围栏禁牧对川西北亚高山高寒草甸群落结构的影响

围栏禁牧4a后,与放牧草地相比较:1)围栏草地物种数量有所下降,群落内出现物种27种,而长期放牧草地为33种.2)围栏草地物种平均高度较高,为20.23cm,群落分层现象明显;放牧草地物种平均高度仅为8.14cm,群落无分层现象.3)围栏草地内,杂草类的盖度(98%)大于禾草类的盖度(14%);放牧草地上,杂草类的盖度(53%)小于禾草类的盖度(56%)。4)围栏草地以禾草为主的优良牧草的生产能力(35.24g/m2)低于放牧草地的生产能力(75.47g/m2).5)围栏草地的地上生物量(272.64g/m2)和地下0～30cm生物量(801.61g/m3)都高于放牧草地的地上生物量(184.84g/m2)和地下0～30cm生物量(683.82g/m3).研究结果表明,围栏草地具有比放牧草地更复杂的群落结构,但其物种组成和优良牧草的生产能力,都低于放牧草地.     

Population structure and historical demography of the thorny skate (<Emphasis Type="Italic">Amblyraja radiata</Emphasis>, Rajidae) in the North Atlantic

Population genetic structure of the thorny skate (Amblyraja radiata) was surveyed in >300 individuals sampled from Newfoundland, Iceland, Norway, the Kattegat and the central North Sea. A 290-bp fragment of the mt cytochrome-b gene was first screened by SSCP. Sequences of SSCP haplotypes revealed 34 haplotypes, 14 of which were unique to Iceland, 3 to Newfoundland, 1 to Norway and 3 to the Kattegat. The global F _ST was weak but significant. Removal of the two Kattegat locations, which were the most differentiated, resulted in no significant genetic differentiation. Haplotype diversity was high and evenly distributed across the entire Atlantic (h = 0.8) with the exception of the North Sea (h = 0.48). Statistical parsimony revealed a star-like genealogy with a central widespread haplotype. A subsequent nested clade analysis led to the inference of contiguous expansion with evidence for long distance dispersal between Newfoundland and Iceland. Historical demographic analysis showed that thorny skates have undergone exponential population expansion that started between 1.1 million and 690,000 years ago; and that the Last Glacial Maximum apparently had little effect. These results strongly differ from those of a parallel study of the thornback ray (Raja clavata) in which clear structure and former refugial areas could be identified. Although both species have similar life history traits and overlapping ranges, the continental shelf edge apparently does not present a barrier to migration in A. radiata, as it does for R. clavata.     

中亚热带丝栗栲次生林群落高度级结构分析

以高度级为参考坐标，应用衡量优势种群及群落结构动态的失稳率、群落垂直空间的分享度、α—多样性及群落高度级梯度β—多样性等指标对中亚热带丝栗栲次生林群落高度级结构特征及其动态进行分析评价。结果表明：丝栗栲群落及其优势种群个体数、群落物种数和种对级的分享度随高度级增加都呈下降趋势；各高度级物种数和个体数呈明显的正相关关系；级间失稳率显示，群落在第2、3、6、7高度级呈增长趋势，第4、5高度级呈衰退趋势，群落整体具有增长性结构；群落随高度级形成丰富度指数(dMa)、Shannon—Wiener指数(H)逐渐降低，均匀度指数(J)先增后减的变化趋势；随高度级梯度的增加，群落相邻高度级间Whittaker指数(βw)呈上升趋势，而Mofisita—Horn指数(CMH)呈不规则地跳跃式变化，表现了共有种在群落不同高度级的数量差异。图3表2参15。     

编码输入法在PCB分配参数预测中的应用

根据Free-Wilson法中化合物结构表达的思想，采用两种简单的编码输入方法对58个多氯联苯(PCB)的结构进行表征，并基于模型简单性原则对多元线性回归(MLR)与误差反向传递(BP)人工神经网络、模拟退火(SA)人工神经网络和遗传算法(GA)人工神经网络PCB分配参数预测模型的预测能力进行了比较，试验证实，粗略考虑PCB结构对称性的简单编码输入规则可以简化PCB分配参数预测模型的数字形式，所获得的MLR模型具备广泛的应用前景。     

Canopy structure versus physiology effects on net photosynthesis of mountain grasslands differing in land use

The present paper aims at investigating how changes in canopy structure and species physiology associated with the abandonment of mountain meadows and pastures affect their net photosynthesis. For this purpose, a multi-layer vegetation–atmosphere transfer (VAT) model is employed, which explicitly takes into account the structural and functional properties of the various canopy components and species. Three sites differing in land use are investigated, a meadow, a pasture and an abandoned area. Model simulations agree reasonably with measured canopy net photosynthetic rates, the meadow featuring the highest daily net photosynthesis, followed by the pasture and, finally, the abandoned area. A detailed process analysis suggests this ranking to be mainly due to bulk canopy physiology, which decreases from the meadow to the pasture and the abandoned area, reflecting species composition and species-specific photosynthetic capacities. Differences between the canopies with regard to canopy structure are found to be of minor importance. The amounts of green, photosynthetically active plant matter are too similar at the three sites to be a major source of variation in net photosynthesis. Large differences exist between the canopies with regard to the amount of photosynthetically inactive phytoelements. Even though a model analysis showed them to be potentially important, most of them are accumulated close to the ground surface, where they exert little influence on canopy net photosynthesis.     

宁夏农牧业发展方向与草地农业结构调整问题的探讨

针对宁夏农牧业发展结构失衡的现状,指出长期推行重农轻牧的农区模式而不是发展草地农业是一种方向性失误。为此探讨了宁夏农牧业结构调整的生态学依据,分区调整方向与拓宽结构调整思路的问题。     

Pitch shifts and song structure indicate male quality in the dawn chorus of black-capped chickadees

The fee-bee song of male black-capped chickadees (Poecile atricapillus) is considered a single-type song that singers transpose up and down a continuous frequency range. While the ability to shift song pitch in this species provides a mechanism for song matching as an aversive signal in male-male territorial song contests, the functional significance of this behaviour during the solo performances of males during the dawn chorus is unclear. We analysed the dawn chorus songs and singing behaviour of males whose winter-flock dominance status we determined. We used correlation analysis to show that pitch shifts were accompanied by changes to other fine structural characteristics in song, including temporal and relative amplitude parameters. We also found that songs of socially dominant males and songs of their most subordinate flockmates could be distinguished using these methods by the way they performed a between-note frequency measure accompanying pitch shifts. That is, a ratio measure of the internote frequency interval remained constant for songs of high-ranking birds despite changes in absolute pitch, while low-ranking males sang a smaller ratio as they shifted to higher absolute pitches. These findings identify previously unrecognised variation in the songs of black-capped chickadees. More importantly, they indicate a mechanism by which pitch shifting during the dawn chorus of black-capped chickadees could provide a reliable indicator of relative male quality.Communicated by I. Hartley     

On the social structure of offspring rearing in the burrower bug,<Emphasis Type="Italic"> Sehirus cinctus</Emphasis> (Hemiptera: Cydnidae)

Maternal-offspring interactions are important in a variety of animals. Understanding the evolution of these interactions requires that we also study the broader social context in which they occur. To date, behavioral studies on burrower bugs, Sehirus cinctus, have focused exclusively on interactions between mothers and offspring. Here we ask whether these interactions occur in a social context that extends beyond the family unit of a mother and her own genetic offspring. Such social structure can arise from behaviors that occur before eggs are laid, or from actions of individuals that occur post-hatching. We present field data showing that lay sites of mothers are spatially aggregated on a scale that would lead to behavioral interactions among families. Microsatellite markers suggest neighboring mothers are unrelated. Laboratory experiments do not support the hypothesis that spatial aggregation results from a direct attraction of females to one another. Other laboratory studies reported here indicate that, after hatching, unrelated clutches sometimes join together to form multifamily groups. Experiments reveal that mothers are not necessary for these joining events to occur. In sum, these data suggest that both mothers and offspring play active, but different, roles in generating the social environment in which offspring rearing occurs.Communicated by N. Wedell     

芜湖市郊土壤污染对土壤动物群落结构的影响

研究表明，芜湖市郊农田土壤动物群落的组成与数量随污染程度的加重而减少，土壤动物密度也呈同样的变化趋势，特别是中小型土壤动物，优势类群数量发生较大消长，常见类群和稀有类群的组成逐渐减少．多样性指数H与重金属污染程度之间关系因受到季节的影响而变得复杂：冬季和初夏污染较重样地优势类群数量减少，群落均匀性指数E增加而优势度指数C减小，多样性指数H较高；而春季处于过渡阶段，某些类群(如螨类)数量爆发，C增高，H较小．土壤动物群落密度一类群指数DG随污染加重而减小．受到重金属污染的农田土壤动物的表聚性减弱，甚至出现逆分布现象．图1表4参15