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1.
Human impact on structure and functioning of ecosystems is rapidly increasing. Virtually all European forests are managed with major implications for diversity and structure of food webs. Centipedes (Chilopoda: Lithobiidae) are abundant arthropod predators in European temperate forest soils with a generalistic feeding behaviour. However, little is known on the variability in the prey spectrum of centipedes with land use and the responsible factors. Combining fatty acid (FA) analysis, which allows determination of the relative contribution of different prey to predator nutrition, and stable isotope analysis, providing insight into the trophic structure of decomposer food webs, we investigated variations in trophic niches of two dominant centipede species, Lithobius mutabilis and Lithobius crassipes, in differently aged beech and spruce forests. FA composition of the two centipede species differed significantly with bacterial marker FAs being more abundant in L. crassipes as compared to L. mutabilis. Differences were most pronounced in spruce as compared to beech forests. The results suggest that dense needle litter in coniferous forests may restrict prey availability to the larger L. mutabilis and confine foraging to the litter surface whereas the smaller L. crassipes is able to also exploit prey of deeper litter layers. Lithobius crassipes was significantly more enriched in 15N and 13C compared to L. mutabilis suggesting that, compared to L. mutabilis, the smaller L. crassipes occupies higher trophic levels and relies more on root derived carbon. The results indicate that trophic niches of centipedes vary in a species specific way between forest types with body size and habitat structure being major determinants of the variations in the prey spectrum. Combining techniques for delineating predator–prey interactions allowed insights into variations in trophic interrelationships and their driving forces in temperate forest soil food webs. 相似文献
2.
Uncovering trophic positions and food resources of soil animals using bulk natural stable isotope composition 总被引:1,自引:0,他引:1
Anton M. Potapov Alexei V. Tiunov Stefan Scheu 《Biological reviews of the Cambridge Philosophical Society》2019,94(1):37-59
Despite the major importance of soil biota in nutrient and energy fluxes, interactions in soil food webs are poorly understood. Here we provide an overview of recent advances in uncovering the trophic structure of soil food webs using natural variations in stable isotope ratios. We discuss approaches of application, normalization and interpretation of stable isotope ratios along with methodological pitfalls. Analysis of published data from temperate forest ecosystems is used to outline emerging concepts and perspectives in soil food web research. In contrast to aboveground and aquatic food webs, trophic fractionation at the basal level of detrital food webs is large for carbon and small for nitrogen stable isotopes. Virtually all soil animals are enriched in 13C as compared to plant litter. This ‘detrital shift’ likely reflects preferential uptake of 13C‐enriched microbial biomass and underlines the importance of microorganisms, in contrast to dead plant material, as a major food resource for the soil animal community. Soil organic matter is enriched in 15N and 13C relative to leaf litter. Decomposers inhabiting mineral soil layers therefore might be enriched in 15N resulting in overlap in isotope ratios between soil‐dwelling detritivores and litter‐dwelling predators. By contrast, 13C content varies little between detritivores in upper litter and in mineral soil, suggesting that they rely on similar basal resources, i.e. little decomposed organic matter. Comparing vertical isotope gradients in animals and in basal resources can be a valuable tool to assess trophic interactions and dynamics of organic matter in soil. As indicated by stable isotope composition, direct feeding on living plant material as well as on mycorrhizal fungi is likely rare among soil invertebrates. Plant carbon is taken up predominantly by saprotrophic microorganisms and channelled to higher trophic levels of the soil food web. However, feeding on photoautotrophic microorganisms and non‐vascular plants may play an important role in fuelling soil food webs. The trophic niche of most high‐rank animal taxa spans at least two trophic levels, implying the use of a wide range of resources. Therefore, to identify trophic species and links in food webs, low‐rank taxonomic identification is required. Despite overlap in feeding strategies, stable isotope composition of the high‐rank taxonomic groups reflects differences in trophic level and in the use of basal resources. Different taxonomic groups of predators and decomposers are likely linked to different pools of organic matter in soil, suggesting different functional roles and indicating that trophic niches in soil animal communities are phylogenetically structured. During last two decades studies using stable isotope analysis have elucidated the trophic structure of soil communities, clarified basal food resources of the soil food web and revealed links between above‐ and belowground ecosystem compartments. Extending the use of stable isotope analysis to a wider range of soil‐dwelling organisms, including microfauna, and a larger array of ecosystems provides the perspective of a comprehensive understanding of the structure and functioning of soil food webs. 相似文献
3.
Food Web Structure and Basal Resource Utilization along a Tropical Island Stream Continuum, Puerto Rico 总被引:5,自引:0,他引:5
Tropical stream food webs are thought to be based primarily on terrestrial resources (leaf litter) in small forested headwater streams and algal resources in larger, wider streams. In tropical island streams, the dominant consumers are often omnivorous freshwater shrimps that consume algae, leaf litter, insects, and other shrimps. We used stable isotope analysis to examine (1) the relative importance of terrestrial and algal‐based food resources to shrimps and other consumers and determine (2) if the relative importance of these food resources changed along the stream continuum. We examined δ15N and δ13C signatures of leaves, algae, macrophytes, biofilm, insects, snails, fishes, and shrimps at three sites (300, 90, and 10 m elev.) along the Río Espíritu Santo, which drains the Caribbean National Forest, Puerto Rico. Isotope signatures of basal resources were distinct at all sites. Results of two‐source δ13C mixing models suggest that shrimps relied more on algal‐based carbon resources than terrestrially derived resources at all three sites along the continuum. This study supports other recent findings in tropical streams, demonstrating that algal‐based resources are very important to stream consumers, even in small forested headwater streams. This study also demonstrates the importance of doing assimilation‐based analysis (i.e., stable isotope or trophic basis of production) when studying food webs. 相似文献
4.
1. Analysis of the stable isotope signatures of carbon (C) and nitrogen (N) of foods and consumers has led to some preliminary understanding of the relative importance of autochthonous and allochthonous resources in tropical streams. However, robust generalizations about the dynamics of food webs in these habitats, and their response to shading gradients or season, are still lacking. In addition, the feasibility of employing a baseline δ15N value for estimating trophic positions (TPs) of consumers in small tropical streams has yet to be explored. 2. We analysed data on stable isotope signatures of food sources and aquatic consumers obtained from 14 studies carried out in small streams in monsoonal Hong Kong (22°30′N, 114°10′E) between 1996 and 2006. Emphasis was placed on determining the relative importance of leaf litter and autochthonous foods in supporting consumer biomass, and the extent to which trophic base and TP vary among streams and seasons. 3. Although allochthonous leaf litter was generally 13C‐ and 15N‐depleted relative to autochthonous foods, there were marked isotopic shifts of food sources and consumers in response to season (dry versus wet) and stream shading. Consumer taxa were generally more 13C‐ and 15N‐enriched in the unshaded streams, but seasonal effects were more variable. Despite these changes, there was consistent evidence that stream food webs were based on periphytic algae and/or cyanobacteria with leaf litter serving as a minor food. 4. Heptageniidae (Ephemeroptera), Tipulidae (Diptera), Elmidae (Coleoptera) and shrimps (Atyidae) were used as a baseline for calculating the TPs of other consumer taxa. The maximum TPs in shaded streams remained fairly constant between seasons (dry = 3.93; wet = 3.97), while those in unshaded streams were higher and showed seasonal fluctuations (dry = 5.13; wet = 4.39). 5. Although variations in consumer isotope signatures in response to season and shading gradients did not confound our interpretation of the stream food base, changes in consumer δ15N did affect the calculation of consumer TPs. Misleading estimates of consumer TPs are likely if samples are collected from a narrow range of streams and/or during one season. Overestimation of the TPs of specialist herbivores (e.g. fish grazers) is also possible when autochthonous resources are substantially more 15N‐enriched than allochthonous foods. 相似文献
5.
Carbon and nitrogen stable isotope ratios (δ13C and δ15N) have been used for more than two decades in analyses of food web structure. The utility of isotope ratio measurements is based on the observation that consumer δ13C values are similar (<1‰ difference) to those of their diet, while consumer δ15N values are about 3‰ higher than those of their diet. The technique has been applied most often to aquatic and aboveground terrestrial food webs. However, few isotope studies have examined terrestrial food web structure that includes both above- and belowground (detrital) components. Here, we review factors that may influence isotopic signatures of terrestrial consumers in above- and belowground systems. In particular, we emphasize variations in δ13C and δ15N in belowground systems, e.g., enrichment of 13C and 15N in soil organic matter (likely related to soil microbial metabolism). These enrichments should be associated with the high 13C (~3‰) enrichment in belowground consumers relative to litter and soil organic matter and with the large variation in δ15N (~6‰) of the consumers. Because such enrichment and variation are much greater than the trophic enrichment generally used to estimate consumer trophic positions, and because many general predators are considered dependent on energy and material flows from belowground, the isotopic variation in belowground systems should be taken into account in δ13C and δ15N analyses of terrestrial food webs. Meanwhile, by measuring the δ13C of key predators, the linkage between above- and belowground systems could be estimated based on observed differences in δ13C of primary producers, detritivores and predators. Furthermore, radiocarbon (14C) measurements will allow the direct estimation of the dependence of predators on the belowground systems. 相似文献
6.
Yutaka Okuzaki Ichiro Tayasu Noboru Okuda Teiji Sota 《Entomologia Experimentalis et Applicata》2010,135(3):263-270
Differences in trophic niches among carabid beetles (Coleoptera: Carabidae) co‐occurring on the forest floors of warm temperate forests in central Japan were studied using carbon (δ13C) and nitrogen (δ15N) stable isotope analyses. Different carabid species showed similar δ15N values, which were higher than those of their possible invertebrate prey (herbivores and detritivores) collected from the litter layer, indicating that these species were consumers in the same trophic level. In contrast, δ13C values differed among carabid species, indicating interspecific differences in prey animals. The variation in the δ13C value was larger in summer than in autumn. In summer, δ13C values indicated that some carabids depended highly on either grazing (low δ13C values) or detrital sources (high δ13C values) within the food chain [Chlaenius posticalis Motschulsky and Haplochlaenius costiger (Chaudoir), respectively], although other species with intermediate δ13C values likely depended on both. The latter group of species comprised mostly two dominant genera (Carabus and Synuchus). Although congeners might have similar feeding habits, the stable isotope ratios indicated trophic niche differences between adults of different species and between adults and larvae of the same genus. 相似文献
7.
The aim of the present study was to identify food sources of bark-living oribatid mites to investigate if trophic niche differentiation
contributes to the diversity of bark living Oribatida. We measured the natural variation in stable isotope ratios (15N/14N, 13C/12C) in oribatid mites from the bark of oak (Quercus robur), beech (Fagus sylvatica), spruce (Picea abies) and pine (Pinus sylvestris) trees and their potential food sources, i.e., the covering vegetation of the bark (bryophytes, lichens, algae, fungi). As
a baseline for calibration the stable isotope signatures of the bark of the four tree species were measured and set to zero.
Oribatid mite stable isotope ratios spanned over a range of about 13 δ units for 15N and about 7 δ units for 13C suggesting that they span over about three trophic levels. Different stable isotope signatures indicate that bark living
oribatid mites feed on different food sources, i.e., occupy distinct trophic niches. After calibration stable isotope signatures
of respective oribatid mite species of the four tree species were similar indicating close association of oribatid mites with
the corticolous cover as food source. Overall, the results support the hypothesis that trophic niche differentiation of bark
living oribatid mites contributes to the high diversity of the group. 相似文献
8.
We investigated community structure, trophic ecology (using stable isotope ratios; 15N/14N, 13C/12C) and reproductive mode of oribatid mites (Acari, Oribatida) along an altitudinal gradient (2,050–2,900 m) in the Central Alps (Obergurgl, Austria). We hypothesized that (1) the community structure changes with altitude, (2) oribatid mites span over four trophic levels, (3) the proportion of sexual taxa increases with altitude, and (4) the proportion of sexual taxa increases with trophic level, i.e. is positively correlated with the δ15N signatures. Oribatid mite community structure changed with altitude indicating that oribatid mites occupy different niches at different altitudes. Oribatid mites spanned over 12 δ15N units, i.e. about four trophic levels, which is similar to lowland forest ecosystems. The proportion of sexually reproducing taxa increased from 2,050 to 2,900 m suggesting that limited resource availability at high altitudes favors sexual reproduction. Sexual taxa more frequently occurred higher in the food web indicating that the reproductive mode is related to nutrition of oribatid mites. Generally, oribatid mite community structure changed from being decomposer dominated at lower altitude to being dominated by fungal and lichen feeders, and predators at higher altitude. This supports the view that resources from dead organic material become less available with increasing altitude forcing species to feed on living resources such as fungi, lichens and nematodes. Our findings support the hypothesis that limited resource accessibility (at high altitudes) favors sexually reproducing species whereas ample resource supply (at lower altitudes) favors parthenogenetic species. 相似文献
9.
Craig T. Symes John W. Wilson Stephan M. Woodborne Zara S. Shaikh Michael Scantlebury 《Austral ecology》2013,38(6):721-729
It is often hypothesized that two species competing for the same resource cannot stably coexist unless they partition their resources in space and time. More recently stable isotope analyses have complemented traditional, observation‐based niche research by conceptualizing many of the characteristics of communities, for example, trophic niche width and the partitioning of resources. Here we quantify resource partitioning of sympatric small mammal species in an African ecosystem by analysing stable isotope ratios of hair collected from a South African forest‐grassland vegetation mosaic, and combine this with known spatial and temporal behavioural data to interpret community competition and resource partitioning. We observe niche separation to different degrees across the entire community, with different species displaying either unique isotopic dietary preferences, or partitioning resources in space and/or time. δ13C values were more enriched in species that inhabited afromontane grassland compared with those that inhabited afromontane forest, a reflection of the dominant vegetation in each habitat. Contrary to expectations, arboreal rodents occupied higher trophic positions than terrestrial rodents and approaching δ15N values similar to insectivorous shrews, suggesting that arboreal rodents feed on items such as arthropods enriched in 15N. While grassland species display phenotypic plasticity in terms of dietary preferences, small mammals that occurred in forests display narrow niche preferences, suggesting these species may be particularly sensitive to habitat modifications. Our results illustrate that the use of stable isotopes can be used in conjunction with spatial and temporal behavioural knowledge to elucidate resource partitioning in small African mammal communities. 相似文献
10.
Roots and root-derived C compounds are increasingly recognised as important resources for soil animal food webs. We used 13C-labelled glucose as a model C compound representing root exudates to follow the incorporation of root-derived C into the soil animal food web of a temperate grassland over a period of 52 weeks. We investigated variations in glucose C incorporation with fertilizer addition and sward composition, i.e. variations in plant functional groups. The approach allowed the differentiation of trophic chains based on primary decomposers feeding on litter and phytophagous species feeding on roots (i.e. not incorporating glucose C) from those based on secondary decomposers feeding on microorganisms (thereby assimilating glucose C). Each of the studied soil animal species incorporated glucose C, indicating that the majority of grassland soil animal species rely on microorganisms as food resources with microorganisms being fuelled by root exudates. However, incorporation of glucose C into soil animal species varied markedly with species identity, suggesting that detritivorous microarthropods complement each other in channelling microbial C through soil food webs. Fertilizer addition markedly reduced the concentration of glucose C in most soil animal species as well as the absolute transfer of glucose C into oribatid mites as major secondary decomposers. The results suggest that fertilizer addition shifts the basis of the decomposer food web towards the use of unlabelled resources, presumably roots, i.e. towards a herbivore system, thereby lessening the link between microorganisms and microbial grazers and hampering the propagation of microbial C to higher trophic levels. 相似文献
11.
Assimilation-based techniques such as stoichiometric analysis, bulk tissue stable isotope analysis (SIA), fatty acid (FA)
profiling and compound-specific SIA of FAs can be used to resolve ambiguities in consumer-resource relationships, but comparisons
of their effectiveness are lacking. Feeding trials and concurrent application of these techniques were used to investigate
the trophic base of two shrimps from Hong Kong streams: the atyid Caridina cantonensis, which is a primary consumer, and predatory Macrobrachium hainanense (Palaemonidae). Leaf litter and periphyton were fed to C. cantonensis (CC-LF and CC-PF, respectively) reared in the laboratory for 2 months, when C. cantonensis, that had fed on a mixed diet (CC-WC), were collected from the field. Atyids from each group (CC-LF, CC-PF and CC-WC) were
fed to M. hainanense (MH-L, MH-P and MH-W, respectively) during a further 2-month trial, at the end of which M. hainanense were also collected from the field (MH-R). FA biomarkers present in CC-WC and CC-PF indicated that C. cantonensis depended primarily on autochthonous foods, and FA profiles of CC-WC were distinct from those of CC-LF. Differences in C/N
ratios and isotope signatures of leaf litter and periphyton were not reflected in tissues of atyids or palaemonid predators.
FA profiles of M. hainanense groups were similar, but FA stable C isotope ratio (δ13C) signatures of MH-R and MH-W were distinct from those of MH-L and leaf litter. FA δ13C signatures of MH-R were similar to those of MH-P and MH-W, indicating that autochthonous resources constituted the trophic
base of production for this predator. This is the first study using compound-specific SIA to study stream food chains. Compound-specific
SIA and FA profiling allowed accurate elucidation of consumer-resource relationships that were not revealed by stoichiometry
or bulk tissue SIA. Compound-specific SIA was particularly sensitive for detecting rapid shifts in the predator trophic base.
This tool will have wide applicability for investigating food webs in a range of ecosystems.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
12.
1. Termites consume a wide range of plant material at different stages of decomposition and, accordingly, have been classified into ‘feeding groups’. African savannah ecosystems harbour many termite species, yet most belong to Termitidae. Especially striking is the co‐occurrence of up to eight Macrotermitinae and five Trinervitermes species, each having apparently identical trophic niches, i.e. fungus‐growers and grass‐feeders, respectively. 2. This study examined stable isotope signatures of 15N and 13C of West African savannah termites to test the validity of existing feeding group concepts and whether there is fine‐scaled niche differentiation of species within feeding groups. Despite a phylogenetic signal that species from the same subfamily and congenerics have correlated isotope signatures, evidence of niche differentiation was found. 3. Interestingly, species with similar δ15N values generally differed in δ13C values, and vice versa. The dominant mound‐building fungus‐grower Macrotermes bellicosus had the lowest δ15N values among all fungus‐growers, indicating that it occupies a different trophic niche. 4. This fine‐scaled differentiation along the trophic niche axis can help to explain the coexistence of so many apparently identical termite species. 相似文献
13.
14.
The functioning and structure of terrestrial ecosystems are shaped and maintained
by plant–decomposer interactions. The food and habitat of animal populations
are biogenic and are mainly of plant origin (plant litter) in terrestrial ecosystems.
Primary resources of the food-habitat template for the organization of soil animals
are provided by the primary production of plants, and are then modified through decomposition
processes by microbial populations. In the microbial decomposition system, the efficiency
of carbon utilization by microbial decomposers characterizes the decomposition processes
between tropical and temperate forest ecosystems. Tropical forests show poor development
of soil reservoir systems because of the high efficiency of lignin decomposition
by microbial populations. The decomposition processes of leaf litter are described
briefly for the understanding of organization of soil animal communities in tropical
and temperate forests. A comparison of decomposition processes shows qualitative
differences in decomposition between temperate and tropical forests. The composition
of functional groups of soil animals is well explained by the decomposition processes
in both forests. 相似文献
15.
Climate change and changes in land use will alter the stores of carbon and turnover of soil organic matter. We have used a theory for carbon cycles in terrestrial ecosystems to analyse changes in soil organic matter turnover in coniferous forests. The central concepts of the theory are a continuously changing substrate quality, a constant decomposer efficiency and a climatically controlled decomposer growth rate. Measurements on litter production and soil carbon stores from field experiments have been used to successfully validate the model predictions. Measured litter production increased with increasing temperature but the response was not identical for forests of different vegetation types which reflect variations in productivity. The temperature response of needle-litter production and decomposition rate were strongest in the most productive forests and weakest for the low productive forests. Initial decay rates of soil C store from steady state showed the same trend in temperature response as decay of a single litter cohort did, but the absolute values are 16% of the decay rates of a single litter cohort. Predicted soil C ranged from 5 to 9 kg C m–2. There exists a remarkable variation in forest soil C store response to temperature; the magnitude and even the sign depends on productivity as defined by vegetation type. The assumption that, in general, decomposition rates increase more than NPP with temperature, and consequently, soil C stores should decrease in response to a climate warming, seems therefore too simplistic. 相似文献
16.
Qian Chen Yang Liu Wei-Tim Ho Shek Kiu Chan Qiu-hua Li Jian-Rong Huang 《Wetlands Ecology and Management》2017,25(1):59-66
In this study, components of the food-web in Macao wetlands were quantified using stable isotope ratio techniques based on carbon and nitrogen values. The δ13C and δ15N values of particulate organic matter (δ13CPOM and δ15NPOM, respectively) ranged from ?30.64 ± 1.0 to ?28.1 ± 0.7 ‰, and from ?1.11 ± 0.8 to 3.98 ± 0.7 ‰, respectively. The δ13C values of consumer species ranged from ?33.94 to ?16.92 ‰, showing a wide range from lower values in a freshwater lake and inner bay to higher values in a mangrove forest. The distinct dietary habits of consumer species and the location-specific food source composition were the main factors affecting the δ13C values. The consumer 15N-isotope enrichment values suggested that there were three trophic levels; primary, secondary, and tertiary. The primary consumer trophic level was represented by freshwater herbivorous gastropods, filter-feeding bivalves, and plankton-feeding fish, with a mean δ15N value of 5.052 ‰. The secondary consumer level included four deposit-feeding fish species distributed in Fai Chi Kei Bay and deposit-feeding gastropods in the Lotus Flower Bridge flat, with a mean δ15N value of 6.794 ‰. The tertiary consumers group consisted of four crab species, one shrimp species, and four fish species in the Lotus Flower Bridge Flat, with a mean δ15N value of 13.473 ‰. Their diet mainly comprised organic debris, bottom fauna, and rotten animal tissues. This study confirms the applicability of the isotopic approach in food web studies. 相似文献
17.
H. Staaf 《Oecologia》1987,72(1):58-64
Summary Leaf litter decomposition, levels of accumulated litter as well as the abundance and biomass of earthworms were measured in three mature beech forests in southern Sweden: one mor site, one poor mull site, and one rich mull site. The disappearance rate of beech litter, measured with litter bags, increased with increasing soil fertility. On the rich mull site, the disappearance rate was much higher than in the two other forests, due to the combined effects of higher earthworm activity, more favouable soil moisture conditions, and higher litter quality. Incubating the litter in finely meshed bags (1-mm mesh) to exclude macrofauna had a great effect on litter mass loss in the rich mull site, but it had only a minor effect in the other sites. Simultaneous incubations of local and transplanted leaf litter on the three study sites showed that the substrate quality of the litter increased in the order: mor site — poor mull site — rich mull site. Lignin, N, and P concentrations of the leaf litter failed to explain the observed differences in decomposition rates, and acid/base properties are suggested to be more important. Earthworm numbers per m2 were 2.5 (1 species) in the mor, 40 (6 species) in the poor mull and 220 (9 species) in the rich mull forest. Soil chemical conditions, notably pH, were suggested as the main factors determining the inter-site differences in abundance and species composition of earthworms. The role of litter decomposition and earthworm activity in the accumulation of organic matter in the forest floor in different types of beech woodlands are discussed. 相似文献
18.
Jamie M. Kneitel 《Hydrobiologia》2014,733(1):71-83
The food source utilization and trophic relationship of the fish assemblage in the Red River mangrove ecosystem, Vietnam were examined using dual isotope analysis. The carbon and nitrogen stable isotope signatures of 23 fish species ranged from ?24.0 to ?15.7‰ and from 8.8 to 15.5‰, respectively. Cluster analysis based on the δ13C and δ15N signatures clearly separated the mangrove fish into five feeding groups, representing detritivores, omnivores, piscivores, zoobenthivores, and zooplanktivores, which concurred with the dietary information. The results suggested that mangrove carbon contributed a small proportion in the diets of the mangrove fish, with dominant food sources coming from benthic invertebrates, including ocypodid and grapsid crabs, penaeid shrimps, bivalves, gastropods, and polychaetes. The δ15N values showed that the food web structure may be divided into different trophic levels (TLs). The lowest TLs associated with Liza macrolepis, Mugil cephalus, and Periophthalmus modestus; 18 fish species had TLs between 3.0 and 3.8; and Pennahia argentata had the highest TL (c. 4.0). 相似文献
19.
Anton M. Potapov Eugenia E. Semenina Alexander V. Kurakov Alexei V. Tiunov 《Ecological Research》2013,28(6):1069-1079
Correctly estimating the trophic fractionation factors (Δ15N and Δ13C) in controlled laboratory conditions is essential for the application of stable isotope analysis in studies on the trophic structure of soil communities. Laboratory experiments usually suggest large 15N/14N and small 13C/12C trophic fractionation, but in field studies litter-dwelling microarthropods and other invertebrates are consistently enriched in 13C relative to plant litter. In the present study, we report data from two laboratory experiments investigating both fungi–collembolans and litter–fungi–collembolans systems. In the fungi–collembolans system, Δ15N and Δ13C averaged 1.4 ± 0.1 and 1.0 ± 0.2 ‰, respectively. In microcosms with fungi-inoculated litter, the difference in δ15N between collembolans and plant litter averaged 1.5 ± 0.2 ‰, confirming the relatively small 15N/14N trophic fractionation at the basal level of detrital foodwebs reported in numerous field studies. In full agreement with field observations, the difference in δ13C between bulk litter and collembolans in laboratory microcosms averaged 3.6 ± 0.1 ‰ and only little depended on collembolan species identities or the presence of water-soluble compounds in the litter. We conclude that increased δ13C values typical of litter-dwelling decomposers are largely determined by an increased 13C content in saprotrophic microorganisms. 相似文献
20.
The community structure, stable isotope ratios (15N/14N, 13C/12C) and reproductive mode of oribatid mites (Acari, Oribatida) were investigated in four habitats (upper tree bark, lower tree
bark, dry grassland soil, forest soil) at two sites in the Central Alps (Tyrol, Austria). We hypothesized that community structure
and trophic position of oribatid mites of dry grassland soils and bark of trees are similar since these habitats have similar
abiotic characteristics (open, dry) compared with forest soil. Further, we hypothesized that derived taxa of oribatid mites
reproducing sexually dominate on the bark of trees since species in this habitat consume living resources such as lichens.
In contrast to our hypothesis, the community structure of oribatid mites differed among grassland, forest and bark indicating
the existence of niche differentiation in the respective oribatid mite species. In agreement with our hypothesis, sexually
reproducing taxa of oribatid mites dominated on the bark of trees whereas parthenogenetic species were more frequent in soil.
Several species of bark-living oribatid mites had stable isotope signatures that were similar to lichens indicating that they
feed on lichens. However, nine species that frequently occurred on tree bark did not feed on lichens according to their stable
isotope signatures. No oribatid mite species could be ascribed to moss feeding. We conclude that sexual reproduction served
as preadaptation for oribatid mites allowing them to exploit new habitats and new resources on the bark of trees. Abiotic
factors likely are of limited importance for bark-living oribatid mites since harsh abiotic conditions are assumed to favor
parthenogenesis. 相似文献