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91.
Keith D. Morrison Jennifer C. Underwood David W. Metge Dennis D. Eberl Lynda B. Williams 《Environmental geochemistry and health》2014,36(4):613-631
As antibiotic-resistant bacterial strains emerge and pose increased global health risks, new antibacterial agents are needed as alternatives to conventional antimicrobials. Naturally occurring antibacterial clays have been identified which are effective in killing antibiotic-resistant bacteria. This study examines a hydrothermally formed antibacterial clay deposit near Crater Lake, OR (USA). Our hypothesis is that antibacterial clays buffer pH and Eh conditions to dissolve unstable mineral phases containing transition metals (primarily Fe2+), while smectite interlayers serve as reservoirs for time release of bactericidal components. Model pathogens (Escherichia coli ATCC 25922 and Staphylococcus epidermidis ATCC 14990) were incubated with clays from different alteration zones of the hydrothermal deposit. In vitro antibacterial susceptibility testing showed that reduced mineral zones were bactericidal, while more oxidized zones had variable antibacterial effect. TEM images showed no indication of cell lysis. Cytoplasmic condensation and cell wall accumulations of <100 nm particles were seen within both bacterial populations. Electron energy loss analysis indicates precipitation of intracellular Fe3+-oxide nanoparticles (<10 nm) in E. coli after 24 h. Clay minerals and pyrite buffer aqueous solutions to pH 2.5–3.1, Eh > 630 mV and contain elevated level (mM) of soluble Fe (Fe2+ and Fe3+) and Al3+. Our interpretation is that rapid uptake of Fe2+ impairs bacterial metabolism by flooding the cell with excess Fe2+ and overwhelming iron storage proteins. As the intracellular Fe2+ oxidizes, it produces reactive oxygen species that damage biomolecules and precipitates Fe-oxides. The ability of antibacterial clays to buffer pH and Eh in chronic non-healing wounds to conditions of healthy skin appears key to their healing potential and viability as an alternative to conventional antibiotics. 相似文献
92.
Maud Bonato Matthew R. Evans Dennis Hasselquist Richard B. Sherley Schalk W. P. Cloete Michael I. Cherry 《Behavioral ecology and sociobiology》2013,67(12):1891-1901
One of the most important measures of offspring performance is growth rate, which is often traded off against another important survival trait, immune function. A particular feature of ostrich chicks maintained in farmed environments is that cohorts of chicks vary widely in size. As parents can have a profound effect on the phenotype and fitness of their offspring, we investigated whether chick growth and immune defence were related to variation in levels of immune defence in their genetic parents. As secondary sexual traits of sires could serve as indicators of male quality, and be used in female mating decisions, we also investigated whether chick growth rate and immune defence were related to male plumage and integumentary colouration. We found that offspring growth rates and humoral responses were related to the humoral responses of their parents, suggesting that at least some components of humoral immune capacity are heritable. The white colour of male ostrich feathers was correlated to the humoral response and growth rate of their offspring, suggesting that this visual cue involved in the male courtship display could serve as an important signal to females of male quality, thereby forming the basis of mate choice in this species. 相似文献
93.
Dennis Kalisch 《Journal of Coastal Conservation》2012,16(4):531-541
Coastal environments are popular sites for tourism and faced with an increasing recreational demand. Most of European coastal areas attract numerous visitors annually. In recreation research this management problem can be described in terms of carrying capacity which expresses the ability of a site or region to absorb recreational use without deterioration of natural resources and the quality of the visitor experience. As social aspects of recreation in Europe still have received little attention, the purpose of this study is to examine the applicability of the concept of social carrying capacity in a German coastal national park. The article addresses if the relationship between perceived visitor encounters, crowding perception and visitor characteristics is applicable by using data from an on-site survey (N?=?509) of visitors conducted on Hamburger Hallig, Germany. It examines whether effects of overcrowding are measurable on a popular daytrip destination with established approaches. Results demonstrate that visitors to Hamburger Hallig are characterised by a heterogeneous visitor composition of local residents and domestic tourists with different motivations and who mainly visited the area for hiking or cycling. Study findings show that valuation for reported encounters and perceived crowding differed substantially among origin of visitors and sampling dates. All in all, respondents report a high level of encounter with others and in contrast a very low level of perceived crowding. 相似文献
94.
Michael Tobler Dennis Hasselquist Henrik G. Smith Maria I. Sandell 《Behavioral ecology and sociobiology》2010,64(5):717-727
Hormone-mediated maternal effects play an important role in the formation of a differentiated phenotype. They have been shown
to influence a wide array of offspring traits, both early in life and in adulthood. One important offspring trait that is
under the influence of maternal androgens is the immune system. In birds, a growing number of studies show that yolk androgens
modulate immune function during the chick stage. However, there is a lack of knowledge regarding long-term effects of prenatal
androgens on offspring immunity. In this study, we therefore investigated the influence of prenatal testosterone (T) on several
measures of immunity in fledgling and adult zebra finches (Taeniopygia guttata). Cell-mediated immune response (towards phytohaemagglutinin, PHA) of fledglings hatching from control eggs was negatively
related to brood size, whereas there was no such association for fledglings hatching from eggs with experimentally elevated
T levels (T fledglings). Male control fledglings showed reduced mass gain compared to female control fledglings within 24 h
after the PHA injection. This pattern was reversed in T fledglings. Total antibody levels in fledglings were not affected
by egg treatment. Neither cell-mediated immunity nor total antibody levels in sexually mature zebra finches were influenced
by egg treatment. However, there was an immuno-enhancing effect of elevated egg T on both primary and secondary humoral immune
responses toward diphtheria and tetanus antigens in ca 5 and 7 month old zebra finches. In addition, the covariation between
different immune components differed between T and control offspring, suggesting that egg treatment may have altered the potential
trade-offs between different parts of the immune system. Our results suggest that prenatal androgens could be an important
factor contributing to individual variation in immune function even in adulthood. 相似文献
95.
Numerical study on the ozone formation inside street canyons using a
chemistry box model 总被引:1,自引:1,他引:0
Tropospheric ozone is a secondary air pollutant produced in the presence of nitrogen oxides (NO_x),volatile organic compounds (VOCs),and solar radiation.In an urban environment,ground-level vehicular exhaust is the major anthropogenic source of ozone precursors.In the cases of street canyons,pollutant dilution is weakened by the surrounding buildings that creates localized high concentration of NO_x and VOCs,and thus leads to high potential of ozone formation.By considering the major physical and chemica... 相似文献
96.
Denys Yemshanov Daniel W. McKenney Peter de Groot Dennis Haugen John Pedlar Derek Sidders Brent Joss 《Journal of environmental management》2011
We present the idea of using potential infringements on annual allowable harvest targets as an approach to estimate threats from invasive species to the forest products sector. The approach uses present-day harvest levels as a reference level to estimate when and where the impact of a nonnative forest pest could become economically damaging. We use a generic model that simulates spread and damage by nonnative invasive species, basic harvest and forest growth through time. The concept is illustrated with a case study of a new nonnative invasive pest, Sirex noctilio Fabricius on pine resources in eastern Canada. Impacts of invasion on wood supply, in particular, the point at which present-day harvest levels are not attainable, were identified for 77 non-overlapping geographical regions that delimit the primary wood supply areas around large mills and wood processing facilities in eastern Canada. The results identify the minimum area of a pest outbreak that could trigger harvest shortages (approximately 12.5–14 M ha of pine forests in Ontario and Quebec). Beyond this level, the amount of host resource available for harvesting in any given year declines rapidly. The failure to sustain broad-scale harvest targets may be an attractive and intuitive indicator for policy makers and regulators interested in developing control and “slow-the-spread” programs for non-native forest pests. 相似文献
97.
In multiply invaded ecosystems, introduced species should interact with each other as well as with native species. Invader-invader interactions may affect the success of further invaders by altering attributes of recipient communities and propagule pressure. The invasional meltdown hypothesis (IMH) posits that positive interactions among invaders initiate positive population-level feedback that intensifies impacts and promotes secondary invasions. IMH remains controversial: few studies show feedback between invaders that amplifies their effects, and none yet demonstrate facilitation of entry and spread of secondary invaders. Our results show that supercolonies of an alien ant, promoted by mutualism with introduced honeydew-secreting scale insects, permitted invasion by an exotic land snail on Christmas Island, Indian Ocean. Modeling of land snail spread over 750 sites across 135 km2 over seven years showed that the probability of land snail invasion was facilitated 253-fold in ant supercolonies but impeded in intact forest where predaceous native land crabs remained abundant. Land snail occurrence at neighboring sites, a measure of propagule pressure, also promoted land snail spread. Site comparisons and experiments revealed that ant supercolonies, by killing land crabs but not land snails, disrupted biotic resistance and provided enemy-free space. Predation pressure on land snails was lower (28.6%), survival 115 times longer, and abundance 20-fold greater in supercolonies than in intact forest. Whole-ecosystem suppression of supercolonies reversed the probability of land snail invasion by allowing recolonization of land crabs; land snails were much less likely (0.79%) to invade sites where supercolonies were suppressed than where they remained intact. Our results provide strong empirical evidence for IMH by demonstrating that mutualism between invaders reconfigures key interactions in the recipient community. This facilitates entry of secondary invaders and elevates propagule pressure, propagating their spread at the whole-ecosystem level. We show that identification and management of key facilitative interactions in invaded ecosystems can be used to reverse impacts and restore resistance to further invasions. 相似文献
98.
David F. Staples Mark L. Taper Brian Dennis Robert J. Boik 《Environmental and Ecological Statistics》2009,16(4):547-560
Estimates of a population’s growth rate and process variance from time-series data are often used to calculate risk metrics
such as the probability of quasi-extinction, but temporal correlations in the data from sampling error, intrinsic population
factors, or environmental conditions can bias process variance estimators and detrimentally affect risk predictions. It has
been claimed (McNamara and Harding, Ecol Lett 7:16–20, 2004) that estimates of the long-term variance that incorporate observed
temporal correlations in population growth are unaffected by sampling error; however, no estimation procedures were proposed
for time-series data. We develop a suite of such long-term variance estimators, and use simulated data with temporally autocorrelated
population growth and sampling error to evaluate their performance. In some cases, we get nearly unbiased long-term variance
estimates despite ignoring sampling error, but the utility of these estimators is questionable because of large estimation
uncertainty and difficulties in estimating correlation structure in practice. Process variance estimators that ignored temporal
correlations generally gave more precise estimates of the variability in population growth and of the probability of quasi-extinction.
We also found that the estimation of probability of quasi-extinction was greatly improved when quasi-extinction thresholds
were set relatively close to population levels. Because of precision concerns, we recommend using simple models for risk estimates
despite potential biases, and limiting inference to quantifying relative risk; e.g., changes in risk over time for a single
population or comparative risk among populations. 相似文献
99.
100.
Optimal biomass allocation in heterogeneous environments in a clonal plant—Spatial division of labor
When interconnected ramets of clonal plants are growing in heterogeneous environments, ramets may specialize to uptake locally abundant resources rather than scarce resources. This biomass allocation pattern may result in more efficient sharing of resources through physiological integration and an overall benefit to the plants (spatial division of labor; DoL). 相似文献