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排序方式: 共有198条查询结果,搜索用时 15 毫秒
1.
Jered M. Studinski Kyle J. Hartman Jonathan M. Niles Patrick Keyser 《Hydrobiologia》2012,686(1):107-117
Forested headwater streams rely on their riparian areas for temperature regulation, woody debris inputs, and sediment retention.
These products and services may be altered by disturbances such as timber harvest, windthrow, or development. This study investigated
the effects of riparian forest disturbance by removing trees using 50 and 90% basal area harvests and by directly felling
some trees into eight streams in eastern West Virginia. On summer afternoons, water temperature increased in the 50 and 90%
BAH treatments at average rates of 0.18 and 0.79°C/100 m, respectively. The 90% BAH treatments had the potential to disrupt
fish and invertebrate communities via increased water temperature. New roads and log landings associated with the riparian
logging had no detectable effect on sedimentation or turbidity. Large woody debris (LWD) additions increased habitat complexity
but no net increase in pool area was observed. Greater morphological instability was observed within the LWD addition sections
as pools were both created and destroyed at significantly higher rates. Experimentally manipulating small riparian patches
may be an analog for small-scale natural and anthropogenic disturbances. These common events are assumed to alter streams,
but there are few experimental studies quantifying their effects. 相似文献
2.
Felicity L. Newell James Sheehan Petra Bohall Wood Amanda D. Rodewald David A. Buehler Patrick D. Keyser Jeffrey L. Larkin Tiffany A. Beachy Marja H. Bakermans Than J. Boves Andrea Evans Gregory A. George Molly E. McDermott Kelly A. Perkins Matthew B. White T. Bently Wigley 《Journal of Field Ornithology》2013,84(3):270-286
Point counts are commonly used to assess changes in bird abundance, including analytical approaches such as distance sampling that estimate density. Point‐count methods have come under increasing scrutiny because effects of detection probability and field error are difficult to quantify. For seven forest songbirds, we compared fixed‐radii counts (50 m and 100 m) and density estimates obtained from distance sampling to known numbers of birds determined by territory mapping. We applied point‐count analytic approaches to a typical forest management question and compared results to those obtained by territory mapping. We used a before–after control impact (BACI) analysis with a data set collected across seven study areas in the central Appalachians from 2006 to 2010. Using a 50‐m fixed radius, variance in error was at least 1.5 times that of the other methods, whereas a 100‐m fixed radius underestimated actual density by >3 territories per 10 ha for the most abundant species. Distance sampling improved accuracy and precision compared to fixed‐radius counts, although estimates were affected by birds counted outside 10‐ha units. In the BACI analysis, territory mapping detected an overall treatment effect for five of the seven species, and effects were generally consistent each year. In contrast, all point‐count methods failed to detect two treatment effects due to variance and error in annual estimates. Overall, our results highlight the need for adequate sample sizes to reduce variance, and skilled observers to reduce the level of error in point‐count data. Ultimately, the advantages and disadvantages of different survey methods should be considered in the context of overall study design and objectives, allowing for trade‐offs among effort, accuracy, and power to detect treatment effects. 相似文献
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Cold storage to overcome dormancy affects the carbohydrate status and photosynthetic capacity of Rhododendron simsii 下载免费PDF全文
A. Christiaens E. De Keyser P. Lootens E. Pauwels I. Roldán‐Ruiz J. De Riek B. Gobin M.‐C. Van Labeke 《Plant biology (Stuttgart, Germany)》2015,17(1):97-105
Global warming leads to increasing irregular and unexpected warm spells during autumn, and therefore natural chilling requirements to break dormancy are at risk. Controlled cold treatment can provide an answer to this problem. Nevertheless, artificial cold treatment will have consequences for carbon reserves and photosynthesis. In this paper, the effect of dark cold storage at 7 °C to break flower bud dormancy in the evergreen Rhododendron simsii was quantified. Carbohydrate and starch content in leaves and flower buds of an early (‘Nordlicht’), semi‐early (‘M. Marie’) and late (‘Mw. G. Kint’) flowering cultivar showed that carbon loss due to respiration was lowest in ‘M. Marie’, while ‘Mw. G. Kint’ was completely depleted of starch reserves at the end of cold treatment. Gene isolation resulted in a candidate gene for sucrose synthase (SUS) RsSus, which appears to be homologous to AtSus3 and had a clear increase in expression in leaves during cold treatment. Photosynthesis measurements on ‘Nordlicht’ and the late‐flowering cultivar ‘Thesla’ showed that during cold treatment, dark respiration decreased 58% and 63%, respectively. Immediately after cold treatment, dark respiration increased and stabilised after 3 days. The light compensation point followed the same trend as dark respiration. Quantum efficiency showed no significant changes during the first days after cold treatment, but was significantly higher than in plants with dormant flower buds at the start of cold treatment. In conclusion, photosynthesis stabilised 3 days after cold treatment and was improved compared to the level before cold treatment. 相似文献
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Marcus A. Lashley Craig A. Harper Gary E. Bates Patrick D. Keyser 《The Journal of wildlife management》2011,75(6):1467-1476
Closed-canopy upland hardwood stands often lack diverse understory structure and composition, limiting available nutrition for white-tailed deer (Odocoileus virginianus) as well as nesting and foraging structure for other wildlife. Various regeneration methods can positively influence understory development; however, non-commercial strategies are needed to improve available nutrition in many stands, as some contain timber that is not ready to harvest and others are owned by landowners who are not interested in harvesting timber. Applications of herbicide and prescribed fire have improved availability of food and cover for deer and other wildlife in pine (Pinus spp.) systems. However, this strategy has not been evaluated in hardwood systems. To evaluate the influence of fire and herbicide treatments on available deer forage in upland hardwood systems, we measured forage availability and calculated nutritional carrying capacity (NCC) at 14% crude protein mixed diet, following 7 silvicultural treatments, including controls, in 4 mixed upland hardwood stands July–September 2007 and 2008. We compared NCC among forest treatments and within 4 paired warm-season forage food plots to evaluate the usefulness of food plots in areas where forests are managed. Nutritional carrying capacity estimates (deer days/ha) were greatest following canopy reduction with prescribed fire treatments in both years. Understory herbicide application did not affect species composition or NCC 1 year or 2 years post-treatment. Production of forage plantings exceeded that of forest treatments both years with the exception of early-maturing soybeans and retention cut with fire 2 years post-treatment. We encourage land managers to use canopy reducing treatments and low-intensity prescribed fire to increase available nutrition and improve available cover where needed in upland hardwood systems. In areas where deer density may limit understory development, high-quality forage food plots may be used to buffer browsing while strategies to reduce deer density and stimulate the forest understory are implemented. © 2011 The Wildlife Society. 相似文献
7.
Catherine Thèves Alice Senescau Stefano Vanin Christine Keyser Fran?ois Xavier Ricaut Anatoly N. Alekseev Henri Dabernat Bertrand Ludes Richard Fabre Eric Crubézy 《PloS one》2011,6(7)
Research of ancient pathogens in ancient human skeletons has been mainly carried out on the basis of one essential historical or archaeological observation, permitting specific pathogens to be targeted. Detection of ancient human pathogens without such evidence is more difficult, since the quantity and quality of ancient DNA, as well as the environmental bacteria potentially present in the sample, limit the analyses possible. Using human lung tissue and/or teeth samples from burials in eastern Siberia, dating from the end of 17th to the 19th century, we propose a methodology that includes the: 1) amplification of all 16S rDNA gene sequences present in each sample; 2) identification of all bacterial DNA sequences with a degree of identity ≥95%, according to quality criteria; 3) identification and confirmation of bacterial pathogens by the amplification of the rpoB gene; and 4) establishment of authenticity criteria for ancient DNA. This study demonstrates that from teeth samples originating from ancient human subjects, we can realise: 1) the correct identification of bacterial molecular sequence signatures by quality criteria; 2) the separation of environmental and pathogenic bacterial 16S rDNA sequences; 3) the distribution of bacterial species for each subject and for each burial; and 4) the characterisation of bacteria specific to the permafrost. Moreover, we identified three pathogens in different teeth samples by 16S rDNA sequence amplification: Bordetella sp., Streptococcus pneumoniae and Shigella dysenteriae. We tested for the presence of these pathogens by amplifying the rpoB gene. For the first time, we confirmed sequences from Bordetella pertussis in the lungs of an ancient male Siberian subject, whose grave dated from the end of the 17th century to the early 18th century. 相似文献
8.
Ostracods were found in two pieces of Baltic amber for the first time. The animals belong to the freshwater genus Cyclocypris. Since Baltic amber was formed during Eocene times in southern Scandinavia, the age of the specimens is estimated at 42–54
million years. As aquatic organisms, ostracods are seldom trapped in amber; it is considered that one specimen, already dead
and dried, was either blown onto sticky resin on a plant stem, or washed there by a high flood level, while the other was
probably splashed, alive, in a drop of water against the flowing resin, again probably during a flood. Associated faunal remains,
including other crustaceans, suggest a coastal palaeoenvironment with some marine as well as freshwater influence. 相似文献
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10.
Jorge Nino Flavius Mitrache Peter Cosyn Robin De Keyser 《仿生工程学报(英文版)》2007,4(4):227-236
This paper is focused on the model identification of a Micro Air Vehicle (MAV) in straight steady flight condition. The identification is based on input-output data collected from flight tests using both frequency and time dorrtain techniques. The vehicle is an in-house 40 cm wingspan airplane. Because of the complex coupled, multivariable and nonlinear dynamics of the aircraft, linear SISO structures for both the lateral and longitudinal models around a reference state were derived. The aim of the identification is to provide models that can be used in future development of control techniques for the MAV. 相似文献