Major Trophic Groups Research Articles

The differences in the trophic structure of semi‐enclosed and open coastal communities under the influence of an alien top predator (red king crab in the Barents Sea)

AbstractThe impact of the introduced red king crab (RKC), Paralithodes camtschaticus, in the Barents Sea was mostly studied through its direct predation on native species. This study uses stable isotope analysis of carbon and nitrogen to characterize major trophic groups (including grazing sea urchins) and specifically looks at RKC's trophic position and niche partitioning with the native hermit and spider crab species. To achieve this, we sampled organisms from the food web of a small fjord‐like Zelenaya Inlet on the Murmansk coast in the southwestern Barents Sea and the open sea coast, just outside the inlet for comparison. There, macrophyte‐derived carbon is the major source of organic matter along with the phytoplankton. In general, the fucoid source of primary production was more prominent within the inlet food web compared to the nearby open coastal zone. Isotopic trophic niches calculated using SIBER analysis showed partition between the native hermit and spider crabs suggesting, some degree of trophic segregation between coevolved species. RKCs are clustered together in the center of native decapod species' niches. There were some distinct differences between the feeding habits of RKCs within the inlet and the open sea coastal waters. The subadult RKCs that are present in the inlet throughout the year have a narrower (in the area and specifically in δ15N dimension) niche than the adults from the open sea. The latter have a wider variety of food items due to their migration and may prey on food items from different trophic levels. Sea urchins are an important trophic link transferring the macrophyte carbon to RKC. However, P. camtschaticus may also directly consume plant residues. Despite generally similar calculated trophic levels of decapod species, our isotopic data and literature data on the food composition of Paralithodes camtschaticus in the Barents Sea do not indicate significant RKC's competition with, and predation on, native species of crabs.

Surface chlorophyll concentration as a mesoplankton biomass assessment tool in the Southern Ocean region

AbstractAimMesoplankton of the Southern Ocean is the key trophic link between phytoplankton and other consumers and an important part of the biological carbon pump, a critical component of climate regulation. Although general patterns of mesoplankton distribution and life cycles are known, we still cannot estimate mesoplankton standing stocks at specified ocean‐basin scales.LocationSouthern Ocean, 34.4−56.9°S, 0–14.4°E.Time periodDecember 2009.Major taxa studiedAll mesoplankton 0.2–20.0 mm.MethodsWe assessed biomass of dominant taxa and total wet mesoplankton biomass (B, mg/m3) using surface chlorophyll a concentration (Chl) as a proxy of phytoplankton biomass and surface temperature (ST), a basic hydrological parameter. We sampled three strata within the layer 0–300 m at 43 stations with a Judey net (0.1 m2, 180 µm).ResultsWe identified 163 taxa and calculated their biomass, biomass of major trophic groups, and total mesoplankton biomass. Monthly Chl and ST derived from satellite imaging were averaged at various temporal and spatial scales. B in the upper layer and in the integrated layer 0–300 m was significantly linked to antecedent Chl signals; the most significant regressions were found between B and monthly Chl and ST averaged two months prior to the survey and 10° upstream of the Antarctic Circumpolar Current. Larger mesoplankton fractions showed longer response periods to Chl signal than smaller fractions.Main conclusionsOur results suggest the integral mesoplankton stock is 2.47–3.69 Gt wet weight wtot (ww), or 0.12–0.18 Gt C, in the whole Southern Ocean. Mesoplankton was dominated by omnivores (69%–74%) followed by carnivores (25%) and herbivores (20%), which suggests the leading role of omnivory in the Southern Ocean pelagic during the austral summer. We anticipate that these results will help to provide a deeper insight into the Southern Ocean ecosystems and will benefit models predicting changes in the carbon–climate Earth system.

The role of canopy gaps in maintaining biodiversity of plants and soil macrofauna in the forests of the northwestern Caucasus

The research was carried out in the coniferous-deciduous forests of the northwestern Caucasus, growing in similar climatic and soil-orographic conditions. Three types of forests of different ages were studied: aspen-hornbeam (50-70 years), beech-fir-hornbeam (80-110 years) and fir-beech forests (over 450 years). The studies were performed on the territory Krasnodar Krai (upper reaches of the Pshekha river, State Nature Reserve Chernogor'e) and the Republic of Adygea (upper reaches of the Belaya river, the Caucasian State Biosphere Reserve) in the summer seasons 2016 and 2019. The research involves geobotanical, population-ontogenetic, and soil-zoological methods. It has been established that in the canopy gaps of all forest types species density of plants is almost twice as high as in under-crown areas or even higher due to good light factor and high soil moisture since the tree stand does not intercept precipitation. Regeneration of tree cenopopulations in all forest types is much more effective in canopy gaps compared to under-crown areas. The undergrowth density of different types of trees is 10 and more times higher in gaps than in the under-crown areas. The maximum number of ecological-coenotic groups of plants is observed in the canopy gaps in all types of forest. All major trophic groups of macrofauna inhabit canopy gaps and under-crown areas, but their biomass in gaps is significantly exceeds that in under-crown areas. Due to the fact that soil moisture supply is an essential factor for moisture-loving saprophages’ activity, biomass of saprophages is on average twice as high in gaps than under-crown areas of all forest types. Only canopy gaps have high biomass of anecic earthworms – there are important ecosystem engineers, which contribute a lot to plant litter processing and the formation of soil porosity.

Planktivores as trophic drivers of global coral reef fish diversity patterns

One of the most prominent features of life on Earth is the uneven number of species across large spatial scales. Despite being inherently linked to energetic constraints, these gradients in species richness distribution have rarely been examined from a trophic perspective. Here we dissect the global diversity of over 3,600 coral reef fishes to reveal patterns across major trophic groups. By analyzing multiple nested spatial scales, we show that planktivores contribute disproportionally to the formation of the Indo-Australian Archipelago (IAA) marine biodiversity hotspot. Besides being "hotter" at the hotspot, planktivorous fishes display the steepest decline in species numbers with distance from the IAA when compared to other trophic groups. Surprisingly, we did not detect differences in diversification, transition, and dispersal rates in extant species phylogenies that would explain this remarkable gradient in planktivorous fish richness. Thus, we identify two potential complementary drivers for this pattern. First, exceptional levels of partitioning among planktivorous coral reef fishes were driven by temporally stable oceanographic conditions and abundant planktonic resources in the IAA. Second, extinctions of planktivores outside the IAA have been particularly pronounced during Quaternary climate fluctuations. Overall, our results highlight trophic ecology as an important component of global species richness gradients.

Composition and structure of macrozoobenthos of lakes in different natural zones and subzones of Western Siberia

In 2003–2016, the composition and structure of macrozoobenthic communities of 49 lakes in three natural zones (taiga, forest-steppe, and steppe) of Western Siberia were investigated. The benthic fauna of the research lakes includes 160 species of nine classes of invertebrates. The trophic structure was characterized, and six major trophic groups were identified. A spatial analysis of the macrozoobenthos of the research lakes showed that from the forest-steppe to the dry steppe subzone, the species diversity decreases on a considerable scale and also dominant taxa of macrozoobenthos change with increasing water salinity. Especially in the forest-steppe and steppe zones, high water salinity is probably a limiting factor in the development of macrozoobenthic communities. In the taiga zone, however, water salinity seems not to have such significance; rather the degree of humification (shown as dark-colored water due to waterlogging) should be taken into account.

Impacts of rainfall extremes predicted by climate-change models on major trophic groups in the leaf litter arthropod community.

Arthropods in the leaf litter layer of forest soils influence ecosystem processes such as decomposition. Climate-change models predict both increases and decreases in average rainfall. Increased drought may have greater impacts on the litter arthropod community. In addition to affecting survival or behaviour of desiccation-sensitive species, lower rainfall may indirectly lower abundances of consumers that graze drought-stressed fungi, with repercussions for higher trophic levels. We tested the hypothesis that trophic structure will differ between the two rainfall scenarios. In particular, we hypothesized that densities of several broadly defined trophic groupings of arthropods would be lower under reduced rainfall. To test this hypothesis, we used sprinklers to impose two rainfall treatments during three growing seasons in roofed, fenced 14-m2 plots and documented changes in abundance from initial, pre-treatment densities of 39 arthropod taxa. Experimental plots were subjected to either LOW (fortnightly) or HIGH (weekly) average rainfall based upon climate models and the previous 100years of regional weekly averages. Unroofed open plots, our reference treatment (REF), experienced higher than average rainfall during the experiment. The two rainfall extremes produced clear negative effects of lowered rainfall on major trophic groups. Broad categories of fungivores, detritivores and predators were more abundant in HIGH than LOW plots by the final year. Springtails (Collembola), which graze fungal hyphae, were 3× more abundant in the HIGH rainfall treatment. Taxa of larger-bodied fungivores and detritivores, spiders (Araneae), and non-spider predators were 2× more abundant under HIGH rainfall. Densities of mites (Acari), which include fungivores, detritivores and predators, were 1.5× greater in HIGH rainfall plots. Abundances and community structure of arthropods were similar in REF and experimental plots, showing that effects of rainfall uncovered in the experiment are applicable to nature. This pattern suggests that changes in rainfall will alter bottom-up control processes in a critical detritus-based food web of deciduous forests. Our results, in conjunction with other findings on the impact of desiccation on arthropods and fungal growth, suggest that drier conditions will depress densities of fungal consumers, causing declines in higher trophic levels, with possible impacts on soil processes and the larger forest food web.

Assessment of Provisioning Ecosystem Services of Irrigated Salt-Affected Soils in Ukraine

Irrigated, withdrawn from irrigation, and nonirrigated areas with southern chernozems (Calcic Chernozems) and dark chestnut soils (Haplic Kastanozems) of different degrees of natural and irrigation-induced salinity and solonetzicity were examined within the Ingulets irrigation system in Kherson and Nikolaev oblasts with the aim to assess provisioning ecosystem services of salt-affected soils in Ukraine. The suggested system is based on the results of the eco-agromeliorative assessment of land for pilot areas and takes into account susceptibility of the ecosystem services of salt-affected and solonetzic soils to different kinds of reclamation. In most cases, the soils of nonirrigated areas were characterized by the satisfactory eco-agromeliorative status, and the soils irrigated by sprinkling and withdrawn from irrigation had the good or satisfactory status depending on the depth and salinity of the groundwater. The soils subjected to drip irrigation were in the unfavorable state because of noncompliance with recommended irrigation technologies. Irrigation with slightly saline water caused changes in the structure of soil microbial cenoses and disturbance of the optimal ratios between different groups of microorganisms. In these soils and in the soils withdrawn from irrigation because of the development of secondary salinization and alkalization, the numbers of major trophic groups of microorganisms (eutrophic and oligotrophic bacteria and actinomycetes) and the total soil enzymatic activity decreased. The assessment of susceptibility of the ecosystem services of salt-affected soils to reclamation impacts (chemical amelioration and deep meliorative plowing) demonstrated certain positive changes in the efficiency of soil ecosystem services, such as the productive capacity, the habitat of species, the storage pool for carbon, and the nitrogen fixation capacity. An expert ten-grade scale to assess the productive ecosystem services of salt-affected soils in Ukraine has been developed. It is based on eight characteristics. According to this scale, the areas with the good state of the soils are virtually absent in the examined territory; the satisfactory state has been assigned to 14 surveyed areas; and the unsatisfactory state, to one area with a shallow depth of saline groundwater. This approach provides for a more efficient use of the provisioning functions of salt-affected soils owing to differentiation of reclamation impacts on them and their adaptation to the functioning of biological systems.

Fish feeding interactions in a subtropical coastal system in the southwestern Atlantic

Feeding interactions, which determine the dynamics, productivity and stability of an ecosystem to a large extent, constitute fundamental knowledge for understanding the functionality of an ecosystem. Within an integrated working context, this study aimed to identify the major prey for the fish species of Araçá Bay through an analysis of stomach contents. Araçá Bay is a sheltered, low tide terrace that presents seasonal hydrodynamics, primary productivity and organism communities. A total of 1253 stomachs from 28 fish species were sampled in March 2013 and January 2014 (austral summer) and in June 2013 (austral winter). A hierarchical cluster analysis (Bray-Curtis similarity index) was performed on the matrix of the index of relative importance (IRI%) of the food items of 15 species collected in both seasons. Five and four major trophic groups were recorded for the summer and winter, respectively (SIMPROF). A two-way PERMANOVA test showed significant differences in the prey compositions among the trophic groups but not the seasons. The annual dendrogram showed four trophic groups: shrimp feeders (8 species), teleostean fish feeders (2 species), copepod feeders (2 species), and benthic invertebrate feeders (3 species). Seasonal species shifts among the trophic groups related to the seasonal recruitment of relatively abundant fish species during the summer were recorded mainly between the teleostean fish feeder and shrimp feeder groups. Overall, the seasonal dynamics of the waters and the consequent prey abundance influenced the resource availability. Resource partitioning and feeding plasticity allowed the species to optimize the use of available prey in the bay. These results represent a contribution toward understanding the local food web, to construct a trophic model, and to contribute to its sustainable integrated management.

Authentic soil microbial communities in primeval forest ecosystems of Uzhanskyi National Nature Park

The article presents the modern aspects of studying and evaluating the biodiversity of soil microbiocenoses in the Carpathian region. The purpose of the work was to investigate the soil microbiota of virgin ecosystems, namely the structure of microbial communities, the number of major ecological trophic groups; to analyze the successional processes occurring in the soil microbiocenosis due to the influence of endogenous and exogenous factors. Anthropogenic impact: soil compaction, sanitary felling has led to changes in the groups of soil microorganisms, reduced their numbers and functional diversity. The primeval forests as etalon ecosystems better combine above resistance and stability with high productivity of biomass. Influence of ecological factors caused changes in the community of soil organisms, varied their abundance and functional diversity. Soil microorganisms have been largely ignored by conservation efforts. However, their role in biogeochemical processes, their diversity and abundance, and their potential as repositories of valuable genetic information and metabolic products make them as important as animals and plants to the biosphere and human welfare. Study of authentic soil microbiota creates the necessary prerequisites for the conservation of microbial diversity and forming the base of the eco-microbiological monitoring.

ДИНАМІКА РИЗОСФЕРНОЇ МІКРОБІОТИ СОНЯШНИКУ

<p>Microflora dynamics analysis of the rhizosphere and rhizoplane of sunflower plant genotypes: varieties, hybrid, line was set out. It was found that the number of major ecological and trophic groups of microorganisms in rhizosphere and rhizoplane of sunflower depends on genotypic features of agriculture populations and transpiration of root exometabolites that determine the development and activity of trophic groups of microorganisms. Throughout the growing season of sunflower (the phase of "4-6 leaves" to the maturation phase) we observed the qualitative changes in the composition of the microbiota. In the rhizosphere of hybrid, the microcenosis structure was the most stable, whereas the rhizosphere of crop culture had different dynamics during crop ontogeny. The depressive effect of root exometabolites was connected with genotypic features of the line regards the microflora of rhizosphere and rhizoplane. These features can be used in the F<sub>1</sub> hybrids cultivation and primary seed production of self-pollinated homozygous lines.</p><p> </p>

Fish Biomass in Tropical Estuaries: Substantial Variation in Food Web Structure, Sources of Nutrition and Ecosystem-Supporting Processes

Quantification of key pathways sustaining ecosystem function is critical for underpinning informed decisions on development approvals, zoning and offsets, ecosystem restoration and for meaningful environmental assessments and monitoring. To develop a more quantitative understanding of the importance and variation in food webs and nutrient flows in tropical estuaries, we investigated the spatio-temporal distribution of biomass of fish across 28 mangrove-lined estuaries in tropical Australia. We evaluated the extent to which nekton biomass in tropical estuaries responded to spatial and temporal factors and to trophic identity. Biomass was dominated by two trophic groups, planktivores and macrobenthos feeders. Contributions by other trophic groups, such as detritivores and microbenthos feeders, were more variable. Total biomass and the biomass of all major trophic groups were concentrated in downstream reaches of estuaries. The consistent concentration of biomass downstream, and spatio-temporal differences in the contributions by the different trophic groups, indicates substantial differences in food web structure, differences in the contributions from different sources of nutrition and probably unequal flow of productivity into higher levels of the food web in different parts of the estuary. In turn, this suggests substantial qualitative and quantitative differences in ecosystem-supporting processes in different estuary reaches.

Reef Fishes at All Trophic Levels Respond Positively to Effective Marine Protected Areas.

Marine Protected Areas (MPAs) offer a unique opportunity to test the assumption that fishing pressure affects some trophic groups more than others. Removal of larger predators through fishing is often suggested to have positive flow-on effects for some lower trophic groups, in which case protection from fishing should result in suppression of lower trophic groups as predator populations recover. We tested this by assessing differences in the trophic structure of reef fish communities associated with 79 MPAs and open-access sites worldwide, using a standardised quantitative dataset on reef fish community structure. The biomass of all major trophic groups (higher carnivores, benthic carnivores, planktivores and herbivores) was significantly greater (by 40% - 200%) in effective no-take MPAs relative to fished open-access areas. This effect was most pronounced for individuals in large size classes, but with no size class of any trophic group showing signs of depressed biomass in MPAs, as predicted from higher predator abundance. Thus, greater biomass in effective MPAs implies that exploitation on shallow rocky and coral reefs negatively affects biomass of all fish trophic groups and size classes. These direct effects of fishing on trophic structure appear stronger than any top down effects on lower trophic levels that would be imposed by intact predator populations. We propose that exploitation affects fish assemblages at all trophic levels, and that local ecosystem function is generally modified by fishing.

The trophodynamics of marine top predators: Current knowledge, recent advances and challenges

We review present understanding of the spatial and temporal diet variability (trophodynamics) of a range of pelagic marine top predators, at both early and adult life history stages. We begin with a review of methodologies used to advance our understanding of the trophodynamics of marine top predators, particularly in relation to climate change. We then explore how these developments are informing our understanding of the major trophic groups in food webs leading to, and including, marine top predators. We examine through specific examples how the impacts of ocean warming may affect pelagic food web relationships from both top-down and bottom-up perspectives. We examine the potential, in the absence of long-term data sets, of using large-scale spatial studies to examine how potential changes in biological oceanography could impact the biomass and composition of prey species, particularly the role of phytoplankton size spectra. We focus on examples from regions where biotic change with respect to climate change is likely. In particular, we detail the effects of climate change on oceanographic and bathymetric “hotspots” and provide the example involving seabirds in the Benguela Current system. We end by urging the development of international collaborations and databases to facilitate comprehensive ocean-scale understanding of climate impacts on marine top predators.

Response of Trophic Groups of Macrobenthos to Organically Enriched Sediments: A Comparative Study between Temperate and Tropical Regions

This study is aimed to detect the level of environmental disturbance caused by farming activities using trophic groups of macrobenthic assemblages, with emphasizes the difference between temperate and tropical regions. The samples of macrobenthic assemblages were taken from 2 (two) farm sites, i.e. Southern Spencer Gulf, South Australia, where farming of southern bluefin tuna ( Thunnus maccoyii ) takes place, representing as a temperate region (Site I) and milk fish ( Chanos chanos ) farms and mangrove area at coastal region of Mngkang Kulon, Semarang, Central Java, Indonesia, representing as a tropical region (Site II). Macrobenthic abundance was categorised based on six major trophic groups. Macrobenthic assemblages dominated by all polychaetes, they are Capitellidae, Cirratullidae, Lumbrineridae, Nephtyidae, and Spionidae at Site I (temperate region), owing to their relatively tolerance to organic enrichment, both at the farm sites and at control sites. Surface deposit feeders (SDF) dominated in abundance at both control and fish farm sites at Site I, whilst subsurface deposit feeders (SSDF) exhibited highest in proportion at Site II over the study period, in particular species of Capittelidae, indicating that both sites has been influenced by fish farm activities. The abundance of deposit feeders was significantly higher at the farm sites than at the reference sites. Organic carbon in the sediment surface is likely to correlate with deposit feeding and sub-surface deposit feeding species richness, whereas total and food particulate matter correlate with species diversity. The result of this comparative study implies that response of trophic groups of macrobenthos to environmental disturbance are considerably similar at both tropical and temperate regions.

Functionally and phylogenetically diverse plant communities key to soil biota

Recent studies assessing the role of biological diversity for ecosystem functioning indicate that the diversity of functional traits and the evolutionary history of species in a community, not the number of taxonomic units, ultimately drives the biodiversity--ecosystem-function relationship. Here, we simultaneously assessed the importance of plant functional trait and phylogenetic diversity as predictors of major trophic groups of soil biota (abundance and diversity), six years from the onset of a grassland biodiversity experiment. Plant functional and phylogenetic diversity were generally better predictors of soil biota than the traditionally used species or functional group richness. Functional diversity was a reliable predictor for most biota, with the exception of soil microorganisms, which were better predicted by phylogenetic diversity. These results provide empirical support for the idea that the diversity of plant functional traits and the diversity of evolutionary lineages in a community are important for maintaining higher abundances and diversity of soil communities.

Structural and Functional Biodiversity of Microbial Communities in the Rhizosphere of Plants Infected with Broomrapes (Orobanchaceae)

ABSTRACTBroomrapes are obligate root parasites from the family Orobanchaceae. Several of them parasitize important crops and have major economical impact. Important features of broomrapes are their great adaptability and flexibility, which hampers the understanding of the factors affecting the host-parasite system. The role of the soil microorganisms as a biotic factor in this system is not well understood yet. A number of recent studies demonstrated that parasitic weeds use a signaling mechanism between host plants and symbiotic arbuscular microbes to establish parasitic associations. Formation of arbuscular mycorrhizal (AM) associations however, significantly suppresses seed germination of parasitic weeds. The aim of this study was to determine whether the established host—parasite associations can also influence the major trophic groups of soil microorganisms in the rhizosphere. The study was conducted on 11 host plant—parasite systems with nine broomrape species. For comparison, similar non-infected host plants were used. The quantities of the autochthonous and oligotrophic microorganisms, streptomycetes, soil fungi, ammonifying microorganisms, assimilating mineral (NH4+) nitrogen and aerobic nitrogen-fixing bacteria of the genus Azotobacter were determined. Microbiological indexes, characterizing the structure of microbial communities were determined. The population density of all microbial communities formed in the presence of broomrapes was considerably decreased, three-to five-fold. Regardless of the exact numbers, in all involved host—parasite systems the trend remained the same. These findings demonstrated that not only can arbuscular flora suppress parasitic weeds, but also, when host-parasitic associations have already been established, parasitic weeds can suppress and influence the level of biodiversity in major trophic groups of soil microorganisms in the rhizosphere. The statistical analysis demonstrated that the observed changes are an adaptive response of the microbial communities precisely to the presence of broomrape. The research in this area should at a next step further characterize the specifics of the host—parasite—AM interactions at different stages of the broomrape life cycle.

Microbiology of Lonar Lake and other soda lakes.

Soda lakes are saline and alkaline ecosystems that are believed to have existed throughout the geological record of Earth. They are widely distributed across the globe, but are highly abundant in terrestrial biomes such as deserts and steppes and in geologically interesting regions such as the East African Rift valley. The unusual geochemistry of these lakes supports the growth of an impressive array of microorganisms that are of ecological and economic importance. Haloalkaliphilic Bacteria and Archaea belonging to all major trophic groups have been described from many soda lakes, including lakes with exceptionally high levels of heavy metals. Lonar Lake is a soda lake that is centered at an unusual meteorite impact structure in the Deccan basalts in India and its key physicochemical and microbiological characteristics are highlighted in this article. The occurrence of diverse functional groups of microbes, such as methanogens, methanotrophs, phototrophs, denitrifiers, sulfur oxidizers, sulfate reducers and syntrophs in soda lakes, suggests that these habitats harbor complex microbial food webs that (a) interconnect various biological cycles via redox coupling and (b) impact on the production and consumption of greenhouse gases. Soda lake microorganisms harbor several biotechnologically relevant enzymes and biomolecules (for example, cellulases, amylases, ectoine) and there is the need to augment bioprospecting efforts in soda lake environments with new integrated approaches. Importantly, some saline and alkaline lake ecosystems around the world need to be protected from anthropogenic pressures that threaten their long-term existence.

Analysing the characteristics of soil nematode communities at pepper (Piper nigrum L.) cultivation area in Loc Hung commune, Loc Ninh district, Binh Phuoc province

Pepper (Piper nigrum L.) is a high economic value plant species that brings the main income to the people at Loc Hung commune. So the pepper’s yield plays a significant role in people’s life in this region. To assess the influence of environmental factors on the growth and development of pepper, we need to analyse the structural characteristics of soil nematode communities in order to promptly detect the levels of parasitic nematodes infection as well as assessment of soil environment status based on nematode communities. Study results at five sampling stations are analyses of 30 genera of nematodes belonging to 6 major trophic groups (bacterial feeders, fungal feeders, algal feeders, omnivores, carnivores and plant parasites). Calculation results of indices such as SUM(MI), SUM(MI2-5), MI and PPI showed that soil nematodes community is very little affected by the bacteria feeder group and the rate of parasitic nematode pepper quite severe. Analysis of correlation between trophic groups showed that nematodes are sensitive to environmental factors. This means the potential use of nematodes as a biological indicator for soil quality is possible.
 Hồ tiêu (Piper nigrum L.) là cây trồng có giá trị kinh tế cao và là nguồn thu nhập chính của người dân tại xã Lộc Hưng. Do đó, năng suất cây tiêu có ý nghĩa rất lớn đối với đời sống người dân trong vùng. Để đánh giá ảnh hưởng của các yếu tố môi trường lên sự sinh trưởng và phát triển của cây tiêu, cần phải phân tích đặc trưng cấu trúc quần xã tuyến trùng đất của vùng nhằm phát hiện kịp thời mức độ nhiễm tuyến trùng ký sinh trên hồ tiêu cũng như đánh giá nhanh hiện trạng môi trường đất dựa trên quần xã tuyến trùng. Kết quả nghiên cứu tại 5 điểm thu mẫu phân tích được 30 giống tuyến trùng thuộc 6 nhóm dinh dưỡng chính (ăn vi khuẩn, ăn nấm, ăn tảo, ăn tạp, ăn thịt và ký sinh thực vật). Kết quả tính toán các chỉ số ∑MI, ∑MI2-5, MI và PPI cho thấy quần xã tuyến trùng đất ở đây rất ít chịu ảnh hưởng của nhóm ăn vi khuẩn và tỷ lệ hồ tiêu nhiễm ký sinh khá nặng. Phân tích tương quan giữa các nhóm dinh dưỡng cho thấy tuyến trùng khá nhạy cảm với các yếu tố môi trường, điều này cho thấy tiềm năng sử dụng tuyến trùng như một sinh vật chỉ thị cho chất lượng môi trường đất.

Changes in Plant Species Richness Induce Functional Shifts in Soil Nematode Communities in Experimental Grassland

BackgroundChanges in plant diversity may induce distinct changes in soil food web structure and accompanying soil feedbacks to plants. However, knowledge of the long-term consequences of plant community simplification for soil animal food webs and functioning is scarce. Nematodes, the most abundant and diverse soil Metazoa, represent the complexity of soil food webs as they comprise all major trophic groups and allow calculation of a number of functional indices.Methodology/Principal FindingsWe studied the functional composition of nematode communities three and five years after establishment of a grassland plant diversity experiment (Jena Experiment). In response to plant community simplification common nematode species disappeared and pronounced functional shifts in community structure occurred. The relevance of the fungal energy channel was higher in spring 2007 than in autumn 2005, particularly in species-rich plant assemblages. This resulted in a significant positive relationship between plant species richness and the ratio of fungal-to-bacterial feeders. Moreover, the density of predators increased significantly with plant diversity after five years, pointing to increased soil food web complexity in species-rich plant assemblages. Remarkably, in complex plant communities the nematode community shifted in favour of microbivores and predators, thereby reducing the relative abundance of plant feeders after five years.Conclusions/SignificanceThe results suggest that species-poor plant assemblages may suffer from nematode communities detrimental to plants, whereas species-rich plant assemblages support a higher proportion of microbivorous nematodes stimulating nutrient cycling and hence plant performance; i.e. effects of nematodes on plants may switch from negative to positive. Overall, food web complexity is likely to decrease in response to plant community simplification and results of this study suggest that this results mainly from the loss of common species which likely alter plant – nematode interactions.

Widespread omnivory and low temporal and spatial variation in the diet of fishes in a hydrologically variable northern Australian river

This article examines the trophic ecology of freshwater fishes (22 species in 15 families) in a wet and dry tropical Australian river of high intra-annual and interannual hydrological variability. Seven major trophic groups were identified by cluster analysis; however, four food items (filamentous algae, chironomid larvae, Trichoptera larvae and Ephemeroptera nymphs) comprised almost half of the average diet of all species. The influence of species, fish size, spatial effects and temporal effects on food use was investigated using redundancy analysis. Size, time and space accounted for little of the perceived variation. Ontogenetic changes in diet were minor and limited to a few large species. Spatial variation in trophic composition of the fish assemblages reflected the effects of the Burdekin Falls and dam, a major geographic barrier, on species distributions. Little spatial variation in diet was detected after accounting for this biogeographical effect. Temporal variations in flow, although marked, had little effect on variations in fish diet composition due to the low temporal diversity of food resources in physically monotonous sand and gravel channels. Species identity accounted for<50% of the observed variation in food choice; omnivory and generalism were pronounced. The aquatic food web of the Burdekin River appears simple, supported largely by autochthonous production (filamentous and benthic microalgae, and to some extent, aquatic macrophytes). Allochthonous food resources appear to be unimportant. The generalist feeding strategies, widespread omnivory and absence of pronounced trophic segregation reported here for Burdekin River fishes may be common to variable and intermittent rivers of subtropical and tropical northern Australia with similar fish communities and may be a general feature of rivers of low habitat diversity and characterized by flow regimes that vary greatly both within and between years.