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1.
Rates of spread of marine pathogens   总被引:6,自引:0,他引:6  
Epidemics of marine pathogens can spread at extremely rapid rates. For example, herpes virus spread through pilchard populations in Australia at a rate in excess of 10 000 km year?1, and morbillivirus infections in seals and dolphins have spread at more than 3000 km year?1. In terrestrial environments, only the epidemics of myxomatosis and calicivirus in Australian rabbits and West Nile Virus in birds in North America have rates of spread in excess of 1000 km year?1. The rapid rates of spread of these epidemics has been attributed to flying insect vectors, but flying vectors have not been proposed for any marine pathogen. The most likely explanation for the relatively rapid spread of marine pathogens is the lack of barriers to dispersal in some parts of the ocean, and the potential for long‐term survival of pathogens outside the host. These findings caution that pathogens may pose a particularly severe problem in the ocean. There is a need to develop epidemic models capable of generating these high rates of spread and obtain more estimates of disease spread rate.  相似文献   

2.
Elephant density over 40 000 km2 of the Luangwa Valley was estimated as 2–17 km-2 to give a population size of around 86 000 in that area, a tally that would probably top 100 000 if unsurveyed areas within the drainage had been included. Seasonal movement is largely restricted to a migration on to the riverine strip during the wet season and reciprocal dispersal across the valley thereafter. The mean annual range of movement is about 25 km.  相似文献   

3.
Western Tennessee contains unusually highly polymorphic populations of southern short-tailed shrews (Blarina carolinensis). We previously documented eight Robertsonian translocations (ROBs) accounting for a variation in diploid number from 46 in most of this species' range to 34-40 in western Tennessee. We have now expanded our study to include data from adjacent areas in Tennessee and Mississippi, 10 localities in all. The new data show a variation in diploid number ranging from 31 to 41, four new ROBs (for a total of 12), and the novel finding of monobrachial translocations in this group. All animals collected from this large area (extending over 12, 000 km(2)) had some level of ROBs, and none represented the 2n = 46 form seen in other parts of the range of this species. Because other species of shrews (genus Sorex) are not affected in the same area, the factors and/or selective forces causing this extensive polymorphism in B. carolinensis must be unique to this species and to this geographic area. Some ROBs were found throughout this large area of over 12,000 km(2). Other translocations (including those with monobrachial homology) were located in one or two localities in this large area, and still other translocations were intermediate in their distribution. There was a concentric pattern to the evolution and presumed spreading of the ROBs. This allowed us to expand the concept of a Robertsonian "fan," introduced by Matthey (1970), to that of concentric evolution of multiple fusion fans: ROBs likely arose independently, separated temporally and geographically, and radiated into surrounding populations to create this complex zone of polymorphism. This is an active process in its infancy, and it is not as mature as that seen in European studies of Mus and Sorex.  相似文献   

4.
Plant dispersal by motor cars   总被引:2,自引:0,他引:2  
W. Schmidt 《Plant Ecology》1989,80(2):147-152
Mud from a car driving more than 15 000 km in the growing season of 1986 in the area surrounding Göttingen (FRG) was sampled systematically to assess the size and nature of the car-borne flora. The sludge from front and back mudguards, wheels and other lower parts of the car was set out for germination in a greenhouse. Until the end of 1987, 124 plant species with a total of 3926 seedlings were identified and counted. Germination success was significantly related to the sampling date, the front or back position of the car and the influence of low temperature during exposure. The nature of this potentially car-dispersed flora was compared with the local flora as a whole as well as the flora and plant communities of road verges in the studied area. It can be supposed that almost all plant species growing in plant communities along roadsides can be carried by cars and therefore belong to the car-dispersed flora.  相似文献   

5.
NOTICES     
P. K. Tubbs 《Ostrich》2013,84(2):127-128
Saurola, P. 1994. African non-breeding areas of Fennoscandian Ospreys Pandion haliaetus: a ring recovery analysis. Ostrich 65:127-136.

More than 36 000 Ospreys have been ringed in Fennoscandia up to 1992 and 638 of these have been reported from 30 different African countries. The recoveries suggest that adult and first-year Ospreys arrive in Northern Africa from earl September and cross the Sahara in late September to October. A record bird migrated 9817 km from Finland to South Africa in less than 40 days, at an average speed of more than 245 km/day. The majority of all age classes of Fennoscandian Ospreys spend December to February in equatorial Africa. The average compass heading from the different parts of the Fennoscandian breeding areas to the sub-Saharan non-breeding areas is roughly the same, ca. 206°. The longitude of the non-breeding area is dependent on the longitude of the breeding area. Western subpopulations spend their non-breeding period further to the west than more eastern subpopulations but there is much overlap. Ospreys are still heavily persecuted in many African countries.  相似文献   

6.
The salt lakes of western Canada: A paleolimnological overview   总被引:2,自引:0,他引:2  
The northern Great Plains of western Canada contain many saline and hypersaline lakes. Deadmoose and Waldsea Lakes in south-central Saskatchewan are meromictic, with saline Mg-Na-SO4-Cl waters overlying denser brines of similar composition. Mineralogical, chemical, palynological, and stable isotope analyses of the sediments in the Waldsea basin indicate the lake was much shallower about 4 000 years ago in response to a warmer and drier climate. Since that time water levels have generally increased in the basin giving rise to higher organic productivity and greater inorganic carbonate precipitation. Within this overall trend there is also evidence of several lower water stages during the last 3 000 years. The stratigraphy preserved in the Deadmoose basin suggests considerably lower water levels about 1 000 years ago.Ceylon Lake, located about 350 km south of the Waldsea-Deadmoose area, is presently a shallow, saline playa. The basin originated about 15 000 years ago as a glacial meltwater spillway. Stratigraphic variation in evaporite and carbonate mineralogy shows that the basin evolved from a relatively low salinity, riverine lake to one in which initially Na-rich and then Mg-rich hypersaline brines dominated.Lake Manitoba is a large, hyposaline lake located in the eastern Great Plains about 700 km from the Deadmoose-Waldsea area. Stable oxygen and carbon isotope analyses of the endogenic carbonates in the basin indicate gradually increasing levels of organic productivity but decreasing temperatures between 9 000 and 5 000 years B.P. Between about 4 000 and 2 000 years ago the isotope ratios suggest relatively stable temperatures followed by a strong decrease during the most recent 2 000 year period.  相似文献   

7.
卧龙自然保护区大熊猫生境破碎化研究   总被引:80,自引:15,他引:65  
生境破碎化主要有两个方面,一是形态(景观结构)上的破碎化;二是生态功能上的破碎化,将景观连接度的概念引入卧龙自然保护区大熊猫的生境评价研究中,通过选择影响大熊猫生存的3种典型景观因子;地形高度,地形坡度和食物来源,从生态功能上研究3种景观因子由于空间组合的不匹配而形成的生境破碎化现状,在生物各景观因子重要性的基础上进行景观连接模糊相对赋值,并建立景观连接度评价模型,在地理信息系统支持下,研究了卧龙  相似文献   

8.
Crop raiding is a major form of human‐wildlife interaction mainly in the ecotone areas of human‐modified natural landscapes. The aim of this study was to examine the spatial pattern of crop raiding and the resultant impacts on how farmers perceive forests at different distances from Yayu Coffee Forest Biosphere Reserve which is located in southwest Ethiopia. For this, thirty transects (each 1 km long) were laid out at 200 m interval parallel to forest edges: ten transects close to forest (<0.5 km), ten at intermediate (0.5–1 km), and ten transects were taken far from forest (>1 km). Along each transect, 2–6 households were randomly selected and interviewed using semistructured questionnaire. The perception of the respondents on forests at different distances from forest edges was analyzed using Pearson''s Chi‐square test. The variation in the amount of damage among these three locations was tested using one‐way ANOVA. Four wild large mammals including olive baboon, vervet monkey, bush pigs, and crested porcupine were identified as top crop raiders in the area. The frequencies of occurrence of crop raiders decreased with increasing distance from forest edges. Similarly, the amount of damage in maize fields was higher close to forests when compared with that of either at intermediate or far from forest edges (p < .001). Eighty‐one percent of the households living close to the forests perceive that forest is a threat to their survival. Overall, our results imply that strategies need to be sought in order to minimize the socio‐ecological impacts of crop raiders mainly in locations close to forest edges.  相似文献   

9.
Medium and large‐sized mammals of Jorgo‐Wato Protected Forest have not yet been documented though the forest established before four decades. Hence, this study aims to document medium and large mammals and the behavioral responses of selected mammals toward anthropogenic activities in the study area. The study was conducted from February 2015 to June 2016, encompassing the wet and dry seasons. Data were collected mainly through camera traps, indirect and direct evidence. The study revealed about 23 medium and large‐sized mammals that belong to seven orders namely Bovidae, Carnivora, Primates, Rodentia, Tubulidentata, Lagomorpha, and Hyracoidea. Papio anubis, C. guereza, and C. aethiops were the most abundant large mammals in JWPF. Because of high anthropogenic activities, African buffalo shifted its activity period from diurnal into crepuscular and nocturnal. African buffalo traveled longer distances during the wet season (mean = 14.33 km, SD = 1.25 km) than during the dry season (mean = 9.00 km, SD = 2.16 km). This could be due to the fact that the local people were less likely to go to the forest for resource exploitation during the wet season as they are fully engaged in agricultural activities. However, low agricultural activities during the dry season allow the local people to extract resources and involve in bushmeat hunting which could limit the movement of mammals to their refugia. African buffalo preferred to rest on and adjacent to a gravel road (22.1%) in the forest, followed by on open rocky hilltops (14.7%) at night time, but rest in the bottomland thicket vegetation during the dry daytime. Regardless of high human pressure in the area, this study has revealed a good number of medium and large‐sized mammals that could be used as baseline information to design a sound conservation and management action plan of large mammals and their habitat in Jorgo‐Wato Protected Forest.  相似文献   

10.
The decrease in threshold shown by the eye during dark adaptation proceeds in two steps. The first is rapid, short in duration, and small in extent. The second is slow, prolonged, and large. The first is probably due to cone function; the second to rod function. In centrally located fields the two parts of adaptation change differently with area. With small, foveal fields the first part dominates and only traces of the second part appear. As the area increases the first part changes a little, while the second part covers an increasing range of intensities and appears sooner in time. Measurements with an annulus field covering only the circumference of a 20° circle show most of the characteristics of a 20° whole field centrally located. Similarly a 2° field located at different distances from the center shows dark adaptation characteristics essentially like those of large centrally located fields whose edges correspond to the position of the central field. Evidently the behavior in dark adaptation of centrally located fields of different size is determined in the main not by area as area, but by the fact that the retina gradually changes in sensitivity from center to periphery, and therefore the larger the field the farther it reaches into peripheral regions of permanently greater sensibility.  相似文献   

11.
陕西汉中地区黑熊的现状,分布及保护措施   总被引:3,自引:0,他引:3  
1991-1993年,作者在陕西省汉中林区采用三阶抽样设计调查并询访群众,求算每个所选择的最小样本单位(三级区)的方差,推算黑熊整体数量。根据黑熊数量将该地林区划分为3个密度区级:高密度区(0.03头/km ̄2以上),秦岭中山区;中密度区(0.01-0.029头/km ̄2),巴山中山区;低密度区(0.01头/km ̄2以下),秦巴低山丘陵区。全区有黑熊312头,平均密度0.035/km ̄2,遍布10县166个乡。分析了各地黑熊数量多寡的原因,提出了相应的保护措施。  相似文献   

12.
While patterns of spore dispersal from single sources at short distances are fairly well known, information about ‘spore rain’ from numerous sources and at larger spatial scales is generally lacking. In this study, I sampled spore rain using a novel method consisting of 0.25–0.5 m2 cotton cloth traps at nine sites in the boreo‐nemoral vegetation zone in eastern Sweden during two seasons, using Sphagnum spores as a model. Traps were located in various landscapes (mainland, islands). Additional trapping was done in an arctic area (Svalbard) without spore production. Spore densities were tested against distance from the nearest source and area of sources (open peatlands) within different radii around each site (5, 10, 20, 50, 100, 200, 300, 400 km). The cloth method appeared reliable when accounting for precipitation losses, retaining approximately 20–60% of the spores under the recorded amounts of precipitation. Estimated spore densities ranged from 6 million m?2 and season within a large area source, via regional deposition of 50 000–240 000 spores m?2, down to 1000 m?2 at Svalbard. Spore rain for all sites was strongly related to distance from the nearest source, but when excluding samples taken within a source peatland, the amount of sources within 200 km was most important. Spores were larger at isolated island sites, indicating that a higher proportion originated from distant, humid areas. Immense amounts of Sphagnum spores are dispersed across regional distances annually in boreal areas, explaining the success of the genus to colonise nutrient poor wetlands. The detectable deposition at Svalbard indicates that about 1% of the regional spore rain has a trans‐ or intercontinental origin. The regional spore rain, originating from numerous sources in the landscape, is probably valid for most organisms with small diaspores and provides a useful insight in ecology, habitat restoration and conservation planning.  相似文献   

13.
农牧交错带土地沙化的本质及其形成研究   总被引:10,自引:0,他引:10  
通过对陕北农牧交错带不同类型沙化土地土体构型、土壤质地、元素组成和理化性质的分析,研究了土地沙化的本质。结果表明:受风沙作用影响,土壤中细粒物质逐渐减少,颗粒组成变粗;表层消失,最终被流沙所取代,原土壤剖面被覆盖在沙层之下;土壤有机质及养分含量减少,保水保肥性能降低,生产力不断下降;现代土壤形成过程以侵蚀和风沙沉积为主,物质淋溶和化学风化微弱。研究区土地沙化可划分为:风沙侵蚀为主、风沙蚀积平衡、风沙沉积为主和土壤形成发育4个阶段;沙化土地的类型有:肥力衰退质地粗化、表层剥蚀、片沙覆盖、流动沙丘与固定沙丘等5种。  相似文献   

14.
Our previous results have demonstrated that km23-2 has functions in TGFß signaling that are distinct from those for km23-1. In the current report, we demonstrate that blockade of km23-2 decreased TGFß activation of the human Smad7 promoter Smad7-Luc, an endogenous Smad3-target promoter. Luminescence-based mammalian interaction mapping (LUMIER) analyses showed that TGFß stimulated the interaction of km23-2 preferentially with Smad3, relative to that with Smad2. Size exclusion chromatography experiments revealed that km23-2 and Smad3 were recruited into the same complex after TGFß treatment. Moreover, in the presence of TGFß, but not in the absence, km23-2 was present in early endosomes with the TGFß receptors (TßRs) and Smad3. Collectively, our data indicate that km23-2 is a critical signaling intermediate in a Smad3-dependent TGFß signaling pathway. We also provide evidence of the novel finding that TGFß stimulates the rapid recruitment of the km23-2 dimer to the dynein intermediate chain (DIC) of the dynein complex, whereas a kinase-deficient form of TßRII prevented this interaction. Finally, we demonstrate for the first time that TGFß stimulated not only assembly of the dynein motor attachment complex, but also triggered the tethering of the km23-2-Smad3 cargo to the other dynein components. Thus, our data demonstrate a novel function for km23-2 as a motor receptor to recruit Smad3 to the dynein complex for intracellular transport, thereby mediating Smad3-dependent TGFß signaling.  相似文献   

15.
内蒙古半干旱区鼠类群落结构及鼠害危害类型的研究   总被引:8,自引:1,他引:7  
自1988-1993年在内蒙古半干旱区约110000km2 的面积上设置样地251个,用夹日法对鼠类群落进行调查,用每个样地主要鼠种捕获率和样地构成分类量刚,应用SAS系统的快速聚类法进行分类;分类结果结合该地区地带性植被分布的特征和地貌、地形特征,将该地区的鼠类群落划分为9个地带性鼠类群落并研究其结构特征,同时根据地带性鼠类群落分布与结构特征及当地实际鼠害状况将内蒙古半干旱区鼠害划分为5大害区的7种危害类型:Ⅰ.荒漠草原鼠害危害区:①小毛足鼠、三趾跳鼠危害类型;②戈壁五趾跳鼠、赤颊黄鼠危害类型;Ⅱ.草原化荒漠鼠害鼠害危害区:③戈壁五趾跳鼠、三趾跳鼠危害类型;Ⅲ.沙地草场鼠害区:④小毛足鼠、三趾跳鼠、子午沙鼠危害类型;Ⅳ.阴山北麓旱作农田危害区:⑤长爪沙鼠、小毛足鼠危害类型;⑥长爪沙鼠、草原黄鼠危害类型;Ⅴ.阴山山脉中段次生林地和人工林地危害区:⑦棕背繙、大林姬鼠危害类型。  相似文献   

16.
AimsTo evaluate the relation between residential distance and total ischaemic time in patients with acute ST-elevation myocardial infarction (STEMI).MethodsSTEMI patients were transported to the Isala Hospital Zwolle with the intention to perform primary percutaneous coronary intervention PCI (pPCI) from 2004 until 2010 (n = 4149). Of these, 1424 patients (34 %) were referred via a non-PCI ‘spoke'' centre (‘spoke’ patients) and 2725 patients (66 %) were referred via field triage in the ambulance (ambulance patients).ResultsA longer residential distance increased median total ischaemic time in ‘spoke’ patients (0–30 km: 228 min, >30-60 km: 235 min, >60-90 km: 264 min, p < 0.001), however not in ambulance patients (0–30 km: 179 min, >30-60 km: 175 min, >60-90 km: 186 min, p = 0.225). After multivariable linear regression analysis, in ‘spoke’ patients residential distance of >30-60 km compared with 0–30 km was not independently associated with ischaemic time; however, a residential distance of >60-90 km (exp (B) = 1.11, 95 % CI 1.01-1.12) compared with 0–30 km was independently related with ischaemic time. In ambulance patients, residential distance of >30-60 and >60-90 km compared with 0–30 km was not independently associated with ischaemic time.ConclusionA longer distance from the patient’s residence to a PCI centre was associated with a small but significant increase in time to treatment in ‘spoke’ patients, however not in ambulance patients. Therefore, referral via field triage in the ambulance did not lead to a significant increase in time to treatment, especially at long distances (up to 90 km).  相似文献   

17.
四合木(Tetraena mongolica)分布区景观结构时空变化分析   总被引:5,自引:0,他引:5  
利用3S技术,1972年航空黑白像片,1988年TM CCT磁带数据以及1995年1:10万TM影像等信息源,以斑块为最小景观结构单元,对西鄂尔多斯特有种四合木(Tetraena mongolica)的分布及其分布区的景观结构进行了研究,结果表明:(1)四合木的分布区面积约为2 754km2;(2)分布区面积及斑块平均面积都在减少,1988年实际占有1456km2,1995年为15.38km2,减少了18.1%;(3)四合木分布面积的减少在不同时空尺度上并不相同,1988-1995年间的年变化率比1972-1988年间的年变化率高5倍,空间尺度上城市工业区的年变化率比放牧分布区高。  相似文献   

18.
Among birds, breeding numbers are mainly limited by two resources of major importance: food supply and nest-site availability. Here, we investigated how differences in land-use and nest-site availability affected the foraging behaviour, breeding success and population trends of the colonial cavity-dependent lesser kestrel Falco naumanni inhabiting two protected areas. Both areas were provided with artificial nests to increase nest-site availability. The first area is a pseudo-steppe characterized by traditional extensive cereal cultivation, whereas the second area is a previous agricultural zone now abandoned or replaced by forested areas. In both areas, lesser kestrels selected extensive agricultural habitats, such as fallows and cereal fields, and avoided scrubland and forests. In the second area, tracked birds from one colony travelled significantly farther distances (6.2 km ±1.7 vs. 1.8 km ±0.4 and 1.9 km ±0.6) and had significant larger foraging-ranges (144 km2 vs. 18.8 and 14.8 km2) when compared to the birds of two colonies in the extensive agricultural area. Longer foraging trips were reflected in lower chick feeding rates, lower fledging success and reduced chick fitness. Availability and occupation of artificial nests was high in both areas but population followed opposite trends, with a positive increment recorded exclusively in the first area with a large proportion of agricultural areas. Progressive habitat loss around the studied colony in the second area (suitable habitat decreased from 32% in 1990 to only 7% in 2002) is likely the main driver of the recorded population decline and suggests that the effectiveness of bird species conservation based on nest-site provisioning is highly constrained by habitat quality in the surrounding areas. Therefore, the conservation of cavity-dependent species may be enhanced firstly by finding the best areas of remaining habitat and secondly by increasing the carrying capacity of high-quality habitat areas through safe nest-site provisioning.  相似文献   

19.
The spatial variation of Wuchereria bancrofti and Plasmodium falciparum infection densities was measured in a rural area of Papua New Guinea where they share anopheline vectors. The spatial correlation of W. bancrofti was found to reduce by half over an estimated distance of 1.7 km, much smaller than the 50 km grid used by the World Health Organization rapid mapping method. For P. falciparum, negligible spatial correlation was found. After mass treatment with anti-filarial drugs, there was negligible correlation between the changes in the densities of the two parasites.  相似文献   

20.
在大田条件下,以大穗型品种泰农18和中穗型品种山农15为材料,研究不同种植密度(泰农18:每公顷135、270、405万株;山农15: 每公顷172.5、345、517.5万株)对冬小麦根系时空分布和氮素利用效率的影响.结果表明:在整个生育期,随种植密度的增加,泰农18的根长密度、根系总吸收面积和活跃吸收面积均显著增加;在生育后期,山农15的根长密度、根系总吸收面积和活跃吸收面积在种植密度为每公顷345万株时最大.泰农18的籽粒产量、氮肥吸收利用效率、氮肥偏生产力和氮素利用效率在种植密度为每公顷405万株时最高,山农15在种植密度为每公顷345万株时最高,但与种植密度为每公顷517.5万株的处理差异不显著.随种植密度的增加,冬小麦成熟期土壤硝态氮、铵态氮和无机态氮在不同土层的积累量均降低.泰农18和山农15种植密度分别为每公顷405万株和345万株时,是兼顾高产和高效利用氮素的适宜种植密度.  相似文献   

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