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1.
We investigated the structure of invertebrate food webs at three glacier foreland sites of an age of 2-34, ca. 60 and ca. 120 years in the European Alps at 2250-2450 m asl. The trophic structure was investigated by analyzing stable isotope ratios of 15N/14N and 13C/12C. The results suggest that the formation of terrestrial food webs during early primary succession heavily relies on prey out of the decomposer system with Collembola being most important. The diet of decomposers likely is based predominantly on allochthonous humus material blown in by wind and deposited by the retreating glacier. Irrespective of the successional stage the animal community consisted mainly of generalist predators with a number of species occurring at each of the successional stages. The results suggest that terrestrial food web formation is associated with a prolongation of food chains caused mainly by predator species switching their diet to include other predators, i.e. by intraguild predation. This suggests that generalist predators, such as cursorial spiders, carabid beetles, harvestman and centipedes, switch prey and include other predators if these are becoming more abundant, i.e. if ecosystems become more productive. Intraguild predation results in complex food webs with high linkage density which likely affects food web functioning and stability.  相似文献   

2.
《Applied soil ecology》2009,41(3):518-528
In the southeastern United States, conservation tillage techniques are used to conserve soil nutrients and structure, providing habitat and substrate for biota, which are largely responsible for the mineralization of nutrients in the soil. A deterrent for growers considering the transition to conservation tillage is the delay in soil response (e.g. increased soil carbon, efficient nutrient cycling, impacts on yield) associated with the equilibration of the soil food web. The objective of this study was to determine if the microbial community composition and biomass changed with transition to conservation tillage. Soils sampled from five sites, representing a chronosequence of conservation tillage (from conventionally tilled to 30 year no-till), were collected for fatty acid analysis. Microbial communities were significantly different among sites. Fungi, characterized by 18:2ω6, 18:1ω9, and 18:3ω6c fatty acids, were typically lowest in the conventionally tilled soil, probably due to repeated disruption of the fungal hyphae associated with tillage. In all soils, soil nutrient concentrations, moisture and microarthropod abundance were correlated with microbial structure. Plots in conservation tillage were significantly different from the conventionally tilled plots, but did not exhibit a clear linear pattern across the chronosequence. This evidence that belowground food webs can respond quickly to a cessation in tillage suggests that the delay in soil response may be due more to the time required to build organic matter than to a slow response by the biota.  相似文献   

3.
Marine inputs from seabirds (in the form of guano) to terrestrial coastal communities play an important role in supporting aboveground food webs. However, little is known about the importance of seabird-derived nutrient inputs for belowground food webs and their function relative to other factors that regulate belowground communities. Here, we tested the relative importance of nutrient enrichment from seabirds and grazing, a known driver of belowground properties, in determining the structure and function of the soil food web in an island system. This was tested by measuring the size and composition of the microbial community, the abundance of nematode feeding groups and rates of decomposition and net nitrogen (N) mineralisation in soil samples collected from grazed and ungrazed plots at coastal and inland locations, representing sites of high and low seabird influence respectively, on the Isle of May in the Firth of Forth, east Scotland. We found that proximity to seabird breeding colonies, and associated greater input of seabird-derived N, stimulated the size of the soil microbial biomass and the abundance of bacteria relative to fungi in the soil microbial community relative to inland areas that received significantly less N. Despite this, proximity to seabird colonies had no detectable effect on rates of decomposition or N-mineralisation. The short-term removal of mammalian grazers, in the form of rabbits, had only limited effects on the structure of the soil food web, mainly affecting the abundance of bactivorous nematodes which were greater in grazed than ungrazed situations. However, cessation of grazing did impact significantly on rates of N-mineralisation and decomposition, which were higher and lower in grazed than ungrazed situations respectively. In conclusion, our study provides evidence that allochthonous nutrient inputs from seabirds have significant impacts on the composition of the soil microbial community, and that these effects outweigh short-term effects of grazers as a driver of soil food web structure in the island system studied. Overall, our results indicate the important roles that natural sources of N and grazing play as drivers of soil food webs and their function.  相似文献   

4.
Fatty acid (FA) analysis is used increasingly to investigate the trophic structure of soil animal food webs as the technique allows separation of the role of detrital resources such as bacteria, fungi and plant material for consumer nutrition. The applicability of FAs as biomarkers for different diets has been verified for Collembola and Nematoda. However, for the analysis of whole food webs it is crucial to know whether marker FA are valid for different taxa and whether they are transferred along the food chain to higher trophic levels, i.e. predators. Top-predators are integrators of lower level energy fluxes in food webs; therefore analysis of their FAs may allow to identify trophic pathways and to separate bacterial vs. fungal based energy channels. Chilopoda and Arachnida are among the main predators in soil food webs. Our aim was to test the applicability of marker FAs for these two predator taxa and to verify the trophic transfer of marker FAs of different basal resources via first order consumers into predators, i.e. over three trophic levels. Therefore, we investigated the transfer of FAs from different basal resources [fungi (Chaetomium globosum), plant leaf litter (Tilia europaea), Gram-positive (Bacillus amyloliquefaciens) and Gram-negative bacteria (Stenotrophomonas maltophilia)] via Collembola (Heteromurus nitidus) as first order consumers into predators [Lithobius forficatus (Chilopoda) and Pardosa lugubris (Arachnida)]. Fatty acid profiles of predators of food chains with different basal resources differed significantly. Marker FAs of basal resources were clearly detectable in predators, suggesting that FA analysis allows to separate trophic channels of soil food webs. By reflecting basal resources, FAs of predators allow tracking energy/resource fluxes through the food web and thereby clarifying the relative importance of bacterial vs. fungal vs. plant resources for soil animal food webs.  相似文献   

5.
《Soil biology & biochemistry》2001,33(12-13):1703-1712
We studied whether the presence of a bacterium can affect the functioning or stability of simple fungal-based decomposer food chains. We constructed microcosms with 60 g washed mineral soil and four different food webs: (1) a fungus (Cladosporium herbarum) alone; (2) a fungus and a fungal-feeding nematode (Aphelenchoides sp.); (3) a fungus and a bacterium (Escherichia coli); and (4) a fungus, a bacterium, a fungal- and a bacterial-feeding nematode (Aphelenchoides sp. and Acrobeloides tricornus). Glucose was supplied as the sole carbon source. One replicate set of microcosms was kept at −2°C for the sixth and seventh week as an experimental disturbance. The microcosms were destructively sampled 10 times for food web effects (non-disturbed controls) and three times for freezing treatment. Fungal biomass growing alone was less efficient (i.e. it had higher respiration rate per unit biomass) than the other food webs. This did not, however, result in the greatest C loss in the long term, because the fungal biomass declined when growing alone. Presence of the bacterium increased the decomposition of dissolved organic carbon as much as the presence of the fungal-feeder, but their effects were not additive. Ammonium nitrogen concentration of the medium was higher in systems containing bacteria. Nematode populations and the bacterial biomass were not sensitive to the disturbance of freezing. Although the freezing disturbance decreased total fungal biomass in the absence of the bacterial energy channel, dissolved organic carbon decomposition was only incidentally retarded. In spite of their distinct role in the system functioning, the bacteria did not significantly alter the stability properties of the system. Thus, our results contradict some recent food-web based decomposition models, which predict that the effects of parallel energy channels on decomposition are additive. We discuss nutrient limitation and the dependence of fungal properties on the food-web configuration as explanations for the contradiction of theory and data. We did not find evidence supporting a hypothesis that an additional energy channel should stabilize flow through a food web, and hence decomposition. This is explained by high resilience of the reference system with a fungus alone, and by redundancy, i.e. the fact that the fungal-feeding nematode induced similar changes in the fungus than the bacterium.  相似文献   

6.
Soil food webs cycle nutrients and regulate parasites and pathogens, services essential for both agricultural productivity and ecosystem health. Nematodes provide useful indicators of soil food web dynamics. This study was conducted to determine if nematode soil food web indicators and crop yield can be enhanced by combinations of cover crops in a conservation tillage system. The effects of three cover crop treatments (vetch/pea, oat/wheat and oat/wheat/pea/vetch) with low, medium and high C:N and a bare fallow control were investigated in Davis, CA. Nematode fauna, soil properties and plant productivity were measured. Soil food web indices, including the Enrichment Index (EI), Structure Index (SI), Basal Index (BI), and Channel Index (CI), based on the composition of nematode assemblages, were calculated to infer soil food web condition. Cover cropped tomato/corn rotations had twice the number of enrichment opportunist bacterial feeding nematodes, active participants in nitrogen mineralization, than fallowed tomato/corn rotations (opportunist bacterial feeders = 163 versus 98). In winter fallowed plots food webs were basal, common in disturbed, nutrient-poor conditions (BI = 37). Total number of enrichment opportunist nematodes, soil NH4-N levels, and inferred nitrogen mineralization, were higher in cover crop treatments with low to mid C:N ratios. Omnivore and predator nematodes were scarce, averaging less than 6 nematodes 100 g?1 in all treatments. In year one, plant productivity was highest after fallow. In contrast, in year two productivity was highest after cover crops with high nitrogen content and productivity significantly correlated with the structure of the soil fauna. Monitoring the abundance of enrichment opportunists may provide managers with a new tool to evaluate soil food web nitrogen mineralization and plant productivity.  相似文献   

7.
This review outlines directions for future research in soil food web ecology. Two lines of research are considered to be most important: the adoption of new methodologies to investigate food relationships and the strengthening of experimentation to investigate the interaction strength between food web components. For a better understanding of food relationships molecular methods, particularly fluorescence in situ hybridization, and stable isotope methodology, including the analysis of variations in the abundance of 13C and 15N, are thought to be most promising. Implications of results of the studies which employed these methodologies for the structure and function of soil food webs are highlighted.  相似文献   

8.
Human activities are causing climatic changes and alter the composition and biodiversity of ecosystems. Climate change has been and will be increasing the frequency and severity of extreme climate events and natural disasters like floods in many ecosystems. Therefore, it is important to investigate the effects of disturbances on ecosystems and identify potential stabilizing features of ecological communities. In this study, soil microbial and nematode communities were investigated in a grassland biodiversity experiment after a natural flood to investigate if plant diversity is able to attenuate or reinforce the magnitude of effects of the disturbance on soil food webs. In addition to community analyses of soil microorganisms and nematodes, the stability indices proportional resilience, proportional recovery, and proportional resistance were calculated. Generally, soil microbial biomass decreased significantly due to the flood with the strongest reduction in gram-negative bacteria, while gram-positive bacteria were less affected by flooding. Fungal biomass increased significantly three months after the flood compared to few days before the flood, reflecting elevated availability of dead plant biomass in response to the flood. Similar to the soil microbial community, nematode community structure changed considerably due to the flood by favoring colonizers (in the broadest sense r-strategists; c–p 1, 2 nematodes), particularly so at high plant diversity. None of the soil microbial community stability indices and few of the nematode stability indices were significantly affected by plant diversity, indicating limited potential of plant diversity to buffer soil food webs against flooding disturbance. However, plant diversity destabilized colonizer populations, while persister populations (in the broadest sense K-strategists; c–p 4 nematodes) were stabilized, suggesting that plant diversity can stabilize and destabilize populations depending on the ecology of the focal taxa. The present study shows that changes in plant diversity and subsequent alterations in resource availability may significantly modify the compositional shifts of soil food webs in response to disturbances.  相似文献   

9.
《Applied soil ecology》2003,22(2):113-126
In an afforested coal mining site at Berzdorf, Germany, the soil nematode community was investigated on the basis of genera distribution, trophic structure, and functional guilds. To assess food web complexity and nutritional status of afforested mine soils, the “weighted faunal analysis” was applied and found to be a useful diagnostic tool to describe the poorly developed, basal or matured food web characters of the Berzdorf mine soils. The tree species used in afforestation was a crucial factor. A comparison between nine mine soils of different age (4–46 years) and afforestation (poplar, alder, pine, mixed deciduous, mixed coniferous) showed particularly poorly structured food webs in poplar afforestations, whilst alder and mixed deciduous sites presented more favourable conditions in terms of soil succession and food web maturity. The results revealed no continuous increase in the complexity of food web interactions from younger successional stages to older stages. However, it was demonstrated that food web development at Berzdorf followed distinct shifts in soil primary succession. Correspondences of nematode community data and environmental parameters are discussed.  相似文献   

10.
Changes in landscape pattern under the control of agriculture intensification are considered to be an important driver of biodiversity and often a threat for conservation. The response of species to landscape changes is complex, including possible time lags, and depends on the taxonomic group. The search for surrogate species or surrogate data for biodiversity is confronted with this complexity.This study was conducted on two taxonomic groups (birds and vascular plants) for 20 sites each of 1 km2 equally distributed in the Seine valley floodplain. For plants, two habitats were studied: grasslands and hedges. We used a generalised additive model (GAM) and co-inertia analyses to determine whether present or past landscape attributes can best explain the biodiversity components (structure and composition). This study confirms the major role of landscape pattern attributes for predicting some metrics of biodiversity, e.g. species richness. But this study shows that potential drivers of biodiversity come from both the past and present landscape patterns. The quality of surrogates for biodiversity is strongly dependent on understanding the importance of past conditions. This suggests the need for more functional surrogates, taking into account the situation of equilibrium or non-equilibrium between biodiversity and its drivers.  相似文献   

11.
土壤动物与土壤健康息息相关,土壤动物多样性和功能能够灵敏反映人类活动和气候变化引起的土壤扰动。同时,土壤动物还通过与生物和非生物组分间的相互作用对地上生态系统产生反馈作用。当前土壤动物在土壤健康评价体系中的应用相对较少,主要集中在土壤线虫、节肢动物和蚯蚓等类群,仍缺乏基于土壤动物的系统性评价指标。因此,本文围绕土壤动物在指示土壤健康方面的潜力,系统总结了现有基于土壤动物的土壤健康评价指标,强调未来应建立和完善土壤动物基因组信息数据库,挖掘土壤动物的功能性状,加强土壤食物网结构和生态功能的研究,建立集成土壤动物物种多样性、功能性状和土壤食物网的指标体系,从而促进土壤健康和生态系统的可持续发展。  相似文献   

12.
基于C、N同位素技术的河流食物网基础碳源研究进展   总被引：1，自引：0，他引：1  
基础碳源是河流生态系统最重要的特征之一,它通过生物间能量传递,影响着河流生态系统生物多样性、群落结构及其稳定性。本文基于稳定性同位素技术综述了河流基础碳源类型、食物网能量贡献率估算模型、食物网基础碳源理论模型(河流生产力模型RPM、河流连续模型RCC和河流脉冲模型FPC)及其交互作用以及它们在实际应用上的利弊,介绍了能较好平衡各种模型利弊、适应于多样化水文特征的河流生态系统综合体(RES)新假说,并展望了稳定性同位素技术与非致命取样方法相结合建立长期河流同位素数据库的重要意义,旨在推动对河流生态系统中不同生物之间营养关系的理解,为河流生态系统的修复与保护提供理论依据。  相似文献   

13.
Fatty acid (FA) analysis investigates changes in the relative contribution of prey from major energy channels in decomposer food webs for predator nutrition. Adopting this approach we investigated whether the trophic niche of centipedes, as major invertebrate predators in forest soil food webs, changes with maturation, season or forest age. Generally, each of the four centipede species studied differed significantly in their FA composition suggesting trophic niche differentiation. FA profiles differed more strongly in the two geophilomorph (Strigamia acuminata and Geophilus ribauti) than in the two lithobiomorph species (Lithobius crassipes and Lithobius mutabilis) suggesting that in particular the former feed on markedly different prey. FA profiles changed during post-embryonic development in each of the four centipede species. Differences were most pronounced in the two lithobiomorph species shifting to predominantly fungal feeding prey. Further, FA profiles varied with season indicating that centipedes exploit more prey out of the bacterial channel in autumn. FA profiles of centipedes varied little with forest age suggesting that soil food webs are remarkably invariant across different forest ecosystems. The results indicate that FA composition of second order consumers closely reflects changes in diet of prey species and composition of basal resources. The study proved FA profiles as powerful tool to gain insight into critical characteristics of soil food web stability, i.e., compartmentalisation and the relative importance and variability of energy channels.  相似文献   

14.
Soil food webs are characterised by complex direct and indirect effects among the organisms. Consumption of microorganisms by soil animals is considered as an important factor that contributes to the stability of communities, though cascading effects within the food web can be difficult to detect. In a greenhouse experiment, an addition of a high number the fungal feeding collembola Folsomia quadrioculata was applied to grassland soil food webs in monocultures of three plant species: Plantago lanceolata (forb), Lotus corniculatus (legume) and Holcus lanatus (grass). The abundance of microorganisms, determined as the abundances of phospholipid fatty acids (PLFAs) and the abundances of resident invertebrates, nematodes and collembolans, did not change due to the addition of F. quadrioculata. Trophic positions of collembolans were determined by analyses of natural abundances of 15N stable isotopes. The use of food resources by microorganisms and collembolans was determined by 13C analysis of microbial PLFAs and solid samples of collembolans. δ13C values of the resident collembola Folsomia fimetaria were lower in the presence of F. quadrioculata than in the control food webs indicating a use of more depleted 13C food resources by F. fimetaria. The δ15N values of F. fimetaria did not change at the addition of F. quadrioculata thus no change of trophic levels was detected. The switch of F. fimetaria to a different food resource could be due to indirect interactions in the food web as the two collembolan species were positioned on different trophic positions, according to different δ15N values.  相似文献   

15.
Biological indicators based on abundances of soil organisms are powerful tools for inferring functional and diversity changes in soils affected by agricultural perturbations. Field plots, combining organic and conventional practices with no tillage, conservation tillage and standard tillage maintained different nematode assemblages and soil food webs. Soil food web indices based on nematode assemblages were reliable predictors of the trophic composition of functional characteristics of soil mite assemblages. Bacterial-feeding and predatory nematodes, together with predatory mites, were abundant in the organic-no till treatments and were associated with high values of the Enrichment and the Structure Index based on nematode assemblages. Conventional-Standard tillage treatments had high abundances of fungal- and plant-feeding nematodes and algivorous mites, associated with high values of the Basal and Channel Index. This study validates the hypothesis that nematode-based soil food web indices are useful indicators of other soil organisms such as mites, with similar functional roles and environmental sensitivities.  相似文献   

16.
Feeding relationships between organisms may be determined by observations of behaviour in manipulative experiments or, as in more recent times, by the use of stable isotope labelling to trace the passage of 13C and 15N through food webs. Here we introduce living bacteria, labelled with both 13C and 15N into intact soil cores to understand further the movement of bacterially sourced C and N into the meso- and macrofauna of a grassland soil. We found that these groups showed a range of isotope levels which relate to their feeding strategies. Some had no label (e.g. dipterous larvae), whilst others were highly labelled which may indicate a preference for the added bacteria. This latter group included Collembola, generally perceived as being predominantly fungal feeders. This work describes a novel technique which has the potential to provide critical information about the dissipation of bacterially derived C and N through the soil food web.  相似文献   

17.
This study presents a comparative analysis of protected and exploited Mediterranean Sea food webs using standardized ecological models of two ecosystems: the Central-North Adriatic Sea (highly exploited) and the Miramare Natural Marine Reserve (Northern Adriatic Sea, protected since 1986). Food webs are analysed in terms of structural and functional traits including trophic levels, transfer efficiency, trophic role of species and keystoneness, trophic spectra and other synthetic ecological indicators. Our results highlight similarities between food webs of the Adriatic Sea, differences that are likely due to the impact of fishing and differences that should be related to other factors. Analysis of biomass distribution along functional groups and of trophic spectra indicates that protected area presents higher mean trophic level of the community, higher biomasses, lower production and generally lower transfer efficiency than fished area. Our results indicate that measures of food web complexity (system omnivory index and ascendency), as well as pelagic/demersal and fish/invertebrates biomass ratios are higher in the protected area than in exploited ecosystem due to fishing-induced changes. Thus, this study highlights that marine protected areas can efficiently contribute to maintain structural and functional traits of marine ecosystems.  相似文献   

18.
Ants are increasingly being recognized as useful tools for land managers to monitor ecosystem conditions. However, despite an abundance of studies on ant responses to both environmental disturbance and land management techniques, an analysis of the practice and value of including ants in monitoring is lacking. Consequently, conservation managers are left with little guidance as to if, when, and how ants can be used to assess conservation activities. Based on our review of approximately 60 published studies, we outline five areas where ants provide valuable information for management-based monitoring: (1) to detect the presence of invasive species, (2) to detect trends among threatened or endangered species, (3) to detect trends among keystone species, (4) to evaluate land management actions, and (5) to assess long-term ecosystem changes. We also discuss practical considerations when designing a monitoring framework for ants, including appropriate methods, taxonomic resolution for sampling, and spatial and temporal scale. We find that when integrated with management goals, monitoring ants can provide information over the short-term on topics such as the status of invasive or keystone species, as well as over longer time frames, for instance the impact of climate change. Overall, we conclude that ants merit monitoring based on their inherent ecological qualities, independent of any “indicator” attributes they might have.  相似文献   

19.
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20.
In a series of community food webs from native and agricultural soils, we modeled energetics and stability, and evaluated the role of the various groups of organisms and their interactions in energy flow and community stability. Species were aggregated into functional groups based on their trophic position in the food webs. Energy flow rates among the groups were calculated by a model using observations on population sizes, death rates, specific feeding preferences and energy conversion efficiencies. From the energetic organization of the communities we derived the strengths of the mutual effects among the populations. These interaction strengths were found to be patterned in a way that is important to community stability. The patterning consisted of the simultaneous occurrence of strong top down effects at lower trophic levels and strong bottom up effects at higher trophic levels. These patterns resulted directly from the empirical data we used to parameterize the model, as we found no stabilizing patterns with random but plausible parameter values. Also, the impact of each individual interaction on community stability was established. This analysis showed that some interactions had a relatively strong impact on stability, whereas other interactions had only a small impact. These impacts on stability were neither correlated with energy flow nor with interaction strength. Comparison of the seven food webs showed that these impacts were sometimes connected to particular groups of organisms involved in the interaction, but sometimes they were not, which might be due to different trophic positions in the food webs. We argue that future research should be directed to answer the question which energetic properties of the organisms form the basis of the patterning of the interaction strengths, as this would improve our understanding of the interrelationships between energetics, community stability, and hence the maintenance of biological diversity.  相似文献   

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