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921.
Jonathan P Freeman Thomas J Stohlgren Molly E Hunter Philip N Omi Erik J Martinson Geneva W Chong Cynthia S Brown 《Ecological applications》2007,17(6):1656-1665
Fire is a natural part of most forest ecosystems in the western United States, but its effects on nonnative plant invasion have only recently been studied. Also, forest managers are engaging in fuel reduction projects to lessen fire severity, often without considering potential negative ecological consequences such as nonnative plant species introductions. Increased availability of light, nutrients, and bare ground have all been associated with high-severity fires and fuel treatments and are known to aid in the establishment of nonnative plant species. We use vegetation and environmental data collected after wildfires at seven sites in coniferous forests in the western United States to study responses of nonnative plants to wildfire. We compared burned vs. unburned plots and plots treated with mechanical thinning and/or prescribed burning vs. untreated plots for nonnative plant species richness and cover and used correlation analyses to infer the effect of abiotic site conditions on invasibility. Wildfire was responsible for significant increases in nonnative species richness and cover, and a significant decrease in native cover. Mechanical thinning and prescribed fire fuel treatments were associated with significant changes in plant species composition at some sites. Treatment effects across sites were minimal and inconclusive due to significant site and site x treatment interaction effects caused by variation between sites including differences in treatment and fire severities and initial conditions (e.g., nonnative species sources). We used canonical correspondence analysis (CCA) to determine what combinations of environmental variables best explained patterns of nonnative plant species richness and cover. Variables related to fire severity, soil nutrients, and elevation explained most of the variation in species composition. Nonnative species were generally associated with sites with higher fire severity, elevation, percentage of bare ground, and lower soil nutrient levels and lower canopy cover. Early assessments of postfire stand conditions can guide rapid responses to nonnative plant invasions. 相似文献
922.
Zero-inflated models with application to spatial count data 总被引:1,自引:2,他引:1
Deepak K. Agarwal Alan E. Gelfand Steven Citron-Pousty 《Environmental and Ecological Statistics》2002,9(4):341-355
Count data arises in many contexts. Here our concern is with spatial count data which exhibit an excessive number of zeros. Using the class of zero-inflated count models provides a flexible way to address this problem. Available covariate information suggests formulation of such modeling within a regression framework. We employ zero-inflated Poisson regression models. Spatial association is introduced through suitable random effects yielding a hierarchical model. We propose fitting this model within a Bayesian framework considering issues of posterior propriety, informative prior specification and well-behaved simulation based model fitting. Finally, we illustrate the model fitting with a data set involving counts of isopod nest burrows for 1649 pixels over a portion of the Negev desert in Israel. 相似文献
923.
Germanic acid was shown to inhibit photosynthetic 14CO2 uptake in marine diatoms. Inhibition was not complete even at concentrations of 20 mg Ge/1 nor in cultures incubated for extended periods of time (up to 24 h). The decrease in photosynthesis due to Ge(OH)4 was independent of the stage of growth of the diatom culture. At 0.5 and 1.0 mg Ge/1, the degree of inhibition was dependent on the concentration of Si(OH)4 in the medium. At 5 and 10 mg Ge/1, inhibition was not affected by Si(OH)4 concentrations as high as those found in the sea-120 g-at Si/1. The effect of Ge(OH)4 on photosynthesis is specific for diatoms; other marine phytoplankton were not inhibited. In mixed cultures of diatoms and marine flagellates, the reduction in 14CO2 fixation upon addition of Ge(OH)4 was used to calculated the proportion of diatom photosynthesis to total photosynthesis, and calculated proportions agreed well with actual proportions. Inhibition by Ge(OH)4 was also used to estimate the percent of diatom photosynthesis in a natural marine community, and this was compared with the diatom portion of the crop. Diatom photosynthesis was higher than one might expect from crop figures, although both diatom photosynthesis and diatom numbers in the crop were low. 相似文献
924.
Nataliya Voloshchuk Mona Knop Thomas Colby Erich Kombrink Lothar Hennig Diana Hofmann Dieter Sicker Andrej Gryganski Margot Schulz 《Chemoecology》2007,17(1):1-12
Summary. Doratomyces stemonitis (Hyphomycetales, Dematiaceae) is a saprotrophic fungus belonging to the mycobiota of the cereal rhizosphere. The fungus is
able to metabolize benzoxazolin-2-(3H)-one and a variety of its derivatives including higher plant detoxification products, microbial degradation products and
the chemically rather stable 2-amino-(3H)-phenoxazin-3-one. D. stemonitis can use all of these compounds as sole C-sources but their utilization, especially that of microbial degradation products
and 2-amino-(3H)-phenoxazin-3-one, seems to be highly energy consuming, resulting in slow mycelium growth and a change of colony morphology.
Benzoxazolin-2-(3H)-one derived compounds induce the synthesis of different isoforms of a glycosylated protein with sequence homologies to the
endo-1,3-β-glucanase Asp f2, an allergen from Aspergillus fumigatus and other Asp f2-like proteins e.g., from Verticillium dahliae or PRA1 antigen from Candida albicans. The induction of the protein is regarded as a stress response. 相似文献
925.
Cumulative ecological and socioeconomic effects of forest policies in coastal Oregon. 总被引:1,自引:0,他引:1
Thomas A Spies K Norman Johnson Kelly M Burnett Janet L Ohmann Brenda C McComb Gordon H Reeves Pete Bettinger Jeffrey D Kline Brian Garber-Yonts 《Ecological applications》2007,17(1):5-17
Forest biodiversity policies in multi-ownership landscapes are typically developed in an uncoordinated fashion with little consideration of their interactions or possible unintended cumulative effects. We conducted an assessment of some of the ecological and socioeconomic effects of recently enacted forest management policies in the 2.3-million-ha Coast Range Physiographic Province of Oregon. This mountainous area of conifer and hardwood forests includes a mosaic of landowners with a wide range of goals, from wilderness protection to high-yield timber production. We projected forest changes over 100 years in response to logging and development using models that integrate land use change and forest stand and landscape processes. We then assessed responses to those management activities using GIS models of stand structure and composition, landscape structure, habitat models for focal terrestrial and aquatic species, timber production, employment, and willingness to pay for biodiversity protection. Many of the potential outcomes of recently enacted policies are consistent with intended goals. For example, we project the area of structurally diverse older conifer forest and habitat for late successional wildlife species to strongly increase. 'Other outcomes might not be consistent with current policies: for example, hardwoods and vegetation diversity strongly decline within and across owners. Some elements of biodiversity, including streams with high potential habitat for coho salmon (Oncorhynchus kisutch) and sites of potential oak woodland, occur predominately outside federal lands and thus were not affected by the strongest biodiversity policies. Except for federal lands, biodiversity policies were not generally characterized in sufficient detail to provide clear benchmarks against which to measure the progress or success. We conclude that land management institutions and policies are not well configured to deal effectively with ecological issues that span broad spatial and temporal scales and that alternative policies could be constructed that more effectively provide for a mix of forest values from this region. 相似文献
926.
The value of small size: loss of forest patches and ecological thresholds in southern Madagascar. 总被引:1,自引:0,他引:1
Orjan Bodin Maria Teng? Anna Norman Jakob Lundberg Thomas Elmqvist 《Ecological applications》2006,16(2):440-451
Many services generated by forest ecosystems provide essential support for human well-being. However, the vulnerability of these services to environmental change such as forest fragmentation are still poorly understood. We present spatial modeling of the generation of ecosystem services in a human-dominated landscape where forest habitat patches, protected by local taboos, are located in a matrix of cultivated land in southern Madagascar. Two ecosystem services dependent on the forest habitats were addressed: (1) crop pollination services by wild and semidomesticated bees (Apoidea), essential for local crop production of, for example, beans, and (2) seed dispersal services based on the presence of ring-tailed lemurs (Lemur catta). We studied the vulnerability of these ecosystem services to a plausible scenario of successive destruction of the smallest habitat patches. Our results indicate that, in spite of the fragmented nature of the landscape, the fraction of the landscape presently covered by both crop pollination and seed dispersal services is surprisingly high. It seems that the taboo system, though indirectly and unintentionally, contributes to upholding the generation of these services by protecting the forest patches. Both services are, however, predicted to be very vulnerable to the successive removal of small patches. For crop pollination, the rate of decrease in cover was significant even when only the smallest habitat patches were removed. The capacity for seed dispersal across the landscape displayed several thresholds with habitat patch removal. Our results suggest that, in order to maintain capacity for seed dispersal across the landscape and crop pollination cover in southern Androy, the geographical location of the remaining forest patches is more crucial than their size. We argue that in heavily fragmented production landscapes, small forest patches should increasingly be viewed as essential for maintaining ecosystem services, such as agricultural production, and also should be considered in the ongoing process of tripling the area of protected habitats in Madagascar. 相似文献
927.
Suzanne L. Reeser Alan E. Donnenfeld Robert C. Miller Beatrice S. Sellinger Beverly S. Emanuel Deborah A. Driscoll M.D. 《黑龙江环境通报》1994,14(11):1029-1034
Cytogenetic studies of cultured amniocytes demonstrated a karyotype of 46, XX/47, XX,+mar. A bisatellited, dicentric, distamycin-DAPI negative, NOR-positive marker was present in 76 per cent of the metaphases examined. Similar markers have been associated with cat eye syndrome (CES). We report on the utilization of fluorescence in situ hybridization (FISH) with a 14/22 a-satellite probe and a chromosome 22-specific cosmid for locus D22S9 to determine the origin of the prenatally detected supernumerary marker chromosome. FISH studies demonstrated that the marker is a derivative of chromosome 22 and enabled us to provide the family with additional prognostic information. 相似文献
928.
Light,timing of biological rhythms,and chronodisruption in man 总被引:3,自引:2,他引:3
This paper reviews abundant evidence suggesting that causes and course of aging and cancers can be considered as being both light- and rhythm-related. We define chronodisruption as a relevant disturbance of orderly biological rhythms over days and seasons and years in man. Light is the primary external mediator and melatonin a primary internal intermediary of such disturbances, which can result in earlier deaths via premature aging and cancers. We conclude that experimental and epidemiological research can provide further insights into common denominators of these chronic processes and may offer novel and uniform targets for prevention. 相似文献
929.
Ronald L. Thomas MD 《黑龙江环境通报》1992,12(11):919-923
Cystic hygromas have historically been associated with a grim prognosis when discovered during prenatal sonographic study of the fetus. This same grim prognosis is not observed by the paediatric surgeon who evaluates the neonate or paediatric patient. We present a fetal patient with a massive anterior cystic hygroma discovered in the third trimester prior to 30 weeks. This case and a review of the literature suggest tailoring the prognosis by category when counselling patients: (1) first trimester, normal karyotype-good; (2) first trimester, abnormal karyotype-poor; (3) second trimester and early third-poor to guarded; and (4) mid to late third trimester-good. 相似文献
930.
Meena Upadhyaya Alan Fryer Graham Foat Denise Robinson Oliver Quarrell Adrian Roberts P. S. Harper 《黑龙江环境通报》1990,10(9):593-603
Chorionic villi were sampled from 125 women who requested prenatal diagnosis, either for genetic disorders or because of advanced maternal age. Of these, 105 samples were obtained by the transcervical route and 20 were obtained by the transabdominal approach. The sampling success rate was 97 per cent (122/125). The mean maternal age of the patients was 31 years (range 17–44) and the mean gestational age at which the chorionic villus sampling was performed was 10 weeks (range 7–13 weeks). Seventy-four of these diagnoses involved the use of DNA markers. The minimal size of the sample used for DNA diagnosis was 5 mg. Maternal contamination was detected in two samples. A diagnosis was provided on all but two samples. The fetal loss rate was high initially but fell to 1·9 per cent in 1988. 相似文献