全球变化对食物网结构影响机制的研究进展

食物网主要依靠基于不同营养级间物种互作形成的上行与下行调控维持其结构。全球变化能够改变种间关系, 威胁生物多样性的维持, 然而目前对全球变化改变食物网结构的机制仍处于探索阶段。近年来通过大时空格局与多营养级食物网研究, 发现全球变化的作用机制主要可归结为3种: 物候错配、关键种丧失与生物入侵。该文聚焦于这3种机制, 综述各种机制造成的食物网结构变化并探讨相关的进化与生态驱动因素。三种干扰机制均通过改变原有种间关系, 影响食物网调控, 改变食物网结构。不同的是, 物候错配造成的种间关系变化是由于不同物种的物候对全球变化产生非同步响应所致; 关键种丧失则使营养级间取食/捕食关系发生变化甚至缺失; 而入侵物种通过竞争排除同营养级物种改变种间关系。最后, 该文提出食物网结构变化的实质是物种是否能够适应快速变化的生态环境, 并据此展望未来研究方向。随着全球变化影响日益加剧, 急需继续深入探索导致全球变化下食物网结构改变的机制, 为制定合理的生物多样性保护与生态修复规划提供重要理论支撑。     

Temperature impacts on deep‐sea biodiversity

Temperature is considered to be a fundamental factor controlling biodiversity in marine ecosystems, but precisely what role temperature plays in modulating diversity is still not clear. The deep ocean, lacking light and in situ photosynthetic primary production, is an ideal model system to test the effects of temperature changes on biodiversity. Here we synthesize current knowledge on temperature–diversity relationships in the deep sea. Our results from both present and past deep‐sea assemblages suggest that, when a wide range of deep‐sea bottom‐water temperatures is considered, a unimodal relationship exists between temperature and diversity (that may be right skewed). It is possible that temperature is important only when at relatively high and low levels but does not play a major role in the intermediate temperature range. Possible mechanisms explaining the temperature–biodiversity relationship include the physiological‐tolerance hypothesis, the metabolic hypothesis, island biogeography theory, or some combination of these. The possible unimodal relationship discussed here may allow us to identify tipping points at which on‐going global change and deep‐water warming may increase or decrease deep‐sea biodiversity. Predicted changes in deep‐sea temperatures due to human‐induced climate change may have more adverse consequences than expected considering the sensitivity of deep‐sea ecosystems to temperature changes.     

Legacy effects of drought alters the aquatic food web of a northern boreal peatland

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Hydrogen cycling in a three-tiered food web growing on the methanogenic conversion of 3-chlorobenzoate

Abstract A defined 3-chlorobenzoate-degrading methanogenic consortium was constructed by recombining key organisms isolated from a 3-chlorobenzoate-degrading methanogenic sludge enrichment. The organisms comprise a three-tiered food chain which includes: (1) reductive dechlorination of 3-chlorobenzoate; (2) oxidation of benzoate to acetate, H₂ and CO₂; (3) removal of H₂ plus CO₂ by conversion into methane. The defined consortium, consisting of a dechlorinating organism (DCB-1), a benzoate degrader (BZ-1) and a lithotrophic methanogen ( Methanospirillum strain PM-1) grew well in a basal salts medium supplemented with 3-chlorobenzoate (3.2 mM) as the sole energy source. The chlorine released from the aromatic ringe was recovered in stoichiometric amounts as the chloride ion. The reducing power required for reductive dechlorination was obtained from the hydrogen produced in the acetogenic oxidation of benzoate. One-third of the benzoate-derived hydrogen was recycled via the reductive dechlorination of 3-chlorobenzoate, indicating that the consortium operated as a food web rather than a food chain.     

Linking soil food web structure to above‐ and belowground ecosystem processes: a meta‐analysis

Soil fauna can be an important regulator of community parameters and ecosystem processes, but there have been few quantitative syntheses of the role of soil fauna in terrestrial soil communities and ecosystems. Here, we conducted a meta‐analysis to investigate the impacts of invertebrate soil micro‐ and mesofauna (grazers and predators) on plant productivity and microbial biomass. Overall our results indicate that an increase in the biomass of soil fauna increased aboveground plant productivity across ecosystems by 35% and decreased microbial biomass by 8%. In addition, we found no evidence for trophic cascades in terrestrial soil food webs, but the bacterivorous component of soil fauna influenced plant productivity and microbial biomass more than did the fungivorous component. Furthermore, changes in the biomass of soil fauna differentially affected plant productivity among plant functional groups: a higher biomass of soil fauna increased aboveground productivity by 70% in coniferous systems. However, in ecosystems dominated by legumes, a functional group with lower inorganic nitrogen requirements, there was no response of aboveground productivity to increases in the biomass of soil fauna. In sum, the results of this meta‐analysis indicate that soil fauna help to regulate ecosystem production, especially in nutrient‐limited ecosystems.     

Trickle-down effects of aboveground trophic cascades on the soil food web

Trophic cascades are increasingly being regarded as important features of aboveground and belowground food webs, but the effects of aboveground cascades on soil food webs, and vice versa, remains essentially unexplored. We conducted an experiment consisting of model synthesised communities containing grassland plant and invertebrate species, in which treatments included soil only, soil+plants, soil+plants+aphids, and soil+plants+aphids+predators; predator treatments consisted of the lacewing Micromus tasmaniae and ladybird beetle Coccinella undecimpunctata added either singly or in combination. Addition of Micromus largely reversed the negative effects of aphids on plant biomass, while both of the predator species caused large changes in the relative abundances of dominant plant species. Predators of aphids also affected several components of the belowground subsystem. Micromus had positive indirect effects on the primary consumer of the soil decomposer food web (microflora), probably through promoting greater input of basal resources to the decomposer subsystem. Predator treatments also influenced densities of the tertiary consumers of the soil food web (top predatory nematodes), most likely through inducing changes in plant community composition and therefore the quality of resource input to the soil. The secondary consumers of the soil food web (microbe‐feeding nematodes) were, however, unresponsive. The fact that some trophic levels of the soil food web but not others responded to aboveground manipulations is explicable in terms of top‐down and bottom‐up forces differentially regulating different belowground trophic levels. Addition of aphids also influenced microbial community structure, promoted soil bacteria at the expense of fungi, and enhanced the diversity of herbivorous nematodes; in all cases these effects were at least partially reversed by addition of Micromus. These results in tandem point to upper level consumers in aboveground food webs as a potential driver of the belowground subsystem, and provide evidence that predator‐induced trophic cascades aboveground can have effects that trickle through soil food webs.     

Litter identity mediates predator impacts on the functioning of an aquatic detritus-based food web

During past decades, several mechanisms such as resource quality and habitat complexity have been proposed to explain variations in the strength of trophic cascades across ecosystems. In detritus-based headwater streams, litter accumulations constitute both a habitat and a resource for detritivorous macroinvertebrates. Because litter edibility (which promotes trophic cascades) is usually inversely correlated with its structural complexity (which weakens trophic cascades), there is a great scope for stronger trophic cascades in litter accumulations that are dominated by easily degradable litter species. However, it remains unclear how mixing contrasting litter species (conferring both habitat complexity and high quality resource) may influence top–down controls on communities and processes. In enclosures exposed in a second-order stream, we manipulated litter species composition by using two contrasting litter (alder and oak), and the presence–absence of a macroinvertebrate predator (Cordulegaster boltonii larvae), enabling it to effectively exert predation pressure, or not, on detritivores (consumptive versus non-consumptive predation effects). Leaf mass loss, detritivore biomass and community structure were mostly controlled independently by litter identity and mixing and by predator consumption. However, the strength of predator control was mediated by litter quality (stronger on alder), and to a lesser extent by litter mixing (weaker on mixed litter). Refractory litter such as oak leaves may contribute to the structural complexity of the habitat for stream macroinvertebrates, allowing the maintenance of detritivore communities even when strong predation pressure occurs. We suggest that considering the interaction between top–down and bottom–up factors is important when investigating their influence on natural communities and ecosystem processes in detritus-based ecosystems.     

Recognizing cross‐ecosystem responses to changing temperatures: soil warming impacts pelagic food webs

The energy and materials that move across ecosystem boundaries influence food web structure and key ecosystem functions. Despite the acknowledged importance of such ecological subsidies, surprisingly little information is available regarding the role of environmental temperature in influencing subsidy quality and the response of the recipient ecosystem. We evaluated the impacts of temperature‐mediated changes in leaves from deciduous trees, an important subsidy from terrestrial to freshwater ecosystems, on both the producer‐based and detritivore‐based components of a pelagic pond food web in a field mesocosm experiment. We hypothesized that variation in leaf chemistry driven by increased soil temperature would alter both the quality of leaf subsidies and the pond response. We collected red maple Acer rubrum leaves from heated and ambient temperature plots from the long‐term soil warming experiment at the Harvard Experimental Forest and added them to 167‐l field mesocosms containing established plankton communities, creating ‘no leaf’, ‘ambient leaf’ and ‘heated leaf’ treatments during autumn 2012. We then monitored physical, chemical, and biological responses to treatments until the mesocosms froze six weeks later. Experimental soil warming altered the chemical composition of deciduous leaves, the physical and chemical environment of the aquatic ecosystems to which leaves were added, and the pelagic pond food webs as measured by community composition. Compared to leaves from ambient‐temperature soils, leaves from warmed soils initially resulted in lower water column phosphorus and dissolved organic carbon, reducing bacterial densities. However, the diminished carbon and phosphorus resulting from soil warming also increased light availability that ultimately stimulated cladoceran zooplankton relative to ambient‐temperature leaves. Our results suggest that changes in temperature can alter ecological subsidies in unanticipated ways, and suggest that accurately predicting the potential consequences of climate change will require conducting research across ecosystem boundaries.     

Above‐ and belowground insect herbivores mediate the impact of nitrogen eutrophication on the soil food web in a grassland ecosystem

Insect herbivores are important drivers of ecosystem processes in grasslands, and can mediate the grassland's response to environmental change. For example, recent evidence shows that above‐ and belowground herbivory, individually and in combination, can modify how a plant community responds to nitrogen (N) eutrophication, an important driver of global change. However, knowledge about how such effects extend to the associated soil food web is lacking. In a mesocosm experiment, we investigated how communities of soil nematodes – an abundant and functionally important group of soil organisms – responded to above‐ and belowground insect herbivory at contrasting N levels. We found that the strongest influence of above‐ and belowground herbivory on the nematode community appeared at elevated N. The abundance of root‐feeding nematodes increased when either above‐ or belowground insect herbivores were present at elevated N, but when applied together the two herbivore types cancelled out one another's effect. Additionally, at elevated N aboveground herbivory increased the abundance of fungal‐feeders relative to bacterial‐feeders, which indicates changes in decomposition pathways induced by N and herbivory. Belowground herbivory increased the abundance of omnivorous nematodes. The shifts in both the herbivorous and detrital parts of the soil food web demonstrate that above‐ and belowground herbivory does not only mediate the response of the plant community to N eutrophication, but in extension also the soil food web sustained by the plant community. We conclude that feedbacks between effects of above‐ and belowground herbivory mediate the response of the grassland ecosystem to N eutrophication.     

Climate change impacts on body size and food web structure on mountain ecosystems

The current distribution of climatic conditions will be rearranged on the globe. To survive, species will have to keep pace with climates as they move. Mountains are among the most affected regions owing to both climate and land-use change. Here, we explore the effects of climate change in the vertebrate food web of the Pyrenees. We investigate elevation range expansions between two time-periods illustrative of warming conditions, to assess: (i) the taxonomic composition of range expanders; (ii) changes in food web properties such as the distribution of links per species and community size-structure; and (iii) what are the specific traits of range expanders that set them apart from the other species in the community—in particular, body mass, diet generalism, vulnerability and trophic position within the food web. We found an upward expansion of species at all elevations, which was not even for all taxonomic groups and trophic positions. At low and intermediate elevations, predator : prey mass ratios were significantly reduced. Expanders were larger, had fewer predators and were, in general, more specialists. Our study shows that elevation range expansions as climate warms have important and predictable impacts on the structure and size distribution of food webs across space.     

Legacy effects of drought on plant growth and the soil food web

Soils deliver important ecosystem services, such as nutrient provision for plants and the storage of carbon (C) and nitrogen (N), which are greatly impacted by drought. Both plants and soil biota affect soil C and N availability, which might in turn affect their response to drought, offering the potential to feed back on each other’s performance. In a greenhouse experiment, we compared legacy effects of repeated drought on plant growth and the soil food web in two contrasting land-use systems: extensively managed grassland, rich in C and with a fungal-based food web, and intensively managed wheat lower in C and with a bacterial-based food web. Moreover, we assessed the effect of plant presence on the recovery of the soil food web after drought. Drought legacy effects increased plant growth in both systems, and a plant strongly reduced N leaching. Fungi, bacteria, and their predators were more resilient after drought in the grassland soil than in the wheat soil. The presence of a plant strongly affected the composition of the soil food web, and alleviated the effects of drought for most trophic groups, regardless of the system. This effect was stronger for the bottom trophic levels, whose resilience was positively correlated to soil available C. Our results show that plant belowground inputs have the potential to affect the recovery of belowground communities after drought, with implications for the functions they perform, such as C and N cycling.     

基于土壤食物网的生态系统复杂性-稳定性关系研究进展

复杂性-稳定性关系是生态学核心问题之一。作为模式食物网,土壤食物网在探索生态系统复杂性-稳定性关系中起了极大的作用。总结了以Moore、de Ruiter、Neutel等为代表的理论生态学家以土壤食物网为工具研究生态系统复杂性-稳定性关系的方法、结论及不足之处,并展望了未来的发展方向。Moore、de Ruiter、Neutel等将土壤食物网功能群生物量数据、土壤食物网Lotka-Volterra模型和面向过程模型三者结合起来,描述相互作用强度大小格局、分室、能流组织形式等复杂性特征;将土壤食物网Lotka-Volterra模型与群落矩阵结合起来分析局域稳定性,进而探讨生态系统复杂性-稳定性关系的一般规律。在此基础上,Moore、de Ruiter、Neutel等证明了与随机食物网相比,真实食物网的相互作用强度格局、分室等复杂性特征提高了生态系统稳定性,生产力与稳定性共同决定了食物链的长度,并指出建立在平衡态基础上的静态土壤食物网模型在探索生态系统复杂性-稳定性关系方面具有较大的不足,动态土壤食物网是未来以土壤食物网为工具研究生态系统复杂性-稳定性关系的发展方向。     

Effects of native and exotic range‐expanding plant species on taxonomic and functional composition of nematodes in the soil food web

Due to climate warming, many plant species shift ranges towards higher latitudes. Plants can disperse faster than most soil biota, however, little is known about how range‐expanding plants in the new range will establish interactions with the resident soil food web. In this paper we examine how the soil nematode community from the new range responds to range‐expanding plant species compared to related natives. We focused on nematodes, because they are important components in various trophic levels of the soil food web, some feeding on plant roots, others on microbes or on invertebrates. We expected that range expanding plant species have fewer root‐feeding nematodes, as predicted by enemy release hypothesis. We therefore expected that range expanders affect the taxonomic and functional composition of the nematode community, but that these effects would diminish with increasing trophic position of nematodes in the soil food web. We exposed six range expanders (including three intercontinental exotics) and nine related native plant species to soil from the invaded range and show that range expanders on average had fewer root‐feeding nematodes per unit root biomass than related natives. The range expanders showed resistance against rather than tolerance for root‐feeding nematodes from the new range. On the other hand, the overall taxonomic and functional nematode community composition was influenced by plant species rather than by plant origin. The plant identity effects declined with trophic position of nematodes in the soil food web, as plant feeders were influenced more than other feeding guilds. We conclude that range‐expanding plant species can have fewer root‐feeding nematodes per unit root biomass than related natives, but that the taxonomic and functional nematode community composition is determined more by plant identity than by plant origin. Plant species identity effects decreased with trophic position of nematodes in the soil food web.     

Conventional farming impairs Rhizoctonia solani disease suppression by disrupting soil food web

Intensive farming in agriculture raises questions in relation to environmental sustainability and the widespread use of agrochemicals. In the present work, we compare the impact of organic and intensive farming, in connection to the soil suppressiveness against the soilborne pathogen Rhizoctonia solani. Three farms were considered in the study: two practicing organic cultivation (for 10 and 20 years, respectively), and one applying conventional cultivation. Soil suppressiveness was assessed in a greenhouse bioassay with lettuce (Lactuca sativa). Soil microbiome was characterized by combining BIOLOG EcoPlates^? with high‐throughput sequencing of bacterial and eukaryotic rRNA gene markers. Suppressiveness towards R. solani was higher in organic than in conventional farming soil, but this property was lost after soil sterilization. Functional biodiversity was significantly higher in the two organic soils, and this parameter was predictive of the suppressiveness towards R. solani. According to our analyses, the overall microbial taxonomic diversity was unlinked to suppressiveness. A correlation analysis, carried out at the genus level for the most abundant bacterial and eukaryotic microbial taxa, showed that 58.7% of the genera had a statistically significant correlation with suppressiveness. In particular, the genera Flavisolibacter, Massilia, Pseudomonas, Ramlibacter, Rhizophus and the oligochaete worms belonging to the Enchytraeidae family positively correlated with the disease suppression.     

Rapid evolution buffers ecosystem impacts of viruses in a microbial food web

Predation and parasitism often regulate population dynamics, community interactions, and ecosystem functioning. The strength of these top-down pressures is variable, however, and may be influenced by both ecological and evolutionary processes. We conducted a chemostat experiment to assess the direct and indirect effects of viruses on a marine microbial food web comprised of an autotrophic host (Synechococcus) and non-target heterotrophic bacteria. Viruses dramatically altered the host population dynamics, which in turn influenced phosphorus resource availability and the stoichiometric allocation of nutrients into microbial biomass. These virus effects diminished with time, but could not be attributed to changes in the abundance or composition of heterotrophic bacteria. Instead, attenuation of the virus effects coincided with the detection of resistant host phenotypes, suggesting that rapid evolution buffered the effect of viruses on nutrient cycling. Our results demonstrate that evolutionary processes are important for community dynamics and ecosystem processes on ecologically relevant time scales.     

Assessing the trophic impacts of marine mammals: From metabolism to food web indices

Marine mammals are an important part of ecosystems, and their trophic role and potential impact have been increasingly studied. One key question is how these large animals interact with fisheries or compete for similar resources. Consequently, some models once used only for fisheries management are now including pinnipeds and cetaceans. However, fish and marine mammals do not share the same ecology and bioenergetics, and complex ecosystem models may not be the best way to assess the impact of pinnipeds or cetaceans in food webs. Indeed, simpler methods based on thermodynamics might give us reasonable answers with limited amounts of data. Here, we present an assessment of two different approaches to assess the trophic role of marine mammals in the northern Gulf of St. Lawrence (Canada): mixed trophic impacts (MTI) based on ecosystem modeling and surface index (SI) impact based on bioenergetics. Our results show that while modeling represents a good way of getting a holistic view of the role of marine mammals in ecosystems, trophic impact estimates based on fundamental thermodynamics principles can also give us answers requiring less data. The body surface area approach presented here might provide a practical tool for ecologists, who are not necessarily ecosystem modelers, to study this issue.     

Protozoan pulses unveil their pivotal position within the soil food web

Protozoa are one of the most abundant groups of bacterivores within the soil and are responsible for mineralisation of bacterial biomass, having a large impact on C and N cycling. Little is known of their contribution to soil nutrient transfers or the identity of their consumers. Here, for the first time indigenous flagellates and ciliates, enriched to 83 atom% for (13)C and 10 atom% for (15)N, were introduced to soil cores from two different land managements, grassland and woodland with the same soil type, to trace the flow of protozoan C and N through the soil food web. Nematodes, Collembola, earthworms and insect larvae obtained the greatest amounts of C and N of protozoan origin, either through direct consumption or uptake of biomass post-cell death. Our results show that changes in management, affect the functioning of the soil food web and the utilisation of protozoa as a food source.     

甲基溴消毒对番茄温室土壤食物网的抑制

甲基溴熏蒸作为一种控制土传病害的技术,不仅对大气臭氧层有破坏作用,而且对土壤中的有益生物也有不利影响。2005-2006年,对山东省寿光市番茄温室土壤进行甲基溴（50 g/m2）熏蒸,调查甲基溴熏蒸对土壤食物网结构和功能群的影响。结果表明：甲基溴熏蒸显著抑制了土壤微生物生物量C及微生物生物量N,减少了原生动物（鞭毛虫、纤毛虫、肉足虫）、线虫（根结线虫二龄幼虫、食细菌线虫、食真菌线虫、食植物线虫、杂食性线虫）及螨类的丰度。在整个番茄生长期间,与对照相比,微生物生物量C、微生物生物量N、原生动物总丰度、线虫总丰度、螨总丰度分别下降了45.9%、44.8%、9.5%、93.6%、895%。熏蒸后,土壤食物网功能群数目、联通度、食物链最大长度和平均长度均降低。由此可见, 甲基溴熏蒸后抑制了土壤中的生物,使整个食物网结构更简单。     

土壤动物食物网研究方法

长期以来关于陆地生态系统的研究都集中在地上部分,而对于地下部分知之甚少。地下生态系统营养关系是生态系统中各生物成员之间最重要的联系,是物质循环、能量流动的重要载体。研究土壤动物食物网已成为现代地下/土壤生态学研究的热点与前沿。由于土壤动物的个体小、食性复杂、栖息环境隐蔽等原因,使得对土壤动物食物网的研究困难重重,所以选择合适的研究方法尤为重要。本文总结了国际上近几十年来土壤动物食物网研究方法,将其分为传统方法(野外直接观察法、室内培养实验观察法、显微镜下肠容物分析法)、常用方法(消化酶分析法、脂肪酸分析法、稳定同位素技术、特定化合物分子的稳定同位素分析技术)和现代分子方法(DNA分子跟踪食物链网络技术、单克隆抗体技术)3大类,具体介绍了每一种方法的发展历史和应用现状。根据土壤动物自身特性及对各方法的优势与劣势的比较,脂肪酸分析法和稳定同位素分析法是当前土壤动物食物网研究的常用方法;随着未来物种分子鉴定技术的改进和数据库的积累,DNA分子跟踪食物链网络技术将会成为未来的主流发展方向。