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1.
放牧对克氏针茅草原植物群落与种群格局的影响 总被引：2，自引：1，他引：1
在内蒙古草原区中部的克氏针茅草原,连续4年(2006-2009年)进行了夏秋季划区轮牧实验;利用摄影和地理信息系统相结合方法,研究了不同放牧强度对植物群落和种群格局的生态作用效应。摄影图像和测定数据的分析结果表明,在不同放牧实验小区形成了大小不一、结构不同的群落斑块,并显示出不同放牧强度与放牧周期的植物群落及种群斑块结构的生态梯度格局。在不放牧的围封对照小区内(G5)保持原有的克氏针茅群落斑块和羊草群落斑块,二者的斑块数量、斑块面积之比、斑块的植物组成与生物量都比较稳定;在不同放牧强度的实验小区(G1、G2、G3),群落斑块的数量、面积、种群结构、植物多度、株丛冠幅、生物量等都形成了相对应的梯度差异。不同放牧强度导致克氏针茅群落与种群斑块的不同破碎化程度和植物个体(株丛)小型化。适度放牧使得斑块结构与生物量表现出中度干扰下植物补偿性生长的效应。结果表明植物群落斑块结构与种群格局的变化是草原植物群落演替过程中种群拓殖与衰退的基本形式,也是生态演替的机制。 相似文献
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植物群落物种多样性对生态系统生产力的影响 总被引：11，自引：3，他引：11
物种多样性对生态系统功能的影响是生态学领域所研究的核心科学问题之一.本研究利用人工构建的一年生植物群落,就植物群落物种多样性、植物功能群多样性和功能群成分对生态系统生产力的影响进行了研究,并对物种多样性-生态系统功能关系的作用机制--取样效应和生态位互补效应进行了验证.结果表明,随着物种多样性的增加,群落生产力呈增加趋势,物种多样性对生态系统功能存在正效应,物种多样性增加的总体效应可通过生产力与物种数的二次函数关系y=-37.463x2 478.63x 1 097.3,(R2＝0.916 7)得到较好的体现.功能群多样性和功能群成分均对系统功能有显著影响.总体而言,物种数一定时,功能群多样性较高的群落其生产力水平也较高,而功能群多样性一致时,含C3、C4功能成分的群落其生产力水平较其他群落的高.分析结果还表明,在多样性-生态系统功能关系中,取样效应和生态位互补效应共同发生作用,说明物种的特性及物种在资源利用方面表现出的异质性对生态系统功能可能都有重要影响. 相似文献
3.
采用VORTEX7.3软件对野牦牛的种群生存力进行了分析。研究结果显示:野牦牛集合种群在100年内的种群动态变化接近于根据野外工作得到的种群动态,种群在100年内的灭绝概率为零。在10年内野牦牛的种群数量呈急剧下降趋势,在20～50年内野牦牛的种群数量下降趋势逐渐缓和,50年后野牦牛种群数量呈稳定下降状态,在95年时野牦牛种群数量最小为50头。在60年内野牦牛的灭绝概率为0,在60～70年内野牦牛的灭绝概率有升高的趋势,在70～90年内野牦牛的灭绝概率急剧升高,在95年时野牦牛的灭绝概率达28%。野牦牛已处在濒危状态,急需保护。野牦牛死亡率的变化对它们种群生存力的影响要大于环境变化;逐步使野牦牛生境良性发展有利于野牦牛种群的良性发展;通过野牦牛种群间进行个体交换有利于保持它们的进化潜力。 相似文献
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为明确种间竞争和种内竞争效应对红色型豌豆蚜生长和繁殖产生的影响,本研究以红色豌豆蚜克隆、绿色型豌豆蚜克隆及豌豆修尾蚜克隆作为试验材料,选用琼脂法,首先制备4种竞争试验区(1头区,2头区,种内竞争区和种间竞争区),观察各试验区蚜虫的种群动态,另准备3个(红色型、绿色型及豌豆修尾蚜)高密度种群处理,分别往里放入1头4龄红色克隆若虫,统计其3日总产蚜数。结果发现,种内竞争区和种间竞争区,二者的竞争效应都非常明显,竞争区混合种群的增殖率高于2头区,种间竞争区红色克隆胜利组单头红色克隆第10天新生蚜数高于其他处理。此外,高密度的绿色克隆和豌豆修尾蚜种群均能抑制红色克隆的繁殖。因此,红色型豌豆蚜能通过评估竞争种和同伴的相对密度来控制繁殖,无论是种间竞争还是种内竞争均能影响其繁殖,且种间竞争可能加速它的繁殖速率。 相似文献
5.
两栖动物的受危及保护 总被引：2，自引：0，他引：2
种群的灭绝两栖动物是脊椎动物的一大类群,从世界范围来看正在不断灭绝,而且种群的灭绝率随时间在加大.如丹麦博恩岛上的无斑雨蛙(Hyla arborea),其灭绝率1950~1960年为36%,1960~1970年为45%,1980~1990年为60%.1977~1986年在丹麦调查的1300个地点与40年代和60年代的资料相比较,发现50%的种群消失了,其余种群也极大地减小了.珍稀种比普通种减少更快.对两栖动物种群的监测需要长期进行,否则有可能得出错误结论.在瑞士伯尔尼 相似文献
6.
通过调查临洮县南屏山、东山造林站区域植物群落中16种共同出现的种群生态位特征值,计测Shannon-Wiener生态位宽度和Petraitis特定重叠指数,并进行t测验。结果表明:1)两区域Shannon-Wiener生态位宽度特征值差异不显著,表明两个群落中种群竞争关系差异不显著,即资源位差异不显著,或尚未呈现资源不足;2)两区域Petraitis特定重叠指数特征值差异极显著,表明两个群落对资源的利用状况有极显著差异,即两种生态恢复模式的生态学效果差异极显著。3)不同群落中相同种群间的Shannn-Wiener生态位宽度和Petraitis特定重叠指数,可量化在不同强度干扰下植物群落中植物种群对资源的利用状况,可以利用生态位理论评价生态恢复效应,拓展生态恢复效应评价的结构体系。 相似文献
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《畜牧兽医科技信息》2007,(5):85
目前人类对环境的改变使得很多保守的生物学家担心会导致很多物种的灭绝,但是与此相反,来自耶鲁大学的生物学家们利用诱导病毒进入陷阱细胞的方法使其灭绝,相关结果发表在了最近的《生态快报》(Ecology Letters)上。 相似文献
9.
采用VORTEX7．3软件对鹅喉羚的种群生存力进行了分析。研究结果显示：鹅喉羚集合种群在100年内的种群动态变化接近于根据野外工作得到的种群动态。种群在100年内的灭绝概率为零，在25年种群数量最大440，25～65年间鹅喉羚的种群数量呈下降趋势，65年时鹅喉羚的灭绝概率最大32%，种群数量约减少20％，之后种群数量处于稳定下降趋势。已经处于濒危状态，需妻保护。鹅喉羚死亡率的变化对它们种群生存力的影响要大于环境变化；逐步使鹅喉羚生境良性发展有利于鹅喉羚种群的良性发展；通过鹅喉羚种群闯进行个体交换有利于保持它们的进化潜力。 相似文献
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11.
Genetic relationships among American donkey populations: insights into the process of colonization 
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下载免费PDF全文 J. Miró F. Goyache A. Loarca O.R. Martínez López J.L. Canelón A. Stemmer L. Aguirre M.A.C. Lara L.A. Álvarez S. Llambí N. Gómez L.T. Gama M.F. Nóvoa R.D. Martínez E. Pérez A. Sierra M.A. Contreras A.M. Guastella D. Marletta G. Arsenos I. Curik V. Landi A. Martínez J.V. Delgado 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2016,133(2):155-164
12.
Plant litter and livestock excreta are two important ways of carbon and nutrient input to soil in grassland grazing systems. Grazing livestock often deposit dung on plant litter, which may affect litter decomposition through a changing microenvironment. We assessed effects of yak dung on litter mixing effects on litter decomposition in a Tibetan alpine grassland. Six common species were selected, including low-quality litter species Kobresia capillifolia, Elymus nutans, and Ligularia virgaurea and high-quality litter species Anemone rivularis, Saussurea nigrescens, and Thermopsis lanceolata. Litter bags containing each species alone and all two-species combinations were allowed to decompose with and without experimental dung addition in the field. Mass loss of the leaf litter was measured after 6 and 12 mo. High-quality litter species had significantly greater mass loss than low-quality litter species. Dung significantly accelerated litter mass loss after both 6 and 12 mo for low-quality litter species, but only after 12 mo for high-quality litter species. Litter mixtures containing both high- and low-quality species showed positive nonadditive effects (NAEs) on mass loss after 6 mo but additive effects after 12 mo. Dung increased the strength of NAEs after 6 mo and shifted litter mixing effects from positive to negative NAEs after 12 mo. Our results support previous findings that litter mixing could produce NAEs on litter decomposition and that these NAEs could change with incubation time. Most importantly, we show that dung can modify NAEs, demonstrating that litter mixing effects are dependent on the microenvironment. Our findings also demonstrate that yak dung can influence soil processes by varying both single-species litter decomposition rates and litter interactions within mixtures. Furthermore, the results suggest yak dung is closely related to material and nutrient cycling, so we believe dung should remain and not be substantially removed from this grazing ecosystem. 相似文献
13.
A considerable fraction of the poultry carcasses becomes contaminated with Campylobacter by cross-contamination from the digestive tract of colonized broilers at slaughter. Campylobacter in the crop may serve as a possible source of cross-contamination, because the crop may contain high numbers of Campylobacter and is more likely to rupture during the slaughtering process than intestines. In this study, the correlation between Campylobacter colonization levels in crop and cecum was assessed in 48 broilers of 31 days of age. In addition, the effect of drinking water supplemented with 0.2% volatile fatty acid (VFA) on these Campylobacter colonization levels was studied. No correlation between crop and cecal colonization levels was found (p = 0.09; P = 0.71), indicating that future studies on cross-contamination should include an examination of not only cecal colonization levels but also crop colonization levels. Supplementation of drinking water with VFA did not result in a significant reduction of colonization levels in either the crop (P = 0.50) or the ceca (P = 0.92), indicating that this is not an effective measure to reduce cross-contamination at slaughter. 相似文献
14.
The pathogenic potential of Salmonella is determined during the complex interaction between pathogen and host, requiring optimal regulation of multiple bacterial genetic systems within variable in vivo environments. The mouse model of systemic disease has been an extremely productive model to investigate the pathogenesis of Salmonella enterica serovar Typhimurium (S. Typhimurium). Although the mouse model is a widely used paradigm for studying the pathogenesis of systemic disease caused by Salmonella, investigations concerning food safety interventions should employ natural hosts to examine gastrointestinal colonization by Salmonella. Recent research has demonstrated specific differences in the attenuation of certain S. Typhimurium mutants in mice compared to swine. This variation in pathogenesis between the mouse model and pigs for the S. Typhimurium mutants is presumably dependent upon either the requirements for specific gene products during systemic disease (mouse) versus gastrointestinal colonization (pig) or host specific differences. In addition, host specific diversity in Salmonella colonization of swine has also been described in comparison to other food-producing animals, including cattle and chickens. Differences in Salmonella colonization and pathogenesis across diverse animal species highlight the importance of species-specific studies of gastrointestinal colonization for the development of Salmonella interventions to enhance pork safety. 相似文献
15.
Experimental colonization of piglets and gilts with systemic strains of Haemophilus parasuis and Streptococcus suis to prevent disease. 总被引：6，自引：0，他引：6
S Oliveira L Batista M Torremorell C Pijoan 《Canadian journal of veterinary research》2001,65(3):161-167
Haemophilus parasuis and Streptococcus suis are both major causes of losses during the nursery period, especially in herds using the segregated early weaning system. In this system, only a few piglets may be colonized with the herd's prevalent systemic strain, which results in infection of naive penmates late in the nursery. In view of these factors, the objectives of this study were: (1) to evaluate the early colonization of piglets with the farm's prevalent systemic strain of H. parasuis and S. suis as an alternative method for disease prevention; and (2) to evaluate 2 different protocols for experimental colonization: direct colonization of piglets and colonization of piglets through nose-to-nose contact with inoculated sows. Haemophilus parasuis and S. suis isolates recovered from diseased nursery pigs were characterized by the rep-PCR technique and the herd's prevalent strains were used for colonization. Piglets in the experimentally colonized groups were inoculated at 5 days of age by the oral route using a spray pump. Sows were colonized at 2 weeks prior to farrowing using a similar protocol. Although both colonization protocols were successful in getting the piglets colonized, direct inoculation of 5-day-old piglets with the herd's systemic strains of H. parasuis and S. suis tended to be more effective in reducing the morbidity and the mortality than the colonization of piglets by nose-to-nose contact with inoculated sows. 相似文献
16.
《The Journal of Applied Poultry Research》2014,23(2):212-220
Outdoor access is an important part of organic and free-range poultry production, yet limited information exists on the effect of various housing and production systems on growth performance and colonization of food-borne pathogens. Therefore, the primary purpose of the current study was to evaluate the influence of different housing systems, particularly fixed versus small, portable houses, with and without outdoor access to pasture, on seasonal growth performance, leg quality, and presence of bacterial food-borne pathogens. In the current study, we used fast-growing broilers, as many small producers use commercial broilers due to their carcass conformation and high breast yield compared with slow-growing hybrids or standard heritage breeds. Although interest in alternative genetics exists because they may be more adapted to outdoor production, they require longer growing periods, with accompanying labor and cost. A pasture containing a mixture of forages was used to simulate the conditions common for small farms in the local region. The experiment had 4 treatment groups: (1) small, portable hoop houses with access to pasture, (2) small, portable hoop houses without access to pasture, (3) a fixed house with access to the outdoors, and (4) a fixed house without access to the outdoors. The present study was repeated at different times of the year to determine if a seasonal effect on the consumption of pasture and carcass quality was present. Overall, raising birds in hoop houses resulted in a reduced growth rate compared with birds raised in the fixed house. None of the production systems altered bone strength or feed conversion. Food-borne pathogens commonly associated with poultry were not found in any of the environments tested. Seasonal production was an issue in the small hoop house birds, as extreme heat in the summer resulted in early termination of that trial. Expanding on forage choice in pastures and customizing hoop houses to deal with weather fluctuations, especially in regions where extreme heat may affect production, are important considerations for these systems. 相似文献
17.
Colonization of suckling pigs by Streptococcus suis with particular reference to pathogenic serotype 2 strains. 总被引：3，自引：3，他引：0 下载免费PDF全文
下载免费PDF全文 Three swine commercial farms with high mortality rates in nursery pigs due to Streptococcus suis serotype 2 were studied. Brain samples from diseased animals were collected for a period of 6 to 10 mo and used to isolate the strain that was responsible for the mortality (virulent strain) in each farm. Tonsil swabs from piglets at 5, 10 and 15 d were taken to assess both total colonization and colonization by the virulent strain. The effect of sow vaccination against S. suis on colonization was evaluated in 1 of the farms. All suspect tonsil isolates were identified biochemically and then tested against serotype 2. The genomic patterns of serotype 2 isolates were compared to that of the virulent strain using Rep-PCR. Results showed that total colonization by S. suis occurred very early in the pigs' life, with most animals being colonized by weaning age. Prevalence of colonization by serotype 2 strains was much lower than total colonization. After comparing serotype 2 isolates with the virulent strains, only 1 tonsillar isolate had the same genomic pattern as the virulent strain and it belonged to a 4-week-old weaned pig. The genomic pattern of the virulent strain was not found in any tonsillar isolate from 15-day-old or younger pigs. Although limited by sample size, sow vaccination against S. suis increased total colonization at the same time significantly decreasing colonization by serotype 2 strains. Even though most pigs are colonized early in age by S. suis, colonization by the virulent strain is of low prevalence and delayed in time. This could constitute a risk factor for developing the disease later in time, because animals would be colonized when maternal immunity is no longer present, allowing the organism to become systemic. 相似文献
18.
本研究通过接种土壤从枝菌根(arbuscular mycorrhizal,AM)真菌孢子,探讨了在温室盆栽条件下,甘肃内生真菌(Epichlo?gansuensis)在不同重金属镉(Cd^2+)离子胁迫下对醉马草(Achnatherum inebrians)根系AM真菌侵染率的影响,以及内生真菌、Cd^2+和AM真菌三者互作对醉马草幼苗生长的影响。结果表明,Cd^2+和内生真菌互作对醉马草菌根侵染率无显著(P>0.05)影响,菌根侵染率随着Cd^2+浓度的增加呈现先升后降的趋势,在高浓度Cd2+(0.9 mmol·L^-1)条件下,内生真菌侵染(endophyte-infected,EI)的醉马草植株菌根侵染率显著(P<0.05)高于不带菌(endophyte-free,EF)的植株。低浓度Cd2+(0.3 mmol·L^-1)显著(P<0.05)促进了醉马草的生长,而高浓度Cd^2+(0.9 mmol·L^-1)条件下显著(P<0.05)抑制了醉马草的生长;内生真菌在高浓度Cd^2+(0.9 mmol·L^-1)胁迫条件下能够减轻其对醉马草的伤害;接种AM真菌显著(P<0.05)促进醉马草地上部分生长的同时显著(P<0.05)抑制了其根系的生长;三者互作显著(P<0.05)促进醉马草叶绿素含量和地上鲜重,但显著(P<0.05)抑制了醉马草根长。以上结果表明,内生真菌和Cd2+均能影响AM真菌对醉马草根系的侵染,但二者无互作效应,内生真菌、AM真菌和Cd2+三者互作会影响醉马草幼苗地上和地下生长。 相似文献
19.
B A Oyofo J R DeLoach D E Corrier J O Norman R L Ziprin H H Mollenhauer 《Avian diseases》1989,33(3):531-534
The effect of carbohydrates in the drinking water of broiler chickens on Salmonella typhimurium colonization was evaluated. Results indicate that mannose and lactose (2.5%) significantly (P less than 0.05) reduced intestinal colonization of S. typhimurium by at least one-half, as compared with dextrose, maltose, and sucrose. Lactose and mannose also significantly reduced (P less than 0.01) the mean log10 number of S. typhimurium in the cecal contents. Although mannose was the most effective sugar at blocking colonization, lactose may be more practical because it is effective and costs much less than mannose. Provision of carbohydrates in the drinking water had no significant effect on weight gain. 相似文献
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Yuri SAKAI Takamitsu TSUKAHARA Noritaka MATSUBARA Kazunari USHIDA 《Animal Science Journal》2007,78(1):92-97
In our previous study, a cell wall preparation of Enterococcus faecalis strain EC‐12 (EC‐12) prevented the colonization of vancomycin‐resistant enterococci (VRE) in newly hatched broiler chicks. Relatively early prevention against VRE colonization by EC‐12 administration may be related to the enhanced innate immune system. In this study we examined the effect of EC‐12 on the kinetics of immunoglobulin A (IgA) concentration in the cecal digesta of chicks from 1 day to 14 days old to evaluate humoral immunity. We also examined the effect of EC‐12 on β‐defensin mRNA expression and lysozyme production. The IgA concentration in the cecal digesta showed a decline in chicks from 2 to 8 days old and then a recovery up to when they were 14 days old. The concentration tended to be higher in EC‐12‐administered chicks than in control chicks at 14 days old. EC‐12 administration did not stimulate the lysozyme activities in the alimentary tract. However, β‐defensin mRNA expression in the tongue and the bursa of Fabricius was higher in chicks administered EC‐12 than in the control chicks at 5 days old. These results indicate that β‐defensin may be one of the major defense mechanisms inhibiting VRE colonization in young chicks. 相似文献