工程外迁移民社区安置中的资源挖掘问题--以江苏省大丰市为例

在对江苏省三峡外迁移民安置试点大丰市的调研基础上，探讨了移民社区安置中的资源挖掘问题，主要是闲置房和土地资源的利用、社会网络资源的开发、投资性资源的启动等，指出资源的充分挖掘，有助于顺利安置移民。     

Long-term dynamics in land resource use and the driving forces in the Beressa watershed, highlands of Ethiopia

Land degradation in the Ethiopian highlands is considered to be one of the major problems threatening agricultural development and food security in the country. However, knowledge about the forces driving the long-term dynamics in land resources use is limited. This research integrates biophysical information with socio-economic processes and policy changes to examine the dynamics of land resource use and farmers' livelihoods in the Beressa watershed for over 40 years during the second half of the 20th century. It was found that there have been substantial dynamics in land resource use in the area. The natural vegetation cover has been extensively cleared, although most of the cleared areas have since been replaced with plantations. Grazing land has expanded remarkably at the expense of cropland and bare land. However, the expansion of cropland was minimal over the 43-year period despite a quadrupling of the population density. Yields have not increased to compensate for the reduction in per capita cropland, and the soil quality appears to be not that good. Though the farmers perceived it otherwise, the long-term rainfall pattern has improved. In response to soil degradation, water shortage, socio-economic and policy changes, farmers have tended to gradually change from annual cropping to tree planting and livestock production to cope with the problems of soil degradation, water scarcity and smaller farms. Income diversification through the sale of wood and cattle dung is becoming a major livelihood strategy. Apparently, however, little attention has been paid to investments in soil and water conservation (SWC) and local soil fertility amendments. In particular, increased erosion and related high nutrient losses in sediments, as well as the removal of potentially available soil nutrients through the sale of manure threatens to damage agricultural sustainability in the area.     

Detecting Density Dependence in Recovering Seal Populations

Time series of abundance estimates are commonly used for analyses of population trends and possible shifts in growth rate. We investigate if trends in age composition can be used as an alternative to abundance estimates for detection of decelerated population growth. Both methods were tested under two forms of density dependence and different levels of environmental variation in simulated time series of growth in Baltic gray seals. Under logistic growth, decelerating growth could be statistically confirmed after 16 years based on population counts and 14 years based on age composition. When density dependence sets in first at larger population sizes, the age composition method performed dramatically better than population counts, and a decline could be detected after 4 years (versus 10 years). Consequently, age composition analysis provides a complementary method to detect density dependence, particularly in populations where density dependence sets in late.     

The nature and frequency of social interactions among free-living prairie voles (Microtus ochrogaster)

Hypotheses relating the behavior of voles to their population cycles often assume that the rate of social interaction increases with population density. To test this assumption, we examined the frequency of social interactions in a population of prairie voles (Microtus ochrogaster) over a 7-year period. In addition, we characterized space use by resident animals, patterns of visitation by nonresidents to nests, and participants in social interactions. Social groups within the population typically displayed little overlap in their use of space, even at high population densities. Nevertheless, nonresidents, particularly wandering males, were captured as visitors at nests. The number of visits per social group did not increase in a simple linear manner with population density and was particularly variable when there were fewer than 100 animals/ha. At such times, more single females and fewer pairs received visits from males than expected based on the frequency of occurrence of these groups in the population; a similar pattern was noted during periods of high population density (≥100 animals/ha) but the comparisons failed to reach statistical significance. Furthermore, at high population density, more communal groups received visits from females than expected. Patterns of visitation to communal groups were influenced by the number of adult male residents (winter only), but not by the number of adult female residents or presence of philopatric female offspring. These data indicate that the frequency of social contact in prairie voles does not increase linearly with population density and is influenced by the spacing and possible mate-guarding behavior of resident animals. Received: 7 January 1998 / Accepted after revision: 16 May 1998     

Review of Recent Ecotoxicological Studies on Cladocerans

Cladocerans have been widely used as the bioassay organisms in evaluating the impact of different toxic substances. Literature survey during the last 10 years revealed that cladoceran ecotoxicological research has been in an exponential phase constituting nearly 10% of publications on this group. Many studies have considered typically planktonic taxa such as Daphnia magna, D. pulex, Moina macrocopa, M. micrura and Ceriodaphania dubia. Experimental data on toxicity tests, to a lesser extent, are also available for littoral-benthic genera such as Simocephalus, Macrothrix and Alona. Most toxicity tests are limited to the derivation of median lethal concentrations of various durations but mostly at 24 or 48 h. Studies related to the evaluation of changes in the life history variables of cladocerans as a result of sublethal exposure to toxic substances are not many, but gaining importance. The common toxic substances used in the cladoceran toxicity tests appear to be heavy metals, pesticides and a few natural toxins such as cyanotoxins. We review here the effect of different toxic substances on cladocerans based on both the field and the laboratory studies from an ecotoxicology point of view. Suggestions for the future cladoceran ecotoxicology are also commented on.     

Conflict-induced displacement and involuntary resettlement in Colombia: putting Cernea's IRLR model to the test

This paper tests Cernea's (1997) impoverishment risks and livelihood reconstruction (IRLR) model in cases of conflict-induced displacement (CID). In applying the model to a situation involving internal conflict, the article illustrates the particular problems encountered by internally displaced people (IDPs) and policymakers charged to respond to them. The article searches for local interpretations of CID and resettlement through a comparative profile of two IDP settlements in Colombia: one urban, the other rural. It concludes that the IRLR model, when contextualised, provides a useful tool to identify and categorise risks of impoverishment and resettlement priorities. At the same time, however, the article demonstrates that the model insufficiently captures the root causes or causality of CID.     

A finite element method to solve a population dynamics stage-structured model of intertidal barnacles

Many marine organisms are fixed or highly sedentary as adults but the adult population may be strongly dependent on the oceanic transport of planktonic larvae. In order to assess interactions between oceanographic and biological processes that determine the population dynamics of marine organisms with a sessile adult phase restricted to the coastline and a planktonic larval phase, we present a stage-structured finite element model for the barnacle Balanus glandula that inhabits the rocky intertidal zone of central California, USA.     

Research on the threshold effect of population aging on the industrial structure upgrading in China

This paper constructs coefficients of the integral and the internal structure upgrading in the secondary and tertiary industries, selects per capita real gross domestic product as a threshold variable and build panel threshold model according to inter-provincial panel data of China from 1998 to 2016. Results indicated that population aging has a double threshold effect on the integral industrial structure upgrading, whose influence increases first and then decreases, significantly promoting the upgrading process. As for internal structure, population aging has no significant threshold effect on the upgrading in the secondary industry, but exerts a single negative threshold effect in the tertiary industry. When economic development is under the threshold, its negative impact is greater. Further analysis also suggests that regional differences exist significantly in the threshold effect of population aging on the industrial structure upgrading.     

中亚热带次生林成林规律及经营技术研究——Ⅰ.次生林环境背景分析与类型划分

本文分析了湖南省中亚热带次生林优势种群间的联结和环境梯度。通过研究,将全省次生林划分为8大类型即暖性针叶林、温性针叶林、干热性常绿阔叶林、干暖性常绿阔叶林、暖湿性常绿阔叶林、温湿性常绿阔叶林、暖性落叶阔叶林和温性落叶阔叶林等。     

Post-disaster resettlement, development and change: a case study of the 1990 Manjil earthquake in Iran

Planned and involuntary resettlement after natural disasters has been a major policy in post-disaster reconstruction in developing countries over the past few decades. Studies show that resettlement can result in significant adverse impacts on the resettled population. Conversely, a well-planned and managed resettlement process can produce positive long-term development outcomes. This article presents the results of a case study undertaken 11 years after the 1990 Manjil earthquake in Iran. During the reconstruction period, a policy of involuntary planned resettlement was pursued extensively. The socioeconomic changes that occurred as a consequence of this policy of involuntary resettlement are analysed. Data were collected via a questionnaire survey that involved a sample of 194 relocated households (grouped into a settlement that later became a town). The paper shows that relocated families face difficult socioeconomic challenges after relocation and regrouping. This is especially true with respect to employment, income, the empowerment of women and lifestyle issues.