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81.
The factors responsible for widespread declines of grassland birds in the United States are not well understood. This study,
conducted in the short-grass prairie of eastern Wyoming, was designed to investigate the relationship between variation in
habitat amount, landscape heterogeneity, prey resources, and spatial variation in grassland bird species richness. We estimated
bird richness over a 5-year period (1994–1998) from 29 Breeding Bird Survey locations. Estimated bird richness was modeled
as a function of landscape structure surrounding survey routes using satellite-based imagery (1996) and grasshopper density
and richness, a potentially important prey of grassland birds. Model specification progressed from simple to complex explanations
for spatial variation in bird richness. An information-theoretic approach was used to rank and select candidate models. Our
best model included measurements of habitat amount, habitat arrangement, landscape matrix, and prey diversity. Grassland bird
richness was positively associated with grassland habitat; was negatively associated with habitat dispersion; positively associated
with edge habitats; negatively associated with landscape matrix attributes that may restrict movement of grassland bird; and
positively related to grasshopper richness. Collectively, 62% of the spatial variation in grassland bird richness was accounted
for by the model (adj-R2 = 0.514). These results suggest that the distribution of grassland bird species is influenced by a complex mixture of factors
that include habitat area affects, landscape pattern and composition, and the availability of prey. 相似文献
82.
Spatial and temporal landscape patterns have long been recognized to influence biological processes, but these processes often
operate at scales that are difficult to study by conventional means. Inferences from genetic markers can overcome some of
these limitations. We used a landscape genetics approach to test hypotheses concerning landscape processes influencing the
demography of Lahontan cutthroat trout in a complex stream network in the Great Basin desert of the western US. Predictions
were tested with population- and individual-based analyses of microsatellite DNA variation, reflecting patterns of dispersal,
population stability, and local effective population sizes. Complementary genetic inferences suggested samples from migratory
corridors housed a mixture of fish from tributaries, as predicted based on assumed migratory life histories in those habitats.
Also as predicted, populations presumed to have greater proportions of migratory fish or from physically connected, large,
or high quality habitats had higher genetic variability and reduced genetic differentiation from other populations. Populations
thought to contain largely non-migratory individuals generally showed the opposite pattern, suggesting behavioral isolation.
Estimated effective sizes were small, and we identified significant and severe genetic bottlenecks in several populations
that were isolated, recently founded, or that inhabit streams that desiccate frequently. Overall, this work suggested that
Lahontan cutthroat trout populations in stream networks are affected by a combination of landscape and metapopulation processes.
Results also demonstrated that genetic patterns can reveal unexpected processes, even within a system that is well studied
from a conventional ecological perspective. 相似文献
83.
84.
85.
补充青贮玉米对复合稻草块体外发酵特性的影响 总被引:1,自引:0,他引:1
应用体外发酵产气技术,研究了青贮玉米以不同比例(0%~100%)替代复合稻草块中稻草对其体外发酵特性的影响。结果表明:随着青贮玉米比例的升高,复合稻草块的24h产气量、产气速度常数、有机物消化率、代谢能呈逐渐上升的趋势(P<0.05)。替代比例低于40%时24h产气量组合效应不显著(P>0.05),替代比例高于40%后出现逐渐增大的正组合效应,当替代比例为50%时,正组合效应值(9.68)显著增加(P<0.05),以后变动幅度不大。综上可见,用青贮玉米替代复合稻草块中40%以上的稻草较为适宜,当替代比例为50%时,就可获得较好的消化率。 相似文献
86.
87.
为了明确内生枯草芽孢杆菌B-001对烟草的促生机制和对烟草青枯病的防治效果,采用温室盆栽试验、内源激素检测及处理烟草植株B-001菌量追踪测定等方法研究内生枯草芽孢杆菌B-001的作用机制及其自身在烟草体内的群体数量动态等。结果表明:施用B-001菌株后,烟草幼苗鲜重增加了43.01%~57.70%;烟草中吲哚乙酸、赤霉素和玉米素核苷的含量增加,而脱落酸的含量降低;苗期至旺长期的烟草K326中B-001数量大幅增加,但到成熟期数量大幅下降;1×107、1×108、1×109、1×1010cfu/mL的菌悬浮液对烟草青枯病的防治效果分别为50.3%、62.8%、70.2%、70.3%。 相似文献
88.
家蚕产卵量的基因效应参数估计 总被引:6,自引:2,他引:4
用产卵量差异较大的两个近交系782和Ekp作亲本,配制了F1、F2正反交及F1与两亲本的回交B1和B2,加上两亲本P1和P2共8个世代,采用多世代平均值的多元回归分析方法对产卵量的基因效应参数进行了估计,得到了如下结果:(1)建立了分析家蚕产卵量的常染色体基因加性、显性和性染色体基因加性效应的非二体遗传模型,并通过实际数据检验表明产卵量遗传符合这个模式;(2)产卵量的遗传主要取决于常染色体上基因加性效应,其次是性染色体基因加性效应,显性效应很小。 相似文献
89.
中草药复合添加剂防治兔球虫病及增重效果研究 总被引:3,自引:1,他引:2
选用无感染幼兔42只,随机分为A、B、C、D、E5组,进行防治兔球虫病和增重试验,其中A组为中药加矿微加喹乙醇组,B组为中药加矿微组,C组为西药对比组,D组为感染不给药组,E组为不感染不给药组;在同样饲料、同等饲养条件下,饲养30天。结果,A组保护率90%,增重率98.2%;B组保护率100%,增重率132.1%;C组保护率90%,增重率76.6%;D组兔于第11天全部死亡;E组保护率100%,增重率96.2%。试验结果证明,保护率以纯中药B组最佳,A组次之,增重率A、B组均高于C组和E组,以B组最佳。 相似文献
90.
在25℃、4℃不同温度条件下,用不同浓度的EMS诱发播娘蒿突变。结果表明,播娘蒿的发芽势、发芽率、出苗率和幼苗高度均随EMS浓度的提高而降低;且EMS在4℃时较25℃时对种子影响较小。EMS诱变播娘蒿的适宜浓度在10%和20%之间。 相似文献