Functional heterogeneity in resources within landscapes and herbivore population dynamics     

Norman Owen-Smith 《Landscape Ecology》2004,19(7):761-771

Large mammalian herbivores are notorious for their propensity towards population irruptions and crashes, yet many herbivore populations remain relatively stable. I explore how resource heterogeneity within landscapes dampens population instability, using a metaphysiological modelling approach considering patch state distributions. Resource heterogeneity is functionally stabilizing through spreading consumption away from preferred resources before these become critically depleted. Lower-quality resources act as a buffer against starvation during critical periods of the seasonal cycle. Enriching resource quality is destabilizing, even if patch diversity is maintained, because food quantity then becomes the limitation. The potential consequences of landscape fragmentation are explored using the Serengeti ecosystem, characterised by broadscale resource gradients, as a hypothetical example. Further insights provided by the model are illustrated with specific examples concerning the effects of patch scales and waterpoint distribution. A metaphysiological modelling approach enables the basic consequences of landscape heterogeneity to be distinguished from further effects that may arise from specific patch scales and configurations, without the distracting detail of spatially explicit models.  相似文献   

毒死蜱和甲氰菊酯对蜜蜂毒性与安全评价研究   总被引：4，自引：0，他引：4  

吴声敢  王强  赵学平  吴长兴  陈丽萍  徐浩  章虎 《农药科学与管理》2004,25(1):14-16,21

通过接触法和摄入法测定了毒死蜱和甲氰菊酯对蜜蜂的毒性。结果表明，毒死蜱和甲氰菊酯对蜜蜂的接触毒性(24h LD50)分别为0．1634μg／蜂和0．0501μg／蜂，胃毒毒性(24h LE50)分别为0．6406mg／L和7．8261mg／L。根据Atkins毒性等级划分标准，毒死蜱和甲氰菊酯对蜜蜂的毒性均为高毒，应禁止在蜜蜂活动区域使用。  相似文献   

Validation of the specificity and sensitivity of species-specific primers that provide a reliable molecular diagnostic for <Emphasis Type="Italic">Xiphinema diversicaudatum</Emphasis>, <Emphasis Type="Italic">X. index</Emphasis> and <Emphasis Type="Italic">X. vuittenezi</Emphasis>     

Judith Hübschen  Lilo Kling  Ulrike Ipach  Volker Zinkernagel  Nathalie Bosselut  Daniel Esmenjaud  Derek J.F. Brown  Roy Neilson 《European journal of plant pathology / European Foundation for Plant Pathology》2004,110(8):779-788

Xiphinema diversicaudatum and X. index are vector nematode species of economic importance in viticulture regions as they can transmit Arabis Mosaic, Grapevine Fanleaf and Strawberry Latent Ringspot viruses to grapevine. Wang et al. (2003) designed species-specific diagnostic primers from ribosomal genes for both these vector species as well as a vector and a non-vector species X. italiae and X. vuittenezi, respectively. Our study aimed to confirm the specificity and determine the sensitivity and reliability of the primers for the two vector species, X. diversicaudatumand X. indexwhen challenged with closely related longidorid species and general nematode communities typical of vineyard soil. With one exception, no PCR product was observed when the primers were tested against six Longidorus, one Paralongidorus and one Xiphinema non-target species. Occasionally (three out of eight replicate PCR reactions) a weak PCR product was noted when primers for X. index were tested with L. elongatus. Furthermore, when challenged with a range of non-target nematode species comprising the nematode community typical of viticulture soil, no PCR product was amplified. An experimental dilution series of extracted DNA rigorously demonstrated that DNA from an equivalent single specimen of the target virus-vector species, X. diversicaudatum and/or X. index, could be detected amongst 1000 equivalent non-targetX. vuittenezi. Also, extracted DNA from an equivalent single target specimen was detected when added to DNA extracted from the overall soil nematode community. The primers were assessed further by using serial mixtures of actual nematodes rather than extracted DNA to simulate field soil. Using this method, a single target nematode could be detected amongst 200 non-target specimens. Given their specificity, sensitivity and reliability, it appears that these diagnostic primers will be of great benefit to phytosanitary/quarantine services related to the viticulture industry.  相似文献   

两种一步法RNA提取试剂的比较   总被引：2，自引：0，他引：2  

孙映雪孙承英  赵永刚陈继明宋翠平  王志亮 《中国动物检疫》2004,21(12):22-23

RNA的提取在生物医学研究和临床检测上应用广泛。本文分别用进口Invitrogen公司生产的以及我们自己研制的一步法RNA提取试剂，提取大肠杆菌RNA、鸡肌肉组织RNA和尿囊液RNA，通过核酸电泳和荧光定量RT-PCR进行比较。结果表明用我们自己研制的和进口的试剂提取的RNA都不含有DNA；这些RNA都可以作为模板进行RT-PCR检测，并且在数量上相互之间没有明显差异。说明我们自己研制的一步法RNA提取试剂可以取代进口试剂。此外，本文还讨论了此类试剂一些评定方法。  相似文献   

黄羽肉鸡育肥期维生素A、E适宜添加量研究   总被引：6，自引：0，他引：6  

赵芸君  文杰  陈继兰  赵桂萍  郑麦清  雒秋江 《畜牧兽医学报》2005,36(7):654-660

选体重和脚胫颜色度接近的56日龄黄羽肉鸡共960只,随机分为16个处理组,每处理60只鸡。采用双因子4×4水平的随机试验设计,4个维生素A添加水平(0、5000、10000、20000IU/kg)和4个维生素E添加水平(0、30、60、120IU/kg)。结果表明:在维生素A0～10000IU/kg、维生素E0～60IU/kg范围内,黄羽肉鸡的日增重和饲料报酬逐渐提高;日粮维生素A添加量超过10000IU/kg,血浆中维生素E含量有下降趋势。高水平维生素A(20000IU/kg),升高血浆TBARS值,大剂量维生素E(120IU/kg),提高机体脂质稳定性。日粮添加20000IU/kg维生素A对色素的沉积有抑制作用,随维生素E水平的上升,皮肤的颜色指数呈现上升趋势。维生素A和E含量及其互作对血清新城疫抗体效价有显著影响。综合考虑,黄羽肉鸡育肥期维生素A、E的适宜添加量分别为5000～10000IU/kg,30～60IU/kg。  相似文献   

黄芩抗鸡大肠杆菌作用的研究     

赵银丽  李国喜 《水禽世界》2005,(11):13-15

通过体外和体内两种方法研究黄芩抗鸡大肠杆菌作用.通过体外抑菌作用测定黄芩水煎液对鸡大肠杆菌的最小抑菌浓度（MIC）为2.5g/ml;体内抑菌作用通过对7日龄雏鸡的攻毒与治疗试验来研究,体内治疗药物浓度5g/ml可使90%以上雏鸡获得保护,10g/ml可使100%雏鸡获得保护.以上说明黄芩可以对抗鸡大肠杆菌,可以防治鸡的大肠杆菌病.  相似文献   

四川猪链球菌Ⅱ型分离株生物学特性的初步研究   总被引：2，自引：0，他引：2  

刘华雷王君玮  赵永刚赵云玲范伟兴  陈义平王志亮 《中国动物检疫》2005,22(10):20-22

猪链球菌Ⅱ型是导致许多国家猪链球菌病的主要病原，自90年代晚期江苏发生猪链球菌Ⅱ型感染以来已成为我国引起人畜共患病的一种重要的新病原菌。最近在四川省部分地区发生了不明原因的猪源人畜共患病，且具有较高的死亡率。我们从病死猪的病料中成功分离到三株猪链球菌分离株，经革兰氏染色、生化试验、血清凝集试验和PCR鉴定，最终证实为猪链球菌Ⅱ型。通过对其毒力因子进行鉴定．结果发现MRP和EF均为阳性。进一步的药敏试验证实：分离菌株对氨苄青霉素、先锋霉素Ⅳ、羧苄青霉素、复方新诺明、头孢肤肟等抗菌药高度敏感。  相似文献   

黄土丘陵区草本群落生物量空间分布格局及其影响因素   总被引：1，自引：0，他引：1  

方昭  张少康  刘海威  焦峰  张军 《草业学报》2018,27(2):26-35

草地是干旱半干旱地区黄土高原植被组成的主体,而草本植物作为草地生态系统的优势群落,在黄土高原恢复植被和水土保持建设方面存在着不可替代的优势。因此本试验选取黄土丘陵区不同纬度下的草本群落为研究对象,分析草本群落地上、地下生物量的空间分布特征及其影响因素,同时并验证等速生长关系,以期为黄土丘陵区恢复植被、改善生态建设方面提供理论指导。结果表明:(1)在纬度梯度35.95°~38.36° N变化范围内,黄土丘陵区不同植被带草本群落地上生物量变化范围为54.60~204.32 g·m^-2,平均值156.968 g·m^-2,变异系数为27.83%;地下生物量变化范围为78.88~829.64 g·m^-2,平均值469.21 g·m^-2,变异系数为48.87%;草本群落地下/地上生物量变化范围为 0.93~4.49,平均值2.89,变异系数为39.18%。草本群落生物量(地下、地上)大小顺序均为:森林-草原带>草原带>森林带>草原-荒漠带,且地上、地下生物量随纬度梯度变化规律均呈现出“先增加后减少”的单峰型变化趋势。(2)草本群落地下与地上生物量呈极显著正相关(P<0.01),决定系数达到0.59,且符合等速生长关系。(3)草本群落地下生物量与年均降水、年均温、土壤有机碳、全氮、全磷含量之间均呈显著相关。气候因子和土壤理化性质对地下生物量都具有重要影响作用,其影响机理还需进一步结合植物生物学和生理生态方面的综合研究才能做出准确结论。  相似文献   

A review on breeding and genetic strategies in Iranian buffaloes (<Emphasis Type="Italic">Bubalus bubalis</Emphasis>)     

Abbas Safari  Navid Ghavi Hossein-Zadeh  Abdol Ahad Shadparvar  Rostam Abdollahi Arpanahi 《Tropical animal health and production》2018,50(4):707-714

The aim of current study was to review breeding progress and update information on genetic strategies in Iranian buffaloes. Iranian buffalo is one of the vital domestic animals throughout north, north-west, south and south-west of Iran with measurable characteristics both in milk and meat production. The species plays an important role in rural economy of the country due to its unique characteristics such as resistance to diseases and parasites, having long productive lifespan and showing higher capability of consuming low-quality forage. In Iran, total production of milk and meat devoted to buffaloes are 293,000 and 24,700 tons, respectively. Selection activities and milk yield recording are carrying out by the central government through the Animal Breeding Centre of Iran. The main breeding activities of Iranian buffaloes included the estimation of genetic parameters and genetic trends for performance traits using different models and methods, estimation of economic values and selection criteria and analysis of population structure. Incorporating different aspects of dairy buffalo management together with improved housing, nutrition, breeding and milking, is known to produce significant improvements in buffalo production. Therefore, identifying genetic potential of Iranian buffaloes, selection of superior breeds, improving nutritional management and reproduction and developing the education and increasing the skills of practical breeders can be useful in order to enhance the performance and profitability of Iranian buffaloes.  相似文献   

Prevalence of <Emphasis Type="Italic">Haemonchus contortus</Emphasis> infection in sheep slaughtered at Jimma town municipal abattoir,Ethiopia     

Amarech Habte  Nuraddis Ibrahim 《Tropical animal health and production》2018,50(8):1865-1870

Haemonchus contortus is a parasite of major economic importance of most sheep-rearing areas of the world. A cross-sectional study was conducted from November 2015 to March 2016 with objectives of determining the prevalence and associated risk factors of Haemonchus contortus infection in sheep slaughtered at Jimma town municipal abattoir, Ethiopia. Of the total 7000 sheep slaughtered during the study time period, 384 sheep were randomly selected and examined for parasites. The overall prevalence of Haemonchus contortus infection was 264 (68.75%). Infection rate of poor body condition animals was significantly (P?=?0.000) higher than good body conditioned animals. The mean packed cell volume (PCV) values (%) of parasitemic and aparasitemic sheep were 23.73?±?3.7 SD and 37.66?±?4.736 SD, respectively. The prevalence in adult sheep (>?1 year) was insignificantly (P?=?0.653) higher than that of young sheep (≤?1 year). The highest prevalence was recorded in sheep that originated from Seka district (73.3%) and the lowest in Kersa district (63.4%) with non-significant variation (P?=?0.691). The highest monthly mean worm burdens and prevalence of Haemonchus contortus infection were recorded in November and lowest in March. The current study revealed that Haemonchus contortus infection is an important and common parasitic disease and requires special attention to its control.  相似文献