Impacts of Aggregation Methods and Trophospecies Number on the Structure and Function of Marine Food Webs

Aggregation of species with similar ecological properties is one of the effective methods to simplify food web researches.However,species aggregation will affect not only the complexity of modeling process but also the accuracy of models’outputs.Selection of aggregation methods and the number of trophospecies are the keys to study the simplification of food web.In this study,three aggregation methods,including taxonomic aggregation(TA),structural equivalence aggregation(SEA),and self-organizing maps(SOM),were analyzed and compared with the linear inverse model–Markov Chain Monte Carlo(LIM-MCMC)model.Impacts of aggregation methods and trophospecies number on food webs were evaluated based on the robustness and unitless of ecological net-work indices.Results showed that aggregation method of SEA performed better than the other two methods in estimating food web structure and function indices.The effects of aggregation methods were driven by the differences in species aggregation principles,which will alter food web structure and function through the redistribution of energy flow.According to the results of mean absolute percentage error(MAPE)which can be applied to evaluate the accuracy of the model,we found that MAPE in food web indices will increase with the reducing trophospecies number,and MAPE in food web function indices were smaller and more stable than those in food web structure indices.Therefore,trade-off between simplifying food webs and reflecting the status of ecosystem should be con-sidered in food web studies.These findings highlight the importance of aggregation methods and trophospecies number in the analy-sis of food web simplification.This study provided a framework to explore the extent to which food web models are affected by dif-ferent species aggregation,and will provide scientific basis for the construction of food webs.

Impacts of species depletion on the food web structure of a marine ecosystem based on topological network analysis

Single-species management ignores the interactions between species,and ecosystem-based fisheries management(EBFM)has become a main method to fisheries management.Understanding food web structures and species interactions is essential for the implementation of EBFM and maintenance of ecosystem functions.Overfishing is one of the main reasons behind the depletion,which could even lead to the depletion of some target species in local areas.So understanding the impacts of species depletion on food web structures is important for the implementation of EBFM.The impacts of species depletion can be transmitted through the food web and cause the local extinction of both target and non-target species.In this study,topological network analysis was applied to examine the impacts of species depletion on the food web structure of Haizhou Bay.Results showed that fine crayfish Leptochela gracilis,squid Loligo sp.,and Japanese snapping shrimp Alpheus japonicus have the highest numbers of outgoing links(48,32 and 31 respectively);thus,these species may be considered key prey species.Whitespotted conger Conger myriaster,fat greenling Hexagrammos otakii,and bluefin gurnard Chelidonichthys kumu were key predators with the highest number of incoming links(37,36 and 35 respectively).The competition graphs derived from the Haizhou Bay food web were highly connected(more than 40%predators sharing over 10 common prey species),and showed close trophic interaction between high trophic level fishes.Simulation analysis showed that the food web structure has small changes to the depletion of species in a highly complex food web.The most-connected target species did not necessarily indicate high structural importance;however,some species with low connectivity may demonstrate stronger trophic interactions and play important ecological roles in the food web.But most species were more sensitive to the depletion of the most-connected target species than other target species(for instance,for zooplankton,closeness centrality 13.876 in D6,but closeness centrality 82.143 in original food web).Therefore,EBFM should focus on the most-connected target species,but also on those species with few but strong links and feeding relationships in the food web.

Spatial variations in food web structures with alternative stable states:evidence from stable isotope analysis in a large eutrophic lake

Food web structures are well known to vary widely among ecosystems. Moreover, many food web studies of lakes have generally attempted to characterize the overall food web structure and have largely ignored internal spatial and environmental variations. In this study, we hypothesize that there is a high degree of spatial heterogeneity within an ecosystem and such heterogeneity may lead to strong variations in environmental conditions and resource availability, in turn resulting in dif ferent trophic pathways. Stable carbon and nitrogen isotopes were employed for the whole food web to describe the structure of the food web in different sub-basins within Taihu Lake. This lake is a large eutrophic freshwater lake that has been intensively managed and highly influenced by human activities for more than 50 years. The results show significant isotopic dif ferences between basins with dif ferent environmental characteristics. Such differences likely result from isotopic baseline dif ferences combining with a shift in food web structure. Both are related to local spatial heterogeneity in nutrient loading in waters. Such variation should be explicitly considered in future food web studies and ecosystem-based management in this lake ecosystem.

Topology-based analysis of pelagic food web structure in the central and eastern tropical Pacific Ocean based on longline observer data

The tropical Pacific Ocean supports many productive commercial fisheries.However,few studies of ecosystem structure in the tropical Pacific Ocean have been carried out.In this study,we analyzed the food web structure in the central and eastern tropical Pacific Ocean based on trophic relationships of 35 pelagic species collected by Chinese tuna longline observers from June to November in 2017.Topology indices(node degree,D;centrality indices,BC and CC;topological importance indices,TI^1,TI^3;keystone indices,K,K_t and K_b)and Key-Player algorithms(KPP-1,KPP-2)were used to select key species and construct a simplified food web combined with body size data.The Kendall rank correlation and hierarchical clustering analysis indicated that different topology indices resulted in consistent rankings of key species.Most key species were the same as those selected in other studies in the Pacific Ocean,such as Shortbill spearfish(Tetrapturus angustirostris),Swordfish(Xiphias gladius),Albacore tuna(Thunnus alalunga),cephalopods and scomber.The food web would be separated into many unconnected parts(F=0.632,FD=0.795,R^D=0.957)after the removal of the five key species,indicating the key roles of these species in the food web structure and stability.Body size was considered an influential indicator in constructing the simplified food web.This study can improve our understanding of the food web structure in the tropical Pacific Ocean and provide scientific basis for further ecosystem dynamics studies.

Food web structure and trophic levels in a saltwater pond sea cucumber and prawn polyculture system

The food sources of aquacultured Apostichopus japonicus and the trophic levels of organisms in a sea cucumber（A. japonicus） and prawn（Penaeus japonica） polyculture system in a saltwater pond in Zhuanghe, Liaoning Province were examined using carbon and nitrogen stable isotopes. Across organisms, δ13C ranged from（–25.47±0.20）‰ to（–16.48±0.17）‰（mean±SD）, and δ15N ranged from（4.23±0.49）‰ to（12.44±0.09）‰. The δ13C and δ15N contents of A. japonicus, P. japonica and Fenneropenaeus chinensis were comparatively higher than those of other organisms. Values of δ13C and δ15N revealed that P. japonica, Hemigrapsus sanguineus and Neomysis japonica comprised the largest component of the diet of A. japonicus. The mean trophic level of the organisms in this saltwater pond polyculture system was（2.75±0.08）. P. japonica, A. japonicus, F. chinensis,Synechogobius hasta and Neomysis japonica were in the 3rd trophic level（2–3）; jellyfish, H. sanguineus and zooplankton were in the 2nd trophic level（1–2）; and Enteromorpha prolifera, benthic microalgae, periphyton and suspended matter primarily consisting of phytoplankton, bacteria and humus were in the primary trophic level（0–1）.

A preliminary study on benthos food web structure oftidal zone in the Laoshan Bay by using stable carbon isotopes

By anayses of carbon isotopic composition (δ13C values) of the benthos collected in the Laoshan Bay in August 1993 and February and May 1994, it is found that the main food sources of the benthos can be divided into four groups in terms of carbon isotope composition: Particulate Organic Matter (POM), benthic diatoms, benthic macroalgae and the organic matter in sediments. The results show that the carbon isotopic composition of the benthic animals has a close relation with that of the food they take in. The Carbon isotopic compositions of benthos may be useful in elucidating their food sources. The carbon isotopic data have confirmed that POM is the main food source of the benthic filter feeders such as bivalves; crustaceans have a wide range of δ13C values, showing their food source has diversity; benthic diatoms are an important fraction of the food for most of gastropods. A preliminary investigation of the benthic-pelagic coupling in that region using the stable carban isotopic tracers has confirmed the importance of POM as a food source for benthos in this region, but the organic matter in sediments and benthic diatoms are also relatively important for a lot of benthic animals. The benthic-pelagic coupling in the Laoshan Bay temperate ecosystem is not so tight as that in ecosystems at higher latitudes such as northeastern water polynya.

Evaluation of the “fishing down marine food web” process in the north-west of Persian Gulf(Khuzestan Province) during the period of 2002–2011

The worldwide increase in commercial fisheries and its impact on ecosystems as well as inefficient fishery management have led to overfishing and frequent breakdown of traditional fish stocks. In this context, an analysis of Khuzestan inshore fisheries data covering the years 2002-2011, was conducted in reliance on testing for occurrence of the fishing down marine food webs （FDMFW） phenomenon in the North of Persian Gulf Large Marine Ecosystem （LME）. In this study, the mean trophic level （mTL） and the fishing-in-balance （FIB）-index of Khuzestan landings during this period of time were estimated using the trophic level of 47 fishery resources. Increase in total landings （I1） was observed, which explained the high fishing yield in major fishery resources （especially demersal）. Moreover, the moderates decreasing trend in mTL per decade, and the increasing trend in FIB-index were observed. The status of fishery resources in Khuzestan inshore waters （under exploited but not overexploited）, the rise in Y, FIB and slightly drop in mTL can be considered as indirect indicators of the fishing impacts on the trophic structure of marine communities. Based on this result, probability occurrence of FDMFW process in Khuzestan inshore waters is low to some extent. However, we suggest that the goal of management programs in Khuzestan inshore waters should prevent the continuance of this trend in the long-term using an ecosystem-based approach.

An assessment of “fishing down marine food webs” in coastal states during 1950–2010

Mean trophic level of fishery landings（MTL） is one of the most widely used biodiversity indicators to assess the impacts of fishing. Based on the landing data compiled by Food and Agriculture Organization combined with trophic information of relevant species in Fish Base, we evaluated the status of marine fisheries from 1950 to 2010 for different coastal states in Pacific, Atlantic and Indian Oceans. We found that the phenomenon of ＂fishing down marine food webs＂ occurred in 43 states. Specifically, 27 states belonged to ＂fishing-through＂ pattern, and 16 states resulted from ＂fishing-down＂ scenario. The sign of recovery in MTL was common in the Pacific, Atlantic and Indian Oceans（occurred in 20 states）, but was generally accompanied by significantly decreased catches of traditional low trophic level species. In particular, 11 states showed significant declining catches of lower trophic levels. The MTL-based assessment of ＂fishing down marine food webs＂ needs to be interpreted cautiously.

Construction of Food Web Model for Liusha Bay-Based on Stable Isotope Analysis

To investigate the food web structure of Liusha Bay,the δ13C and δ15N values of various organisms collected in Liusha Bay were measured via stable isotope technique.Based on the calculated δ15N value,the correlation between stable isotope ratio and trophic level were established to predict the trophic levels of shrimps,crabs,cephalopods and fishes.By comparing the analysis results of stomach contents of 24 organisms,two methods gave a similar consistence in approximately 71% of organisms within a 0.5 trophic level.It is concluded that stable isotope technique could be an effective method for studying ocean food web trophic level.

Removal of Agricultural Non-Point Source Pollutants by Artificial Aquatic Food Web System: A Study Case of the Control of Cynobacterial Bloom in Jiyu River

An artificial aquatic food web (AAFW) system was designed to remove the non-point source pollutants in eutrophic Jiyu river. A certain amount of Scenedesmus obliquus and Daphnia pulex was cultured in the system for the control of serious cyanobacterial bloom. The AAFW system was a continuous-flow system including one storage basin of 3 m3 capacity with polluted river water (the total nitrogen-TN: 4.49 mg⋅l-1;the total phosphorus-TP: 0.192 mg⋅l-1), one phytoplankton tank of 3 m3 capacity with an initial concentrations of S. obliquus about 5.8 × 103 ind⋅l-1, and one zooplankton growth chamber of 1.5 m3 capacity with an initial abundance of D. pulex about 22.5 ind⋅l-1. The system was optimized by setting hydraulic retention time of phytoplankton tank as 5 days and the experiments were operated for 45 days. Compared with the polluted river, TN and TP were removed about 28% and 47% by the AAFW system, respectively. The biomass of phytoplankton decrease from 6.33 mg⋅l-1 to 1.48 mg⋅l-1 and the percentage of cyanobacteria decrease from 43.93% to 2.36%, the biomass of Crustacean zooplankton increase from 0.34 mg⋅l-1 to 1.53 mg⋅l-1 and the percentage of D. pulex increase from 19.19% to 57.62%. Our results indicated that the AAFW system not only is an efficient, flexible system for reducing nutrient levels in tributary rivers, but also has an ability to control the cyanobacteria bloom and rebuilding the aquatic ecosystem from the polluted river water.

Stable isotopes in aquatic food web of an artificial lagoon in the Hangzhou Bay,China

Stable isotope values, δ13C and δ15N, were determined for four primary producers and 19 dominant consumers in a small artificial lagoon located in Hangzhou Bay. Based on these results the major pathways for energy flow and trophic structure of the artificial lagoon ecosystem were characterized. The mean δ13C values for the 19 consumers ranged from -22.99‰ to -14.24‰. Apart from so-iny mullet Liza haematocheila, the other 18 consumers had intermediate δ13C values between those of epibenthic microalgae and particulate organic matter (POM). The results of a multiple source linear mixing model (IsoSource model) indicated that 50% or more of the organic carbon in the tissues of most consumers was derived from epibenthic microalgae. This indicated that these primary producers were the main food source fueling the lagoon food web. The mean δ15N values for the 19 consumers varied between 4.93‰ and 12.97‰ and indicated four trophic levels in the lagoon. Four macroinvertebrates and zooplankton represented the primary consumers, whilst the other 14 consumers occupied the secondary and tertiary consumer levels. The 19 consumers were divided into three trophic guilds (detritivores/suspension feeders, omnivores and carnivores).

Colonization–competition dynamics of basal species shape food web complexity in island metacommunities

Exploring how food web complexity emerges and evolves in island ecosystems remains a major challenge in ecology.Food webs assembled from multiple islands are commonly recognized as highly complex trophic networks that are dynamic in both space and time.In the context of global climate change,it remains unclear whether food web complexity will decrease in a monotonic fashion when undergoing habitat destruction(e.g.,the inundation of islands due to sea-level rise).Here,we develop a simple yet comprehensive patch-dynamic framework for complex food web metacommunities subject to the competition-colonization tradeof between basal species.We found that oscillations in food web topological complexity(characterized by species diversity,mean food chain length and the degree of omnivory)emerge along the habitat destruction gradient.This outcome is robust to changing parameters or relaxing the assumption of a strict competitive hierarchy.Having oscillations in food web complexity indicates that small habitat changes could have disproportionate negative efects on species diversity,thus the success of conservation actions should be evaluated not only on changes in biodiversity,but also on system robustness to habitat alteration.Overall,this study provides a parsimonious mechanistic explanation for the emergence of food web complexity in island ecosystems,further enriching our understanding of metacommunity assembly.

Establishment of trophic continuum in the food web of the Yellow Sea and East China Sea ecosystem: Insight from carbon and nitrogen stable isotopes

Stable carbon and nitrogen isotope ratios (δ13C and δ15N) are used to study the trophic structure of food web in the Yellow Sea and East China Sea ecosystem. The trophic con-tinuum of pelagic food web from phytoplankton to top preyer was elementarily established, and a trophic structure diagram in the Yellow Sea and East China Sea was outlined in combination with carbon isotopic data of benthic organisms, which is basically consistent with and makes some improvements on the simplified Yellow Sea food web and the trophic structure diagram drawn based on the biomass of main resource population during 1985―1986. This result indicates that the stable isotope method is a potential useful means for further studying the complete marine food web trophic continuum from viruses to top predators and food web stability.

Determination of trophic relationships within a Bohai Bay food web using stable δ^(15)N and δ^(13)C analysis

This study measured stable carbon and nitro- gen isotope ratios in phytoplankton, zooplankton, five inver- tebrates species, eight fishes species and three seabirds spe- cies collected in Bohai Bay. δ 13C ranged from ?25.38‰ to ?11.08‰ showing a relative low enrichment in the food web from Bohai Bay. The mean δ 13C of mullet is higher than that of other organisms, and this might be due to that mullet is migration fish and feeds mainly on inshore sources. δ 15N ranged from 4.08‰ to 13.98‰, and showed a step-wise en- richment with trophic level of 3.8‰. The δ 15N enrichment factor was used to construct an isotopic food web model to establish trophic relationships within this marine food web. According to this model, exact trophic levels of all organisms were estimated as 1.46?2.10, 1.91?3.32, 2.55?4.23 and 2.98?4.28 for plankton, invertebrates, fishes, and seabirds.

Ecological controls on biogeochemical fluxes in the western Antarctic Peninsula studied with an inverse foodweb model

Sea ice in the western Antarctic Peninsula （WAP） region is both highly variable and rapidly changing. In the Palmer Station region, the ice season duration has decreased by 92 d since 1978. The sea-ice changes affect ocean stratification and freshwater balance and in turn impact every component of the polar marine ecosystem. Long-term observations from the WAP nearshore and offshore regions show a pattern of chlorophyll （Chl） variability with three to five years of negative Chl anomalies interrupted by one or two years of positive anomalies （high and low Chl regimes）. Both field observations and results from an inverse food-web model show that these high and low Chl regimes differed significantly from each other, with high primary productivity and net community production （NCP） and other rates associated with the high Chl years and low rates with low Chl years. Gross primary production rates （GPP） averaged 30 mmolC.m^-2.d^-1 in the low Chl years and 100 mmolC.m-2.d1 in the high Chl years. Both large and small phytoplankton were more abundant and more productive in high Chl years than in low Chl years. Similarly, krill were more important as grazers in high Chl years, but did not differ from microzooplankton in high or low Chl years. Microzooplankton did not differ between high and low Chl years. Net community production differed significantly between high and low Chl years, but mobilized a similar proportion of GPP in both high and low Chl years. The composition of the NCP was uniform in high and low Chl years. These results emphasize the importance of microbial components in the WAP plankton system and suggest that food webs dominated by small phytoplankton can have pathways that funnel production into NCP, and likely, export.

表征与非表征视角下饮食地域刻板印象的验证与测量

饮食在地域之间不断交融,跨越国界、民族及社区,既成为一种表征的文化意义结构,也成为非表征的日常参与和实践,在表征与非表征视角下,饮食地域刻板印象的存在与具体内容值得探讨。为了厘清这一问题,本研究采用混合研究法对饮食地域刻板印象进行验证和测量。子研究1使用了问卷调查法检验外显层面的饮食地域刻板印象,子研究2采用语义启动的实验范式检验内隐层面的饮食地域刻板印象。研究发现,被试在内隐和外显层面均持有饮食地域刻板印象,主要包括主食偏好、口味偏好、份量偏好和具体菜品4个维度。本研究验证了饮食地域刻板印象具有外显和内隐、经验与情景并存的特征,这扩展了表征与非表征理论相结合的饮食社会文化地理知识。

稳定同位素模型在水生生态系统食物网中的研究进展

水生生态系统食物网具有错综复杂的营养关系。稳定同位素技术的发展对了解生物间的摄食关系和食物网结构发挥着极为重要的作用。其中,稳定同位素混合模型(stable isotope mixing models,SIMMs)近年来的迅猛发展为进一步解决水生食物网的复杂性问题提供了有力的手段,尤其是在确定食物来源贡献和构建营养生态位方面。在本研究中,作者综述了稳定同位素模型的发展历程、主要模型的特点以及运行这类模型的条件;同时,对稳定同位素混合模型在水生生态系统食物网领域中的应用前景与局限性进行了总结与展望,以期为相关研究者提供参考。

基于稳定同位素技术的辽宁浑太河流域水生食物网研究

为探究辽宁省浑太河流域水生生物营养结构特征及其变化,分别于2020年秋季(10月)和2021年春季(5月)对该流域开展渔业资源调查,依据主要消费者及饵料生物样品的碳、氮稳定同位素值(δ13C和δ15N),利用SIBER和MixSIAR模型分析渔获物群落营养结构的时空差异,并初步构建该流域的食物网。结果表明,主要渔获物的δ13C和δ15N值分别为–37.18‰—–19.28‰和7.98‰—16.51‰,且季节性差异不显著(P>0.05),但δ13C值空间差异极显著(P<0.01)。浑太河流域渔获物的营养级为1.71—4.39,同种鱼类营养级具有极显著的时空差异(P<0.01)。与春季相比,鱼类在秋季摄食的食物资源更丰富、所占的生态位更宽,同时太子河的各项群落营养结构指标均优于浑河。基础食源分析结果表明水生植物与陆生植物分别为浑太河两个季度的主要碳源,陆生植物和POM分别为浑河和太子河中鱼类的主要碳源。研究填补了对浑太河流域水生生物食物网及群落营养结构研究的空缺,为该流域后续的保护、修复及进一步开发提供参考依据。

水体富营养化及物种入侵对星云湖食物网的影响

以云南浅水富营养化湖泊星云湖为研究区域,于2019~2020年对星云湖水质样品、初级生产者浮游植物(浮游碳源)、沉水植物(底栖碳源)、流域有机质(陆源)以及消费者浮游动物、底栖动物、鱼类等生物样品进行系统采集,甄别了星云湖初级生产者和消费者的碳、氮稳定同位素组成特征,并使用MixSIAR模型对消费者食物来源进行量化,对比分析以初级生产者(模式A)、以碳源贡献权重(模式B)和以初级消费者(模式C)3种不同氮稳定同位素基准计算的消费者营养级结果,进而构建适用于浅水富营养化湖泊的食物网结构,探讨富营养化以及外来入侵物种可能对星云湖食物网产生的影响.结果表明,MixSIAR模型结果显示浮游碳源、底栖碳源、陆源对消费者的贡献分别为77.3%、12.2%、10.5%,且沿岸带、敞水区不同生境鱼类的碳同位素信号不存在显著性差异,与浮游碳源的相近,指示浮游碳源是富营养湖泊消费者最主要的食物来源,其能量传输以浮游路径为主.对于不同食性的鱼类,杂食性鱼类的基础食物源(CR)跨度大,而肉食性鱼类营养长度(NR)更高,两者的核心生态位分离,且杂食性鱼类的核心生态位面积(3.79)高于肉食性鱼类(2.46),表明杂食性鱼类具有更高的适应性.模式B计算的营养级结果与消费者的食性较一致,可应用于星云湖消费者营养级计算.模式B结果显示,星云湖食物链长度为3.73,顶级掠食者为抚仙鲇,入侵物种太湖新银鱼营养级(3.37)次之,且与星云白鱼(3.01)在食物和生存空间上存在竞争.研究认为,富营养化导致的物源和能流的改变以及外来物种的入侵是造成星云湖土著鱼类资源衰退、食物网结构中生物多样性减少及生态系统功能弱化的主要原因.