trophic level in the blue phase. These results show that different modes of ecological organization can emerge from relatively small changes in the composition of aquatic communities coping with environmental variability. This highlights a significant plasticity in the internal structure of plankton webs, which should be taken into account in predictions of the potential effects of climatic oscillations on aquatic ecosystems and biogeochemical cycles therein.  相似文献   

3.
为了解大亚湾西南海域食物网的营养结构特征, 本研究于2020年1月份使用底拖网采集了该海域的渔业生物, 并分析了35种主要渔业生物的碳氮稳定同位素值。根据δ13C和δ15N值, 计算出该海域食物网6种营养结构的生态指标和主要渔业生物的营养级, 并绘制了连续营养谱。本次调查渔业生物主要为鱼类和虾蟹类, 鱼类的δ13C和δ15N值范围分别为-17.63‰ ~ -14.85‰和12.92‰~15.46‰, 平均值分别为-16.47‰和13.80‰; 虾蟹类的δ13C和δ15N值范围分别为-17.67‰ ~ -15.51‰和11.05‰~12.62‰, 平均值分别为-16.30‰和11.85‰。根据δ15N值, 用相加模型(trophic position by the additive model, TPA)和缩比模型(trophic position by the scaled model, TPS)分别计算了主要渔业生物的营养级, 结果显示两个模型计算的结果无显著性差异(P>0.1), 呈现鱼类平均营养级>虾蟹类的趋势。本研究发现大亚湾西南海域食物网初始食物来源较为单一, 存在食物链营养层级较少和长度不足, 食物网营养级多样性较低和营养结构冗余程度高的现象。与30多年前相比, 大亚湾近年高营养级生物量减少, 食物网结构由复杂趋向简单化, 生态系统稳定性较差。本研究结果不仅为了解大亚湾食物网结构组成提供了基础资料, 也为保护大亚湾渔业资源, 维持生态系统结构的稳定性提供参考依据。  相似文献   

4.
热带太平洋是金枪鱼类、旗鱼类等渔业的主要作业海域，但目前针对此海域食物网的研究仍十分缺乏。本文根据2017年6月-11月中国金枪鱼科学观察员在热带太平洋中东部海域（13°09''N -34°27''S, 100°03''-176°17''W）采集的鱼类样品，结合胃含物及其他分析方法以35个物种间的摄食关系为基础对此海域的食物网结构进行了分析。拓扑学指标（节点强度，D；中心性指数，BC和CC；拓扑重要性指数，TI1和TI3；关键性指数，K、Kt和Kb）和Key-Player算法（KPP-1和KPP-2）用来筛选关键种，并结合体长数据建立了基于关键种的简化食物网。肯德尔相关性分析和聚类分析结果表明，不同拓扑学指标筛选出的关键种是一致的。大多数关键种与太平洋其他海域的研究结果是相同的，如剑鱼（Xiphias gladius）、长鳍金枪鱼（Thunnus alalunga）、小吻四鳍旗鱼（Tetrapturus angustirostris）头足类和鲭属。移除5个关键种后，食物网将被离散为许多互不连接的部分（F=0.632，FD=0.795，RD=0.957），表明这些物种在维持食物网结构和稳定性中的必要性。物种体长是本研究构建简化食物网时的决定性因素。研究结果有助于提高对热带太平洋食物网结构的认识，同时为进一步的生态系统动力学研究提供科学依据。  相似文献   

5.
基于拓扑网络研究海州湾食物网结构与复杂性   总被引：1，自引：0，他引：1  
针对食物网结构与复杂性的研究有助于深入解析食物网的功能、营养动力和能量转化过程。本文根据2011年3?12月在海州湾及其邻近海域进行的5个航次的渔业资源底拖网调查资料以及胃含物分析数据，基于11个拓扑网络指数，构建了海州湾拓扑网络，研究海州湾食物网的结构与复杂性。结果表明，本文分析的海州湾食物网物种数S为93，连接数L为1 021，每个物种的相互作用数量L/S为10.98，连接性L/S2为0.12；顶级物种、中间物种、基础物种的比例分别为29%、69%和2%；食物网的杂食性指数为87%，连接复杂性指数SC为22.20，特征路径长度ChPath为2.11，聚类系数CC为0.23。通过每个物种的相互作用数量和连接性的研究显示，L/S和L/S2的值都处在正常范围内，所以海州湾食物网的复杂性仍保持较高水平。通过物种比例、杂食性指数、连接复杂性指数、特征路径长度、聚类系数对食物网结构分析，发现海州湾食物网结构处于稳定状态，能够在一定程度上抵御外界环境的扰动，保证生态系统功能的正常运行。通过对海州湾食物网结构与复杂性的研究，将为今后海州湾食物网功能的深入研究以及海州湾渔业资源的科学管理提供重要依据。  相似文献   

6.
The spatial variability in the food web structure of a Mediterranean semi-enclosed coastal environment (Stagnone di Marsala, Italy) was investigated using stable carbon and nitrogen isotopes. Organic matter sources and consumers were sampled in two locations with different environmental features (e.g. hydrodynamic regime, open-sea influence, vegetal coverage). Overall more 13C-enriched and 15N-depleted values were found in the central location than in the southern for organic matter sources and consumers. Pelagic consumers (zooplankton and juveniles of transient fish) showed slight spatial differences and in both locations seemed to depend on phytoplankton as the ultimate energy source. In contrast, benthic consumers (epifauna and resident fish) exhibited remarkable differences between locations. Spatial differences in organic matter sources were smaller than in benthic consumers and thus consumers presumably exploited different ultimate organic matter sources in the two locations. Sedimentary organic matter and epiphytes appeared to be the main primary producers transferred within the food web in both locations, and seagrasses seemed to play a non-negligible trophic role in the central location. The results of this paper corroborate the finding food webs are characterised by high spatial variability even on a small spatial scale and environmental heterogeneity more than primary production that seems to influence the trophic role of autotrophs.  相似文献   

7.
The identification of energy sources, pathways and trophic linkages among organisms is crucial for the understanding of food web dynamics. Stable isotopes were used to identify the trophic level of food web components and track the incorporation of organic matter of different origins in the coastal ecosystem adjacent to the Tagus estuary. It was shown that the river Tagus is a major source of organic carbon to this system. Also, the wide difference in δ13C among the primary consumers allowed the identification of the pelagic and the benthic energy pathways. The maximum trophic level observed was 2.4 for Sepia officinalis. This value is indicative of a short food web. It was concluded that the diet of the upper trophic level species relies directly on the lower food web levels to a considerable extent, instead of relying mostly on intermediate trophic level species. Moreover, the δ15N values of primary consumers were very close to that of particulate organic matter, probably due to poorly known processes occurring at the basis of the food web. This lowers the trophic length of the whole food web. Reliance on benthic affinity prey was high for all upper trophic level secondary consumers.  相似文献   

8.
Carbon and nitrogen stable isotope ratios (13C and 15N) and trophic level (TL) estimates based on stomach content analysis and published data were used to assess the contribution of autotrophic sources to 55 consumers in an intertidal mangrove creek of the Curuçá estuary, northern Brazil. Primary producers showed δ13C signatures ranging between −29.2 and −19.5‰ and δ15N from 3.0 to 6.3‰. The wide range of the isotopic composition of carbon of consumers (−28.6 to −17.1‰) indicated that different autotrophic sources are important in the intertidal mangrove food webs. Food web segregation structures the ecosystem into three relatively distinct food webs: (i) mangrove food web, where vascular plants contribute directly or indirectly via POM to the most 13C-depleted consumers (e.g. Ucides cordatus and zooplanktivorous food chains); (ii) algal food web, where benthic algae are eaten directly by consumers (e.g. Uca maracoani, mullets, polychaetes, several fishes); (iii) mixed food web where the consumers use the carbon from different primary sources (mainly benthivorous fishes). An IsoError mixing model was used to determine the contributions of primary sources to consumers, based on δ13C values. Model outputs were very sensitive to the magnitude of trophic isotope fractionation and to the variability in 13C data. Nevertheless, the simplification of the system by a priori aggregation of primary producers allowed interpretable results for several taxa, revealing the segregation into different food webs.  相似文献   

9.
Kelp holdfasts are highly reticulated structures which host a large diversity of small fauna. These microhabitats have been reported to play a crucial role in the biodiversity associated to kelp forest ecosystems. This study aimed at identifying trophic links and the main food sources sustaining food webs within communities associated with kelp holdfasts, through a stable isotope (δ13C and δ15N) approach. Sampling of the main invertebrates inhabiting Laminaria digitata holdfasts, and of their potential food sources, took place in February and May 2007. Stable isotope results reveal that most of the primary consumers, including filter-feeders and deposit-feeders, rely on the particulate organic matter sedimented within kelp holdfasts. Only three grazers departed from this general pattern. The correspondence between the stable isotope ratios of predators and sediment consumers indicated that this source is at the base of the main pathway through which energy and matter transit in the food web. δ15N ranges found for consumers revealed that the food web associated with kelp holdfasts is composed of 3.5 levels. In spite of the low diversity of food sources at the base of the food web, these microhabitats can therefore be considered micro-scale ecosystems, from a functional perspective.  相似文献   

10.
Trophic studies are fundamental to understanding the dynamics of assemblages and functional roles of species within ecosystems, contributing to the identification of factors responsible for the organization and structure of communities. This study aimed to analyse the trophic organization of tidepool fish assemblages in the tropical Southwestern Atlantic, based on the underlying idea that food resources are not limiting and that trophic guild formation is not driven by food competition. Diets were based on feeding index values of food categories for 12 representative species collected in six tidepools (20º49′ S, 40º36′ W) at quarterly intervals (2005 to 2007). The main food categories were small crustaceans, polychaetes and macroalgae. Multivariate techniques evidenced two multispecific trophic guilds: small‐prey carnivores, including Bathygobius soporator, Bathygobius geminatus, Malacoctenus delalandii and Halichoeres poeyi, and herbivores, including Sparisoma axillare and Acanthurus bahianus. Other species presented significantly different diets and were classified into the following guilds: omnivores feeding on filamentous algae and copepods (Abudefduf saxatilis); large‐prey carnivores (Labrisomus nuchipinnis); omnivores feeding on polychaetes and filamentous algae (Stegastes fuscus); and polychaete feeders (Ahlia egmontis). Gymnothorax funebris and Gymnothorax moringa were classified as carcinophagores and piscivores, respectively. Trophic organization appears related to species convergence toward the use of abundant food resources, driven by a combination of factors allowing some resource partitioning through inter‐specific differences in consumer size, microhabitat, behavior, and trophic specialization.  相似文献   

11.
Large physical changes that alter reef macrobenthos and fish assemblages occur with increasing depth, so the biological processes that regulate communities at different depths are expected to diverge. We used analyses of stable isotopes (δ13C and δ15N) and fatty acids to establish whether shallow (11–25 m) and deep (45–75 m) warm-temperate reef communities within a South African marine protected area differ in their trophic organisation and nutritional condition. We found evidence of enhanced nutritional condition in plankton from the deeper reef as compared with the shallow reef based on the essential fatty acid content, but this effect was generally not observed in the macrobenthos or the fish communities. Community-based indices derived from the stable isotope data indicated that the shallow-reef community had significantly greater niche diversification (greater diversity of carbon sources at the base of the food web) and more niche space occupied than the deep-reef community. One obvious difference in available carbon sources between reef communities was the absence of benthic primary production on the deep reef, where light is limiting. Our results highlight that the decreased trophic diversity, and to an extent functional redundancy, associated with the simplification of food webs at depth may translate into greater vulnerability of deep reefs to disturbance.  相似文献   

12.
Gut content examination and trophic markers (fatty acids, stable isotopes of C and N) were combined to delineate the diet of the dominant species of amphipods from Mediterranean Posidonia oceanica seagrass meadows and to highlight trophic diversity among this community. Our results indicate that, although all dominant species heavily relied on macroalgal epiphytes, considerable interspecific dietary differences existed. Carbon stable isotope ratios notably showed that some of the amphipod species favored grazing on epiphytes from leaves or litter fragments (Apherusa chiereghinii, Aora spinicornis, Gammarus aequicauda), while others such as Dexamine spiniventris preferred epiphytes from rhizomes. The remaining amphipods (Caprella acanthifera, Ampithoe helleri and Gammarella fucicola) readily consumed both groups. In addition, SIAR modeling suggested that most species had a mixed diet, and relied on several food items. Fatty acid analysis and gut contents revealed that contributions of microepiphytic diatoms and of benthic and suspended particulate organic matter to the diet of amphipods were anecdotal. None of the examined species seemed to graze on their seagrass host [low 18:2(n‐6) and 18:3(n‐3) fatty acids contents], but Gammarus aequicauda partly relied on seagrass leaf detritus, as demonstrated by the lesser 13C‐depletion of their tissues. Overall, our findings suggest that amphipods, because of their importance in the transfer of organic matter from primary producers and detritus to higher rank consumers, are key items in P. oceanica‐associated food webs.  相似文献   

13.
The relative contribution of chemosynthesis in heterotrophic fauna at seeps is known to be influenced by depth and by habitat. Using stable isotopes of carbon and nitrogen, we investigated macro‐ and megafaunal nutritional patterns in Norwegian margin cold seeps by comparing food webs both among habitats within a seep site and between different sites. The very active Håkon Mosby mud volcano (HMMV) is characterized by geochemical gradients, microbial activity and faunal zonation from the centre to the periphery. The Storegga Slide (600–900 m depth) has pockmarks with patchy less active seeps, and also shows concentric zonation of habitats but at much smaller spatial scale. The dominant carbon source for macrofaunal nutrition in both areas was chemosynthetically fixed and the bulk of organic carbon was derived from sulphur‐oxidizing bacteria. In HMMV, food chains were clearly separated according to habitats, with significantly lighter δ13C signatures on microbial mats and adjacent sediment (?33.06 to ?50.62‰) than in siboglinid fields (?19.83 to ?35.03‰). Mixing model outputs revealed that the contribution of methane‐derived carbon was small in siboglinid fields (0–17%) but significant (39–61%) in the microbial mats. Moreover, the variability of macrofauna signatures within this later habitat suggests the co‐occurrence of two food chains, one based on primary production via methanotrophy and the other via sulphide oxidation. The length of the food chains also varied among habitats, with at least one more trophic level in the siboglinid fields located at the periphery of the volcano. Conversely, in Storrega pockmarks, faunal δ13C signatures did not vary among habitats but among species, although separate food chains seem to co‐occur. The small size of the seepage areas and their lower fluxes compared to HMMV allow more background species to penetrate the seep area, increasing the range of δ15N and the trophic level number. Probably due to the higher flux of photosynthetic particulate organic carbon, the overall chemosynthesis‐based carbon contribution in invertebrate nutrition was lower than that in HMMV.  相似文献   

14.
Carbon and nitrogen isotopic composition was used to identify the main sources of carbon and describe the main trophic pathways in Deluge Inlet, a near-pristine mangrove estuary in tropical north Queensland, Australia. Producers' δ13C varied from −28.9‰ for mangroves to −18.6‰ for seagrass. Animals were also well separated in δ13C (−25.4‰ to −16.3‰ for invertebrates and −25.2‰ to −17.2‰ for fish), suggesting considerable differences in ultimate sources of carbon, from a substantial reliance on mangrove carbon to an almost exclusive reliance on seagrass. In general, invertebrates had lower δ15N than fish, indicating lower trophic levels. Among fish, δ15N values reflected well the assumed trophic levels, as species from lower trophic levels had lower δ15N than species from higher trophic levels. Trophic levels and trophic length were estimated based on δ15N of invertebrate primary consumers (6.1‰), with results suggesting a food web with four trophic levels. There was also evidence of a high level of diet overlap between fish species, as indicated by similarities in δ13C for fish species of higher trophic levels. Stable isotope data was also useful to construct a general model for this food web, where five main trophic pathways were identified: one based on both mangrove and microphytobenthos, one on plankton, two on both microphytobenthos and seagrass, and one based mainly on seagrass. This model again suggested the presence of four trophic levels, in agreement with the value calculated based on the difference in δ15N between invertebrate primary consumers and top piscivores.  相似文献   

15.
Studies of the trophic structure in methane‐seep habitats provide insight into the ecological function of deep‐sea ecosystems. Methane seep biota on the Chilean margin likely represent a novel biogeographic province; however, little is known about the ecology of the seep fauna and particularly their trophic support. The present study, using natural abundance stable isotopes, reveals a complex trophic structure among heterotrophic consumers, with four trophic levels supported by a diversity of food sources at a methane seep area off Concepción, Chile (~36° S). Although methanotrophy, thiotrophy and phototrophy are all identified as carbon fixation mechanisms fueling the food web within this area, most of the analysed species (87.5%) incorporate carbon derived from photosynthesis and a smaller number (12%) use carbon derived from chemosynthesis. Methane‐derived carbon (MDC) incorporation was documented in 22 taxa, including sipunculids, gastropods, polychaetes and echinoderms. In addition, wide trophic niches were detected in suspension‐feeding and deposit‐feeding taxa, possibly associated with the use of organic matter in different stages of degradation (e.g. from fresh to refractory). Estimates of Bayesian standard ellipses area (SEAB) reveal different isotopic niche breadth in the predator fishes, the Patagonian toothfish Dissostichus eleginoides and the combtooth dogfish Centroscyllium nigrum, suggesting generalist versus specialist feeding behaviors, respectively. Top predators in the ecosystem were the Patagonian toothfish D. eleginoides and the dusky cat shark, Bythaelurus canescens. The blue hake Antimora rostrata also provides a trophic link between the benthic and pelagic systems, with a diet based primarily on pelagic‐derived carrion. These findings can inform accurate ecosystem models, which are critical for effective management and conservation of methane seep and adjacent deep‐sea habitats in the Southeastern Pacific.  相似文献   

16.
《Ocean & Coastal Management》2000,43(8-9):615-655
Almost 50 yr of global multispecies harvests are represented in the FAO capture production database, and offer a broad perspective on events that underlie the major observed changes in global marine harvests. The likely relevance of top–down and bottom–up trophic interactions, versus the impacts of changes in fishing technology and markets on the trophic level of landings, are discussed on a regional basis. Despite the low resolution of this global data set, several common features emerge. Rapid increases in fleet size and technological advance, and imperfect fisheries management measures, are probably responsible for declines in peak multispecies production in many areas since the 1970s, and internal evidence suggests that peak production is not far away in the remainder. Staggered dates of peak landings in different world areas seem to reflect the spread of industrial fishing fleets from `core areas’ to the rest of the world's oceans, which largely took place from the 1960s to 1990s. A general move to higher exploitation of piscivores in global landings is implied in some areas. The hypothesis that top–down removal of predators is affecting lower trophic production is however only one explanation for declining mean trophic levels, and is more likely to emerge from local food web studies. In some regions an increased proportion of short-lived invertebrates in harvests later in the time series supports a move downwards in trophic level targeting. In the North Atlantic and some other areas, fishing down marine food webs may be a likely cause of the increase in landings of shelf planktivores. A shift from depleted apical resources to species lower in the food web may have been made on economic grounds however, independent of possible effects of a release of predatory pressure. Sharp increases in planktivores later in the time series show up in the Eastern Central Atlantic and in the Southeast Pacific and do not appear to be primarily related to depletion of predators. They seem to reflect intermittent strength of upwelling systems, and hence bottom–up effects on food web production, together with changes in harvest technology. For some areas, piscivore landings increased later in the time series than those of planktivores. In the Mediterranean, this seems mainly a bottom–up response to increased marine productivity associated with land run-off and consequent improvements in predatory foraging. In some tropical areas, later increases in piscivorous landings mainly result from expansion of distant water tuna fleets, and are probably unrelated to exploitation of forage fishes. The technological revolution of the 1950s and 1960s involved rapid application of synthetic fibres to improved gear. This led to large-scale mid-water trawling and purse seining by industrial fleets and has especially increased vulnerability of small pelagic stocks over the last few decades. This appears mainly responsible for the apparent decline in mean trophic level of harvests in areas with large stocks of these resources. From an analysis of variances of the sample data set, `Punctuated equilibrium', involving actual changes in ecosystems, rather than just continuous change in the relative harvest rates of species in a given ecosystem, is suggested as an important phenomenon, reflecting both ecological change and changing exploitation strategies.  相似文献   

17.
End-to-end models that represent ecosystem components from primary producers to top predators, linked through trophic interactions and affected by the abiotic environment, are expected to provide valuable tools for assessing the effects of climate change and fishing on ecosystem dynamics. Here, we review the main process-based approaches used for marine ecosystem modelling, focusing on the extent of the food web modelled, the forcing factors considered, the trophic processes represented, as well as the potential use and further development of the models. We consider models of a subset of the food web, models which represent the first attempts to couple low and high trophic levels, integrated models of the whole ecosystem, and size spectrum models. Comparisons within and among these groups of models highlight the preferential use of functional groups at low trophic levels and species at higher trophic levels and the different ways in which the models account for abiotic processes. The model comparisons also highlight the importance of choosing an appropriate spatial dimension for representing organism dynamics. Many of the reviewed models could be extended by adding components and by ensuring that the full life cycles of species components are represented, but end-to-end models should provide full coverage of ecosystem components, the integration of physical and biological processes at different scales and two-way interactions between ecosystem components. We suggest that this is best achieved by coupling models, but there are very few existing cases where the coupling supports true two-way interaction. The advantages of coupling models are that the extent of discretization and representation can be targeted to the part of the food web being considered, making their development time- and cost-effective. Processes such as predation can be coupled to allow the propagation of forcing factors effects up and down the food web. However, there needs to be a stronger focus on enabling two-way interaction, carefully selecting the key functional groups and species, reconciling different time and space scales and the methods of converting between energy, nutrients and mass.  相似文献   

18.
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19.
本研究基于稳定同位素技术对江苏近海春、夏、秋季采集的不同生物类群(鱼类、甲壳类、头足类和底栖动物等)进行稳定同位素的分析,利用SIBER模型计算不同季节消费者的营养生态位,并计算出6种营养结构的量化指标.结果表明,3个季节的δ13C值、δ15N值均差异不显著(p>0.05).春季δ13C值范围为?24.47‰～?14....  相似文献   

20.
To obtain information on food web structure in salt marshes of the Changjiang (Yangtze) River Estuary, the δ13C and δ15N values of primary producers and consumers were determined. The mean δ13C values of 31 dominant consumers ranged from -23.13‰ to -14.37‰. Except for several species (Eriocheir sinensis, Sinonovacula constricta and Potamocorbula ustulata), consumers had intermediate δ13C values between those of benthic microalgae and Spartina alterniflora. The mean δ15N values of 31 dominant consumers varie...  相似文献   

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