Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Plants

  • Arabidopsi plant
  • Arabidopsi thaliana plant
  • adult plant
  • alfalfa plant
  • alien plant
  • alpine plant
  • annual plant
  • arctic plant
  • aromatic plant
  • artificial plant
  • asymptomatic plant
  • attractive plant
  • barley plant
  • bean plant
  • benthamiana plant
  • bird-dispersed plant
  • branch plant
  • brassica plant
  • c3 plant
  • c4 plant
  • cam plant
  • carnivorous plant
  • cassava plant
  • chemical plant
  • citrus plant
  • clonal plant
  • coal-fired power plant
  • control plant
  • corn plant
  • cotton plant
  • crop plant
  • cucumber plant
  • cultivated plant
  • cushion plant
  • damaged plant
  • deciduous plant
  • dicotyledonous plant
  • different host plant
  • different plant
  • dioecious plant
  • disease-resistant plant
  • diseased plant
  • domesticated plant
  • dominant plant
  • doubled haploid plant
  • edible plant
  • endemic plant
  • entire plant
  • established plant
  • exotic plant
  • experimental plant
  • f1 plant
  • f2 plant
  • female plant
  • field-grown plant
  • flowering plant
  • food plant
  • forest plant
  • fossil plant
  • genetically modified plant
  • gm plant
  • grafted plant
  • grassland plant
  • green plant
  • growing plant
  • haploid plant
  • healthy plant
  • hemiparasitic plant
  • herbaceous plant
  • heterozygous plant
  • higher plant
  • host plant
  • host-infested plant
  • hybrid plant
  • hydropower plant
  • hyperaccumulator plant
  • indian medicinal plant
  • indigenous plant
  • individual plant
  • industrial plant
  • infected plant
  • inoculated plant
  • intact plant
  • introduced plant
  • invasive alien plant
  • invasive plant
  • invasive woody plant
  • juvenile plant
  • land plant
  • large plant
  • larger plant
  • larval host plant
  • leaf plant
  • leguminous plant
  • lettuce plant
  • local plant
  • maize plant
  • male plant
  • manufacturing plant
  • many plant
  • marsh plant
  • maternal plant
  • mature plant
  • medicinal plant
  • melon plant
  • milkweed plant
  • model plant
  • modified plant
  • monocotyledonous plant
  • mother plant
  • municipal wastewater treatment plant
  • mutant plant
  • mycorrhizal plant
  • native plant
  • natural host plant
  • natural plant
  • neighbouring plant
  • new plant
  • nicotiana benthamiana plant
  • non-host plant
  • non-native plant
  • nonlinear plant
  • novel host plant
  • nuclear plant
  • nuclear power plant
  • nurse plant
  • of plant
  • old plant
  • ornamental plant
  • other plant
  • overexpressing plant
  • parasitic plant
  • parent plant
  • pea plant
  • pepper plant
  • perennial plant
  • petrochemical plant
  • pilot plant
  • pioneer plant
  • pitcher plant
  • potato plant
  • potted plant
  • power plant
  • process plant
  • processing plant
  • production plant
  • progeny plant
  • rare plant
  • relate plant
  • resistant plant
  • resurrection plant
  • rice plant
  • riparian plant
  • same host plant
  • same plant
  • seed plant
  • selected plant
  • several plant
  • sewage treatment plant
  • single plant
  • small plant
  • smaller plant
  • solanaceous plant
  • source plant
  • soybean plant
  • submerged plant
  • sunflower plant
  • susceptible plant
  • symptomatic plant
  • tall fescue plant
  • tall plant
  • target plant
  • terrestrial plant
  • test plant
  • thaliana plant
  • thermal power plant
  • tobacco plant
  • tolerant plant
  • tomato plant
  • transgenic Arabidopsi plant
  • transgenic cotton plant
  • transgenic plant
  • transgenic rice plant
  • transgenic tobacco plant
  • transgenic tomato plant
  • trap plant
  • treated plant
  • treatment plant
  • tundra plant
  • type plant
  • uncertain plant
  • undamaged plant
  • understorey plant
  • understory plant
  • uninfected plant
  • unknown plant
  • unstable plant
  • untreated plant
  • variety of plant
  • various plant
  • vascular plant
  • virus-free plant
  • wastewater treatment plant
  • water treatment plant
  • well-watered plant
  • wetland plant
  • wheat plant
  • whole plant
  • wild plant
  • wild type plant
  • wild-type plant
  • woody plant
  • wt plant
  • young maize plant
  • young plant

  • Terms modified by Plants

  • plant Arabidopsi
  • plant Arabidopsi thaliana
  • plant ability
  • plant abundance
  • plant adaptation
  • plant age
  • plant architecture
  • plant assemblage
  • plant association
  • plant attribute
  • plant availability
  • plant b
  • plant biodiversity
  • plant biology
  • plant biomass
  • plant biomass production
  • plant body
  • plant breeder
  • plant breeding
  • plant bug
  • plant c
  • plant canopy
  • plant cell
  • plant cell culture
  • plant cell wall
  • plant characteristic
  • plant colonization
  • plant community
  • plant community composition
  • plant community diversity
  • plant community response
  • plant community structure
  • plant compartment
  • plant competition
  • plant component
  • plant composition
  • plant compound
  • plant conservation
  • plant constitutively
  • plant cover
  • plant cytoplasm
  • plant damage
  • plant data
  • plant death
  • plant debris
  • plant decreased
  • plant defence
  • plant defence mechanism
  • plant defence reaction
  • plant defence response
  • plant defense
  • plant deficient
  • plant density
  • plant design
  • plant development
  • plant diet
  • plant disease
  • plant disease resistance
  • plant dispersal
  • plant distributed
  • plant distribution
  • plant diversity
  • plant dna
  • plant dry mass
  • plant dynamics
  • plant ecologist
  • plant ecology
  • plant endemic
  • plant enzyme
  • plant essential oil
  • plant establishment
  • plant evolution
  • plant experiment
  • plant extract
  • plant factor
  • plant family
  • plant fitness
  • plant food
  • plant form
  • plant function
  • plant functional groups
  • plant functional trait
  • plant functional type
  • plant gene
  • plant genetic engineering
  • plant genetic resource
  • plant genome
  • plant genotype
  • plant genus
  • plant group
  • plant groups
  • plant growth
  • plant growth and development
  • plant growth form
  • plant growth promotion
  • plant growth rate
  • plant growth regulator
  • plant growth stage
  • plant health
  • plant height
  • plant hormone
  • plant hormones
  • plant host
  • plant hosts
  • plant immunity
  • plant individual
  • plant ingredient
  • plant innate immunity
  • plant input
  • plant interaction
  • plant invader
  • plant invasion
  • plant invasion ecology
  • plant invasiveness
  • plant kingdom
  • plant leaf
  • plant lectin
  • plant level
  • plant life cycle
  • plant line
  • plant litter
  • plant m
  • plant macrofossil analysis
  • plant management
  • plant managers
  • plant market
  • plant mass
  • plant material
  • plant matter
  • plant maturity
  • plant metabolism
  • plant metabolite
  • plant mitochondria
  • plant mixture
  • plant model
  • plant morphology
  • plant nitrogen
  • plant nitrogen concentration
  • plant nucleus
  • plant nutrient
  • plant nutrition
  • plant oil
  • plant only
  • plant operation
  • plant organ
  • plant origin
  • plant output
  • plant parameter
  • plant parasitic nematodes
  • plant part
  • plant patch
  • plant pathogen
  • plant pathogenic bacteria
  • plant pathogenic bacterium
  • plant pathogenic fungus
  • plant pathology
  • plant performance
  • plant pest
  • plant phenolic
  • plant phenology
  • plant phenotype
  • plant photosynthesi
  • plant phylogeny
  • plant physiology
  • plant pigment
  • plant plasma membrane
  • plant polyphenol
  • plant polysaccharide
  • plant population
  • plant population dynamics
  • plant population size
  • plant preference
  • plant process
  • plant production
  • plant productivity
  • plant products
  • plant propagule
  • plant property
  • plant protection
  • plant protein
  • plant protein source
  • plant protoplast
  • plant quality
  • plant range
  • plant record
  • plant regeneration
  • plant relationships
  • plant reproduction
  • plant research
  • plant residue
  • plant resistance
  • plant resource
  • plant respiration
  • plant response
  • plant richness
  • plant root
  • plant sample
  • plant sap
  • plant scale
  • plant science
  • plant secondary metabolite
  • plant seed
  • plant selection
  • plant senescence
  • plant shoot
  • plant size
  • plant source
  • plant species
  • plant species composition
  • plant species distribution
  • plant species diversity
  • plant species present
  • plant species richness
  • plant stage
  • plant stem
  • plant sterol
  • plant strategy
  • plant strategy theory
  • plant stress response
  • plant structure
  • plant studies
  • plant substrate
  • plant succession
  • plant surface
  • plant survival
  • plant system
  • plant taxa
  • plant tissue
  • plant tissue culture
  • plant tolerance
  • plant toxin
  • plant trait
  • plant transpiration
  • plant trichome
  • plant type
  • plant uncertainty
  • plant uptake
  • plant use
  • plant used
  • plant variety
  • plant vascular system
  • plant vigour
  • plant virus
  • plant viruse
  • plant volatile
  • plant water relation
  • plant water status
  • plant weight
  • plant yield

  • Selected Abstracts

    Resistance to cassava mosaic disease in transgenic cassava expressing antisense RNAs targeting virus replication genes

    Peng Zhang
    Summary African cassava mosaic virus (ACMV) is a major contributor to cassava mosaic disease (CMD), the economically most important and devastating disease of cassava in Africa. We have developed transgenic cassava plants with increased ACMV resistance using improved antisense RNA technology by targeting the viral mRNAs of Rep (AC1), TrAP (AC2) and REn (AC3). Viral DNA replication assays in detached leaves demonstrated that replication of two ACMV isolates was strongly reduced or inhibited in most transgenic lines. After ACMV infection of plants using biolistic inoculation, several lines remained symptomless at lower infection pressure (100 ng viral DNA/plant). Symptom development was reduced and attenuated even at higher DNA doses. Transgenic ACMV-resistant plants had significantly reduced viral DNA accumulation in their infected leaves. Short sense and antisense RNAs specific to AC1 were identified in transgenic lines expressing AC1 antisense RNA, suggesting that the short RNAs mediate interference by post-transcriptional gene silencing. Our results demonstrate that resistance to ACMV infection of cassava can be achieved with high efficacy by expressing antisense RNAs against viral mRNAs encoding essential non-structural proteins, providing a new tool to combat CMD in Africa. [source]


    EVOLUTION, Issue 4 2010
    Adam M. Siepielski
    The raw material for evolution is variation. Consequently, identifying the factors that generate, maintain, and erode phenotypic and genetic variation in ecologically important traits within and among populations is important. Although persistent directional or stabilizing selection can deplete variation, spatial variation in conflicting directional selection can enhance variation. Here, we present evidence that phenotypic variation in limber pine (Pinus flexilis) cone structure is enhanced by conflicting selection pressures exerted by its mutualistic seed disperser (Clark's nutcracker Nucifraga columbiana) and an antagonistic seed predator (pine squirrel Tamiasciurus spp.). Phenotypic variation in cone structure was bimodal and about two times greater where both agents of selection co-occurred than where one (the seed predator) was absent. Within the region where both agents of selection co-occurred, bimodality in cone structure was pronounced where there appears to be a mosaic of habitats with some persistent habitats supporting only the seed disperser. These results indicate that conflicting selection stemming from spatial variation in community diversity can enhance phenotypic variation in ecologically important traits. [source]


    EVOLUTION, Issue 6 2009
    Keiko Miyake
    After over a half century of empirical and theoretical research regarding the evolution and maintenance of gynodioecy in plants, unexplored factors influencing the relative fitnesses of females and hermaphrodites remain. Theoretical studies suggest that hermaphrodite self-fertilization (selfing) rate influences the maintenance of gynodioecy and we hypothesized that population sex ratio may influence hermaphrodite selfing rate. An experimental test for frequency-dependent self-fertilization was conducted using replicated populations constructed with different sex ratios of the gynodioecious plant Silene vulgaris. We found that hermaphrodite selfing increased with decreased hermaphrodite frequency, whereas evidence for increased inbreeding depression was equivocal. We argue that incorporation of context dependent inbreeding into future models of the evolution of gynodioecy is likely to yield novel insights into sex ratio evolution. [source]


    EVOLUTION, Issue 1 2008
    Bruce Anderson
    Although coevolution is widely accepted as a concept, its importance as a driving factor in biological diversification is still being debated. Because coevolution operates mainly at the population level, reciprocal coadaptations should result in trait covariation among populations of strongly interacting species. A long-tongued fly (Prosoeca ganglbaueri) and its primary floral food plant (Zaluzianskya microsiphon) were studied across both of their geographical ranges. The dimensions of the fly's proboscis and the flower's corolla tube length varied significantly among sites and were strongly correlated with each other. In addition, the match between tube length of flowers and tongue length of flies was found to affect plant fitness. The relationship between flower tube length and fly proboscis length remained significant in models that included various alternative environmental (altitude, longitude, latitude) and allometric (fly body size, flower diameter) predictor variables. We conclude that coevolution is a compelling explanation for the geographical covariation in flower depth and fly proboscis length. [source]


    EVOLUTION, Issue 2 2007
    Dietmar Schwarz
    Homoploid hybrid speciation,speciation via hybridization without a change in chromosome number,is rarely documented and poorly understood in animals. In particular, the mechanisms by which animal homoploid hybrid species become ecologically and reproductively isolated from their parents are hypothetical and remain largely untested by experiments. For the many host-specific parasites that mate on their host, choosing the right host is the most important ecological and reproductive barrier between these species. One example of a host-specific parasite is the Lonicera fly, a population of tephritid fruit flies that evolved within the last 250 years likely by hybridization between two native Rhagoletis species following a host shift to invasive honeysuckle. We studied the host preference of the Lonicera fly and its putative parent species in laboratory experiments. The Lonicera fly prefers its new host, introduced honeysuckle, over the hosts of both parental species, demonstrating the rapid acquisition of preference for a new host as a means of behavioral isolation from the parent species. The parent taxa discriminate against each other's native hosts, but both accept honeysuckle fruit, leaving the potential for asymmetric gene flow from the parent species. Importantly, this pattern allows us to formulate hypotheses about the initial formation of the Lonicera fly. As mating partners from the two parent taxa are more likely to meet on invasive honeysuckle than on their respective native hosts, independent acceptance of honeysuckle by both parents likely preceded hybridization. We propose that invasive honeysuckle served as a catalyst for the local breakdown of reproductive isolation between the native parent species, a novel consequence of the introduction of an exotic weed. We describe behavioral mechanisms that explain the initial hybridization and subsequent reproductive isolation of the hybrid Lonicera fly. These results provide experimental support for a combination of host shift and hybridization as a model for hybrid speciation in parasitic animals. [source]


    Article first published online: 24 SEP 200
    Pedersen, A.1,2, Knutzen, J.2, Walday, M.2, Molvær, M.2 & Johnsen, T.2 1Department of Ecology and Evolutionary Biology, University of Connecticut at Stamford, Stamford, CT. 06901 U.S.A;. 2Norwegian Institute for Water Research, P.O.B. 173 Kjelsås, 0411 Oslo, Norway. "Hydro Agri Glomfjord" a fertilizer producer has been discharging large quantities of ammonium, nitrate and phosphate into Glomfjord (in northern Norway, N 66,48°, E 13,57°) since 1947. The effects of the nutrient load to the Fjord have resulted in classical eutrophication symptoms. Elevated nutrient levels have resulted in frequent plankton blooms and seasonally reduced O2 levels in the deep-water bodies as well as an eradication of the normal littoral assemblages. The fucoid belt had been replaced by various green algae 6 km from the outlet and outward the fjord. The effect is only seen on the northern side of the Fjord. After some improvement in the discharge loads in the 1980's, the condition in the pelagic column improved with regard to plankton blooms and deep water O2 concentration. The littoral communities didn't, show any indication of recovery and a pollution indication index based on algal composition, showed even increased eutrophication. [source]

    Strategic Planning for Municipalities: A Users' Guide By THOMAS E. PLANT

    Lionel D. Feldman
    No abstract is available for this article. [source]


    Michael F. Fay
    Among the many advances in our understanding of angiosperm relationships in recent decades due to the advent of DNA sequence data is the confirmation that all plants (apart from Drypetes) that produce mustard oil precursors are related to each other and should be treated as one order, Brassicales. Due to the lack of obvious shared morphological characters, this is one of the more unexpected of these advances. Here we give the background to this development and introduce the families in Brassicales, including Tropaeolaceae, the subject of this issue. [source]


    Brent Elliott
    First page of article [source]


    EVOLUTION, Issue 5 2010
    Katy D. Heath
    Studying how the fitness benefits of mutualism differ among a wide range of partner genotypes, and at multiple spatial scales, can shed light on the processes that maintain mutualism and structure coevolutionary interactions. Using legumes and rhizobia from three natural populations, I studied the symbiotic fitness benefits for both partners in 108 plant maternal family by rhizobium strain combinations. Genotype-by-genotype (G × G) interactions among local genotypes and among partner populations determined, in part, the benefits of mutualism for both partners; for example, the fitness effects of particular rhizobium strains ranged from uncooperative to mutualistic depending on the plant family. Correlations between plant and rhizobium fitness benefits suggest a trade off, and therefore a potential conflict, between the interests of the two partners. These results suggest that legume,rhizobium mutualisms are dynamic at multiple spatial scales, and that strictly additive models of mutualism benefits may ignore dynamics potentially important to both the maintenance of genetic variation and the generation of geographic patterns in coevolutionary interactions. [source]


    EVOLUTION, Issue 12 2007
    Nadir Alvarez
    The hypothesis of isolation by distance (IBD) predicts that genetic differentiation between populations increases with geographic distance. However, gene flow is governed by numerous factors and the correlation between genetic differentiation and geographic distance is never simply linear. In this study, we analyze the interaction between the effects of geographic distance and of wild or domesticated status of the host plant on genetic differentiation in the bean beetle Acanthoscelides obvelatus. Geographic distance explained most of the among-population genetic differentiation. However, IBD varied depending on the kind of population pairs for which the correlation between genetic differentiation and geographic distance was examined. Whereas pairs of beetle populations associated with wild beans showed significant IBD (P < 10,4), no IBD was found when pairs of beetle populations on domesticated beans were examined (P= 0.2992). This latter result can be explained by long-distance migrations of beetles on domesticated plants resulting from human exchanges of bean seeds. Beetle populations associated with wild beans were also significantly more likely than those on domesticated plants to contain rare alleles. However, at the population level, beetles on cultivated beans were similar in allelic richness to those on wild beans. This similarity in allelic richness combined with differences in other aspects of the genetic diversity (i.e., IBD, allelic diversity) is compatible with strongly contrasting effects of migration and drift. This novel indirect effect of human actions on gene flow of a serious pest of a domesticated plant has important implications for the spread of new adaptations such as resistance to pesticides. [source]


    EVOLUTION, Issue 9 2007
    Janette A. Steets
    Although a large portion of plant and animal species exhibit intermediate levels of outcrossing, the factors that maintain this wealth of variation are not well understood. Natural enemies are one relatively understudied ecological factor that may influence the evolutionary stability of mixed mating. In this paper, we aim for a conceptual unification of the role of enemies in mating system expression and evolution in both hermaphroditic animals and plants. We review current theory and detail the potential effects of enemies on fundamental mating system parameters. In doing so, we identify situations in which consideration of enemies alters expectations about the stability of mixed mating. Generally, we find that inclusion of the enemy dimension may broaden conditions in which mixed mating systems are evolutionarily stable. Finally, we highlight avenues ripe for future theoretical and empirical work that will advance our understanding of enemies in the expression and evolution of mixed mating in their hosts/victims, including examination of feedback cycles between victims and enemies and quantification of mating system-related parameters in victim populations in the presence and absence of enemies. [source]


    EVOLUTION, Issue 2 2003
    William E. Friedman
    Abstract The monosporic seven-celled/eight-nucleate Polygonumtype female gametophyte has long served as a focal point for discussion of the origin and subsequent evolution of the angiosperm female gametophyte. In Polygonumtype female gametophytes, two haploid female nuclei are incorporated into the central cell, and fusion of a sperm cell with the binucleate central cell produces a triploid endosperm with a complement of two maternal and one paternal genomes, characteristic of most angiosperms. We document the development of a four-celled/four-nucleate female gametophyte in Nuphar polysepala (Engelm.) and infer its presence in many other ancient lineages of angiosperms. The central cell of the female gametophyte in these taxa contains only one haploid nucleus; thus endosperm is diploid and has a ratio of one maternal to one paternal genome. Based on comparisons among flowering plants, we conclude that the angiosperm female gametophyte is constructed of modular developmental subunits. Each module is characterized by a common developmental pattern: (1) positioning of a single nucleus within a cytoplasmic domain (pole) of the female gametophyte; (2) two free-nuclear mitoses to yield four nuclei within that domain; and (3) partitioning of three uninucleate cells adjacent to the pole such that the fourth nucleus is confined to the central region of the female gametophyte (central cell). Within the basal angiosperm lineages Nymphaeales and Illiciales, female gametophytes are characterized by a single developmental module that produces a four-celled/four-nucleate structure with a haploid uninucleate central cell. A second pattern, typical of Amborella and the overwhelming majority of eumagnoliids, monocots, and eudicots, involves the early establishment of two developmental modules that produce a seven-celled/eight-nucleate female gametophyte with two haploid nuclei in the central cell. Comparative analysis of onto-genetic sequences suggests that the seven-celled female gametophyte (two modules) evolved by duplication and ectopic expression of an ancestral Nuphar- like developmental module within the chalazal domain of the female gametophyte. These analyses indicate that the first angiosperm female gametophytes were composed of a single developmental module, which upon double fertilization yielded a diploid endosperm. Early in angiosperm history this basic module was duplicated, and resulted in a seven-celled/eight-nucleate female gametophyte, which yielded a triploid endosperm with the characteristic 2:1 maternal to paternal genome ratio. [source]


    EVOLUTION, Issue 12 2002
    Pärk. Ingvarsson
    Abstract., Partial self-fertilization is common in higher plants. Mating system variation is known to have important consequences for how genetic variation is distributed within and among populations. Selfing is known to reduce effective population size, and inbreeding species are therefore expected to have lower levels of genetic variation than comparable out crossing taxa. However, several recent empirical studies have shown that reductions in genetic diversity within populations of inbreeding species are far greater than the expected reductions based on the reduced effective population size. Two different processes have been argued to cause these patterns, selective sweeps (or hitchhiking) and background selection. Both are expected to be most effective in reducing genetic variation in regions of low recombination rates. Selfing is known to reduce the effective recombination rate, and inbreeding taxa are thus thought to be particularly vulnerable to the effects of hitchhiking or background selection. Here I propose a third explanation for the lower-than-expected levels of genetic diversity within populations of selfing species; recurrent extinctions and recolonizations of local populations, also known as metapopulation dynamics. I show that selfing in a metapopulation setting can result in large reductions in genetic diversity within populations, far greater than expected based the lower effective population size inbreeding species is expected to have. The reason for this depends on an interaction between selfing and pollen migration. [source]


    JOURNAL OF PHYCOLOGY, Issue 6 2009
    Dariusz Dziga
    Several cyanobacterial species have a high potential to dominate in marine environments and freshwater reservoirs, and the ecological and physiological reasons for this phenomenon are not understood comprehensively. In this study, the ability of a Microcystis aeruginosa Kütz. strain to produce free dissolved enzymes was documented. We have observed that this highly toxic strain releases alkaline phosphatase, leucine aminopeptidase, and ,-glucosidase into the ambient environment. Additionally, the inhibitory activity of selected phenols produced by aquatic plants on the activity of these enzymes was analyzed. The investigated compounds, pyrogallol and, to a lesser degree, hydroquinone, decreased the activity of extracellular enzymes produced by M. aeruginosa, with leucine aminopeptidase being the most sensitive to the inhibitors. The noncompetitive character of enzymatic inhibition suggests that the polyphenols produced by aquatic plants are able to influence the activity of different extracellular or membrane-bound enzymes. [source]


    JOURNAL OF PHYCOLOGY, Issue 2 2002
    Russell L. Chapman
    First page of article [source]


    Sandy Smith-Nonini
    First page of article [source]


    Konstantin Yu.
    ABSTRACT The sampled-data H2 -optimization problem for plants with multiple input and output delays is considered. An equivalent discrete-time system is constructed and numerical algorithm for computing matrices of its state-space realization is presented. It is proved that stability of this system is equivalent to stability of original sampled-data system. The proposed method can be applied to a wide class of digital control problems for continuous-time plants with multiple input and output delays. [source]


    Jingxin Zhang
    ABSTRACT This paper analyzes the performance of discrete linear time varying (LTV) control of discrete linear periodically time varying (LPTV) plants for l2 disturbance rejection. It extends the results of [11,13] for linear periodic controllers to general LTV control of LPTV plants. It is shown that LPTV control provides strictly better control performance than linear strictly time varying control for LPTV plants. The analysis is carried out in frequency domain. This approach provides not only new results on disturbance rejection of LTV control but also some new insight into properties of general LTV systems. [source]

    Using Population Count Data to Assess the Effects of Changing River Flow on an Endangered Riparian Plant

    análisis de viabilidad poblacional; gestión ribereña; método de difusión; presas; riesgo de extinción Abstract:,Methods for using simple population count data to project extinction risk have been the focus of much recent theoretical work, but few researchers have used these approaches to address management questions. We analyzed 15 years of census data on the federally endangered endemic riparian plant Pityopsis ruthii (Small) with the diffusion approximation (DA). Our goals were to evaluate relative extinction risk among populations in two different watersheds (in Tennessee, U.S.A.) and potential effects of variation in managed river flow on population dynamics. Populations in both watersheds had high projected risks of extinction within 50 years, but the causes of this risk differed. Populations of P. ruthii on the Hiwassee River had higher initial population sizes but significantly lower average growth rates than those on the Ocoee River. The only populations with low predicted short-term extinction risk were on the Ocoee. Growth rates for populations on both rivers were significantly reduced during periods of lower river flow. We found only marginal evidence of a quadratic relationship between population performance and flow. These patterns are consistent with the idea that low flows affect P. ruthii due to growth of competing vegetation, but the degree to which very high flows may reduce population growth is still unclear. Simulations indicated that populations were most sensitive to growth rates in low-flow years, but small changes in the frequency of these periods did not strongly increase risk for most populations. Consistent with results of other studies, DA estimates of extinction risk had wide confidence limits. Still, our results yielded several valuable insights, including the need for greater monitoring of populations on the Hiwassee and the importance of low-flow years to population growth. Our work illustrates the potential value of simple methods for analyzing count data despite the challenges posed by uncertainty in estimates of extinction risk. Resumen:,Los métodos que utilizan datos de conteos simples de la población para proyectar el riesgo de extinción han sido el foco reciente de mucho trabajo teórico, pero pocos investigadores han utilizado estos métodos para responder preguntas de gestión. Analizamos 15 años de datos de censos de la planta ribereña, endémica y federalmente en peligro Pityopsis ruthii (Small) mediante el método de difusión. Nuestras metas fueron evaluar el riesgo de extinción de poblaciones en dos cuencas hidrológicas distintas y con dos efectos potenciales de la variación del flujo de agua sobre la dinámica de la población. Las poblaciones en ambas cuencas tenían alto riesgo de extinción proyectado a 50 años, pero las causas de este riesgo difirieron. Las poblaciones de P. ruthii en el Río Hiwassee tuvieron poblaciones iniciales más grandes, pero tasas de crecimiento significativamente menores, que las poblaciones en el Río Ocoee. Las únicas poblaciones con bajo riesgo de extinción pronosticado estaban en el Ocoee. Las tasas de crecimiento de las poblaciones en ambos ríos se redujeron significativamente durante períodos de bajo flujo en el río. Sólo encontramos evidencia marginal de la relación cuadrática entre el funcionamiento de la población y el flujo. Estos patrones son consistentes con la idea de que los bajos flujos afectan a P. ruthii debido al crecimiento de vegetación competitiva, pero aun no es claro el grado en que flujos muy grandes pueden reducir el crecimiento poblacional. Las simulaciones indicaron que las poblaciones son más sensibles a las tasas de crecimiento en años con bajo flujo en los ríos, pero pequeños cambios en la frecuencia de esos períodos no aumentaron el riesgo en la mayoría de las poblaciones. Consistentemente con los resultados de otros estudios, las estimaciones del riesgo de extinción mediante el método de difusión tienen amplios límites de confianza. Aun así, nuestros resultados aportaron varios conocimientos valiosos, incluyendo la necesidad de mayor monitoreo de las poblaciones en el Hiwassee y la importancia para el crecimiento poblacional de los años con bajo flujo. Nuestro trabajo ilustra el valor potencial de métodos sencillos de análisis de datos de conteo a pesar de los retos impuestos por la incertidumbre en las estimaciones del riesgo de extinción. [source]

    Matrix Models as a Tool for Understanding Invasive Plant and Native Plant Interactions

    competencia; invasión biológica; plantas invasoras; modelo matricial; perturbación Abstract:,Demographic matrix models are an increasingly standard way to evaluate the effects of different impacts and management approaches on species of concern. Although invasive species are now considered among the greatest threats to biodiversity, matrix methods have been little used to explore and integrate the potentially complicated effects of invasions on native species. I developed stage-structured models to assess the impacts of invasive grasses on population growth and persistence of a federally listed (U.S.A.) endemic plant, the Antioch Dunes evening primrose (Oenothera deltoides subsp. howellii [Munz] W. Klein). I used these models to evaluate two frequently made assumptions: (1) when rare plant populations decline in invaded habitats, invasive species are the cause and (2) invasive plants suppress rare plants primarily through direct resource competition. I compared two control and two removal matrices based on previous experimental work that showed variable effects of invasive grasses on different life-history stages of O. deltoides. Matrix analysis showed that these effects translated into substantial changes in population growth rates and persistence, with control matrices predicting a mean stochastic population growth rate (,) of 0.86 and removal matrices predicting growth rates from 0.92 to 0.93. Yet even the most optimistic invasive removal scenarios predicted rapid decline and a probability of extinction near one in the next 100 years. Competitive suppression of seedlings had much smaller effects on growth rates than did lowered germination, which probably resulted from thatch accumulation and reduced soil disturbance. These results indicate that although invasive grasses have important effects on the population growth of this rare plant, invasion impacts are not solely responsible for observed declines and are likely to be interacting with other factors such as habitat degradation. Further, changes in the disturbance regime may be as important a mechanism creating these impacts as direct resource competition. My results highlight the value of demographic modeling approaches in creating an integrated assessment of the threats posed by invasive species and the need for more mechanistic studies of invasive plant interactions with native plants. Resumen:,Los modelos demográficos matriciales son una forma cada vez más utilizada para evaluar los efectos de diferentes impactos y métodos de gestión sobre las especies en cuestión. Aunque actualmente se considera a las plantas invasoras entre las mayores amenazas a la biodiversidad, los modelos matriciales han sido poco utilizados para explorar e integrar los efectos potencialmente complicados de las invasiones sobre las especies nativas. Desarrollé modelos estructurados por etapas para evaluar los impactos de pastos invasores sobre el crecimiento poblacional y la persistencia de una especie de planta endémica, enlistada federalmente (E.U.A.), Oenothera deltoides ssp. howellii [Munz] W. Klein. Utilicé estos modelos para evaluar dos suposiciones frecuentes: (1) cuando las poblaciones de plantas raras declinan en hábitats invadidos, las especies invasoras son la causa y (2) las plantas invasoras suprimen a las plantas raras principalmente mediante la competencia directa por recursos. Comparé dos matrices de control y dos de remoción con base en trabajo experimental previo que mostró efectos variables de los pastos invasores sobre las diferentes etapas de la historia de vida de O. deltoides. El análisis de la matriz mostró que estos efectos se tradujeron en cambios sustanciales en las tasas de crecimiento y persistencia de la población, las matrices de control predijeron una tasa media de crecimiento poblacional estocástica (,) de 0.86 y las matrices de remoción predijeron tasas de crecimiento de 0.92-0.93. Aun los escenarios más optimistas de remoción de invasores predijeron una rápida declinación y una probabilidad de extinción en 100 años cerca de uno. La supresión competitiva de plántulas tuvo mucho menor efecto sobre las tasas de crecimiento que la disminución en la germinación, que probablemente resultó de la acumulación de paja y reducción en la perturbación del suelo. Estos resultados indican que, aunque los pastos invasores tienen efectos importantes sobre el crecimiento poblacional de esta planta rara, los impactos de la invasión no son los únicos responsables de las declinaciones observadas y probablemente están interactuando con otros factores como la degradación del hábitat. Más aun, los cambios en el régimen de perturbación pueden ser un mecanismo tan importante en la creación de estos impactos como la competencia directa por recursos. Mis resultados resaltan el valor del enfoque de los modelos demográficos para la evaluación integral de las amenazas de especies invasoras y la necesidad de estudios más mecanicistas de las interacciones de plantas invasoras con plantas nativas. [source]

    Spatiotemporal changes of beetle communities across a tree diversity gradient

    Stephanie Sobek
    Abstract Aim, Plant and arthropod diversity are often related, but data on the role of mature tree diversity on canopy insect communities are fragmentary. We compare species richness of canopy beetles across a tree diversity gradient ranging from mono-dominant beech to mixed stands within a deciduous forest, and analyse community composition changes across space and time. Location, Germany's largest exclusively deciduous forest, the Hainich National Park (Thuringia). Methods, We used flight interception traps to assess the beetle fauna of various tree species, and applied additive partitioning to examine spatiotemporal patterns of diversity. Results, Species richness of beetle communities increased across the tree diversity gradient from 99 to 181 species per forest stand. Intra- and interspecific spatial turnover among trees contributed more than temporal turnover among months to the total ,-beetle diversity of the sampled stands. However, due to parallel increases in the number of habitat generalists and the number of species in each feeding guild (herbivores, predators and fungivores), no proportional changes in community composition could be observed. If only beech trees were analysed across the gradient, patterns were similar but temporal (monthly) species turnover was higher compared to spatial turnover among trees and not related to tree diversity. Main conclusions, The changes in species richness and community composition across the gradient can be explained by habitat heterogeneity, which increased with the mix of tree species. We conclude that understanding temporal and spatial species turnover is the key to understanding biodiversity patterns. Mono-dominant beech stands are insufficient to conserve fully the regional species richness of the remaining semi-natural deciduous forest habitats in Central Europe, and analysing beech alone would have resulted in the misleading conclusion that temporal (monthly) turnover contributes more to beetle diversity than spatial turnover among different tree species or tree individuals. [source]

    Plant,soil feedbacks: a meta-analytical review

    ECOLOGY LETTERS, Issue 9 2008
    Andrew Kulmatiski
    Abstract Plants can change soil biology, chemistry and structure in ways that alter subsequent plant growth. This process, referred to as plant,soil feedback (PSF), has been suggested to provide mechanisms for plant diversity, succession and invasion. Here we use three meta-analytical models: a mixed model and two Bayes models, one correcting for sampling dependence and one correcting for sampling and hierarchical dependence (delta-splitting model) to test these hypotheses. All three models showed that PSFs have medium to large negative effects on plant growth, and especially grass growth, the life form for which we had the most data. This supports the hypothesis that PSFs, through negative frequency dependence, maintain plant diversity, especially in grasslands. PSFs were also large and negative for annuals and natives, but the delta-splitting model indicated that more studies are needed for these results to be conclusive. Our results support the hypotheses that PSFs encourage successional replacements and plant invasions. Most studies were performed using monocultures of grassland species in greenhouse conditions. Future research should examine PSFs in plant communities, non-grassland systems and field conditions. [source]

    Plant,soil feedbacks and invasive spread

    ECOLOGY LETTERS, Issue 9 2006
    Jonathan M. Levine
    Abstract Plant invaders have been suggested to change soil microbial communities and biogeochemical cycling in ways that can feedback to benefit themselves. In this paper, we ask when do these feedbacks influence the spread of exotic plants. Because answering this question is empirically challenging, we show how ecological theory on ,pushed' and ,pulled' invasions can be used to examine the problem. We incorporate soil feedbacks into annual plant invasion models, derive the conditions under which such feedbacks affect spread, and support our approach with simulations. We show that in homogeneous landscapes, strong positive feedbacks can influence spreading velocity for annual invaders, but that empirically documented feedbacks are not strong enough to do so. Moreover, to influence spread, invaders must modify the soil environment over a spatial scale larger than is biologically realistic. Though unimportant for annual invader spread in our models, feedbacks do affect invader density and potential impact. We discuss how future research might consider the way landscape structure, dispersal patterns, and the time scales over which plant,soil feedbacks develop regulate the effects of such feedbacks on invader spread. [source]

    Plant,soil biota interactions and spatial distribution of black cherry in its native and invasive ranges

    ECOLOGY LETTERS, Issue 12 2003
    Kurt O. Reinhart
    Abstract One explanation for the higher abundance of invasive species in their non-native than native ranges is the escape from natural enemies. But there are few experimental studies comparing the parallel impact of enemies (or competitors and mutualists) on a plant species in its native and invaded ranges, and release from soil pathogens has been rarely investigated. Here we present evidence showing that the invasion of black cherry (Prunus serotina) into north-western Europe is facilitated by the soil community. In the native range in the USA, the soil community that develops near black cherry inhibits the establishment of neighbouring conspecifics and reduces seedling performance in the greenhouse. In contrast, in the non-native range, black cherry readily establishes in close proximity to conspecifics, and the soil community enhances the growth of its seedlings. Understanding the effects of soil organisms on plant abundance will improve our ability to predict and counteract plant invasions. [source]

    A performance comparison of individual and combined treatment modules for water recycling

    Stuart Khan
    Abstract An Advanced Water Recycling Demonstration Plant (AWRDP) was commissioned and constructed by the Queensland State Government in Australia. The AWRDP was used to study the effectiveness of a variety of treatment processes in the upgrading of municipal wastewater for water recycling applications. The AWRDP consists of eight modules, each housing an individual specific treatment process. These processes are flocculation, dissolved air flotation, dual media filtration, ozonation, biological activated carbon adsorption, microfiltration, reverse osmosis, and ultraviolet disinfection. The individual performances of the treatment processes were determined, as well as their interdependence in series. A range of chemical water quality parameters were investigated. The study provides a broad process comparison on the basis of an important catalogue of these key parameters. This will be valuable in the selection and optimization of treatment processes trains in full-scale water recycling applications. © 2005 American Institute of Chemical Engineers Environ Prog, 2005 [source]

    Ultra-trace analysis of multiple endocrine-disrupting chemicals in municipal and bleached kraft mill effluents using gas chromatography,high-resolution mass spectrometry

    Michael G. Ikonomou
    Abstract A comprehensive gas chromatographic,high-resolution mass spectrometric (GC-HRMS),based method was developed that permitted the simultaneous determination of 30 estrogenic endocrine-disrupting chemicals (EDCs) and related compounds, including surfactants, biogenic and synthetic steroids, fecal sterols, phytoestrogens, and plasticizers, in wastewater. Features of the method include low sample volume (,40 ml), optimized Florisil® cleanup to minimize matrix interferences and optimized analyte derivatization to improve sensitivity via GC-HRMS. Detection limits were in the low- to mid-ng/L range, and recoveries were greater than 60% for most target analytes. This new method allows for high throughput analysis of many organic wastewater contaminants in a complex matrix with relative standard deviation of less than 15% for most measurable compounds. The applicability of the method was demonstrated by examining wastewater samples from different origins. Compounds such as di(2-ethylhex-yl)phthalate, cholesterol, cholestanol, and other cholesterol derivatives were measured in much higher concentrations in untreated sewage and were reduced substantially in concentration by the treatment process. However, steroidal compounds, particularly estrone (E1), 17,-estradiol (E2), and estriol (E3), as well as plant sterols (except stigmastanol), were greater in the treated municipal wastewater versus the untreated effluent. Plant and fungi sterols, stigmastanol and ergosterol, were found largely associated with bleached kraft mill effluent (BKME) as compared to the municipal effluents. [source]

    Using artificial streams to assess the effects of metal-mining effluent on the life cycle of the freshwater midge (Chironomus tentans) in situ

    Kimberly A. Hruska
    Abstract In 2002, we developed an in situ life-cycle bioassay with Chironomus tentans in artificial streams to evaluate the effects of a complex metal mine effluent under ambient environmental conditions. The bioassay was tested in the field using effluent from the Copper Cliff Waste Water Treatment Plant at INCO (Sudbury, ON, Canada). Chironomus tentans were exposed throughout the life cycle to 45% Copper Cliff effluent, which is the average effluent concentration measured in Junction Creek (ON, Canada), the natural receiving environment. Chironomus tentans in the effluent treatment exhibited reduced survival (p = 0.001), reduced total emergence (p = 0.001), increased time-to-emergence (p = 0.001), and reduced hatching success (p = 0.001) relative to animals in the reference water treatment. Chironomus tentans in the effluent treatment were not significantly different from the reference in terms of growth, sex ratio, number of egg cases/female, and number of eggs/egg case. This research showed how a life-cycle bioassay could be used in situ to assess metal mine effluent effects on a benthic invertebrate. [source]

    Environmental exposure to polychlorinated biphenyls among raccoons (Procyon lotor) at the Paducah Gaseous Diffusion Plant, Western Kentucky, USA,

    Philip N. Smith
    Abstract An investigation involving raccoons (Procyon lotor) as a sentinel species at the Paducah Gaseous Diffusion Plant (PGDP) in Western Kentucky (USA) delineated the extent of exposure to polychlorinated biphenyls (PCBs) and PCB spatial distribution. Raccoon exposure to PCBs was demonstrated through analysis of subcutaneous fat, abdominal fat, liver, and brain tissues from raccoons collected at the PGDP but also was clearly evident in raccoons from a reference area situated along the Ohio River (USA). Raccoons with the highest tissue PCB concentrations appeared to be those inhabiting areas nearest the plant itself and most likely those that ventured into the plants interior. Male raccoons at the PGDP had similar concentrations of total PCBs in subcutaneous fat (1.86 ± 0.64 ,g/g) as males from the reference site (1.41 ± 0.35 ,g/g), but females had higher PCB body burdens than those at the reference site (9.90 ± 6.13 ,g/g vs 0.75 ± 0.40 ,g/g). Gross measurements of exposure to radiation-producing materials revealed that counts per minute exceeded background in 61% of PGDP raccoons compared with 27% at the reference site and five raccoons at the PGDP had beta counts that were more than twice the background. Differences among trapping success, growth rates, and serum chemistry parameters were noted but may have been related to habitat and other environmental and population density factors. [source]

    Environmental polychlorinated biphenyl exposure and cytochromes P450 in raccoons (Procyon lotor),

    Philip N. Smith
    Abstract An investigation involving raccoons as a sentinel species at the Paducah Gaseous Diffusion Plant (PGDP) and Ballard Wildlife Management Area in western Kentucky (USA) delineated the extent of exposure to polychlorinated biphenyls (PCBs). Three separate measures of hepatic cytochrome P450 (CYP) induction were used to evaluate raccoon physiological responses to PCB exposure. Hepatic CYP induction was estimated via determination of total CYP, dealkylase activities, and immunoreactive proteins. There were no differences in raccoon biomarker responses between study sites. Significant relationships between and among PCB residues and biomarkers indicated that hepatic CYP induction had occurred in response to PCB exposure. Pentoxy-resorufin O -deethylase (PROD) activity, CYP1A1, and CYP1A2 were biomarkers most closely associated with PCB exposure. The rank order of responses was CYP1A1 > CYP1A2 > PROD > ethoxyresorufin O -deethylase (EROD) as related to raccoon liver PCB concentrations, whereas the order was CYP1A1 > PROD > EROD > CYP1A2 when regressed with total PCB concentrations in abdominal fat. [source]