山区社会-生态系统转型测度——以三峡典型库区为例

三峡库区是集农村和山区为一体的社会-生态系统，研究其系统内部的相互作用和系统间的耦合转型有利于推动库区高质量的可持续发展。通过构建社会-生态系统耦合转型研究框架，采用地形位指数、耦合协调度模型等方法，以库区腹地草堂溪流域为例，揭示其社会-生态系统转型与否、转型路径的多样性及其驱动机制。结果表明：(1)2000—2020年三峡库区社会-生态系统数量-结构-功能均发生了显著变化，表明库区社会-生态系统发生了转型；(2)库区低地形位社会-生态系统表现为由社会生态型向生态经济型转变，中地形位表现为由生态社会型向生态主导、生态经济为辅转变，高地形位则表现为由生态调节型愈加趋向于生态主导型；(3)农户和政府需求变化是驱动社会-生态系统由传统耕地种植系统向新型经果林种植系统转型的根本因素；(4)研究方法证实对山区具有普适性，构建的研究框架较适合刻画山区社会-生态系统转型路径，在其他地方也能同样适用。     

The effects of natural enemies,competition, and host plant water availability on an aphid population

Summary I used a factorial experiment repeated in two years to assess the relative effects of natural enemy attack, interspecific competition, and water availability to the host plant, and of interactions among these factors, on the population dynamics of the aphid Aphis varians feeding on fireweed (Epilobium angustifolium). The impact of a suite of coccinellid and syrphid predators emerged as the predominant factor affecting the success of aphid colonies: colonies protected from natural enemies grew in size at a rate of ten percent per day, were only one tenth as likely to go extinct, and produced over ten times more dispersing alates. In contrast, I found only minor effects of removing flea beetles, the most abundant herbivore with which A. varians colonies cohabit fireweed stems, and of supplementing water availability to fireweed host plants, in spite of a significant effect of watering frequency on aphid growth in the green-house. There was no evidence of significant two- or three-way interactions among factors. Hence, despite the potential complexity of the food web in which it is embedded, the dynamics of A. varians appears to be driven predominantly by a single factor, i.e. interactions with natural enemies.     

Reproductive investment in the Silurus meridionalis

A comparison of pre- and postspawning Silurus meridionalis showed that 20·7% of body stored energy was utilized during spawning for a standard male (74·5 cm) and 23·8% for a standard female (85·3 cm). About one-third of the loss of the stored energy was released as eggs by females, and almost all of the energy loss for males and about two-thirds for females were expended in metabolism. Stored lipid as fuel for metabolism supplied 90·0% of energy in males and 95·2% in females, and protein supplied the rest of the energy. Models for predicting energy in released gametes ( G _g), deposited in the body as somatic growth ( G _s), utilized in spawning activity ( S _a), expended in maintenance ( M , including metabolism, faeces and excretion), and food energy ( C ) were developed, and annual energy budgets were compiled. The balanced budget for a male aged 4 was: 100 C =0·06 G _g+11·17 S _a+19·5 G _s+69·2 M , and for a female aged 5: 100 C =5·48 G _g+8·51 S _a+15·8 G _s+70·2 M .     

The volterra model for three species predator-prey systems: Boundedness and stability

Summary The classical Volterra equations modelling three species predatorprey interactions are considered with the intention of developing global properties of their solutions. Thirty-four different cases are exhibited. Global asymptotic stability is established for all non-loop cases. Global boundedness is established for all but one kind of loop case, and a condition is exhibited which insures boundedness for that case also. Finally a particular case is shown to have unbounded solutions.     

多尺度滑坡灾害生态风险评价与风险管理——以三峡库区万州-巫山段为例

进行生态风险多尺度综合评价，对环境管理及风险决策具有重要意义。以三峡库区滑坡重点监测县域为例，基于“危险性-脆弱性-潜在损失”三维模型，以随机森林模型评估滑坡危险性，采用景观格局指数表征生态脆弱性，利用生境质量核算潜在生态损失，进行格网、行政、子流域多尺度下的滑坡灾害生态风险评价，提出适合各尺度的风险管理措施，在此基础上选择最适宜尺度并结合研究区实际情况进行验证。结果表明，生态风险等级较高区域集中于长江两岸沿线，三峡库区建设对研究区滑坡生态风险产生较大影响；两两尺度风险分布结果具有一定相似性，而三种尺度共同作用结果又存在一定差异；子流域尺度在保证生态结构完整性的前提下评价结果好于其他两种尺度，更适合三峡库区县域的生态风险评价；研究区东部风险防范类型相对单一，而西部风险防范类型较多，需做到精细化管理。研究增加了多尺度综合评价实例，对今后开展整个三峡库区滑坡生态风险研究奠定一定理论和实践基础。     

Growth-form regulates the altitudinal variation of interspecific seed mass of woody plants in Mt. Dalaoling,the Three Gorges Region,China

Aims Seed size is one of the most important characteristics of plant seeds, and has significant implications in plant ecological functions. Exploring the altitudinal pattern of seed size would help to detect environmental constraints on species distribution and understand the linkage between plant ecological function traits Methods The present study measured the quantitative features of seed size, including weight of 1 000 grain seeds, lengths of longer and shorter axes, and analyzed the relationships between seed size and altitude, as well as the influence of growth form. Seed samples were all collected from 201 locally common woody plants (belonging to 59 families and 87 genera) in the Dalaoling Natural Reserve in Yichang City, Hubei Province.Important findings Measured values of the seed mass, the longer axis, and the shorter axis of the 201 woody plant species all follow the lognormal distribution. Measurements of seed mass vary across five orders of magnitude. Significant correlation was found between seed mass, seed length of the longer and shorter axes (R² = 0.755; 0.819; 0.630, p < 0.01). Moreover, seed mass of trees and small trees are significantly heavier than those of shrubs and woody vines. Seed mass values of evergreen broad leaved species are significantly heavier than those of deciduous broad leaved species and needle leaved species. Seed mass of all 201 species shows a slightly but statistically significant decreasing trend with the increase of altitude. In addition, altitudinal patterns of seed mass varied between species with different growth form. Our results indicated the variation of altitudinal trends of seed mass for different structural components of plant communities, implying the local community structure as a critical aspect of variation in macro-ecological patterns.