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Dominant Species (dominant + species)
Selected AbstractsWater Sources of Dominant Species in Three Alpine Ecosystems on the Tibetan Plateau, ChinaJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 3 2008De-Yu Duan Abstract Plant water sources were estimated by two or three compartment linear mixing models using hydrogen and oxygen isotope (,D and ,18O) values of different components such as plant xylem water, precipitation and river water as well as soil water on the Tibetan Plateau in the summer of 2005. Four dominant species (Quercus aquifolioides, Pinus tabulaeformis, Salix rehderiana and Nitraria tangutorum) in three typical ecosystems (forest, shrub and desert) were investigated in this study. Stable isotope ratios of the summer precipitations and the soil water presented variations in spatial and temporal scales. ,18O values of N. tangutorum xylem water were constant in the whole growth season and very similar to those of deep soil water. Water sources for all of the plants came from both precipitations and soil water. Plants switched rapidly among different water sources when environmental water conditions changed. Rainwater had different contributions to the plants, which was influenced by amounts of precipitation. The percentage of plant xylem water derived from rainwater rose with an increase in precipitation. Water sources for broad-leaved and coniferous species were different although they grew in the same environmental conditions. For example, the broad-leaved species Q. aquifolioides used mainly the water from deep soil, while 92.5% of xylem water of the coniferous species P. tabulaeformis was derived from rainwater during the growth season. The study will be helpful for us to fully understand responses of species on the Tibetan Plateau to changes in precipitation patterns, and to assess accurately changes of vegetation distribution in the future. [source] Resource discovery in ant communities: do food type and quantity matter?ECOLOGICAL ENTOMOLOGY, Issue 5 2010JESSICA M. C. PEARCE-DUVET 1. Omnivorous woodland ant species trade off between the ability to find and behaviourally control food resources. Dominant species can limit the ability of subordinates to harvest certain food items. However, subordinate species, by being faster discoverers, could gain access to such food items by arriving at them first. 2. In this study, we tested the hypothesis that resource-directed discovery occurs in ant communities and that good discoverers preferentially discover high value resources. We did this by measuring time to discovery and the number of discoveries of high and low levels of two resource types, crickets and honey, for species occurring in Texas and Arizona woodland ant communities. 3. Ants discovered resources roughly 10 times faster in Texas than in Arizona. They discovered crickets more rapidly than honey in both communities, but there was no difference in the discovery of different resource levels. We also found that species were not biased in their discovery of different resource types or levels. 4. These results provide indirect evidence that discovery is directed by resource stimuli but that such directedness does not impact interspecific exploitative competition. [source] Negative per capita effects of purple loosestrife and reed canary grass on plant diversity of wetland communitiesDIVERSITY AND DISTRIBUTIONS, Issue 4 2006Shon S. Schooler ABSTRACT Invasive plants can simplify plant community structure, alter ecosystem processes and undermine the ecosystem services that we derive from biotic diversity. Two invasive plants, purple loosestrife (Lythrum salicaria) and reed canary grass (Phalaris arundinacea), are becoming the dominant species in many wetlands across temperate North America. We used a horizontal, observational study to estimate per capita effects (PCEs) of purple loosestrife and reed canary grass on plant diversity in 24 wetland communities in the Pacific Northwest, USA. Four measures of diversity were used: the number of species (S), evenness of relative abundance (J), the Shannon,Wiener index (H,) and Simpson's index (D). We show that (1) the PCEs on biotic diversity were similar for both invasive species among the four measures of diversity we examined; (2) the relationship between plant diversity and invasive plant abundance ranges from linear (constant slope) to negative exponential (variable slope), the latter signifying that the PCEs are density-dependent; (3) the PCEs were density-dependent for measures of diversity sensitive to the number of species (S, H,, D) but not for the measure that relied solely upon relative abundance (J); and (4) invader abundance was not correlated with other potential influences on biodiversity (hydrology, soils, topography). These results indicate that both species are capable of reducing plant community diversity, and management strategies need to consider the simultaneous control of multiple species if the goal is to maintain diverse plant communities. [source] The distribution and prevalence of sponges in relation to environmental gradients within a temperate sea lough: vertical cliff surfacesDIVERSITY AND DISTRIBUTIONS, Issue 6 2000James J. Bell Abstract. The prevalence and distribution of sponges was surveyed on vertical cliff surfaces at Lough Hyne Marine Nature Reserve, Co. Cork, Ireland. The number of sponge species was recorded at 6-metre depth intervals at four sites within Lough Hyne, and at one site on the adjacent Atlantic coastline to examine differences in abundance and zonation patterns. Sites ranged from an exposed turbulent regime to sheltered, sedimented environments. Individual species showed different distributions and prevalence between sites and with increasing depth. Greatest differences were observed between the most- and least-disturbed sites. Distinct sponge zonation patterns were evident at all sites sampled. Twenty-five species were considered dominant at all five sites with the remaining 48 species considered rare. Only four of the 25 most-dominant species occurred at the site experiencing the most turbulent flow conditions, whereas 12 species were found at the site of unidirectional fast flow. At sites of moderate to slight water movement and high sedimentation, between 18 and 24 of the most dominant species were present. Encrusting forms constituted high proportions of sponge communities at all five sites sampled (although consisting of different species). At sites of turbulent and unidirectional fast flow massive forms also dominated whereas at the least turbulent sites, where sedimentation was high, arborescent sponges were abundant. Few species showed exclusive distribution to a single depth and site, but there was some degree of correlation between species distributions and abiotic factors such as sedimentation rate and flow regimes. Sponge distributions and densities are discussed with respect to the suitability of species' morphologies to particular environments, intra-specific and inter-specific competition and physiological adaptations that enable them to survive in different habitats. [source] Parasitism and ant protection alter the survival of the lycaenid Hemiargus isolaECOLOGICAL ENTOMOLOGY, Issue 2 2003Jennifer A. Weeks Abstract. 1. Although the majority of lycaenid,ant associations is facultative, few studies have documented the protection benefits provided by ants to lycaenids that are tended facultatively (Pierce & Easteal, 1986; Peterson, 1993). 2. Larvae of Hemiargus isola (Lepidoptera: Lycaenidae) feeding on Dalea albiflora are tended facultatively by several species of ant. In 1999 and 2000, the levels of parasitism and the identities of attendant ants were determined for larvae of H. isola. In addition, the presence of ants was manipulated experimentally to determine the efficacy of protection provided by attendant ants to H. isola. 3. Lycaenids were parasitised by a braconid wasp, Cotesia cyaniridis (Riley), and a tachinid fly, Aplomya theclarum (Scudder). In 1999 and 2000, 62 and 65% of larvae were parasitised; the percentage of the population parasitised did not differ significantly between years. In both 1999 and 2000, parasitism by the braconid wasp C. cyaniridis accounted for >,99% of all parasitism events. 4. Four species of ant, Crematogaster sp., Dorymyrmex sp., Forelius sp., and Formica sp., were associated with 88,99% of the tended lycaenids collected in both 1999 and 2000. For both years, there was a single, numerically dominant species associated with >80% of the tended larvae collected, but the identity of this numerically dominant ant differed between years. 5. Experimental exclusion of ants from D. albiflora plants resulted in 78% larval mortality as a result of parasitism, nearly twice that of larvae that were tended by ants on unmanipulated plants. [source] Seasonal and spatial variation in a prairie stream-fish assemblageECOLOGY OF FRESHWATER FISH, Issue 3 2002K. G. Ostrand Abstract,,,Stream-fish assemblage and environmental data for 13 sites in the upper Brazos River, Texas, USA during 1997 and 1998 were used to assess the relationship between environmental conditions, and seasonal and spatial variation in fish species abundance and distribution patterns. There was considerable spatial variation in environmental conditions among sites. Spatial variation in species diversity and species composition was related to variation in conductance (salinity), depth and current velocity among sites and streams. Species diversity increased downstream and species composition shifted from primarily cyprinodontids upstream to cyprinids downstream. Among all dominant species, spatial components of variation in fish abundance were greater than seasonal components, suggesting that assemblage structure is determined more by average or persistent differences in environmental conditions among sites than by seasonal variation in environmental conditions. [source] Naturally occurring egg parasitoids of the genus Trichogramma (Hymenoptera: Trichogrammatidae) in a pomegranate orchard in TunisiaENTOMOLOGICAL SCIENCE, Issue 1 2010Ines KSENTINI Abstract Four Trichogramma species were found in a pomegranate orchard in Gabès, an arid region of Tunisia, from parasitized eggs of Ectomyelois ceratoniae Zeller (Lepidoptera: Pyralidae), an economically important insect pest. Identification based on assessment of male genitalia and internal transcribed spacer 2 (ITS2) sequences showed that they were T. bourarachae Pintureau and Babault, 1988, T. oleae Voegelé and Pointel, 1979, T. cacoeciae Marchal, 1927 and T. evanescens Westwood, 1833. Trichogramma evanescens is reported for the first time in Tunisia. Trichogramma cacoeciae was the largely dominant species in the analyzed samples, whereas T. bourarachae was present in a minor portion of 1.38%. The implications of these results for attempts at controlling E. ceratoniae are discussed. [source] Faunal makeup of wild bees and their flower utilization in a semi-urbanized area in central JapanENTOMOLOGICAL SCIENCE, Issue 2 2006Masaki HISAMATSU Abstract The species composition of wild bees and their flower utilization patterns were surveyed from April to November in 1996 in a semi-urbanized area adjacent to Sugao Marsh, Ibaraki, central Japan. A total of 750 individuals belonging to 43 species in six families were collected. The most dominant family was Halictidae, for which 13 species and 251 individuals were collected. The most dominant species was Colletes patellatus (120 individuals) of the Colletidae. The results at Sugao were compared with those obtained from three other areas of Ibaraki Prefecture, which have similar climatic conditions, yet have different environmental characteristics in terms of human impact. The four sites in Ibaraki can be classified into two groups: the first comprising Sugao and Mito in cultivated and/or human-dwelling areas, and the second comprising Yamizo and Gozen'yama, in forest areas with more natural elements. The number of species at Sugao was the smallest among the four study sites. On the other hand, the values for species evenness at Sugao were the second-highest of the four study sites. These findings show that the different characteristics of different bee communities reflect their local environmental conditions, including their floral compositions. The bees visited 36 flower species in 20 families, and 70.7% of all individuals studied visited Compositae flowers. The heavy utilization of composite flowers is possibly because of the existence of a simplified flora consisting of a few dominant composite plant species. Among these plants, Solidago altissima and Lactuca indica made large contributions to supporting autumn bees, especially Colletes patellatus and Colletes perforator, which are solitary and oligolectic on Compositae. [source] Effects of parasitoids on a mycophagous drosophilid community in northern Japan and an evaluation of the disproportionate parasitism hypothesisENTOMOLOGICAL SCIENCE, Issue 1 2006Hiroshi YOROZUYA Abstract In a host,parasitoid system comprising mycophagous drosophilids and their parasitoids, the drosophilid and parasitoid species assemblages, host use, and the prevalence of parasitism were assessed, and the "disproportionate parasitism hypothesis" was examined with consideration given to yearly variations. The mycophagous drosophilids, their fungal food resources and parasitoids were studied by carrying out an intensive census throughout the activity seasons of 4 years (2000,2003) in Hokkaido, northern Japan. Five hymenopterous parasitoid species, four braconids and one eucoilid, were found. Parasitoids of mycophagous drosophilids are reported for the first time from Asia. Most parasitism (99.2%) was by braconids, in contrast to the dominance of eucoilids in Europe. Parasitism was restricted to the summer, and the rate was high from early July to early August every year. There was considerable yearly variation in the composition of abundant fungus, drosophilid and parasitoid species, especially between 2000 and 2001. The alternation of dominant host species was coupled with the alternation of dominant parasitoid species that differed in host use. Despite the yearly variation in the system, the most dominant host species suffered disproportionately heavy parasitism by the correspondingly dominant parasitoid species every year. The parasitism rate was positively correlated with the relative host abundance. This thus indicates that the disproportionate parasitism mechanism may operate, via which species coexistence is promoted by a higher rate of parasitism of the dominant species. [source] Ascomycetes associated with ectomycorrhizas: molecular diversity and ecology with particular reference to the HelotialesENVIRONMENTAL MICROBIOLOGY, Issue 12 2009Leho Tedersoo Summary Mycorrhizosphere microbes enhance functioning of the plant,soil interface, but little is known of their ecology. This study aims to characterize the ascomycete communities associated with ectomycorrhizas in two Tasmanian wet sclerophyll forests. We hypothesize that both the phyto- and mycobiont, mantle type, soil microbiotope and geographical distance affect the diversity and occurrence of the associated ascomycetes. Using the culture-independent rDNA sequence analysis, we demonstrate a high diversity of these fungi on different hosts and habitats. Plant host has the strongest effect on the occurrence of the dominant species and community composition of ectomycorrhiza-associated fungi. Root endophytes, soil saprobes, myco-, phyto- and entomopathogens contribute to the ectomycorrhiza-associated ascomycete community. Taxonomically these Ascomycota mostly belong to the orders Helotiales, Hypocreales, Chaetothyriales and Sordariales. Members of Helotiales from both Tasmania and the Northern Hemisphere are phylogenetically closely related to root endophytes and ericoid mycorrhizal fungi, suggesting their strong ecological and evolutionary links. Ectomycorrhizal mycobionts from Australia and the Northern Hemisphere are taxonomically unrelated to each other and phylogenetically distant to other helotialean root-associated fungi, indicating independent evolution. The ubiquity and diversity of the secondary root-associated fungi should be considered in studies of mycorrhizal communities to avoid overestimating the richness of true symbionts. [source] New concepts in bilirubin encephalopathyEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 11 2003J. D. Ostrow Abstract Revised concepts of bilirubin encephalopathy have been revealed by studies of bilirubin toxicity in cultured CNS cells and in congenitally jaundiced Gunn rats. Bilirubin neurotoxicity is related to the unbound (free) fraction of unconjugated bilirubin (Bf), of which the dominant species at physiological pH is the protonated diacid, which can passively diffuse across cell membranes. As the binding affinity of plasma albumin for bilirubin decreases strikingly as albumin concentration increases, previously reported Bf values were underestimated. Newer diagnostic tests can detect reversible neurotoxicity before permanent damage occurs from precipitation of bilirubin (kernicterus). Early toxicity can occur at Bf only modestly above aqueous saturation and affects astrocytes and neurons, causing mitochondrial damage, resulting in impaired energy metabolism and apoptosis, plus cell-membrane perturbation, which causes enzyme leakage and hampers transport of neurotransmitters. The concentrations of unbound bilirubin in the cerebro-spinal fluid and CNS cells are probably limited mainly by active export of bilirubin back into plasma, mediated by ABC transporters present in the brain capillary endothelium and choroid plexus epithelium. Intracellular bilirubin levels may be diminished also by oxidation, conjugation and binding to cytosolic proteins. These new concepts may explain the varied susceptibility of neonates to develop encephalopathy at any given plasma bilirubin level and the selective distribution of CNS lesions in bilirubin encephalopathy. They also can suggest better strategies for predicting, preventing and treating this syndrome. [source] "Tail,Tail Dimerization" of Ferrocene Amino Acid DerivativesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 25 2010Daniel Siebler Abstract Acid anhydrides of N-protected 1,-aminoferrocene-1-carboxylic acid (Fca) have been prepared and spectroscopically characterized (protection group Boc, Fmoc, Ac; 4a,4c). The structure of the Boc-derivative 4a has been determined by single-crystal X-ray crystallography. An intramolecular N,H···O hydrogen bond involving the carbamate units results in a ring structure containing the two ferrocene units, the anhydride moiety, and the hydrogen bond. In the crystal, the individual molecules are connected by intermolecular N,H···O hydrogen bonds of the carbamate unit. Experimental and theoretical studies suggest that the ring motif is also a dominant species in solution. Electronic communication across the anhydride moiety is found to be very weak as judged from electrochemical, spectroscopic, and theoretical experiments. [source] Yeast species composition differs between artisan bakery and spontaneous laboratory sourdoughsFEMS YEAST RESEARCH, Issue 4 2010Gino Vrancken Abstract Sourdough fermentations are characterized by the combined activity of lactic acid bacteria and yeasts. An investigation of the microbial composition of 21 artisan sourdoughs from 11 different Belgian bakeries yielded 127 yeast isolates. Also, 12 spontaneous 10-day laboratory sourdough fermentations with daily backslopping were performed with rye, wheat, and spelt flour, resulting in the isolation of 217 yeast colonies. The isolates were grouped according to PCR-fingerprints obtained with the primer M13. Representative isolates of each M13 fingerprint group were identified using the D1/D2 region of the large subunit rRNA gene, internal transcribed spacer sequences, and partial actin gene sequences, leading to the detection of six species. The dominant species in the bakery sourdoughs were Saccharomyces cerevisiae and Wickerhamomyces anomalus (formerly Pichia anomala), while the dominant species in the laboratory sourdough fermentations were W. anomalus and Candida glabrata. The presence of S. cerevisiae in the bakery sourdoughs might be due to contamination of the bakery environment with commercial bakers yeast, while the yeasts in the laboratory sourdoughs, which were carried out under aseptic conditions with flour as the only nonsterile component, could only have come from the flour used. [source] Interannual and seasonal variability of the diversity and structure of ichthyoplankton assemblages in the central Mexican PacificFISHERIES OCEANOGRAPHY, Issue 3 2008C. FRANCO-GORDO Abstract We examined larval fish diversity and assemblage structure off the central coast of the Mexican Pacific from December 1995 through December 1998, including the 1997,98 El Niño event. A total of 132 taxa were recorded, the dominant species being Bregmaceros bathymaster, Dormitator latifrons, and Harengula thrissina (90, 1.9, and 0.8% of the total abundance, respectively). Only B. bathymaster, D. latifrons, and Gobionellus sp. occurred in all samples. The effects of the 1997,98 El Niño on ichthyoplankton diversity were significant, but typical seasonal patterns were also detected. Diversity null models were used to determine the structural changes in the assemblage related to El Niño; both richness and evenness of the species were highest during this event. The most parsimonious models of assemblage organization include El Niño and seasonality as the most significant environmental variability sources. The small-scale spatial variability expressed as the cross-shore gradient was not significant. The dominant species group formed by B. bathymaster, D. latifrons, and Vinciguerria lucetia typifies, in terms of similarity, both the pre-El Niño and El Niño periods; abundance differed between periods. The El Niño period was characterized locally by the dominant Bentosema panamense and H. thrissina, by the rare Euthynnus lineatus, and species of Lutjanus. Seasonality produced changes also in the relative frequencies of the dominant species plus the occurrence of rare forms. The average taxonomical distinctness, considered herein as an indicator of functional diversity, reflected the seasonal variability of the assemblages, aside from El Niño; this index showed lowest values during tropical and transitional periods, both characterized by warm, oligotrophic waters. The high dominance of B. bathymaster in the area and its effect on diversity stabilized the local ichthyoplankton assemblage. An upgraded analysis of diversity allowed a more detailed description of the variability in this assemblage, thus stressing the differential effects of El Niño at distinct latitudes. [source] Associations between Pityogenes bidentatus and fungi in young managed Scots pine stands in PolandFOREST PATHOLOGY, Issue 3 2008R. Jankowiak Summary The association between Pityogenes bidentatus and fungi was studied in young, managed Pinus sylvestris stands in Poland. Fungi were isolated from emerged adults and their galleries collected from four populations. In total, 2089 fungal isolates including 42 species, were obtained. Penicillium sp. 1 and Geosmithia sp. 1 were the most commonly isolated fungi from beetles (49% and 41% of beetles respectively). Geosmithia sp. 1 species was the dominant species in P. bidentatus galleries with a frequency of occurrence of 57.9%. Hormonema dematioides was the second most abundant fungus in gallery systems (17.1% of wood samples). Two of the isolated Geosmithia species were previously undescribed. Pityogenes bidentatus also vectored three ophiostomatoid species: Ophiostoma minus, O. piceae and Graphium sp. ,W'. These species were occasionally isolated from beetles and their galleries, suggesting a non-specific relationship. [source] Hosts and distribution of Collybia fusipes in France and factors related to the disease's severityFOREST PATHOLOGY, Issue 1 2002D. PIOU Using data collected by two different observation networks, it was possible to clarify the distribution of Collybia fusipes in France. It is frequently found in the western and northern parts of France, mainly on Quercus rubra and Quercus robur, and to a somewhat lesser extent on Quercus petraea. When the relative areas covered by these species are compared, it is evident that Q. rubra is much the most susceptible of the three species. The fungus has been less frequently reported in the south-eastern quarter of France, where Quercus ilex and Quercus pubescens are the dominant species. Complementary observations carried out at the National Arboretum of Les Barres indicate that a large number of oak species are susceptible to infection by this fungus, particularly those in the subgenus Erythrobalanus. These observations are discussed with reference to reports of this fungus throughout Europe. In a Q. rubra stand, fruit-body clumps were monitored and root damage was assessed on 73 final-crop trees and 40 codominant trees. The results suggest that C. fusipes does not preferentially infect weakened trees. Both the severity of root damage and the number of fruit-body clumps increased with increasing depth to signs of waterlogging. Répartition et hôtes de Collybia fusipes en France et facteurs de gravité de la maladie D'après les données collectées par deux réseaux de surveillance distincts, la répartition de Collybia fusipes en France a été précisée. Le champignon est fréquent dans les moitiés ouest et nord du pays, principalement sur Quercus rubra et Q. robur, et dans une moindre mesure sur Q. petraea. Quand on considère la surface relative occupée par ces espèces, il apparaît évident que Q. rubra est le plus sensible. Il a été moins souvent signalé dans le quart sud-est oùQ. ilex et Q. pubescens sont dominants. Des observations complémentaires réalisées à l'Arboretum National des Barres indiquent qu'un grand nombre d'espèces de chênes sont susceptibles d'être attaquées par ce champignon, particulièrement celles du sous-genre Erythrobalanus. Ces observations sont discutées et comparées avec les données disponibles en Europe. L'apparition des carpophores a été suivie dans un peuplement de Q. rubra, et les dégâts aux racines ont étéévalués sur 73 arbres de place et 40 arbres codominants. Les résultats indiquent que C. fusipes n'infecte pas plus gravement les arbres affaiblis. Le degré d'hydromorphie influence significativement l'importance des dégâts racinaires ainsi que le nombre de carpophores produits. Cette étude confirme que C. fusipes se développe préférentiellement dans les sites où l'hydromorphie n'est pas trop sévère. Wirtspflanzen und Verbreitung von Collybia fusipes in Frankreich sowie mit der Krankheitsintensität assoziierte Umweltfaktoren Mit Hilfe der Daten von zwei unterschiedlichen Beobachtungsnetzwerken konnte die Verbreitung von Collybia fusipes in Frankreich präzisiert werden. Der Pilz ist im Westen und Norden des Landes häufig auf Quercus rubra und Quercus robur zu finden, etwas weniger häufig auf Quercus petraea. Beim Vergleich der von diesen Arten bestockten Flächen wird deutlich, dass Q. rubra die anfälligste der drei Eichenarten ist. Im südöstlichen Teil Frankreichs, wo Quercus ilex und Quercus pubescens dominieren, wurde der Pilz weniger häufig nachgewiesen. Ergänzende Beobachtungen im Arboretum National des Barres ergaben, dass zahlreiche Eichenarten gegen C. fusipes anfällig sind, insbesondere die des Subgenus Erythrobalanus. Diese Ergebnisse werden im Vergleich mit der aus Europa über diesen Pilz verfügbaren Literatur diskutiert. In einem Q. rubra, Bestand wurde das Auftreten von Fruchtkörpern und von Wurzelschäden an 73 herrschenden und 40 mitherrschenden Bäumen registriert. Die Ergebnisse zeigen, dass C. fusipes geschwächte Bäume nicht bevorzugt befällt. Sowohl die Intensität der Wurzelschäden als auch die Anzahl der Fruchtkörper erhöhte sich mit zunehmender Tiefe der Anzeichen für Staunässe im Bodenprofil. [source] Among- and within-species variation in plant litter decomposition in contrasting long-term chronosequencesFUNCTIONAL ECOLOGY, Issue 2 2009David A. Wardle Summary 1Following major disturbances ecosystem development occurs but in the prolonged absence of disturbance a decline (retrogressive) phase follows in which productivity and nutrient availability diminishes. Although it is recognized that litter quality and decomposition rates decrease as retrogression proceeds, little is known about the extent to which this is driven among- vs. within-species variation across these sequences. 2We selected six long-term chronosequences that each included retrogressive stages, in New Zealand, Hawaii, Sweden, Alaska and Australia. Two involve significant species turnover across the sequence so that different species dominate at different stages, two involve low species turnover so that the same dominant species occur at all stages, and two involve some turnover of species but with certain species persisting throughout most of the sequence. 3For each chronosequence, we collected litter from each dominant plant species at each stage of that sequence. For each litter collection we measured concentrations of N and P, and performed laboratory decomposition bioassays to measure mass loss, N and P loss, and the response of mass loss to mixture with litters of coexisting species. 4We found that litter N and P concentrations often declined with increasing ecosystem age, both among- and within-species. However, the relative importance of among- and within-species effects varied across the six chronosequences. Rates of litter mass, N, and P loss during decomposition sometimes decreased with increasing ecosystem age, but most often at the among-species rather than the within-species level. 5Litter mixing effects often varied across chronosequence stages, but the magnitude and direction of these effects was inconsistent among sequences. Variation in litter mixing effects across chronosequence stages was driven mainly by among- rather than within-species variation. 6Although several recent studies have emphasized the role of within-species variation on ecosystem properties, our results point to among-species variation as a consistently important ecological driver, with within-species variation being important only for some variables and in some instances. As such they highlight that decomposition processes are most likely to be highly responsive to gradients of soil fertility (such as across chronosequences) when significant species turnover occurs across the gradient. [source] Competitive relationships of Andropogon gerardii (Big Bluestem) from remnant and restored native populations and select cultivated varietiesFUNCTIONAL ECOLOGY, Issue 3 2004D. J. GUSTAFSON Summary 1Although genetic differentiation among plant populations is well known, its relevance for preserving the integrity of native ecosystems has received little attention. In a series of competition experiments with Andropogon gerardii Vitman, a dominant species of the North American Tallgrass Prairie, plant performance was related to seed provenance and restoration activities. 2Glasshouse experiments showed plant performance to be a function of seed source. Differential target plant performance relative to competitor identity was observed when plant performance was assessed across a range of competitor densities. Local and non-local plants were larger when competing against non-local plants relative to the local and cultivar plants, while cultivar plants were consistently larger than local and non-local plants regardless of competitor identity or density. The consistency of cultivar performance could reflect directional selection during cultivar development for consistently high fecundity, vigorous vegetative growth and resistance to pathogens. 3In a field experiment, non-local plants were half the size of local and cultivar plants, supporting recognition of seed provenances of A. gerardii based on differences in plant performance among source populations observed in the glasshouse study, and previous genetic analyses of the same populations. 4This study establishes that seed provenance and restoration activities influence the competitive ability of a dominant species which, in turn, may affect plant community structure and potential ecosystem function. [source] Ostracode faunas of bottom sediments from the continental shelf, south Marmara Sea, NW Turkey, and their comparison with other shelf environments in the Mediterranean and Aegean regionsGEOLOGICAL JOURNAL, Issue 2 2001Atike Nazik Abstract This study describes the ostracode faunal composition and distribution on the continental shelf of the southern Marmara Sea in Turkey. Twenty-three bottom samples were collected from the shelf. These samples are characterized by silt-clay (mud), sand and gravel in the studied area. A total of 46 species belonging to 32 genera were determined from these samples. Seven species were dominant from 46 ostracode species. Three assemblages were identified by their dominant species. These are characterized by: Costa edwardsii (Roemer); a mixed assemblage which consists of Cytheridea neapolitana Kollmann, Pterygocythereis ceratoptera (Bosquet), Tegmenia rugosa (Costa), Acanthocythereis hystrix (Reuss) and Xestoleberis communis (G.W. Müller); and Aurila convexa (Baird). The relations between the dominant species, lithology and CaCO3 concentration have been investigated, and the results are compared with other shelf environments within the Mediterranean and Aegean regions. Pterygocythereis, Costa, Tegmenia and Cytheridea are abundant in muddy substrates; Aurila and Acanthocythereis are abundant in sandy substrates. Acanthocythereis hystrix (Reuss), Aurila convexa (Baird), Buntonia subulata Ruggieri, Carinocythereis antiquata (Baird), Carinocythereis carinata (Roemer), Costa batei (Brady), Costa edwardsii (Roemer), Cytheridea neapolitana Kollmann, Celtia quadridentata (Baird), Loxoconcha rhomboidea (Fischer), Pterygocythereis jonesii (Baird) and Semicytherura acuticostata (Sars) are common, and similar species are recorded from other continental shelves of the Mediterranean. Copyright © 2001 John Wiley & Sons, Ltd. [source] Decline in a dominant invertebrate species contributes to altered carbon cycling in a low-diversity soil ecosystemGLOBAL CHANGE BIOLOGY, Issue 8 2008J. E. BARRETT Abstract Low-diversity ecosystems cover large portions of the Earth's land surface, yet studies of climate change on ecosystem functioning typically focus on temperate ecosystems, where diversity is high and the effects of individual species on ecosystem functioning are difficult to determine. We show that a climate-induced decline of an invertebrate species in a low-diversity ecosystem could contribute to significant changes in carbon (C) cycling. Recent climate variability in the McMurdo Dry Valleys of Antarctica is associated with changes in hydrology, biological productivity, and community composition of terrestrial and aquatic ecosystems. One of the greatest changes documented in the dry valleys is a 65% decrease in the abundance of the dominant soil invertebrate (Scottnema lindsayae, Nematoda) between 1993 and 2005, illustrating sensitivity of biota in this ecosystem to small changes in temperature. Globally, such declines are expected to have significant influences over ecosystem processes such as C cycling. To determine the implications of this climate-induced decline in nematode abundance on soil C cycling we followed the fate of a 13C tracer added to soils in Taylor Valley, Antarctica. Carbon assimilation by the dry valley nematode community contributed significantly to soil C cycling (2,7% of the heterotrophic C flux). Thus, the influence of a climate-induced decline in abundance of a dominant species may have a significant effect on ecosystem functioning in a low-diversity ecosystem. [source] Monoterpene emissions from rubber trees (Hevea brasiliensis) in a changing landscape and climate: chemical speciation and environmental controlGLOBAL CHANGE BIOLOGY, Issue 11 2007YONG-FENG WANG Abstract Emissions of biogenic volatile organic compounds (VOCs) have important roles in ecophysiology and atmospheric chemistry at a wide range of spatial and temporal scales. Tropical regions are a major global source of VOC emissions and magnitude and chemical speciation of VOC emissions are highly plant-species specific. Therefore it is important to study emissions from dominant species in tropical regions undergoing large-scale land-use change, for example, rubber plantations in South East Asia. Rubber trees (Hevea brasiliensis) are strong emitters of light-dependent monoterpenes. Measurements of emissions from leaves were made in the dry season in February 2003 and at the beginning of the wet season in May 2005. Major emitted compounds were sabinene, , -pinene and , -pinene, but , -ocimene and linalool also contributed significantly at low temperature and light. Cis -ocimene was emitted with a circadian course independent of photosynthetic active radiation (PAR) and temperature changes with a maximum in the middle of the day. Total isoprenoid VOC emission potential at the beginning of the wet season (94 ,g gdw,1 h,1) was almost two orders of magnitude higher than measured in the dry season (2 ,g g dw,1 h,1). Composition of total emissions changed with increasing temperature or PAR ramps imposed throughout a day. As well as light and temperature, there was evidence that assimilation rate was also a factor contributing to seasonal regulating emission potential of monoterpenes from rubber trees. Results presented here contribute to a better understanding of an important source of biogenic VOC associated with land-use change in tropical South East Asia. [source] Variable sensitivity of plant communities in Iceland to experimental warmingGLOBAL CHANGE BIOLOGY, Issue 4 2005Ingibjörg S. Jónsdóttir Abstract Facing an increased threat of rapid climate change in cold-climate regions, it is important to understand the sensitivity of plant communities both in terms of degree and direction of community change. We studied responses to 3,5 years of moderate experimental warming by open-top chambers in two widespread but contrasting tundra communities in Iceland. In a species-poor and nutrient-deficient moss heath, dominated by Racomitrium lanuginosum, mean daily air temperatures at surface were 1,2°C higher in the warmed plots than the controls whereas soil temperatures tended to be lower in the warmed plots throughout the season. In a species-rich dwarf shrub heath on relatively rich soils at a cooler site, dominated by Betula nana and R. lanuginosum, temperature changes were in the same direction although more moderate. In the moss heath, there were no detectable community changes while significant changes were detected in the dwarf shrub heath: the abundance of deciduous and evergreen dwarf shrubs significantly increased (>50%), bryophytes decreased (18%) and canopy height increased (100%). Contrary to some other studies of tundra communities, we detected no changes in species richness or other diversity measures in either community and the abundance of lichens did not change. It is concluded that the sensitivity of Icelandic tundra communities to climate warming varies greatly depending on initial conditions in terms of species diversity, dominant species, soil and climatic conditions as well as land-use history. [source] Root production and demography in a california annual grassland under elevated atmospheric carbon dioxideGLOBAL CHANGE BIOLOGY, Issue 9 2002Paul A. T. Higgins Abstract This study examined root production and turnover in a California grassland during the third year of a long-term experiment with ambient (LO) and twice-ambient atmospheric CO2 (HI), using harvests, ingrowth cores, and minirhizotrons. Based on one-time harvest data, root biomass was 32% greater in the HI treatment, comparable to the stimulation of aboveground production during the study year. However, the 30,70% increase in photosynthesis under elevated CO2 for the dominant species in our system is considerably larger than the combined increase in above and belowground biomass. One possible explanation is, increased root turnover, which could be a sink for the additional fixed carbon. Cumulative root production in ingrowth cores from both treatments harvested at four dates was 2,3 times that in the single harvested cores, suggesting substantial root turnover within the growing season. Minirhizotron data confirmed this result, demonstrating that production and mortality occurred simultaneously through much of the season. As a result, cumulative root production was 54%, 47% and 44% greater than peak standing root length for the no chamber (X), LO, and HI plots, respectively. Elevated CO2, however, had little effect on rates of turnover (i.e. rates of turnover were equal in the LO and HI plots throughout most of the year) and cumulative root production was unaffected by treatment. Elevated CO2 increased monthly production of new root length (59%) only at the end of the season (April,June) when root growth had largely ceased in the LO plots but continued in the HI plots. This end-of-season increase in production coincided with an 18% greater soil moisture content in the HI plots previously described. Total standing root length was not affected by CO2 treatment. Root mortality was unaffected by elevated CO2 in all months except April, in which plants grown in the HI plots had higher mortality rates. Together, these results demonstrate that root turnover is considerable in the grassland community and easily missed by destructive soil coring. However, increased fine root turnover under elevated CO2 is apparently not a major sink for extra photosynthate in this system. [source] The effect of additives in silages of pure timothy and timothy mixed with red clover on chemical composition and in vitro rumen fermentation characteristicsGRASS & FORAGE SCIENCE, Issue 3 2003M. Hetta Abstract The aim was to compare the effects of additives on direct cut silages of pure timothy and timothy mixed with tetraploid red clover. First and second growth cuts were ensiled during three consecutive years, 1994, 1995 and 1996, either without any additive or with the addition of formic acid, or lactic acid bacteria in combination with molasses. Effects of the additives on the degradation characteristics of the herbage and the silages were analysed using an automatic in vitro gas production (GP) technique. At the end of the in vitro procedures, organic matter and neutral-detergent fibre (NDF) degradabilities were determined. The tetraploid red clover persisted in the leys during the 3 years and was the dominant species at the second growth in the mixed leys. The herbage from the mixed crops had lower dry-matter contents, higher crude protein concentrations and higher buffering capacity compared with the pure timothy at both cuts. In general, the additives reduced pH, and the concentrations of ammonium-N and acetic acid in the silages. The treated silages had a more rapid faster GP in both crops. The silages from the mixed crop benefited more from the additives compared with the grass silages. The additives affected the soluble fractions as well as the NDF degradability of the silages of the mixed crop more than those fractions of the grass silages. The addition of molasses in combination with a commercial inocula resulted in increased production of lactic acid and ethanol in silages from both crops. The silages without additives could not meet the requirements for good silages according to the standards of the Swedish dairy industry. [source] Photophysical and Photochemical Studies of PyridoxamineHELVETICA CHIMICA ACTA, Issue 10 2003Claudio Bueno The absorption and fluorescence emission of pyridoxamine were studied as function of pH and solvent properties. In the ground state, pyridoxamine exhibits different protonated forms in the range of pH,1.5,12. Fluorescence studies showed that the same species exist at the lowest singlet excited state but at different pH ranges. The phenol group is by ca. 8,units more acidic in the excited state than in the ground state. On the other hand, the pyridine N-atom is slightly more basic in the lowest excited state than in the ground state. Excitation spectra and emission decays in the pH range of 8,10 indicate the protonation of the pyridine N-atom by proton transfer from the amine group, in the ground and singlet excited states. Spectroscopic studies in different solvents showed that pyridoxamine in the ground or excited states exhibits intramolecular proton transfer from the pyridine N-atom to the phenol group, which is more favorable in solvents of low hydrogen-bonding capacity. The cationic form with the protonated phenolic group, which emits at shorter wavelength, is the dominant species in nonprotic solvents, but, in strong proton-donor solvents, both forms exist. The fluorescence spectra of these species exhibit blue shift in protic solvents. These shifts are well-correlated with the polarity and the H-donor ability of the solvent. [source] Seeing without being seen: a removal experiment with mixed flocks of Willow and Crested Tits Parus montanus and cristatusIBIS, Issue 4 2001INDRIK IS KRAMS This paper tests the hypothesis that foraging site selection reflects a trade-off between the various needs for concealment from predators, to find food, and for the individual to maintain some view of its surroundings. After removal of Crested Tits Parus cristatus (the dominant species in mixed flocks), Willow Tits P. montanus did not decrease their foraging heights as expected but remained in the most exposed parts of young pines. In contrast, after removal of Willow Tits, Crested Tits increased their foraging height from the sheltered lower canopy to sites previously occupied by Willow Tits. When flock size was reduced, the birds maintained the same high levels of vigilance without concealing themselves in dense vegetation. I suggest that flock members may benefit from foraging in sites that afford good anti-predator vigilance. [source] A randomisation program to compare species-richness valuesINSECT CONSERVATION AND DIVERSITY, Issue 3 2008JEAN M. L. RICHARDSON Abstract., 1Comparisons of biodiversity estimates among sites or through time are hampered by a focus on using mean and variance estimates for diversity measures. These estimators depend on both sampling effort and on the abundances of organisms in communities, which makes comparison of communities possible only through the use of rarefaction curves that reduce all samples to the lowest sample size. However, comparing species richness among communities does not demand absolute estimates of species richness and statistical tests of similarity among communities are potentially more straightforward. 2This paper presents a program that uses randomisation methods to robustly test for differences in species richness among samples. Simulated data are used to show that the analysis has acceptable type I error rates and sufficient power to detect violations of the null hypothesis. An analysis of published bee data collected in 4 years shows how both sample size and hierarchical structure in sample type are incorporated into the analysis. 3The randomisation program is shown to be very robust to the presence of a dominant species, many rare species, and decreased sample size, giving quantitatively similar conclusions under all conditions. This method of testing for differences in biodiversity provides an important tool for researchers working on questions in community ecology and conservation biology. [source] Surveys of rodent-borne disease in Thailand with a focus on scrub typhus assessmentINTEGRATIVE ZOOLOGY (ELECTRONIC), Issue 4 2008Kriangkrai Lerdthusnee Abstract The epidemiology of many rodent-borne diseases in South-East Asia remains ill-defined. Scrub typhus and lep-tospirosis are common and medically significant, while other zoonotic diseases, such as spotted fever group Rickettsiae have been identified, but their overall medical significance is unknown. Rodent surveillance was conducted from June 2002 to July 2004 in 18 provinces from Thailand. Traps were set up for one to three nights. Blood and serum samples and animal tissue samples (liver, spleen, kidney and urinary bladder) were collected. Chiggermites, ticks and fleas were removed from captured rodents. A total of 4536 wild-caught rodents from 27 species were captured over two years of animal trapping. Rattus rattus was the dominant species, followed by Rattus exulans and Bandicota indica. Almost 43 000 ectoparasites were removed from the captured animals. Approximately 98% of the ectoparasites were chigger-mites, of which 46% belonged to the genus Leptotrombidium (scrub typhus vector). Other genera included Schoengastia and Blankaartia. Tick and flea specimens together comprised less than 1% of the sample. Among the five species of ticks collected, Haemaphysalis bandicota was the predominant species caught, followed by Ixodes granulatus other Haemaphysalis spp., Rhipicephalus spp. and Dermacentor spp. Only two species of fleas were collected and Xenopsylla cheopis (rat flea) was the predominant species. Using both commercial diagnostic kits and in-house molecular assays, animal tissue samples were examined and screened for zoonotic diseases. Seven zoonotic diseases were detected: scrub typhus, leptospirosis, murine typhus, tick typhus, bartonella, babesiosis and trypanosomiasis. Most samples were positive for scrub typhus. Other zoonotic diseases still under investigation include borrelosis, ehrlichiosis, the plague, and other rickettsial diseases. Using geographic information systems, global positioning systems and remote sensing technology, epidemiological and environmental data were combined to assess the relative risk in different biotopes within highly endemic areas of scrub typhus in Thailand. [source] Importance of O(3P) atoms and OH radicals in hydrocarbon oxidation during the nonthermal plasma treatment of diesel exhaust inferred using relative-rate methods,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2003John Hoard The consumption of acetylene and propene during passage of simulated diesel exhaust through a nonthermal plasma at 453 K and atmospheric pressure was studied using experimental and computational techniques. Experimental observations of the relative decay rates of acetylene and propene and computer modeling of the chemical and physical processes in the plasma suggest that O(3P) atoms and, to a lesser extent, OH radicals are the dominant species responsible for initiating hydrocarbon oxidation in this system. Results are discussed in terms of the gas-phase chemistry occurring during the nonthermal plasma treatment of diesel exhaust. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 231,238, 2003 [source] Temporal and Spatial Distributions of Rotifers in Xiangxi Bay of the Three Gorges Reservoir, ChinaINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 5 2009Shuchan Zhou Abstract From July 2003 to June 2005, investigations of rotifer temporal and spatial distributions were car-ried out in a bay of the Three Gorges Reservoir, Xiangxi Bay, which is the downstream segment of the Xiangxi River and the nearest bay to the Three Gorges Reservoir dam in Hubei Province, China. Thirteen sampling sites were selected. The results revealed a high species diversity, with 76 species, and 14 dominant species; i.e., Polyarthra vulgaris, Keratella cochlearis, Keratella valga, Synchaeta tremula, Synchaeta stylata, Trichocerca lophoessa, Trichocerca pusilla, Brachionus angularis, Brachionus calyciflorus, Brachionus forficula forficula, Ascomorpha ovalis, Conochilus unicornis, Ploesoma truncatum and Anuraeopsis fissa. After the first year of the reservoir impoundment, the rotifer community was dominated by ten species; one year later it was dominated by eight species. The community in 2003/2004 was dissimilar to that in 2004/2005, which resulted from the succes-sion of the dominant species. The rotifer community exhibited a patchy distribution, with significant heterogeneity observed along the longitudinal axis. All rotifer communities could be divided into three groups, corresponding to the riverine, the transition and the lacustrine zone, respectively. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||||||||||||||||||||