首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
  1. The shift from shade‐intolerant species to shade‐tolerant mesophytic species in deciduous and mixed forests of the temperate zone is well described in studies from North America. This process has been termed mesophication and it has been linked to changes in fire regime. Fire suppression results in the cessation of establishment of heliophytic, fire‐dependent tree species such as oak (Quercus) and pine (Pinus). Due to the scarcity of old‐growth forests in Europe, data on long‐term compositional changes in mixed forests are very limited, as is the number of studies exploring whether fire played a role in shaping the dynamics.
  2. The aim of this study was to reconstruct tree succession in a 43‐ha natural mixed deciduous forest stand in Bia?owie?a Forest (BF), Poland using dendrochronological methods. In addition, the presence of aboveground fire legacies (charred and fire‐scarred deadwood) enabled the fire history reconstruction.
  3. Dendrochronological data revealed tree establishment (Quercus) back to the end of the 1500s and fires back to 1659. Under a regime of frequent fires until the end of the 18th century, only oak and pine regenerated, sporadically. A shift in the fire regime in the first half of the 19th century triggered oak and pine cohort regeneration, then gradually spruce (Picea) encroached. Under an increasingly dense canopy and less flammable conditions, regeneration of shade‐tolerant Carpinus, Tilia, and Acer began simultaneously with the cessation of oak and pine recruitment.
  4. Synthesis. The study reports the first evidence of mesophication in temperate Europe and proves that fire was involved in shaping the long‐term dynamics of mixed deciduous forest ecosystems. Our data suggest that fire exclusion promoted a gradual recruitment of fire‐sensitive, shade‐tolerant species that inhibited the regeneration of oak and pine in BF.
  相似文献   

2.
Understanding how species respond to differences in resource availability is critical to managing biodiversity under the increasing pressures associated with climate change and growing human populations. Over the last century, the floodplain forests of Australia's largest river system, the Murray‐Darling Basin, have been much affected by intensive harvesting of timber and firewood, and increasingly stressed by river regulation and, recently, an extended drought. Fallen timber – logs and shed branches – is known to play a key role in the ecology of several important species on these floodplains. Here, we monitored the response of the ant assemblages of a floodplain forest along the Murray River to a large‐scale (34 ha) experimental manipulation of fallen‐timber load (0 to 80 t ha?1) over 4 years. The forest was subjected to an incidental, extensive flood that enabled us to examine how two important stressors (timber removal and river regulation) affect ant assemblages. Ants showed little response to the proximity of fallen timber within plots, prior to the flood, or to different loads among plots, unlike other floodplain biota. After the flood, both ant abundance and species richness increased and species composition changed. However, this increase in species richness after flooding was less pronounced in plots with higher amounts of fallen timber. Managing river red gum forest using a mosaic of flood regimes, more representative of historical conditions, is likely to be the most effective way to maintain and enhance the diversity of ants and other biota on these important floodplains.  相似文献   

3.
We assessed the impacts of damming on the biological quality of Estonian streams. A total of 24 dammed sites on 22 streams were sampled. Standard samples were taken during two consecutive springs, 2009 and 2010 in three habitat locations: above dam (reservoir), immediately below dam, and at an undisturbed (reference) site nearby. To estimate biological quality, the national multimetric index (based on five pollution‐sensitive and/or general quality metrics) was used. To estimate direct hydromorphological effects on macroinvertebrates, the locally adapted index, Macroinvertebrates in Estonia: Score of Hydromorphology (MESH) was employed. We found a significant decrease in the biological quality of the above‐dam sites compared to the undisturbed sites (probably due to accumulation of fine sediments and lower flow velocity). Of the five ordinary quality indicators tested, only one (ASPT index) was significantly different between the below‐dam sites and the undisturbed sites. However, the MESH indicated significant stress of macroinvertebrates both at the above‐dam and below‐dam sites, even when flow velocity and bottom type at the below‐dam sites was similar to that at the undisturbed sites. At the same time, hydrochemical parameters were constant among the three habitats. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

4.
Franz Essl  Johannes Kobler 《Flora》2009,204(7):485-494
In this paper, we analyse the patterns and determinants of cacti invasion in 22 European countries. We compiled a checklist for each country. Cacti were classified for each country according to their invasion status as casuals, locally established (1–5 localities of small population size) and widely established (>5 localities of considerable population size).We used generalised linear models (GLM) from the Poisson family with a log-link function and a set of seven country-specific explanatory variables to account for geographical, climatic, habitat-related and economic determinants to test which features of the recipient area determine invasion success and if distribution patterns of species at different invasion stages are governed by the same interplay of explanatory variables. Separate models were fitted with the same predictor variables for casual, locally established, widely established and all cacti. Further, we analysed the temporal invasion trend, and tested if niche breadth (expressed as the number of habitat types colonized) is influenced by the range size (measured as the number of countries invaded). Finally, we reviewed the consequences of cacti invasion for nature conservation.In total, 26 cacti species have been recorded in Europe. Ten species are more widespread and occur in at least three countries, Opuntia humifusa (six countries) being the most widespread species. The country with most cacti is Spain (21 species), whereas in 13 countries no cactus species have been recorded. By far the most important genus is Opuntia with 20 alien species. The temporal invasion pattern shows an exponential increase of the cumulative number of invasion events, increasing from three (1801–50) to nine (1951–2000) invasion events over a 50-year period.Regardless of the invasion stage, the factor explaining most of the variance in the models is the presence of the Mediterranean biogeographic region, and a significant positive effect of the country size on species numbers was identified.Considering the invasion stage, some interesting deviations in the models can be observed. Invasion of casual cacti is only influenced by the presence of the Mediterranean biogeographic region. For locally established cacti, precipitation is negatively correlated with the invasion rate, and the presence of the Alpine biogeographic region is positively correlated; the latter is due the local occurrence of few hardy cacti (Opuntia phaeacantha, O. humifusa) in low-lying valleys of the Alps. As all widely established cactus species are restricted to the Mediterranean region, only this factor was included in the model.All cacti are confined to dry, open habitats on acid siliceous bedrock. Thus, the predominant habitats invaded are rock vegetation, dry grassland, open Mediterranean scrub and dry ruderal habitats. The niche breadth of cacti increases with the numbers of countries colonized. Further, the niche breadth of cacti exhibits a geographic gradient towards the Mediterranean region.Until the 19th century, the dominant pathway of invasion was agriculture, as some cactus species had been introduced for the production of forage and fruits. However, in the last decades horticulture and deliberate planting in the wild have become the dominant pathways.The invasion of cacti in natural and semi-natural habitats in the Mediterranean region changes habitat structure and species composition. However, dense and extensive stands of cacti are restricted to few species (e.g. Opuntia ficus-indica).  相似文献   

5.
Aim We assessed how avian biodiversity and above‐ground carbon storage were related in different forest age‐classes, including mature stands (> 100 years), in a managed, mixed‐species eucalypt forest. Location Gippsland, south‐eastern Australia. Methods In 50 2‐ha stands ranging in age from ≤ 5 years to mature stands > 100 years, we undertook repeated avian surveys, performed detailed habitat measurements and estimated amounts of above‐ground carbon. Extensive wildfire reduced the number of sites to 28 (seven in each of four age classes) upon which analyses and inferences were made. We also analysed data on carbon storage and some bird responses from previously published studies. Results Mature vegetation (> 100 years) had the greatest richness, abundance and biomass of birds. Key ecological resources, such as tree‐hollows for nesting, generally occurred mostly in stands > 60 years. Avian richness per unit of above‐ground carbon storage was relatively low for stands of 20–60 years. While above‐ground carbon storage appeared to increase in a monotonic fashion as stands age and mature, there were quantum increases in all measures of avian biodiversity in mature stands (> 100 years). Main conclusions Our results suggest that carbon is organized in a different way, with substantially greater biodiversity benefits, in very old stands. Mature vegetation simultaneously maximizes both avian biodiversity and above‐ground carbon storage. These results bolster arguments for allocating highest priorities to the preservation of old‐growth forest stands rather than alternative investments (e.g. reafforestation for carbon sequestration).  相似文献   

6.
Climate change threatens the provisioning of forest ecosystem services and biodiversity (ESB). The climate sensitivity of ESB may vary with forest development from young to old‐growth conditions as structure and composition shift over time and space. This study addresses knowledge gaps hindering implementation of adaptive forest management strategies to sustain ESB. We focused on a number of ESB indicators to (a) analyze associations among carbon storage, timber growth rate, and species richness along a forest development gradient; (b) test the sensitivity of these associations to climatic changes; and (c) identify hotspots of climate sensitivity across the boreal–temperate forests of eastern North America. From pre‐existing databases and literature, we compiled a unique dataset of 18,507 forest plots. We used a full Bayesian framework to quantify responses of nine ESB indicators. The Bayesian models were used to assess the sensitivity of these indicators and their associations to projected increases in temperature and precipitation. We found the strongest association among the investigated ESB indicators in old forests (>170 years). These forests simultaneously support high levels of carbon storage, timber growth, and species richness. Older forests also exhibit low climate sensitivity of associations among ESB indicators as compared to younger forests. While regions with a currently low combined ESB performance benefitted from climate change, regions with a high ESB performance were particularly vulnerable to climate change. In particular, climate sensitivity was highest east and southeast of the Great Lakes, signaling potential priority areas for adaptive management. Our findings suggest that strategies aimed at enhancing the representation of older forest conditions at landscape scales will help sustain ESB in a changing world.  相似文献   

7.
The ability of bottom‐dwelling marine epifauna to regenerate injured or lost body parts is critical to the survival of individuals from disturbances that inflict wounds. Numerous studies on marine sponges (Phlyum Porifera) and corals (of the orders Scleractinia and Alcyonacea) suggest that regeneration is limited by many intrinsic (individual‐dependent) and extrinsic (environment‐dependent) factors, and that other life history processes may compete with regeneration for energetic and cellular resources. We review how intrinsic (size, age, morphology, genotype) and extrinsic (wound characteristics, water temperature, food availability, sedimentation, disturbance history, selection) factors limit regeneration in sponges and corals. We then review the evidence for impaired somatic growth and sexual reproduction, and altered outcomes of interactions (anti‐predator defenses, competitive abilities, self‐ and non‐self recognition abilities) with other organisms in regenerating sponges and corals. We demonstrate that smaller, older sponges and corals of decreasing morphological complexities tend to regenerate less well than others, and that regeneration can be modulated by genotype. Large wounds with small perimeters inflicted away from areas where resources are located tend to be regenerated less well than others, as are injuries inflicted when food is limited and when the animal has been previously or recently injured. We also demonstrate that regeneration strongly impairs somatic growth, reduces aspects of sexual reproduction, and decreases the ability for sponges and corals to defend themselves against predators, to compete, and to recognize conspecifics. Effects of limited regeneration and impaired life histories may manifest themselves in higher levels of biological assembly e.g., reduced accretion of epifaunal biomass, reduced recruitment and altered biotic associations, and thus affect marine community and ecosystem recovery from disturbances. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

8.
To date, over 1800 gene therapy clinical trials have been completed, are ongoing or have been approved worldwide. Our database brings together global information on gene therapy clinical trials from official agency sources, published literature, conference presentations and posters kindly provided to us by individual investigators or trial sponsors. This review presents our analysis of clinical trials that, to the best of our knowledge, have been or are being performed worldwide. As of our June 2012 update, we have entries on 1843 trials undertaken in 31 countries. We have analysed the geographical distribution of trials, the disease indications (or other reasons) for trials, the proportions to which different vector types are used, and which genes have been transferred. Details of the analyses presented, and our searchable database are available on The Journal of Gene Medicine Gene Therapy Clinical Trials Worldwide website at: http://www.wiley.co.uk/genmed/clinical . We also provide an overview of the progress being made in clinical trials of gene therapy approaches around the world and discuss the prospects for the future. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

9.
10.
Aim When hypotheses of historical biogeography are evaluated, age estimates of individual nodes in a phylogeny often have a direct impact on what explanation is concluded to be most likely. Confidence intervals of estimated divergence times obtained in molecular dating analyses are usually very large, but the uncertainty is rarely incorporated in biogeographical analyses. The aim of this study is to use the group Urophylleae, which has a disjunct pantropical distribution, to explore how the uncertainty in estimated divergence times affects conclusions in biogeographical analysis. Two hypotheses are evaluated: (1) long‐distance dispersal from Africa to Asia and the Neotropics, and (2) a continuous distribution in the boreotropics, probably involving migration across the North Atlantic Land Bridge, followed by isolation in equatorial refugia. Location Tropical and subtropical Asia, tropical Africa, and central and southern tropical America. Methods This study uses parsimony and Bayesian phylogenetic analyses of chloroplast DNA and nuclear ribosomal DNA data from 56 ingroup species, beast molecular dating and a Bayesian approach to dispersal–vicariance analysis (Bayes‐DIVA) to reconstruct the ancestral area of the group, and the dispersal–extinction–cladogenesis method to test biogeographical hypotheses. Results When the two models of geographic range evolution were compared using the maximum likelihood (ML) tree with mean estimates of divergence times, boreotropical migration was indicated to be much more likely than long‐distance dispersal. Analyses of a large sample of dated phylogenies did, however, show that this result was not consistent. The age estimate of one specific node had a major impact on likelihood values and on which model performed best. The results show that boreotropical migration provides a slightly better explanation of the geographical distribution patterns of extant Urophylleae than long‐distance dispersal. Main conclusions This study shows that results from biogeographical analyses based on single phylogenetic trees, such as a ML or consensus tree, can be misleading, and that it may be very important to take the uncertainty in age estimates into account. Methods that account for the uncertainty in topology, branch lengths and estimated divergence times are not commonly used in biogeographical inference today but should definitely be preferred in order to avoid unwarranted conclusions.  相似文献   

11.
12.
13.
Peat mosses (Sphagnum) largely govern carbon sequestration in Northern Hemisphere peatlands. We investigated functional traits related to growth and decomposition in Sphagnum species. We tested the importance of environment and phylogeny in driving species traits and investigated trade‐offs among them. We selected 15 globally important Sphagnum species, representing four sections (subgenera) and a range of peatland habitats. We measured rates of photosynthesis and decomposition in standard laboratory conditions as measures of innate growth and decay potential, and related this to realized growth, production, and decomposition in their natural habitats. In general, we found support for a trade‐off between measures of growth and decomposition. However, the relationships are not strong, with r ranging between 0.24 and 0.45 for different measures of growth versus decomposition. Using photosynthetic rate to predict decomposition in standard conditions yielded R2 = 0.20. Habitat and section (phylogeny) affected the traits and the trade‐offs. In a wet year, species from sections Cuspidata and Sphagnum had the highest production, but in a dry year, differences among species, sections, and habitats evened out. Cuspidata species in general produced easily decomposable litter, but their decay in the field was hampered, probably due to near‐surface anoxia in their wet habitats. In a principal components analysis, PCA, photosynthetic capacity, production, and laboratory decomposition acted in the same direction. The species were imperfectly clustered according to vegetation type and phylogeny, so that some species clustered with others in the same section, whereas others clustered more clearly with others from similar vegetation types. Our study includes a wider range of species and habitats than previous trait analyses in Sphagnum and shows that while the previously described growth–decay trade‐off exists, it is far from perfect. We therefore suggest that our species‐specific trait measures offer opportunities for improvements of peatland ecosystem models. Innate qualities measured in laboratory conditions translate differently to field responses. Most dramatically, fast‐growing species could only realize their potential in a wet year. The same species decompose fast in laboratory, but their decomposition was more retarded in the field than that of other species. These relationships are crucial for understanding the long‐term dynamics of peatland communities.  相似文献   

14.
The concept of accident in evolution refers to causes which are stochastic with respect to selective demands arising from the external environment and acting on the organism, while the concept of design refers to causes which meet the requirement of these selective demands. The condition ‘with respect to selective demands’ is generally forgotten so that evolutionary changes are described as being design modifications. Design is an invalid synonym for adaptation. Further it implies a designer and has been used by some authors since before Darwin to argue that design in organisms demonstrates the existence of a designer and hence a plan. Yet if evolution depends on two simultaneously acting causes, one of which is accidental, then the process of evolution and all attributes of organisms are accidental. The concept of design is inappropriate in biology and should be eliminated from all biological explanations.  相似文献   

15.
Increased deployment of renewable energy can contribute towards mitigating climate change and improving air quality, wealth and development. However, renewable energy technologies are not free of environmental impacts; thus, it is important to identify opportunities and potential threats from the expansion of renewable energy deployment. Currently, there is no cross‐national comprehensive analysis linking renewable energy potential simultaneously to socio‐economic and political factors and biodiversity priority locations. Here, we quantify the relationship between the fraction of land‐based renewable energy (including solar photovoltaic, wind and bioenergy) potential available outside the top biodiversity areas (i.e. outside the highest ranked 30% priority areas for biodiversity conservation) within each country, with selected socio‐economic and geopolitical factors as well as biodiversity assets. We do so for two scenarios that identify priority areas for biodiversity conservation alternatively in a globally coordinated manner vs. separately for individual countries. We show that very different opportunities and challenges emerge if the priority areas for biodiversity protection are identified globally or designated nationally. In the former scenario, potential for solar, wind and bioenergy outside the top biodiversity areas is highest in developing countries, in sparsely populated countries and in countries of low biodiversity potential but with high air pollution mortality. Conversely, when priority areas for biodiversity protection are designated nationally, renewable energy potential outside the top biodiversity areas is highest in countries with good governance but also in countries with high biodiversity potential and population density. Overall, these results identify both clear opportunities but also risks that should be considered carefully when making decisions about renewable energy policies.  相似文献   

16.
The European catfish Silurus glanis is an important fish species in both commercial and recreational fisheries. Catfish is a spreading species that was reported to potentially benefit from increasing temperatures. The goal of this study was to estimate long‐term changes in harvest rates of catfish in Central Europe. This study used individual mandatory angling logbooks collected by the Czech Fishing Union in the Czech Republic (Central Europe) over the course of years 1986–2017 (32 years) to assess harvest rates of catfish. This study discovered that harvest of catfish has been increasing over time. Moreover, rivers that previously showed zero harvested catfish are beginning to display higher harvest rates of catfish. Increasing average air temperature and angling effort in the study area have positively affected harvest rates of catfish. The increased harvest of catfish could not be reliably explained by intensive fish stocking. In conclusion, while other studies show that many fish species are negatively affected by human activities and therefore show decreased harvest rates, catfish angling seems to benefit from anthropogenic changes.  相似文献   

17.
Melanin, the major determinant of skin colour, is a tyrosine‐based heteropolymer of indeterminate molecular weight. In vivo, melanin synthesis occurs within highly specialized organelles called melanosomes. Coated vesicles encapsulating the enzyme tyrosinase and tyrosinase related proteins, fuse with premelanosomes that contain structural proteins to form mature melanosomes. Coated vesicles and premelanosomes have been shown to have only melanin monomers but not the polymer. Our earlier results have clearly shown that the presence of proteins other than tyrosinase are critical for the post‐tyrosinase steps of melanin polymerization at acidic pH. Proteins in melanosomes are difficult to purify because of their firm association with melanin. Thus, with progressive melanization, melanoproteins become progressively insoluble. In this paper, we discuss the isolation and purification of melanosomal proteins and their role in melanin polymerization. We have hypothesized that the initiation of polymerization and the binding of melanin to proteins are two discrete events and we have developed assays to quantify these events. Purified melanosomal proteins differ in their ability to polymerize melanin monomers. Further, we have also shown that two polypeptides (28 and 45 kDa) purified from melanosomes inhibit melanin polymerization but can bind preformed melanin. In conclusion, melanosomal proteins regulate melanin polymerization and differ in their ability to bind melanin. Polymerization and binding abilities of melanosomal proteins are specific to each protein and melanin–protein interaction is not nonspecific.  相似文献   

18.
19.
Radiolabelled peptides with high specificity and affinity towards receptors that are overexpressed by tumour cells are used in nuclear medicine for the diagnosis (imaging) and therapy of cancer. In some cases, the sequences of peptides under investigations contain methionine (Met), an amino acid prone to oxidation during radiolabelling procedures. The formation of oxidative side products can affect the purity of the final radiopharmaceutical product and/or impair its specificity and affinity towards the corresponding receptor. The replacement of Met with oxidation resistant amino acid analogues, for example, norleucine (Nle), can provide a solution. While this approach has been applied successfully to different radiolabelled peptides, a Met → Nle switch only preserves the length of the amino acid side chain important for hydrophobic interactions but not its hydrogen‐bonding properties. We report here the use of methoxinine (Mox), a non‐canonical amino acid that resembles more closely the electronic properties of Met in comparison to Nle. Specifically, we replaced Met15 by Mox15 and Nle15 in the binding sequence of a radiometal‐labelled human gastrin derivative [d ‐Glu10]HG(10‐17), named MG11 (d ‐Glu‐Ala‐Tyr‐Gly‐Trp‐Met‐Asp‐Phe‐NH2). A comparison of the physicochemical properties of 177Lu‐DOTA[ X 15]MG11 ( X = Met, Nle, Mox) in vitro (cell internalization/externalization properties, receptor affinity (IC50), blood plasma stability and logD) showed that Mox indeed represents a suitable, oxidation‐stable amino acid substitute of Met in radiolabelled peptide conjugates. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.  相似文献   

20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号