Environmental Conditions (environmental + condition)

Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Environmental Conditions

  • adverse environmental condition
  • certain environmental condition
  • changing environmental condition
  • constant environmental condition
  • different environmental condition
  • extreme environmental condition
  • favourable environmental condition
  • harsh environmental condition
  • local environmental condition
  • of environmental condition
  • other environmental condition
  • particular environmental condition
  • prevailing environmental condition
  • same environmental condition
  • severe environmental condition
  • similar environmental condition
  • stressful environmental condition
  • unfavourable environmental condition
  • variety of environmental condition
  • various environmental condition
  • varying environmental condition

  • Selected Abstracts


    EVOLUTION, Issue 6 2002
    Lukas F. Keller
    Abstract Understanding the fitness consequences of inbreeding (inbreeding depression) is of importance to evolutionary and conservation biology. There is ample evidence for inbreeding depression in captivity, and data from wild populations are accumulating. However, we still lack a good quantitative understanding of inbreeding depression and what influences its magnitude in natural populations. Specifically, the relationship between the magnitude of inbreeding depression and environmental severity is unclear. We quantified inbreeding depression in survival and reproduction in populations of cactus finches (Geospiza scandens) and medium ground finches (Geospiza fortis) living on Isla Daphne Major in the Galapagos Archipelago. Our analyses showed that inbreeding strongly reduced the recruitment probability (probability of breeding given that an adult is alive) in both species. Additionally, in G. scandens, first-year survival of an offspring withf= 0.25 was reduced by 21% and adults withf= 0.25 experienced a 45% reduction in their annual probability of survival. The magnitude of inbreeding depression in both adult and juvenile survival of this species was strongly modified by two environmental conditions, food availability and number of competitors. In juveniles, inbreeding depression was only present in years with low food availability, and in adults inbreeding depression was five times more severe in years with low food availability and large population sizes. The combination of relatively severe inbreeding depression in survival and the reduced recruitment probability led to the fact that very few inbred G. scandens ever succeeded in breeding. Other than recruitment probability, no other trait showed evidence of inbreeding depression in G. fortis, probably for two reasons: a relatively high rate of extrapair paternity (20%), which may lead to an underestimate of the apparent inbreeding depression, and low sample sizes of highly inbred G. fortis, which leads to low statistical power. Using data from juvenile survival, we estimated the number of lethal equivalents carried by G. scandens, G. fortis, and another congener, G. magnirostris. These results suggest that substantial inbreeding depression can exist in insular populations of birds, and that the magnitude of the inbreeding depression is a function of environmental conditions. [source]


    ARCHAEOMETRY, Issue 4 2004
    The occurrence of coarse-grained vivianite and mitridatite aggregates in a potsherd, a grand ring and a timber imprint from the Second Iron Age site of Adria (Rovigo, northeastern Italy) suggest contrasting environmental conditions of burial. In particular, bone fragments were replaced by vivianite at relatively low pH and Eh, due to the presence of deteriorating organic matter, together with slag and iron flakes. Subsequent interactions with Ca-rich groundwater characterized by higher pH and Eh determined the growth of mitridatite after vivianite. Although phosphates crystallized after burial, the examined samples were not involved in pervasive chemical contamination. [source]

    Healthy Country, Healthy People: Policy Implications of Links between Indigenous Human Health and Environmental Condition in Tropical Australia

    Stephen T. Garnett
    Investment in programs that help Indigenous people undertake work maintaining the environmental health of their country has benefits for the environment as well as the physical, mental and cultural health of the Indigenous people involved. For health these findings have direct implications for some national health policies, service provision to homelands, health promotion and Indigenous health research. There are also direct implications for environmental investment in northern Australia and the design and regulation of markets in resource entitlements. Indirectly the findings should be important for economic, employment and education policies as well as those promoting social harmony. Given the range of benefits there is a strong argument for cross-agency investment in working on country by Indigenous people. [source]

    The Stability of Collected Human Scent Under Various Environmental Conditions,

    Davia T. Hudson Ph.D.
    Abstract:, Human scent evidence collected from objects at a crime scene is used for scent discrimination with specially trained canines. Storage of the scent evidence is usually required yet no optimized storage protocol has been determined. Storage containers including glass, polyethylene, and aluminized pouches were evaluated to determine the optimal medium for storing human scent evidence of which glass was determined to be the optimal storage matrix. Hand odor samples were collected on three different sorbent materials, sealed in glass vials and subjected to different storage environments including room temperature, ,80°C conditions, dark storage, and UVA/UVB light exposure over a 7-week period. Volatile organic compounds (VOCs) in the headspace of the samples were extracted and identified using solid-phase micro-extraction,gas chromatography/mass spectrometry (SPME,GC/MS). Three-dimensional covariance mapping showed that glass containers subjected to minimal UVA/UVB light exposure provide the most stable environment for stored human scent samples. [source]

    133 Studies on the Life History of the Portuguese Red Alga Porphyra Dioica (Brodie and Irvine) Under Varying Environmental Conditions

    R. Pereira
    The life history of Porphyra dioica collected in Porto, Portugal, was investigated under laboratory conditions. This is one of the most common Porphyra species on the North Coast of Portugal and can be found throughout the year. Field studies showed higher percentage cover, from 23 to 66%, during February through May. Varying temperature, light intensities and photoperiods were tested. The zygotospores germinated faster at 15°C, and at 25 ,mol m,2·s,1. Growth rate of the conchocelis was affected by temperature rather than by photoperiod. In the three photoperiods tested, growth rate was always higher at 15°C, under 25 to 75 ,mol m,2·s,1, although not significantly different from that at 20° C. Difference between these two temperatures and 5 and 10°C was significant. Conchosporangia formation was higher in 15°C and at short-day, 8:16, Light:Dark and 25 to 75 ,mol m,2·s,1 and was almost non-existent in free floating conditions. Optimal conditions for conchosporangia maturation, 15° C, 8:16, Light:Dark and 5 to 25 ,mol m,2·s,1 also promoted spore release after 18 weeks. Aeration appeared to be crucial for normal blade development. No archeospores were observed. The first findings of the optimal conditions for growth of the gametophyte stage will also be discussed. [source]

    Degradation of Poly(methyl methacrylate) Model Compounds Under Extreme Environmental Conditions

    Francesca Bennet
    No abstract is available for this article. [source]

    Can distribution models help refine inventory-based estimates of conservation priority?

    A case study in the Eastern Arc forests of Tanzania, Kenya
    Abstract Aim, Data shortages mean that conservation priorities can be highly sensitive to historical patterns of exploration. Here, we investigate the potential of regionally focussed species distribution models to elucidate fine-scale patterns of richness, rarity and endemism. Location, Eastern Arc Mountains, Tanzania and Kenya. Methods, Generalized additive models and land cover data are used to estimate the distributions of 452 forest plant taxa (trees, lianas, shrubs and herbs). Presence records from a newly compiled database are regressed against environmental variables in a stepwise multimodel. Estimates of occurrence in forest patches are collated across target groups and analysed alongside inventory-based estimates of conservation priority. Results, Predicted richness is higher than observed richness, with the biggest disparities in regions that have had the least research. North Pare and Nguu in particular are predicted to be more important than the inventory data suggest. Environmental conditions in parts of Nguru could support as many range-restricted and endemic taxa as Uluguru, although realized niches are subject to unknown colonization histories. Concentrations of rare plants are especially high in the Usambaras, a pattern mediated in models by moisture indices, whilst overall richness is better explained by temperature gradients. Tree data dominate the botanical inventory; we find that priorities based on other growth forms might favour the mountains in a different order. Main conclusions, Distribution models can provide conservation planning with high-resolution estimates of richness in well-researched areas, and predictive estimates of conservation importance elsewhere. Spatial and taxonomic biases in the data are essential considerations, as is the spatial scale used for models. We caution that predictive estimates are most uncertain for the species of highest conservation concern, and advocate using models and targeted field assessments iteratively to refine our understanding of which areas should be prioritised for conservation. [source]

    Growth in relation to microclimatic conditions and physiological characteristics of four Lobaria pulmonaria populations in two contrasting habitats

    ECOGRAPHY, Issue 1 2004
    Gisela Gaio-Oliveira
    The aim of the present study was to compare the physiological characteristics of various populations of the lichen Lobaria pulmonaria in Portugal and Sweden. For this, indirect markers of algal (photobiont) and fungal (mycobiont) activity were measured, as well as their CO2 gasexchange characteristics. Microclimatic conditions and the lichens growth performance in the two countries were compared using reciprocal transplantation. Two populations of L. pulmonaria represented each country: one collected from forest interior conditions and one from forest edge habitats. A non-transplanted "wild" population was also studied in each country, in order to evaluate any transplantation effects per se. The main hypothesis were that; 1) growth should be faster in Portugal due to higher light availability; 2) the energy use efficiency of lichen biomass gain should be similar for the native populations in their respective native habitat; 3) if the lichens were able to adapt to the environmental conditions in the foreign habitat this should be revealed as similar growth rates among all thalli transplanted at the same site, regardless of their origin. Physiologically, the Portuguese and Swedish populations were very similar, both concerning their CO2 gas exchange characteristics and distribution of resources between photo- and mycobiont tissue. Environmental conditions were more advantageous for L. pulmonaria growth in Portugal, i.e. higher photon flux densities and ambient temperatures when the lichens were wet and active, and a lower fraction of the active time occurring in darkness. However, despite similar physiological characteristics of all the studied populations, the Swedish lichens were not able to grow as well in Portugal as the native, while all populations had similarly low growth rates in Sweden. [source]

    Temperature and Ca2+ ion as modulators in cellular immunity of the Sunn pest Eurygaster integriceps Puton (Heteroptera: Scutelleridae)

    Arash ZIBAEE
    Abstract Environmental conditions in addition to divalent cations may affect the interactions between pathogens and insects. Elucidation of factors which modulate insect immune responses could be a significant part of investigations in this area. In this study, adults of Eurygaster integriceps, as the destructive pest of wheat, were kept at different temperatures in addition to injection with different concentrations of Ca2+ to find the effect on cellular immune reactions against Beauveria bassiana. Results showed that total and differentiate hemocyte numbers, nodule formation and phenoloxidase activity increased with elevation of temperature so that the higher values were obtained at 30 and 40°C at various intervals. Higher concentrations of Ca2+ ion (5 mM) caused an increase in plasmatocyte length and width especially after 60 min. Similar results were observed for nodule formation and phenoloxidase activity of E. integriceps adults after injection by B. bassiana spores and phenoloxidase activity. It is clear from the current study that thermoregulation and Ca2+ ion can positively affect the hemocyte numbers especially plasmatocytes and granulocytes, nodule formation and phenoloxidase activity in E. integriceps. The understanding of modulators of the insect immune response may directly influence novel approaches to obtain safe and effective biological control agents. [source]

    Swarmer cell differentiation in Proteus mirabilis

    Philip N. Rather
    Summary Under the appropriate environmental conditions, the Gram-negative bacterium Proteus mirabilis undergoes a remarkable differentiation to form a distinct cell type called a swarmer cell. The swarmer cell is characterized by a 20- to 40-fold increase in both cell length and the number of flagella per cell. Environmental conditions required for swarmer cell differentiation include: surface contact, inhibition of flagellar rotation, a sufficient cell density and cell-to-cell signalling. The differentiated swarmer cell is then able to carry out a highly ordered population migration termed swarming. Genetic analysis of the swarming process has revealed that a large variety of distinct loci are required for this differentiation including: genes involved in regulation, lipopolysaccharide and peptidoglycan synthesis, cell division, ATP production, putrescine biosynthesis, proteolysis and cell shape determination. The process of swarming is important medically because the expression of virulence genes and the ability to invade cells are coupled to the differentiated swarmer cell. In this review, the genetic and environmental requirements for swarmer cell differentiation will be outlined. In addition, the role, of, the, differentiated, swarmer, cell, in, virulence and its possible role in biofilm formation will be discussed. [source]

    Identity of active methanotrophs in landfill cover soil as revealed by DNA-stable isotope probing

    Aurélie Cébron
    Abstract A considerable amount of methane produced during decomposition of landfill waste can be oxidized in landfill cover soil by methane-oxidizing bacteria (methanotrophs) thus reducing greenhouse gas emissions to the atmosphere. The identity of active methanotrophs in Roscommon landfill cover soil, a slightly acidic peat soil, was assessed by DNA-stable isotope probing (SIP). Landfill cover soil slurries were incubated with 13C-labelled methane and under either nutrient-rich nitrate mineral salt medium or water. The identity of active methanotrophs was revealed by analysis of 13C-labelled DNA fractions. The diversity of functional genes (pmoA and mmoX) and 16S rRNA genes was analyzed using clone libraries, microarrays and denaturing gradient gel electrophoresis. 16S rRNA gene analysis revealed that the cover soil was mainly dominated by Type II methanotrophs closely related to the genera Methylocella and Methylocapsa and to Methylocystis species. These results were supported by analysis of mmoX genes in 13C-DNA. Analysis of pmoA gene diversity indicated that a significant proportion of active bacteria were also closely related to the Type I methanotrophs, Methylobacter and Methylomonas species. Environmental conditions in the slightly acidic peat soil from Roscommon landfill cover allow establishment of both Type I and Type II methanotrophs. [source]

    Environmental effects on recruitment and productivity of Japanese sardine Sardinops melanostictus and chub mackerel Scomber japonicus with recommendations for management

    Abstract We compared a wide range of environmental data with measures of recruitment and stock production for Japanese sardine Sardinops melanostictus and chub mackerel Scomber japonicus to examine factors potentially responsible for fishery regimes (periods of high or low recruitment and productivity). Environmental factors fall into two groups based on principal component analyses. The first principal component group was determined by the Pacific Decadal Oscillation Index and was dominated by variables associated with the Southern Oscillation Index and Kuroshio Sverdrup transport. The second was led by the Arctic Oscillation and dominated by variables associated with Kuroshio geostrophic transport. Instantaneous surplus production rates (ISPR) and log recruitment residuals (LNRR) changed within several years of environmental regime shifts and then stabilized due, we hypothesize, to rapid changes in carrying capacity and relaxation of density dependent effects. Like ISPR, LNRR appears more useful than fluctuation in commercial catch data for identifying the onset of fishery regime shifts. The extended Ricker models indicate spawning stock biomass and sea surface temperatures (SST) affect recruitment of sardine while spawning stock biomass, SST and sardine biomass affect recruitment of chub mackerel. Environmental conditions were favorable for sardine during 1969,87 and unfavorable during 1951,67 and after 1988. There were apparent shifts from favorable to unfavorable conditions for chub mackerel during 1976,77 and 1985,88, and from unfavorable to favorable during 1969,70 and 1988,92. Environmental effects on recruitment and surplus production are important but fishing effects are also influential. For example, chub mackerel may have shifted into a new favorable fishery regime in 1992 if fishing mortality had been lower. We suggest that managers consider to shift fishing effort in response to the changing stock productivity, and protect strong year classes by which we may detect new favorable regimes. [source]

    Tracing energy flow in stream food webs using stable isotopes of hydrogen

    FRESHWATER BIOLOGY, Issue 5 2010
    Summary 1. Use of the natural ratios of carbon and nitrogen stable isotopes as tracers of trophic interactions has some clear advantages over alternative methods for food web analyses, yet is limited to situations where organic materials of interest have adequate isotopic separation between potential sources. This constrains the use of natural abundance stable isotope approaches to a subset of ecosystems with biogeochemical conditions favourable to source separation. 2. Recent studies suggest that stable hydrogen isotopes (,D) could provide a robust tracer to distinguish contributions of aquatic and terrestrial production in food webs, but variation in ,D of consumers and their organic food sources are poorly known. To explore the utility of the stable hydrogen isotope approach, we examined variation in ,D in stream food webs in a forested catchment where variation in ,13C has been described previously. 3. Although algal ,D varied by taxa and, to a small degree, between sites, we found consistent and clear separation (by an average of 67,) from terrestrial carbon sources. Environmental conditions known to affect algal ,13C, such as water velocity and stream productivity did not greatly influence algal ,D, and there was no evidence of seasonal variation. In contrast, algal ,13C was strongly affected by environmental factors both within and across sites, was seasonally variable at all sites, and partially overlapped with terrestrial ,13C in all streams with catchment areas larger than 10 km2. 4. While knowledge of isotopic exchange with water and trophic fractionation of ,D for aquatic consumers is limited, consistent source separation in streams suggests that ,D may provide a complementary food web tracer to ,13C in aquatic food webs. Lack of significant seasonal or spatial variation in ,D is a distinct advantage over ,13C for applications in many aquatic ecosystems. [source]


    Susy Svatek Ziegler
    ABSTRACT. Landscape diversity has increased with the surprising postfire establishment of aspen at upper elevations (700,945 meters above sea level) in the High Peaks of Adirondack Park in upstate New York. Tree seedlings returned quickly to the charred slopes west of Noonmark Mountain after an accidental fire consumed the forest in 1999. Aspen stands have replaced the spruce-fir-birch forests in the burned area even though mountain paper birch is expected to colonize burned sites at these elevations. Environmental conditions, historical events, and unique circumstances help explain why quaking aspen and bigtooth aspen rather than paper birch blanket the burned mountainside. Climate change over the past century to warmer, wetter conditions may have fostered this marked shift in species composition. In the unburned firebreak that people cleared to contain the flames, pin cherry has regenerated from seeds stored in the soil for nearly a century. The history of pin cherry on the site suggests that large fires or severe windthrow may have been more common in the region than was previously documented. [source]

    Environmental factors during seed development of narrow-leaved bird's-foot-trefoil (Lotus tenuis) influences subsequent dormancy and germination

    GRASS & FORAGE SCIENCE, Issue 4 2003
    A. A. Clua
    Abstract Narrow-leaved bird's-foot-trefoil (Lotus tenuis) is a perennial forage legume adapted to waterlogged and heavy and infertile soils and can replace alfalfa (Medicago sativa) in areas with these soils in Argentina. Its seeds are hard and water-impermeable but the effects of environmental factors on seed dormancy and germination are not known. The objective was to evaluate the hypothesis that water availability during seed development and maturation affects the degree of hardseededness in L. tenuis by changing seed coat properties, conditioning water uptake through the seed coat; and subsequently affecting dormancy, germination and speed of germination. Seeds were harvested in December/January and in February in both 1993/1994 and 1994/1995 from a permanent pasture of L. tenuis growing in a Hapludol soil in San Miguel del Monte province of Buenos Aires. Environmental conditions of each anthesis-harvest period were determined. Seeds of each harvest were subjected to chilling, washing and mechanical scarification. After 12 months seeds from each harvest were observed in a scanning electron microscope. The water deficit of the soil and relative humidity were greater in the second than the first anthesis-harvest period in both seasons. In 1993/1994 the control treatment in December had a higher germination rate than the February control seeds (0·40 vs. 0·20) and a faster germination rate. Mechanical scarification and chilling significantly enhanced the germination rate (0·95) and its speed in seeds of both harvests. Low temperatures significantly enhanced germination rate, starting after 60 d for the seeds harvested in December, and 90 d for the seeds harvested in February. In 1994/1995 the results were similar but both the January and February control treatments had higher germination rates (0·60 vs. 0·40) than in the previous year. Seeds harvested in February were more dormant in both years. These differences could be explained by the conditions in February anthesis-harvest period in both years that could have hastened the natural dehydration process of seed, changing integument structure and enhancing its impermeability. [source]

    Environmental conditions impinge on dragline silk protein composition

    K.-H. Guehrs
    Abstract The silk formed in the major ampullate (MA) gland of the orb weaving spider Nephila clavipes is composed of two silk fibroins, which are called major ampullate spidroins 1 (MaSp1) and 2 (MaSp2). Analysis of proteolytic peptides and reactivity to spidroin type specific antibodies indicated that MaSp2 constituted only a minor part in the spinning dope as well as in the spun filaments. Upon starvation, a change in the silk's characteristic features was observed that was concomitant of a decrease in the contribution of MaSp2. The silk became less elastic and stiffer, which will better tailor its usability for the safety line, albeit at the expense of its employment as the web frame threads. In addition, since MaSp2 production requires greater ATP consumption, such a shift in the protein ratio cuts down on the energy costs to produce the silk. From this change in protein composition the spider might therefore benefit twice, by synthesizing ,cheaper' silk that into the bargain has properties that potentially can better support foraging in times of food shortage. [source]

    Environmental conditions in relation to stress in cherry tomato fruits in two experimental Mediterranean greenhouses

    Miguel A Rosales
    Abstract BACKGROUND: Considering the economic importance of tomato and its nutritional benefits to human health, a study was conducted on how different environmental factors (temperature, solar radiation and vapour pressure deficit (VPD)) influence hydrogen peroxide detoxification and several stress indicators in cherry tomato (Solanum lycopersicum cv. Naomi) fruits grown in two experimental Mediterranean greenhouses of parral (low-technology) type and multispan (high-technology) type. RESULTS: Three fruit samplings were made at the beginning, middle and end of the fruit production period. Values of temperature, solar radiation and VPD peaked at the third sampling in both greenhouses, being higher in the parral-type greenhouse, while there was a reduction in market production at the third sampling. Peroxidation (malondialdehyde content and lipoxygenase activity) increased significantly at the third sampling, indicating the presence of oxidative stress caused by the rise in temperature, solar radiation and VPD. The ascorbate content, the activities of superoxide dismutase, catalase and ascorbate peroxidase and other stress indicators (proline and sucrose degradation) also increased at the third sampling. CONCLUSION: This study showed that conditions of higher environmental stress occurred at the third sampling and in the parral-type greenhouse, leading to the accumulation of ascorbic acid in cherry tomato fruits and therefore to higher nutritional quality. Copyright © 2009 Society of Chemical Industry [source]

    Epicutaneous aeroallergen sensitization in atopic dermatitis infants , determining the role of epidermal barrier impairment

    ALLERGY, Issue 2 2008
    F. Boralevi
    Background:, Sensitization to atopens is an early phenomenon that overlaps with the onset of atopic dermatitis (AD) in infancy. Early epidermal barrier impairment may facilitate the epicutaneous penetration of atopens. Objective:, To correlate transepidermal water loss (TEWL) and aeroallergen sensitization in infants with AD. Methods:, In this cross-sectional study we enrolled 59 AD children and 30 controls aged 3,12 months. Transepidermal water loss in uninvolved skin, specific immunoglobulin E, atopy patch test (APT) and skin prick tests were performed with respect to seven aeroallergens, i.e., Dermatophagoides pteronyssinus, D. farinae, cat, dog, birch pollen, ambrosia, and cockroach. Environmental conditions were assessed by a questionnaire, and the house dust mite (HDM) concentration was determined in dust samples. Results:, Eighty-nine percent of AD infants had a positive APT vs one out of eleven controls. AD infants had a significantly higher mean TEWL than controls (27.4 vs 11.1 g/m2/h, P < 0001). Children with two or more positive APT had higher TEWL than the others (31.1 vs 19.0 g/m2/h, P < 0.025). No correlation was found between indoor APT results and exposure to HDM, cats, and dogs at home. Conclusions:, This study confirms the high prevalence of delayed sensitization to indoor and outdoor aeroallergens in AD infants, and shows that the higher the TEWL, the higher the prevalence of sensitization to aeroallergens. These data are in favor of a major role of a constitutive epidermal barrier impairment in determining early atopen sensitization in infants with AD. [source]

    Environmental conditions influencing Sclerotinia sclerotiorum infection and disease development in lettuce

    PLANT PATHOLOGY, Issue 4 2004
    C. S. Young
    The environmental factors that influence infection of lettuce by ascospores of Sclerotinia sclerotiorum, and subsequent disease development, were investigated in controlled environment and field conditions. When lettuce plants were inoculated with a suspension of ascospores in water or with dry ascospores and exposed to a range of wetness durations or relative humidities at different temperatures, all plants developed disease but there was no relationship between leaf wetness duration or humidity and percentage of diseased plants. Ascospores started to germinate on lettuce leaves after 2,4 h of continuous leaf wetness at optimum temperatures of 15,25°C. The rate of development of sclerotinia disease and the final percentage of plants affected after 50 days were greatest at 16,27°C, with disease symptoms first observed 7,9 days after inoculation, and maximum final disease levels of 96%. At lower temperatures, 8,11°C, disease was first observed 20,26 days after inoculation, with maximum final disease levels of 10%. Disease symptoms were always observed first at the stem base. In field-grown lettuce in Norfolk, 2000 and 2001, inoculated with ascospore suspensions, disease occurred only in lettuce planted in May and June, with a range of 20,49% of plants with disease by 8 weeks after inoculation. In naturally infected field-grown lettuce in Cheshire, 2000, disease occurred mainly in lettuce planted throughout May, with a maximum of 31% lettuce diseased within one planting, but subsequent plantings had little (, 4%) or no disease. Lack of disease in the later plantings in both Norfolk and Cheshire could not be attributed to differences in weather factors. [source]

    Floral color patterns in a tropical orchid: Are they associated with reproductive success?

    Abstract We sought to measure phenotypic selection on petal color variation in populations of Lepanthes rupestris, a diminutive epilithic orchid of Puerto Rico that exhibits a polymorphism in petal color patterns (unicolor or bicolored). We censused seven populations monthly for 20 months and noted flower production and petal color pattern. Each flower was checked for pollinarium removal (male fitness measure) and fruit production (female fitness). In all populations, plants with bicolored petals dominated and comprised 63,82% of individuals. Aside from petal color differences, the two types were indistinguishable. Flower color pattern was generally not associated with either male or female reproductive success within or among populations or over time. Environmental conditions, rainfall and humidity, may account for both temporal and spatial variation in the reproductive success observed among sites. Although we were unable to tag fitness to petal color patterns, the consistent ratio of color morphs among populations suggests that factors other than just drift are responsible for the frequencies we observed. [source]

    Effect of abiotic factors on the foraging strategy of the orb-web spider Argiope keyserlingi (Araneae: Araneidae)

    AUSTRAL ECOLOGY, Issue 6 2003
    M. E. Herberstein
    Abstract Environmental conditions such as light level, background contrast and temperature might influence a spider's prey capture success and risk of predation. Thus it may often be advantageous for spiders to adjust web-building behaviour in response to variation in these environmental conditions. This hypothesis was examined in a study of the construction of webs and web decorations (conspicuous strands of silk at the hub of the web) of the orb-web spider Argiope keyserlingi. Web decorations are thought to have one or more separate functions. They may attract prey, deter predators or advertise the web to oncoming birds, thus preventing web damage. In this series of experiments, relationships between weather parameters and the construction of webs and web decorations were considered. In complementary laboratory experiments, A. keyserlingi spiders were exposed to two different light levels (700 and 90 lx), background contrasts (black and white) and temperature conditions (20 and 26°C). Of the available weather parameters, only temperature was significantly related to web decorating behaviour but not to web size. In the laboratory, temperature also influenced web-decorating behaviour, and spiders in dim light (700 lx) constructed larger webs and longer decorations. Background contrast did not significantly alter web size or web decorations. These data suggest that when prey availability is reduced at low temperatures, spiders may use web decorations to attract prey to the web. Similarly, in dim light, spiders may build more and larger decorations to increase the visual signal to approaching prey or to advertise the web to oncoming birds. [source]

    Species richness,environment relationships within coastal sclerophyll and mesophyll vegetation in Ku-ring-gai Chase National Park, New South Wales, Australia

    AUSTRAL ECOLOGY, Issue 4 2003
    Andrew F. Le Brocque
    Abstract Patterns in species richness from a wide range of plant communities in Ku-ring-gai Chase National Park, New South Wales, Australia, were examined in relation to a number of environmental variables, including soil physical and chemical characteristics. Total species richness and richness of three growth-form types (trees, shrubs and ground cover) were determined in duplicate 500-m2 quadrats from 50 sites on two geological substrata: Hawkesbury Sandstone and Narrabeen shales and sandstones. Generalized linear models (GLM) were used to determine the amount of variation in species richness that could be significantly explained by the measured environmental variables. Seventy-three per cent of the variation in total species richness was explained by a combination of soil physical and chemical variables and site attributes. The environmental variables explained 24% of the variation in tree species richness, 67% of the variation in shrub species richness and 62% of the variation in ground cover species richness. These results generally support the hypothesis of an environmental influence on patterns in total species richness and richness of shrubs and ground cover species. However, tree species richness was not adequately predicted by any of the measured environmental variables; the present environment exerts little influence on the richness of this growth-form type. Historical factors, such as fire or climatic/environmental conditions at time of germination or seedling establishment, may be important in determining patterns in tree species richness at the local scale. [source]

    Behaviourally structured populations persist longer under harsh environmental conditions

    ECOLOGY LETTERS, Issue 5 2003
    Sergei V. Petrovskii
    Abstract The factors and mechanisms that enhance population persistence in a fragmented habitat and/or under harsh environmental conditions are of significant current interest. We consider the dynamics of a population in an isolated habitat surrounded by an unfavourable environment subject to different behavioural responses between the individuals. We assume that there are two responses available: one of them is aggression in its extreme form, the other is its contrary when an individual takes flight in order to avoid any contact with its conspecific. We show that a behaviourally structured population consisting of individuals with fixed behavioural responses is intrinsically less prone to extinction under harsh environmental condition than a population where the individuals can ,choose' between the two given behaviours. We also show that, contrary to an intuitively expected negative impact of aggression on population persistence, the optimal conditions for population persistence are reached when a considerable proportion of the individuals exhibit aggressive behaviour. [source]

    Assessment of methane and nitrous oxide flux from mangroves along Eastern coast of India

    GEOFLUIDS (ELECTRONIC), Issue 4 2008
    Abstract Mangroves are considered to be a minor source of greenhouse gases (CH4 and N2O) in pristine environmental condition. However, estimates of efflux suggest that anthropogenic activities have led to a pronounced increase in greenhouse gas emission. Along the east coast of India, mangroves vary substantially in area, physiography and freshwater input, which ultimately modify the biogeochemical processes operating within this ecosystem. An attempt has here been made to elucidate the existing variation and role of climatic variability on the emission of greenhouse gases from mangroves. The flux estimates of CH4 and N2O have been quantified from Bhitarkanika mangrove accounting for spatial and temporal (seasonal) variation. The annual rates were estimated to be 0.096 × 10 9 g CH4 year,1 and 5.8 × 103g N2O year,1 for the whole mangrove area of the east coast of India. Upscaling these estimates yield an annual emission of 1.95 × 10 12 g CH4 year,1 and 1.1 × 10 11 g N2O year,1 from worldwide mangrove areas. The influence of elevated nutrient inputs through anthropogenic influence enhances the emission of greenhouse gas. The present article shows the need to develop an inventory on greenhouse gas flux from mangrove ecosystem. [source]

    How to overcome (and exploit) tumor hypoxia for targeted gene therapy

    Olga Greco
    Tumor hypoxia has long been recognized as a critical issue in oncology. Resistance of hypoxic areas has been shown to affect treatment outcome after radiation, chemotherapy, and surgery in a number of tumor sites. Two main strategies to overcome tumor hypoxia are to increase the delivery of oxygen (or oxygen-mimetic drugs), and exploiting this unique environmental condition of solid tumors for targeted therapy. The first strategy includes hyperbaric oxygen breathing, the administration of carbogen and nicotinamide, and the delivery of chemical radiosensitizers. In contrast, bioreductive drugs and hypoxia-targeted suicide gene therapy aim at activating cytotoxic agents at the tumor site, while sparing normal tissue from damage. The cellular machinery responds to hypoxia by activating the expression of genes involved in angiogenesis, anaerobic metabolism, vascular permeability, and inflammation. In most cases, transcription is initiated by the binding of the transcription factor hypoxia-inducible factor (HIF) to hypoxia responsive elements (HREs). Hypoxia-targeting for gene therapy has been achieved by utilizing promoters containing HREs, to induce selective and efficient transgene activation at the tumor site. Hypoxia-targeted delivery and prodrug activation may add additional levels of selectivity to the treatment. In this article, the latest developments of cancer gene therapy of the hypoxic environment are discussed, with particular attention to combined protocols with ionizing radiation. Ultimately, it is proposed that by adopting specific transgene activation and molecular amplification systems, resistant hypoxic tumor tissues may be effectively targeted with gene therapy. J. Cell. Physiol. 197: 312,325, 2003© 2003 Wiley-Liss, Inc. [source]

    Diet and social conditions during sexual maturation have unpredictable influences on female life history trade-offs

    E. L. B. BARRETT
    Abstract The trade-off between gametes and soma is central to life history evolution. Oosorption has been proposed as a mechanism by which females can redirect nutrients invested in oocytes into survival when conditions for reproduction are poor. Although positive correlations between oocyte degradation and lifespan have been documented in oviparous insects, the adaptive significance of this process in species with more complex reproductive biology has not been explored. Further, environmental condition is a multivariate state, and combinations of environmental stresses may interact in unpredictable ways. Previous work on the ovoviviparous cockroach, Nauphoeta cinerea, revealed that females manipulated to mate late relative to sexual maturation experience age-related loss in fecundity because of loss of viable oocytes via apoptosis. This loss in fecundity is correlated with a reduction in female mate choice. Food deprivation while mating is delayed further increases levels of oocyte apoptosis, but the relationship between starvation-induced apoptosis and life history are unknown. To investigate this, virgin females were either fed or starved from eclosion until provided with a mate at a time known to be suboptimal for fertility. Following mating, females were fed for the duration of their lifespan. We measured lifetime reproductive performance. Contrary to predictions, under conditions of delayed mating opportunity, starved females had greater fecundity, gave birth to more high-quality offspring and had increased longevity compared with that of fed females. We suggest that understanding proximal mechanisms underlying life history trade-offs, including the function of oocyte apoptosis, and how these mechanisms respond to varied environmental conditions is critical. [source]

    Changes in Plasma Cortisol, Glucose, and Selected Blood Properties in the Summer Flounder Paralichthys dentatus Associated with Sequential Movement to Three Experimental Conditions

    James A. Sulikowski
    To determine the changes in blood chemistry associated with sequential transfer of summer flounder Paralichthys dentatus (320,480 g), 300 hatchery-reared fish were moved to three different environmental conditions during a 20-d period. Fish were transferred in progression from a recirculating seawater system (22 ppt, 22.5 C) to a flow-thru seawater system (31 ppt, 20.0 C), to three small coastal net pens (33 ppt, 15.5 C), and finally to a large open ocean net pen (33 ppt, 16.0 C). For this study, eight random fish were captured at each progressive step (environmental condition), anesthetized (MS222), and bled from the caudal vein (2 mL). Transferred flounder were bled every 12 h for 48 h to collect plasma cortisol and glucose samples. Fish were bled 24 h after transport and every 3 d thereafter for osmolarity, hematocrit, hemoglobin concentration, mean corpuscular hemoglobin content, glucose, cortisol, and the electrolytes Cl - Na+, K+ and Ca+. The most significant perturbations to blood chemistry (P < 0.05) occurred within 24 h of initial transfer from the recirculating to flow-thru seawater systems, suggesting an osmoregulatory rather than handling or transfer related stress. Osmolarity, electrolyte, and hematological parameters fluctuated and then recovered to stable levels by day 8 in the flow-thru seawater system. However, unlike the initial transfer, successive movement to the coastal and then the open ocean net pens produced transient increases in both plasma cortisol and glucose levels, suggesting a high level of stress associated with extended flounder handling and transfer. [source]

    Mechanical and Chemical Analysis of Gelatin-Based Hydrogel Degradation

    Gabriel J. Martínez-Díaz
    Abstract The interrelated effect of environmental pH and temperature, gelatin backbone modification and content on the tensile and degradative property of interpenetrating networks (IPNs) containing gelatin and poly(ethylene glycol) diacrylate (PEGdA) was examined. Either increasing the PEGdA content or modifying the gelatin backbone with PEG-monoacetate ester and/or polyanions decreased the IPN elasticity at ambient room temperature (rt). Under an aqueous environment of varying pH levels and elevated temperature, the degradation of IPN tensile properties was further accelerated. IPNs showed an enhanced elasticity and strength when compared to glutaraldehyde-fixed gelatin hydrogels. Under an aqueous condition, IPNs showed a wider range of degradation products than hydrogels cross-linked with glutaraldehyde, as characterized with gel permeation chromatography. The nature of IPN degradation products was independent of the type of gelatin backbone modification. The presence of loaded drug, chlorohexidine digluconate, which was found to interact with PEG-monoacetate esters of the modified gelatin backbone, resulted in unique degradation products. The tensile and chemical degradation of IPNs is a complex interrelationship of the environmental condition, time, and material modification. Stress-strain curves of some IPNs studied here. [source]

    Stage, age and individual stochasticity in demography

    OIKOS, Issue 12 2009
    Hal Caswell
    Demography is the study of the population consequences of the fates of individuals. Individuals are differentiated on the basis of age or, in general, life cycle stages. The movement of an individual through its life cycle is a random process, and although the eventual destination (death) is certain, the pathways taken to that destination are stochastic and will differ even between identical individuals; this is individual stochasticity. A stage-classified demographic model contains implicit age-specific information, which can be analyzed using Markov chain methods. The living stages in the life cycles are transient states in an absorbing Markov chain; death is an absorbing state. This paper presents Markov chain methods for computing the mean and variance of the lifetime number of visits to any transient state, the mean and variance of longevity, the net reproductive rate R0, and the cohort generation time. It presents the matrix calculus methods needed to calculate the sensitivity and elasticity of all these indices to any life history parameters. These sensitivities have many uses, including calculation of selection gradients. It is shown that the use of R0 as a measure of fitness or an invasion exponent gives erroneous results except when R0=,=1. The Markov chain approach is then generalized to variable environments (deterministic environmental sequences, periodic environments, iid random environments, Markovian environments). Variable environments are analyzed using the vec-permutation method to create a model that classifies individuals jointly by the stage and environmental condition. Throughout, examples are presented using the North Atlantic right whale (Eubaleana glacialis) and an endangered prairie plant (Lomatium bradshawii) in a stochastic fire environment. [source]

    X-ray atomic orbital analysis.


    The scattering unit of X-ray crystal structure analysis is changed from atoms to the subshell electrons by X-ray atomic orbital analysis (XAO). All the atoms in the unit cell are divided into groups of subshell electrons in the XAO analysis. Each subshell is treated as an independent pseudo-atom, which enables the atomic orbitals (AO's) and the electron population of each AO expressed as a linear combination of s/p/d/f orbitals in each subshell to be determined. When the environmental condition of the sample is varied, the electron transfer among the AO's in the crystal can be traced with XAO. It is applicable mainly to analyses of the electron-density distribution in ionic solids including those with a nonstoichiometric structure. The expansion coefficients of each AO are calculated with the perturbation theory putting a point charge on each atom in the unit cell. This automatically makes the perturbation potential have the point-group symmetry of the atom in the crystal field. Then the coefficients of each AO are refined to fit to the observed structure factors keeping the orthonormal relationships among the AO's. Complex basis functions with , or , spin as well as real ones are employed for heavy atoms and the relationships among the coefficients for the AO's of an electron in the crystal fields of the 32 point-group symmetries are derived for p, d and f orbitals. The AO's thus derived can be applicable to an anti-symmetrized multi-electron system, although X-ray diffraction cannot specify the atomic terms occupied when the crystal symmetry permits the atom to have many terms. [source]