Late Famennian gastropoda from south-west England

The gastropod fauna of the Upper Devonian Baggy and Pilton formations in south‐west England is revised and includes some 30 taxa. The topmost part of the Upper Famennian succession in Devon is represented by clastic near‐shore and shallow shelf sediments, indicating a short‐term transgressive phase (‘Strunian Transgression’). The sequence yields a highly diverse fauna dominated by brachiopods and ostracodes, locally supplemented by crinoids, bryozoans, trilobites and molluscs. The taxa ‘Patellostium’britannicum sp. nov., Angyomphalus (Angyomphalus) junius sp. nov. and Dictyotomaria eurocapillaria sp. nov. are erected; a junior homonym is replaced by Macrochilina? piltonensis nom. nov. The gastropod fauna displays an independent character, where latest Devonian faunal elements overlap with Late Palaeozoic taxa expressing a transition similar to that of the bivalves, brachiopods, echinoderms and corals, without a sharp faunal break at the Devonian/Carboniferous boundary. Apart from the Caenogastropoda, all subclasses of gastropods are represented. Members of the bellerophontoids, pleurotomarioids and loxonematoids are most abundant, followed by murchisonioids, naticimorphs, euomphalomorphs and platyceratoids. The various gastropod groups represent different ecological demands and trophic categories, and together with the accompanying fauna indicate that nearly all habitats and niches were occupied in the shallow South Laurussian Shelf.     

Cavity-dwelling organisms in Lower Cambrian patch reefs from southern Labrador

An intact and well-preserved biota of cavity-dwelling organisms (coelobionts) of early Cambrian age is found within growth-framework cavities in archaeocyathid patch reefs of the lower Forteau Formation (upper Bonnia-Olenellus Zone) of southern Labrador. The biota was diverse, and consisted of encrusting and vagrant organisms. Renalcis , a Renalcis-like form, Epiphyton, Girvanella , and Serligia , all lived attached to walls and roofs of the cavities; other attached forms were Bija, Archaeotrypa , and two types of Wetheredella , an agglutinated foraminifer. Other organisms, including trilobites, probable calcareous ostracodes, brachiopods, echinoderms, and worms, as well as fungi, are also found preserved within the cavities. The structure of the coelobiontic community is surprisingly modern; it indicates that as early as the Lower Cambrian coelobiontic organisms were well-established in reefs, and were an important part of the reef community as a whole.     

Changhsingian brachiopod communities along a marine depth gradient in South China and their ecological significance in the end-Permian mass extinction

Diversity indices (dominance and evenness) and ecological spatial structure (lifestyles and relative abundances) are important features of Changhsingian brachiopod communities prior to the end-Permian mass extinction (EPME) and could predict temporal and spatial extinction patterns during the EPME. In South China, Changhsingian brachiopod communities show higher diversity than other contemporaneous brachiopod communities in the world and have been reported from a variety of sedimentary environments. In this paper, brachiopods from 18 sections in South China were selected to divide communities and compare their ecological structure. Based on the results of network analysis, cluster analysis and quantitative data from the selected sections, we show that Changhsingian brachiopod communities in South China can be categorized into three assemblages along a marine depth gradient: the Neochonetes–Fusichonetes–Paryphella Assemblage from the shallow-water clastic-rock facies, Spinomarginifera–Peltichia–Oldhamina Assemblage from the shallow-water carbonate platform facies and Fusichonetes–Crurithyris Assemblage from the deep-water siliciclastic intracontinental basin facies. Compared with communities from carbonate platform facies, the communities from siliciclastic facies were characterized by high dominance, low evenness and low lifestyle diversity, which might be important biotic factors leading to earlier extinctions. After the extinction began in all environments, the whole earliest Triassic brachiopod community was first dominated by Fusichonetes and then by Crurithyris. These patterns of domination and replacement could be explained by morphological and ecological advantages. The domination of these two genera, which were already adapted to the oxygen and food-limited deep-water habitat, indicates that the cooler deep-water environment might have been a relatively less stressed habitat after the beginning of the EPME. This suggests that global warming might be the main trigger among the previously proposed synergistic environmental stresses, while anoxia might not, at least for the beginning of EPME.     

A stressed stream ecosystem: macroinvertebrate community integrity and microbial trophic response

A year-long study of a second-order stream in Southwestern Virginia was carried out from 1979–80. One of the objectives of the study was to evaluate the effects of sewage and electroplating plant effluent stress on the trophic response of aquatic invertebrate assemblages and microbial communities in the stream. Quantitative benthic samples were collected periodically at three reference stations and four stressed stations below the outfalls. Invertebrates were counted, identified taxonomically, and classified into functional groups based on their feeding strategies. Ash-free dry weights were obtained for each functional group by date and station, and the number and density of different taxa were calculated as well. Reference stations had diverse invertebrate assemblages; scrapers were well represented and all functional groups were present in reasonably equivalent proportions. Stressed stations were dominated by collector gatherers and filterers to the virtual exclusion of scrapers. The trophic status of the microbial community was determined by suspending artificial substrates in the stream for 1-week periods. The community that colonized the substrates was assayed for ATP and chlorophyll a, and an autotrophy index (AI) was calculated using these values. The autotrophic component of the microbial community was greatest at the reference stations, and the community became primarily heterotrophic below the outfalls. The AI correlated well with the proportion of scrapers. Aquatic invertebrate assemblages and microbial communities responded to stress by changing their trophic structure to fit best the available energy sources. Where heterotrophic microbes dominated, gathering and filtering invertebrates utilized the abundant organic matter. In areas where a mainly autotrophic microbial community existed, scrapers, gatherers, and filterers were all present in balanced proportions.     

Lower-Middle Cambrian boundary in open shelf facies of the Siberian Platform

In the Early and Middle Cambrian (of traditional usage), three broad facies belts were developed over the Siberian Platform. The lithofacies belts comprise evaporitic-carbonate, reef-shoal, and open-marine environments.Trilobites assemblages are most diverse in the open-marine lithofacies (Judoma-Olenek facies), represented especially by the Kuonamka Formation, in the eastern part of the platform. Species, genera and families of trilobites gradually increased through the Middle-Cambrian boundary interval in the Kuonamka Formation. Protolenidae dominated in the time represented by the Lermontovia Zone. In strata assigned to the Anabaraspis Zone, the protolenids disappear, the paradoxidids appear, and the diversity of dorypygids increases. The number of trilobite families increases in the Oryctocara and Kounamkites zones.Well represented in the Kuonamka formation of the eastern Siberian Platform are three levels of trilobites that have potential for global correlation. They are the Oryctocephalus reticulatus (=O. indicus latus), Oryctocephalus indicus, and Ovatoryctocara granulatus levels. The Lower-Middle Cambrian boundary in the South China correlates to the lower part of the Kounamkites Zone of the Siberian Platform.     

Indirect food web interactions: sea otters and kelp forest fishes in the Aleutian archipelago

Although trophic cascades—the effect of apex predators on progressively lower trophic level species through top-down forcing—have been demonstrated in diverse ecosystems, the broader potential influences of trophic cascades on other species and ecosystem processes are not well studied. We used the overexploitation, recovery and subsequent collapse of sea otter (Enhydra lutris) populations in the Aleutian archipelago to explore if and how the abundance and diet of kelp forest fishes are influenced by a trophic cascade linking sea otters with sea urchins and fleshy macroalgae. We measured the abundance of sea urchins (biomass density), kelp (numerical density) and fish (Catch per unit effort) at four islands in the mid-1980s (when otters were abundant at two of the islands and rare at the two others) and in 2000 (after otters had become rare at all four islands). Our fish studies focused on rock greenling (Hexagrammos lagocephalus), the numerically dominant species in this region. In the mid-1980s, the two islands with high-density otter populations supported dense kelp forests, relatively few urchins, and abundant rock greenling whereas the opposite pattern (abundant urchins, sparse kelp forests, and relatively few rock greenling) occurred at islands where otters were rare. In the 2000, the abundances of urchins, kelp and greenling were grossly unchanged at islands where otters were initially rare but had shifted to the characteristic pattern of otter-free systems at islands where otters were initially abundant. Significant changes in greenling diet occurred between the mid-1980s and the 2000 although the reasons for these changes were difficult to assess because of strong island-specific effects. Whereas urchin-dominated communities supported more diverse fish assemblages than kelp-dominated communities, this was not a simple effect of the otter-induced trophic cascade because all islands supported more diverse fish assemblages in 2000 than in the mid-1980s.     

Structure of a pond community in Central Mexico

The community structure of a tropical pond located in Mexico City was described. Primary producers were diverse and abundant and macrophyte components provide a broad habitat diversity. Major biotic components in the water column were algae of the genera Microcystis, Scenedesmus and Chlamydomonas. Mats of Cyclotella were located in deeper, shaded areas associated with the bottom. Three species of emergent macrophytes characterize the large primary producers. The zooplankton was dominated by protozoa, which were more abundant than rotifers and Crustacea. Dominant invertebrate species of the pond bottom were insect larvae, gastropod mollusks, oligochaete annelids and nematodes. Vertebrates (fish, amphibians, reptiles) feed on this variety of biotic components. A flow diagram depicted the major biological interactions and suggested a complex trophic structure.     

Carboniferous reef succession of the Panthalassan open-ocean setting: example from Omi Limestone, central Japan

Summary The Carboniferous-Permian (Visean-Midian) Omi Limestone in the Akiyoshi Terrane, central Japan is a large carbonate unit developed on a seamount in the Panthalassa Ocean. As the seamount subsided during Carboniferous and Permian time, the carbonate deposition at the top of a seamount was almost continous. Terrigenous siliciclastic sediments are absent, because the seamount was situated in an open-ocean setting. The lower part of this seamount-type limestone records a nearly continuous Carboniferous reef succession. Sedimentary facies in the Carboniferous part of the Omi Limestone are generally highly diverse, but their diversity varies in each age. The Upper Carboniferous part consists of highly diversified facies including fore reef, reef front, reef crest, sand shoal, and lagoon facies, while a simple facies assemblage, composed only of fore reef, reef front, and sand shoal facies, occurs in the Lower Carboniferous. The Carboniferous reef succession consists of four phases characterized, in ascending order, by the coralbryozoan-crinoid community, problematic skeletal organism-microencruster community, chaetetid-microencruster community, and calcareous algal community. The first phase, comprising the coral-bryozoan-crinoid community, occurs in theEndothyra spp. Zone to theEostaffella kanmerai Zone (Visean to Serpukhovian). This community acted only as sediment-bafflers and/or contributors. The second phase, represented by the problematic skeletal organism-microencruster community, is developed in theMillerella sp. Zone to theAkiyoshiella ozawai Zone (Bashkirian to lowermost Moscovian), and the third phase, comprising the chaetetid-microencruster community, occurs in the overlyingFusulinella biconica Zone (Lower Moscovian). These two communities are characterized by highly diversified reef-building organisms that had the ability to build rigid frameworks. Calcareous algae and incertae sedis such asHikorocodium, solenoporaceans and phylloid algae characterize the fourth phase, which occurs in theBeedeina sp. Zone (Upper Moscovian). The changes of the reef communities were sucessive for a long period of more than 40 m.y., and each community was distributed in various environments. In addition, the continuous subsidence of the isolated seamount resulted in environmental stability. These properties indicate that this succession represents the biotic evolution of reef-building organisms. The problematic skeletal organism-microencruster community and chaetetid-microencruster community of the Late Carboniferous formed wave-resistant and rigid frameworks along with abundant submarine cements. The growth of these reef frameworks resulted in the formation of highly diversified sedimentary facies comparable to those of a modern reef complex. Such reefs are also recognized in the seamount-type Akiyoshi Limestone, but rare on Carboniferous Pangean shelves. Therefore, the formation of these types of reefs appear to be characteristic of open-ocean seamount settings, which differed from epicontinental shelf settings in having no siliciclastic input, being exposed to relatively strong openocean waves and swells, and probably more environmental stability resulting from the relatively continuous subsidence of the seamount.     

Into the wild blueberry (Vaccinium angustifolium) rhizosphere microbiota

The ability of wild blueberries to adapt to their harsh environment is believed to be closely related to their symbiosis with ericoid mycorrhizal fungi, which produce enzymes capable of organic matter mineralization. Although some of these fungi have been identified and characterized, we still know little about the microbial ecology of wild blueberry. Our study aims to characterize the fungal and bacterial rhizosphere communities of Vaccinium angustifolium (the main species encountered in wild blueberry fields). Our results clearly show that the fungal order Helotiales was the most abundant taxon associated with V. angustifolium. Helotiales contains most of the known ericoid mycorrhizal fungi which are expected to dominate in such a biotope. Furthermore, we found the dominant bacterial order was the nitrogen-fixing Rhizobiales. The Bradyrhizobium genus, whose members are known to form nodules with legumes, was among the 10 most abundant genera in the bacterial communities. In addition, Bradyrhizobium and Roseiarcus sequences significantly correlated with higher leaf-nitrogen content. Overall, our data documented fungal and bacterial community structure differences in three wild blueberry production fields.     

Temporal Changes in the Bacterial Communities of Soil, Rhizosphere, and Endorhiza Associated with Field-Grown Cucumber (Cucumis sativus L.)

Abstract In order to understand how bacterial communities develop in natural ecosystems, the culturable aerobic-heterotroph bacterial communities of three habitats (rhizosphere, endorhiza, and soil) associated with field-grown cucumber roots were examined for quantitative and qualitative changes in structure, over time. Soil and root samples were taken 0, 7, 14, 21, 35, and 70 days after planting (DAP) in 1994, and 0, 7, 14, 28, 42, and 70 DAP in 1995. Individual bacterial colonies of aerobic- heterotroph bacteria were sampled randomly and characterized using the Sherlock System (Microbial ID, Inc., Newark, Del), for fatty acid methyl ester analysis. More than 6,000 bacterial isolates were identified to the genus level and used in calculating richness, diversity, and similarity indices for the three habitats. Diversity was assessed using Hill's modifications of Shannon's index and Simpson's index (N1 and N2, respectively), while similarity was determined using the coefficient of biotic similarity. The same general trends were observed for the community structures of each habitat in both years. The soil was the least diverse and the rhizosphere was most diverse throughout both growing seasons. Bacillus and Arthrobacter spp. were dominant in soil, while Gram-negative bacteria tended to be more abundant in the rhizosphere and endorhiza. The initial membership of the endorhiza (7–14 DAP) appeared to be a function of the rhizosphere community, since both habitats were composed of similar genera. However, the endorhiza was less diverse than the rhizosphere because one or two genera tended to be dominant in each sample, particularly Agrobacterium and Enterobacter spp. Analysis of community similarity indicated that the soil was a distinct habitat and remained relatively unchanged throughout the study. The rhizosphere and endorhiza were dissimilar from the soil and from each other at particular sampling times. These results indicate that the soil, rhizosphere, and endorhiza communities are structurally distinct (the relative abundance of a particular bacterial genera differs among habitats) but share a common membership. Thus, when examining bacterial communities, both the qualitative (i.e., membership) and quantitative (i.e., abundance) aspects must be examined in order to study shifts in community structure. Received: 19 July 1996; Accepted: 20 December 1996     

The structured diversity of specialized gut symbionts of the New World army ants

Symbiotic bacteria play important roles in the biology of their arthropod hosts. Yet the microbiota of many diverse and influential groups remain understudied, resulting in a paucity of information on the fidelities and histories of these associations. Motivated by prior findings from a smaller scale, 16S rRNA‐based study, we conducted a broad phylogenetic and geographic survey of microbial communities in the ecologically dominant New World army ants (Formicidae: Dorylinae). Amplicon sequencing of the 16S rRNA gene across 28 species spanning the five New World genera showed that the microbial communities of army ants consist of very few common and abundant bacterial species. The two most abundant microbes, referred to as Unclassified Firmicutes and Unclassified Entomoplasmatales, appear to be specialized army ant associates that dominate microbial communities in the gut lumen of three host genera, Eciton, Labidus and Nomamyrmex. Both are present in other army ant genera, including those from the Old World, suggesting that army ant symbioses date back to the Cretaceous. Extensive sequencing of bacterial protein‐coding genes revealed multiple strains of these symbionts coexisting within colonies, but seldom within the same individual ant. Bacterial strains formed multiple host species‐specific lineages on phylogenies, which often grouped strains from distant geographic locations. These patterns deviate from those seen in other social insects and raise intriguing questions about the influence of army ant colony swarm‐founding and within‐colony genetic diversity on strain coexistence, and the effects of hosting a diverse suite of symbiont strains on colony ecology.     

Changes in bacterial and archaeal communities during the concentration of brine at the graduation towers in Ciechocinek spa (Poland)

This study evaluates the changes in bacterial and archaeal community structure during the gradual evaporation of water from the brine (extracted from subsurface Jurassic deposits) in the system of graduation towers located in Ciechocinek spa, Poland. The communities were assessed with 16S rRNA gene sequencing (MiSeq, Illumina) and microscopic methods. The microbial cell density determined by direct cell count was at the order of magnitude of 10⁷ cells/mL. It was found that increasing salt concentration was positively correlated with both the cell counts, and species-level diversity of bacterial and archaeal communities. The archaeal community was mostly constituted by members of the phylum Euryarchaeota, class Halobacteria and was dominated by Halorubrum-related sequences. The bacterial community was more diverse, with representatives of the phyla Proteobacteria and Bacteroidetes as the most abundant. The proportion of Proteobacteria decreased with increasing salt concentration, while the proportion of Bacteroidetes increased significantly in the more concentrated samples. Representatives of the genera Idiomarina, Psychroflexus, Roseovarius, and Marinobacter appeared to be tolerant to changes of salinity. During the brine concentration, the relative abundances of Sphingobium and Sphingomonas were significantly decreased and the raised contributions of genera Fabibacter and Fodinibius were observed. The high proportion of novel (not identified at 97% similarity level) bacterial reads (up to 42%) in the 16S rRNA gene sequences indicated that potentially new bacterial taxa inhabit this unique environment.

     

Intertidal meiofauna of a high-latitude glacial Arctic fjord (Kongsfjorden, Svalbard) with emphasis on the structure of free-living nematode communities

Meiofauna communities of four intertidal sites, two sheltered and two more exposed, in Kongsfjorden (Svalbard) were investigated in summer 2001 at two different tidal levels (i.e. the low-water line and close below the driftline, referred to as mid-water (MW) level). A total of seven meiofaunal higher taxa were recorded with nematodes, oligochaetes and turbellarians being numerically dominant. Mean total meiofaunal densities ranged between 50 ind. 10 cm⁻² and 903 ind. 10 cm⁻². Our data showed a clear decrease in total meiofaunal densities with increasing coarseness of the sediment. Total meiofaunal biomass varied from 0.2 g dwt m⁻² to 2 g dwt m⁻² and, in general, was high even at low meiofaunal densities, i.e. larger interstitial spaces in coarser sediments supported larger meiofauna, especially turbellarians. The results on the vertical distribution of meiofauna contrasted sharply with typical meiobenthic depth profiles on other beaches, probably in response to ice-scouring and concomitant salinity fluctuations. Oligochaetes were the most abundant taxon, with a peak density of 641 ind. 10 cm⁻² at Breoyane Island. They were mainly comprised of juvenile Enchytraeidae, which prohibited identification to species/genus level. Nematode densities ranged between 4 ind. 10 cm⁻² and 327 ind. 10 cm⁻². Nematodes were identified up to genus level and assigned to trophic guilds. In total, 28 nematode genera were identified. Oncholaimus and Theristus were the most abundant genera. The composition of the nematode community and a dominance of predators and deposit feeders were in agreement with results from other arctic and temperate beaches. Nematode genus diversity was higher at the more sheltered beaches than at the more exposed ones. Low-water level stations also tended to harbour a more diverse nematode communities than stations at the MW level. Differences in nematode community structure between low- and MW stations of single beaches were more pronounced than community differences between different beaches and were mainly related to resources quality and availability.     

塔中隆起上奥陶统凯迪阶良里塔格组生物群及其古生态特征

塔中隆起区的良里塔格组含菌藻类微生物岩、植物类的钙藻、原生动物中的有孔虫、后生动物中的海绵、珊瑚、苔藓虫、介形类、三叶虫、腹足类、腕足动物、棘皮动物等化石门类。根据其生物成分的埋葬学特征,分为原地或近源成分占优势的群落和远源异地成分占优势的组合,群落和组合的类型展布受水深、水动力、坡折带地貌等因素控制。     

Influence of wildfire on diversity of culturable soil microfungal communities in the Mount Carmel forest,Israel

The fire-related variations in culturable microfungal communities in the soil of the Mount Carmel forest, Israel, were examined by comparing the communities from burned and adjacent unburned soil plots under pine and oak trees – collected 6, 18, and 26 months after the fire. A total of 82 species representing 44 genera were isolated using the soil dilution plate method. The results showed that the fire had strongly influenced the composition and structure of microfungal communities. The fire remarkably changed physical and chemical properties of the environment, decreasing water holding capacity, organic matter and total nitrogen content in the burned soil. These changes supported abundant development of fast-growing mycoparasitic species (Clonostachys rosea and Trichoderma spp.) and caused significant decrease in species richness. The variations in community composition were much more expressed in the burned soils under oak vegetation as compared with the pine trees. In the oak burned soils, the contribution of the “mesic” component, Penicillium spp., was markedly lower, whereas the contribution of the “xeric”, stress-selected component, melanin-containing species, was higher than in the unburned communities. Such variations can be also considered as a community response to the fire-related decrease in water and nutrient content in the burned soils.     

Microbial communities in bulk fluids and biofilms of an oil facility have similar composition but different structure

The oil-water-gas environments of oil production facilities harbour abundant and diverse microbial communities that can participate in deleterious processes such as biocorrosion. Several molecular methods, including pyrosequencing of 16S rRNA libraries, were used to characterize the microbial communities from an oil production facility on the Alaskan North Slope. The communities in produced water and a sample from a 'pig envelope' were compared in order to identify specific populations or communities associated with biocorrosion. The 'pigs' are used for physical mitigation of pipeline corrosion and fouling and the samples are enriched in surface-associated solids (i.e. paraffins, minerals and biofilm) and coincidentally, microorganisms (over 10(5) -fold). Throughout the oil production facility, bacteria were more abundant (10- to 150-fold) than archaea, with thermophilic members of the phyla Firmicutes (Thermoanaerobacter and Thermacetogenium) and Synergistes (Thermovirga) dominating the community. However, the structure (relative abundances of taxa) of the microbial community in the pig envelope was distinct due to the increased relative abundances of the genera Thermacetogenium and Thermovirga. The data presented here suggest that bulk fluid is representative of the biofilm communities associated with biocorrosion but that certain populations are more abundant in biofilms, which should be the focus of monitoring and mitigation strategies.     

不同生长季节黑果枸杞的根际细菌群落结构

【目的】黑果枸杞是一种耐盐植物,是我国西北干旱区盐渍土改良的优良植物物种,其根际土壤细菌群落结构在不同生长时期的变化特征尚不清楚。【方法】本研究采用Illumina MiSeq高通量测序研究了黑果枸杞3个生长阶段的根际土壤细菌群落结构的动态变化。【结果】所有样品中共获得317467条序列,对应于7028个细菌/古细菌OTUs。根际土壤细菌群落的α多样性显著高于非根际土壤。衰老期根际细菌的多样性和丰富度明显低于营养生长期和花/果期。变形菌门和酸杆菌门的相对丰度随生长时期的演变而逐渐降低,而蓝细菌门则相反。厚壁菌门的丰度在衰老期明显高于营养生长期和花/果期。优势属的组成也随生长期的演变而改变,营养生长期、花/果期、衰老期的优势属数量分别为17、16、4,且组成也具有差异。相似性分析表明营养生长期和花/果期的根际细菌群落具有很高的相似性,衰老期根际细菌群落组成与生长期和花/果期具有很高差异,然而与非根际土壤的群落结构具有较高的相似性。【结论】根际土壤细菌群落多样性和组成随生长期的改变而表现出明显的动态变异性,表明黑果枸杞生长时期对根际土壤细菌群落结构具有重要的影响。     

Molecular approach to describing a seed‐based food web: the post‐dispersal granivore community of an invasive plant

Communities of post‐dispersal granivores can shape the density and dispersion of exotic plants and invasive weeds, yet plant ecologists have a limited perception of the relative trophic linkages between a seed species and members of its granivore community. Dandelion seeds marked with Rabbit IgG were disseminated into replicated plots in the recipient habitat (South Dakota) and the native range (Czech Republic). Arthropods were collected in pitfall traps, and their guts were searched for the protein marker using enzyme‐linked immunosorbent assay (ELISA). Seed dishes were placed in each plot, and dandelion seed removal rates were measured. The entire experiment was repeated five times over the dandelion flowering period. Gut analysis revealed that approximately 22% of specimens tested positive for the seed marker. A more diverse granivore community had trophic linkages to seeds than has been previously realized under field conditions. This community included taxa such as isopods, millipedes, weevils, rove beetles, and caterpillars, in addition to the traditionally recognized ants, crickets, and carabid beetles. Rarefaction and Chao analysis estimated approximately 16 and 27 species in the granivore communities of the Czech Republic and South Dakota, respectively. Synthesis: Generalist granivore communities are diverse and polyphagous, and are clearly important as a form of biotic resistance to invasive and weedy plants. These granivore communities can be managed to limit population growth of these pests.     

Comparative analysis of rotifer community structure in five subtropical shallow lakes in East China: role of physical and chemical conditions

Worldwide, there have been few comparative studies on rotifer communities in subtropical lakes. We studied changes in rotifer community structure over 1 year and its relationship to several physicochemical variables in five subtropical shallow lakes in East China, covering a nutrient gradient from mesotrophy to moderate eutrophy. In these lakes, the genera Brachionus, Lecane, and Trichocerca dominated the rotifer species composition, and Polyarthra dolichoptera, Keratella cochlearis, Filinia longiseta, T. pusilla, and Anuraeopsis fissa were the dominant species. With increased nutrient loading, total rotifer abundance and species dominance increased, indicating that rotifer abundance might be a more sensitive indicator of trophic state than species composition. Comparative analyses of the six rotifer community indices calculated in this study and redundancy analysis (RDA) revealed that the two slightly eutrophic lakes and the other two moderately eutrophic lakes exhibited a high degree similarity in community structure. This suggests that the trophic state of a lake determines the rotifer community structure. In contrast, in the two moderately eutrophic lakes, the mass ratios of TN:TP and the contents of TP suggested N-limitation and cyanobacteria dominance in phytoplankton communities might be possible. In these lakes TN played a more important role in shaping the rotifer community according to stepwise multiple regression and RDA. RDA analysis also suggested that rotifer species distribution was strongly associated with trophic state and water temperature, with water temperature being the most important factor in determining seasonality.     

A preliminary study of aquatic insect communities and leaf decomposition in acid streams near Dorset,Ontario

Some streams near Dorset in south-central Ontario suffer from acid precipitation via run-off and seepage from thin soils with little buffering capacity. A spring-summer survey of eight headwater streams revealed some characteristics of their insect communities which could be correlated with pH. The streams could be divided into three groups according to pH and community structure. In the most acid group (annual pH range 4.3–4.8), Ephemeroptera were absent from two streams although mature Leptophlebia were collected just after spring thaw from the most acid one (pH 4.3–4.5). One of these three streams also lacked Plecoptera but the others had two or three genera, all shredders. The second group of three streams (pH 5.0–6.3), with one exception, did support Ephemeroptera (3–4 genera) and Plecoptera (1–4 genera), most of the latter being shredders. In all six of these acid streams, Trichoptera were more diverse and more dense than Ephemeroptera and Plecoptera; again, shredders were clearly dominant, especially the limnephilid caddisfly, Frenesia difficilis (Walker). These six streams also had similar chironomid communities (densities were an order of magnitude higher than other insects). Dominance by Chironomini and abundant Tanypodinae typified the most acid streams. In contrast, the two streams in the third group (pH 5.3–6.7) had richer and more balanced communities in general with relatively fewer shredders (no Frenesia), more collectors, and fewer Chironomini and Tanypodinae. As a field experiment showed that autumn-shed leaves decomposed more slowly in acid than in non-acid streams, summer-growing shredders may benefit from the pulse of acidity at snowmelt.