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121.
This study compares demographic parameters and population dynamics for high disturbance (maquis) and low disturbance (rain forest) environments of the montane conifer, Araucaria laubenfelsii, in New Caledonia. The establishment, growth, survival and reproduction of ca 2500 individuals were followed in permanent plots over 10 yr. Growth and survival rates for A. laubenfelsii show that it is a long-lived, slow growing tree, with evidence of suppression in the sapling size classes in mature rain forest. Growth rates for all size classes are generally faster in maquis than rain forest. Transition matrix analyses estimated positive rates of population increase (λ values>1), with populations expanding in maquis, and stable in mature forest. Araucaria laubenfelsii is able to regenerate continuously in maquis and early successional rain forest, but recruitment is limited in older stands. Life table response experiment analyses showed that reproduction, and transitions from sapling to mature tree stage, contributed positively to λ in maquis, but negatively in forest. Araucaria laubenfelsii on Mont Do can be considered a long-lived pioneer, with early maquis colonizers helping to drive succession from maquis to forest. While opportunities for recruitment decline with time as rain forest sites develop a closed canopy, occasional gap phase recruitment, combined with disturbance by cyclones, landslides and fire, provide opportunities to ensure species persistence. Understanding contrasting population dynamics of A. laubenfelsii in maquis and rain forest will better facilitate conservation management of this species, particularly given current high rates of land conversion and degradation in New Caledonia. Abstract in French is available at http://www.blackwell-synergy.com/loi/btp 相似文献
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123.
It is hypothesized that perennial freshwater tidal wetland habitat exports inorganic and organic material needed to support
the estuarine food web and to create favorable habitat for aquatic organisms in San Francisco Estuary. It is also hypothesized
that most of the material flux in this river-dominated region is controlled by river flow. The production and export of material
by Liberty Island were measured and compared using discrete monthly and continuous (15 min) measurements of a suite of inorganic
and organic materials and flow between 2004 and 2005. Seasonal material flux was estimated from monthly discrete data for
inorganic nutrients, suspended solids and salts, organic carbon and nitrogen and phytoplankton and zooplankton group carbon
and chlorophyll a and pheophytin pigment. Estimates of material flux from monthly values were compared with measured daily material flux values
for chlorophyll a concentration, salt and suspended solids obtained from continuous measurements (15 min) using YSI water quality sondes. Phytoplankton
carbon produced within the wetland was estimated by in situ primary productivity. Most inorganic and organic materials were
exported from the wetland on an annual basis, but the magnitude and direction varied seasonally. Dissolved inorganic nutrients
such as nitrate, soluble phosphorus, total phosphorus and silica as well as total suspended solids were exported in the summer
while total and dissolved organic carbon were exported in the winter. Salts like chloride and bromide were exported in the
fall. Chlorophyll a and pheophytin were exported in the fall and associated with diatom and cyanobacteria carbon. Mesozooplankton carbon was
dominated by calanoid copepods and exported most of the year except summer. Continuous sampling revealed high hourly and daily
variation in chlorophyll a, salt and total suspended solids flux due to high frequency changes in concentration and tidal flow. In fact, tidal flow
rather than river discharge was responsible for 90% or more of the material flux of the wetland. These studies indicate that
freshwater tidal wetlands can be a source of inorganic and organic material but the export of material is highly variable
spatially and temporally, varies most closely with tidal flow and requires high frequency measurements of both tidal flow
and material concentration for accurate estimates. 相似文献
124.
Expression of the antimicrobial peptides in plants to control phytopathogenic bacteria and fungi 总被引:9,自引:0,他引:9
Three antimicrobial peptides exhibiting in vitro antifungal activity were expressed in Arabidopsis to compare their in planta activity. β-Purothionin, cecropin B, and phor21 were expressed under an endogenous promoter with moderate-level activity and excreted extracellularly. Expression of β-purothionin rendered the greatest antibacterial and antifungal resistance while cecropin B enhanced only antibacterial activity and phor21 did not improve antimicrobial resistance. The transgenic β-purothionin arrested fungal growth on leaf surfaces and infection of stomata. Leaf extracts from plants producing β-purothionin and cecropin B displayed membrane permeabilizing activity. The in planta antimicrobial activity of the tested peptides was consistent with previously reported in vitro experiments. The expression strategy allowed enhanced antifungal resistance without high-level transgene expression.Electronic Supplementary Material Supplementary material is available for this article at 相似文献
125.
126.
Spatial genetic variation within species is influenced by both contemporary and historical factors. We attempted to assess the impact of increased aridity and lower temperatures associated with the last glacial maximum on possible refugia and the structuring of genetic variation in Banksia hookeriana, a shrub species restricted to deep sands on the Eneabba sandplain and adjacent Gingin Scarp/Dandaragan Plateau, centred 300 km north of Perth, Western Australia. We used optically stimulated luminescence (OSL) dating to estimate the last time these sands were mobile, as well as amplified fragment length polymorphisms (AFLP) to infer spatial patterns and the phylogeographical history of genetic variation among 15 populations of B. hookeriana. While genetic variation at the species level was high, with 96.6% of 238 AFLP markers polymorphic, average within population gene diversity was low (H(pop) = 0.16). Of the total genetic variation, an analysis of molecular variance (amova) partitioned 70% within populations, 24% among populations within substrate and 6% between substrates. There was an isolation-by-distance effect among populations within the same substrate, but not across substrates, and ordination highlighted genetic differentiation between the sandplain and scarp/plateau populations. A neighbour-joining tree identified the sandplain populations as a distinct clade, with the exception of the most northern sandplain population, which clustered with two northern and eastern plateau populations. The most southern plateau populations formed a clade sister to the sandplain clade. OSL dating of sand at six extant populations suggested that dunes were last mobile 15,000-35,000 years ago, with no clear difference in the ages of sandplain and plateau dunes. These data are consistent with a historical scenario of (re)colonization from isolated refugia of smaller populations either within the patchily vegetated sandplain and/or refugia at the northern, eastern and southern sandplain/scarp margins following postglacial climate amelioration and dune stabilization. Historic interpretations were confounded by the possible effects of long-distance dispersal, natural selection by substrate, and weak and/or ancient introgression with the sister species, Banksia prionotes. 相似文献
127.
Lyndsey O. Hudson Courtney R. Murphy Brian G. Spratt Mark C. Enright Kristen Elkins Christopher Nguyen Leah Terpstra Adrijana Gombosev Diane Kim Paul Hannah Lydia Mikhail Richard Alexander Douglas F. Moore Susan S. Huang 《PloS one》2013,8(4)
There is a need for a regional assessment of the frequency and diversity of MRSA to determine major circulating clones and the extent to which community and healthcare MRSA reservoirs have mixed. We conducted a prospective cohort study of inpatients in Orange County, California, systematically collecting clinical MRSA isolates from 30 hospitals, to assess MRSA diversity and distribution. All isolates were characterized by spa typing, with selective PFGE and MLST to relate spa types with major MRSA clones. We collected 2,246 MRSA isolates from hospital inpatients. This translated to 91/10,000 inpatients with MRSA and an Orange County population estimate of MRSA inpatient clinical cultures of 86/100,000 people. spa type genetic diversity was heterogeneous between hospitals, and relatively high overall (72%). USA300 (t008/ST8), USA100 (t002/ST5) and a previously reported USA100 variant (t242/ST5) were the dominant clones across all Orange County hospitals, representing 83% of isolates. Fifteen hospitals isolated more t008 (USA300) isolates than t002/242 (USA100) isolates, and 12 hospitals isolated more t242 isolates than t002 isolates. The majority of isolates were imported into hospitals. Community-based infection control strategies may still be helpful in stemming the influx of traditionally community-associated strains, particularly USA300, into the healthcare setting. 相似文献
128.
129.
KLARA BJÖRG JAKOBSDÓTTIR þÓRA DÖGG JÖRUNDSDÓTTIR SIGURLAUG SKÍRNISDÓTTIR SIGRÍÐUR HJÖRLEIFSDÓTTIR GUÐMUNDUR Ó. HREGGVIÐSSON ANNA KRISTÍN DANÍELSDÓTTIR CHRISTOPHE PAMPOULIE 《Molecular ecology resources》2006,6(2):337-339
Nine out of 22 microsatellite primers tested were successfully amplified on three samples of cod Gadus morhua L. (two contemporary and one archived otolith samples). All loci were polymorphic (5–23 alleles/locus). The average observed heterozygosity across loci and samples was 0.625, ranging from 0.294 to 0.895 at each locus. All loci were under Hardy–Weinberg equilibrium, except PGmo56 that showed significant excess of heterozygotes in all studied samples. The isolated loci were suitable for degraded DNA and therefore useful for conducting a long‐term temporal study with DNA obtained from archived otoliths of cod. 相似文献
130.
Abstract 1. Body size in parasitic insects can be subjected to contrasting selective pressures, especially if they complete their development within a single host. On the one hand, a larger body size is associated with a higher fitness. On the other hand, the host offers a discrete amount of resources, thus constraining the evolution of a disproportionate body size. 2. The present study used the weevil Curculio elephas as a study model. Larvae develop within a single acorn, feeding on its cotyledons, and larval body size is strongly related to individual fitness. 3. The relationship between larval and acorn size was negatively exponential. Larval growth was constrained in small acorns, which did not provide enough food for the weevils to attain their potential size. Larval size increased and levelled off in acorns over a certain size (inflexion point), in which cotyledons were rarely depleted. When there were more than one larva per acorn, a larger acorn was necessary to avoid food depletion. 4. The results show that C. elephas larvae are sometimes endoparasitic, living on the edge of host holding capacity. If they were smaller they could avoid food depletion more easily, but the fitness benefits linked to a larger size have probably promoted body size increase. The strong negative effects of conspecific competition may have possibly influenced female strategy of laying a single egg per seed. 5. Being larger and fitter, but always within the limits of the available host sizes, may be one main evolutionary dilemma in endoparasites. 相似文献