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141.
Lisa M. Schloegel Jean-Marc Hero Lee Berger Rick Speare Keith McDonald Peter Daszak 《EcoHealth》2006,3(1):35-40
Infectious diseases are increasingly recognized as the cause of mass mortality events, population declines, and the local
extirpation of wildlife species. In a number of cases, it has been hypothesized that pathogens have caused species extinctions
in wildlife. However, there is only one definitively proven case of extinction by infection, and this was in a remnant captive
population of a Polynesian tree snail. In this article, we review the potential involvement of infectious disease in the recent
extinction of the sharp-snouted day frog Taudactylus acutirostris. Our review of available evidence suggests that a virulent pathogen of amphibians, Batrachochytrium dendrobatidis, caused a rapid, catastrophic decline of this species, from which it did not recover. We propose that this is the first case
of extinction by infection of a free-ranging wildlife species where disease acted as both the proximate and ultimate cause
of extinction. This highlights a probable underreporting of infectious disease as a cause of biodiversity loss historically
and currently. 相似文献
142.
Mangrove species are well adapted to the harsh ecological conditions of their environment throughout the tropics. However,
in the islands of Guadeloupe and Martinique (Lesser Antilles), deficient forest recovery was evidenced in 43 mangrove sites
(>1000 m2) affected by apparently natural tree mortality. Such sites were recorded from four chronological sets of aerial photographs
between 1950 and 1995, and field-investigated in terms of environment and vegetation characteristics. Given the speculative
relationship between the slow-regenerating vegetation and its present environment within non-steady state, disturbed sites,
statistical analyses arbitrarily matching physicochemical and biological data were primarily avoided. On one hand, principal
component analysis (PCA), combined with an agglomerative hierarchical classification, was performed on environmental, rank-ordered
data; on the other hand, multidimensional scaling (MDS) was implemented on vegetation data. Discriminant analyses (DA) further
characterized the environment/vegetation interrelationships for each site type. Ultimately, three main types of mortality
sites have been distinguished among the study areas. One type clustered the sites showing the lowest salinity values and the
highest surge vulnerability whose dominant mangrove species is Rhizophora. Another type presented highly saline sites having clayey soils with pure, stunted, Avicennia stands. The last type consisted of peculiar forest gaps on deep, compact, peat soils. During the rainy season, these sites
turned into shallow ponds scattered with living, young Rhizophora and large, standing, dead Avicennia. The authors suggest that this classification may serve as a comprehensive framework to test subsequent hypotheses (hurricanes,
droughts…) on the origins of natural massive tree mortality and the causes of recovery deficiency in mangroves of the Caribbean. 相似文献
143.
We measured root and stem mass at three sites (Piedmont (P), Coastal Plain (C), and Sandhills (S)) in the southeastern United States. Stand density, soil texture and drainage, genetic makeup and environmental conditions varied with site while differences in tree size at each site were induced with fertilizer additions. Across sites, root mass was about one half of stem mass when estimated on a per hectare basis. Stem mass per hectare explained 91% of the variation in root mass per hectare, while mean tree diameter at breast height (D), site, and site by measurement year were significant variables explaining an additional 6% of the variation in root mass per hectare. At the S site, the root:stem ratio decreased from 0.7 to 0.5 when mean tree D increased from 10 to 22 cm. At the P and C sites, where mean root:stem ratios were 0.40 and 0.47, respectively, no significant slope in the root:stem to mean tree D relationship was found over a more narrow range in mean tree D (12–15 and 12–18 cm, respectively). Roots were observed in the deepest layers measured (190, 190, and 290 cm for the P, C, and S sites, respectively); however, the asymptotically decreasing root mass per layer indicated the bulk of roots were measured. Root growth relative to stem growth would need to change with increased mean tree D to explain the results observed here. While these changes in growth rate among plant components may differ across sites, stem mass alone does a good job of estimating root mass across sites. 相似文献
144.
Charlotte Vandenberghe Franois Frelchoux Fawziah Gadallah Alexandre Buttler 《植被学杂志》2006,17(4):481-488
Question: What is the effect of gap size on the seedling emergence, growth and survival of four common tree species in wooded pastures? Location: A pasture in the Jura mountains, Switzerland. Methods: Seeds were sown in a complete three‐way factorial design with eight blocks in May 2003. Each block consisted of a competition treatment (four gap sizes including zero) and a mowing treatment (mown and unmown). Emergence, survival and total biomass of tree seedlings of three species (Picea abies, Acer pseudoplatanus and Fagus sylvatica) were measured. A fourth species (Abies alba) failed to germinate. Results: Gaps had a positive influence on the early stages of tree development for all species. Larger gaps favoured growth and survival more than small gaps. Seedling growth was higher when vegetation around the openings was mown. Mowing the vegetation at gap size zero enhanced both growth and survival compared to unmown vegetation. Mown gaps larger than zero had increased seedling desiccation but decreased seedling predation. Species showed similar trends in their emergence and growth responses to gap size and mowing treatments but for Picea emergence rate was higher and survivorship was lower than for Acer and Fagus. Conclusions: Gap size does matter for tree seedling success but even in more favourable large gaps only a small percentage of seedlings emerged and survived. The effects of gaps on tree seedling establishment are complex as a result of interactions between biotic and abiotic changes caused by gaps. 相似文献
145.
Jönsson U 《The New phytologist》2006,171(1):55-68
Here, a conceptual model is presented for the development of Phytophthora disease in pedunculate oak. The model is presented using the causal loop diagram tool and gives an overview of how various abiotic and biotic factors, such as soil moisture, nutrient availability and mycorrhizal colonization, may affect the reproduction and the infective capacity of soil-borne Phytophthora species, the susceptibility of the host and subsequent disease development. It is suggested that the link between the root damage caused by Phytophthora species and overall tree vitality is in the assimilation and allocation of carbon within the plants. The potential impact of environmental factors on these processes is discussed. The model is presented with reference to scenarios related to variation in soil moisture and nutrient availability. The need for species-specific validation of the model and the implications of the model are discussed. 相似文献
146.
147.
Donald P Tashkin He-Jing Wang David Halpin Eric C Kleerup John Connett Ning Li Robert Elashoff 《Respiratory research》2012,13(1):70
Background
The impact of interventions on the progressive course of COPD is currently assessed by the slope of the annual decline in FEV1 determined from serial measurements of the post-, in preference to the pre-, bronchodilator FEV1. We therefore compared the yearly slope and the variability of the slope of the pre- versus the post-bronchodilator FEV1 in men and women with mild to moderate COPD who participated in the 5-year Lung Health Study (LHS).Methods
Data were analyzed from 4484 of the 5887 LHS participants who had measurements of pre- and post-bronchodilator FEV1 at baseline (screening visit 2) and all five annual visits. The annual rate of decline in FEV1 (±SE) measured pre- and post-bronchodilator from the first to the fifth annual visit was estimated separately using a random coefficient model adjusted for relevant covariates. Analyses were performed separately within each of the three randomized intervention groups. In addition, individual rates of decline in pre- and post-bronchodilator FEV1 were also determined for each participant. Furthermore, sample sizes were estimated for determining the significance of differences in slopes of decline between different interventions using pre- versus post-bronchodilator measurements.Results
Within each intervention group, mean adjusted and unadjusted slope estimates were slightly higher for the pre- than the post-bronchodilator FEV1 (range of differences 2.6-5.2 ml/yr) and the standard errors around these estimates were only minimally higher for the pre- versus the post-bronchodilator FEV1 (range 0.05-0.11 ml/yr). Conversely, the standard deviations of the mean FEV1 determined at each annual visit were consistently slightly higher (range of differences 0.011 to 0.035 L) for the post- compared to the pre-bronchodilator FEV1. Within each group, the proportion of individual participants with a statistically significant slope was similar (varying by only 1.4 to 2.7%) comparing the estimates from the pre- versus the post-bronchodilator FEV1. However, sample size estimates were slightly higher when the pre- compared to the post-bronchodilator value was used to determine the significance of specified differences in slopes between interventions.Conclusion
Serial measurements of the pre-bronchodilator FEV1 are generally sufficient for comparing the impact of different interventions on the annual rate of change in FEV1. 相似文献148.
利用DNA ISSR分子标记技术对芍药属植物栽培品种的分类鉴定方法 总被引:2,自引:1,他引:1
以利用DNA ISSR分子标记逐级区分品种为主要研究目标,通过ISSR引物的设计与实验筛选,取得了进展。该方法类似于经典的植物形态检索表式的分类策略,不同之处在于利用基因组DNA分子性状作为品种分类的依据,即"ISSR引物结合位点"与"DNA ISSR片段长度差异"的组合信息。该方法不仅可以有效鉴定品种,而且可以很容易地生成富含遗传变异信息的0、1矩阵,通过运算揭示品种间的遗传关系与演化规律。该方法成本低廉、操作便捷,对于建立客观、科学的牡丹及芍药品种分类体系,对于芍药属品种种质资源的保存、评价与合理利用具有重要价值。应该加大支持力度推进其实际应用。 相似文献
149.
Julian Aherne Maximilian Posch Martin Forsius Jussi Vuorenmaa Pekka Tamminen Maria Holmberg Matti Johansson 《Biogeochemistry》2008,88(3):233-256
The dynamic hydro-geochemical Model of Acidification of Groundwater in Catchments (MAGIC) was used to predict the response
of 163 Finnish lake catchments to historic and future atmospheric deposition (1880–2100) and future tree harvesting practices.
Deposition was assumed to follow current legislated European emission reduction policies (CLe) and a scenario based on maximum
(technically) feasible reductions (MFR). Future harvesting was assumed to shift from stem-only harvesting (SOH) to whole-tree
harvesting (WTH) owing to the potential increased utilisation of biofuels. Despite the modest changes in atmospheric deposition
under CLe (compared to current day), these reductions are predicted to halt the decline in soil base saturation; however,
further reductions are required to improve soil and lake water chemistry. The MFR scenario predicted a significant long-term
improvement in soil base saturation leading to continued long-term recovery in surface waters (all lakes with ANC > 0 by 2100).
However under the WTH scenario, significant long-term impacts (re-acidification) were predicted for soil and surface water
chemistry (14 lakes with ANC < 0 by 2100). To some extent the long-term negative impacts were reduced under MFR, indicating
that increased utilisation of biofuels will necessitate ‘trading emissions for timber’, or soil amendment, to maintain ecosystem
quality and sustainable forest growth. The current practice of SOH is close to the sustainable maximum harvesting under current
(legislated) atmospheric deposition in Finland. 相似文献
150.
Walter Oberhuber Werner Kofler Klaus Pfeifer Andrea Seeber Andreas Gruber Gerhard Wieser 《Trees - Structure and Function》2008,22(1):31-40
Although growth limitation of trees at Alpine and high-latitude timberlines by prevailing summer temperature is well established,
the loss of thermal response of radial tree growth during last decades has repeatedly been addressed. We examined long-term
variability of climate–growth relationships in ring width chronologies of Stone pine (Pinus cembra L.) by means of moving response functions (MRF). The study area is situated in the timberline ecotone (ca. 2,000–2,200 m
a.s.l.) on Mt. Patscherkofel (Tyrol, Austria). Five site chronologies were developed within the ecotone with constant sample
depth (≥19 trees) throughout most of the time period analysed. MRF calculated for the period 1866–1999 and 1901–1999 for ca.
200- and ca. 100-year-old stands, respectively, revealed that mean July temperature is the major and long-term stable driving
force of Pinus cembra radial growth within the timberline ecotone. However, since the mid-1980s, radial growth in timberline and tree line chronologies
strikingly diverges from the July temperature trend. This is probably a result of extreme climate events (e.g. low winter
precipitation, late frost) and/or increasing drought stress on cambial activity. The latter assumption is supported by a <10%
increase in annual increments of ca. 50-year-old trees at the timberline and at the tree line in 2003 compared with 2002,
when extraordinary hot and dry conditions prevailed during summer. Furthermore, especially during the second half of the twentieth
century, influence of climate variables on radial growth show abrupt fluctuations, which might also be a consequence of climate
warming on tree physiology. 相似文献