A trait specific model of competition in a spatially structured plant community

The non-random dispersal of plant propagules is thought to counter competitive exclusion and thus promote the survival of competitively inferior species. We investigated this process by modelling the outcome of interactions between species with competitive ability defined as a function of both life-history traits and the environment with both random and clustered dispersal strategies and in environmentally homogeneous and heterogeneous environments. Four main results emerged: (1) environmental heterogeneity was seen to promote co-existence in conjunction with associated trait variation for tolerance to the environmental variable and where this trait variation was effectively limited by ‘trade-off’ such that no single species had an overall competitive advantage, (2) consistent with theory, random dispersal appeared to enhance the likelihood of competitive exclusion, whereas clustering favoured co-existence, (3) the ecological outcome of interactions between dispersal and competitive relationships varied as a function of the trait determining the competitive advantage within a particular environment, and (4) promotion of co-existence by clustered dispersal was most marked when associated with environmental heterogeneity. It is argued that these results suggest that current ecological models of species interactions may need to be modified to incorporate a more realistic understanding of competitive ability if we are to better understand the factors effecting species co-existence.     

Removal potential of anti-estrogenic activity in secondary effluents by coagulation

Anti-estrogenic activity in wastewater is gaining increased attention because of its endocrine-disrupting function. In this study, the level and removal efficiency by coagulation of anti-estrogenic activity in secondary effluents of domestic wastewater treatment plants were studied. Anti-estrogenic activity was detected in secondary effluent samples at a tamoxifen (TAM) equivalent concentration level of 0.38–0.94 mg-TAM L⁻¹. Dissolved organic matters (DOM) with the molecular weight (MW) less than 3000 Da in hydrophobic acids (HOA) and hydrophobic neutrals (HON) fractions of the secondary effluent were the key fractions related to anti-estrogenic activity. Coagulation with FeCl₃ and polyaluminium chloride (PAC) can remove the anti-estrogenic activity of the secondary effluents, but the removal efficiency was limited. The removal efficiency using FeCl₃ coagulant was higher than that induced by PAC. Dissolved organic carbon was continuously removed with increased coagulant dose (0–120 mg L⁻¹ FeCl₃ or 0–60 mg L⁻¹ PAC). However, the removal of anti-estrogenic activity was not enhanced further when the coagulant concentration was beyond a critical value (30 mg L⁻¹ FeCl₃ or 10 mg L⁻¹ PAC). The highest removal of anti-estrogenic activity was about 36% by FeCl₃ and 20% by PAC. Size exclusion chromatography results indicated difficulty in removing DOM with MW less than 3000 Da in the secondary effluent during coagulation even at a high coagulant concentration, which led to low removal efficiency of anti-estrogenic activity.     

Spectroscopic study of the degradation of antibiotics and the generation of representative EfOM oxidation products in ozonated wastewater

This study examined effects of ozonation on thirteen fluoroquinolone, macrolide and lincosamide antibiotics present in municipal wastewater. Transformations of effluent organic matter (EfOM) caused by ozonation were characterized using absorbance/fluorescence spectroscopy and high performance size exclusion chromatography (HPSEC). Concentrations of aldehydes and carboxylic acids generated via the oxidation of EfOM were also determined. The absorbance and fluorescence of ozonated wastewater decreased with increasing ozone dose or treatment time. HPSEC data showed that these phenomena corresponded to the oxidation of all EfOM fractions, with some preference towards the degradation of the EfOM molecules with high apparent molecular weight. The removal of antibiotics and production of aldehydes and carboxylic acids were strongly correlated with the changes in both EfOM absorbance and fluorescence. Applications of a model describing the concurrent degradation of trace level contaminants and relative changes of EfOM emission allowed achieving a good fitting between the experimental and modeled ΔC/C₀ vs. ΔA/A₀ and ΔC/C₀ vs. ΔF/F₀ data.     

Impact of soil quality on elemental uptake by,and distribution in,Colocasia esculenta (Amadumbe), an edible root

In this study the elemental distribution of selected essential (Ca, Mg, Al, Mn, Cu, Fe, Co, Cr, Zn, Ni and Se) and the non-essential (Pb, Hg and As) elements were determined in the bulb and peel of Amadumbe (Colocasia esculenta) samples from eight different sites in KwaZulu-Natal, South Africa. The concentration of Se and As in the soil and in the Amadumbe bulbs were below the detection limit of 0.09 μg g^?1. The total and bioavailable concentrations of the elements in conjunction with pH, soil organic matter (SOM) and cation exchange capacity (CEC) were determined in the soil samples from the eight sites. Statistical analysis was done to evaluate the impact of soil quality parameters on the chemical composition of the Amadumbe root. The results show accumulation or exclusion of certain elements by the bulb as evidenced by the noticeable increase or decrease of the concentrations of elements, respectively. Ca and Mg were found to be major elements in the range (2000–12000 μg g^?1), whilst Mn, Zn, Fe and Al were found to be minor elements in the range (20–400 μg g^?1). A general trend observed was that the plant favours the absorption of Zn over Cu. A positive correlation between Mg & Ca, Cu & Fe and Co & Ni was also observed. Statistical analysis revealed that the plant tended to accumulate Mg, Ca, Co, Cr and Pb whilst it excluded Hg and Fe, to a lesser extent.     

Extra-pair paternity in the monogamous Alpine marmot revealed by nuclear DNA microsatellite analysis

The genetic parentage and pedigrees of 35 litters from 12 family groups of monogamous Alpine marmot (Marmota marmota) in the French Alps were analyzed using six hypervariable sequence repeat nuclear loci (microsatellites). All of the members of these family groups were sampled during a 5-year period. Hairs taken directly from animals served as a source of DNA for amplification of the loci. Our results indicate that the genetic mating system of the Alpine marmot is quite different from a strictly monogamous breeding system. Extra-pair paternity occurred in 11 of the 35 litters (31.4%). Of the 134 juveniles typed, 26 (19.4%) could be attributed to extra-pair copulation (EPC). We examine hypotheses which could explain the evolution of EPC and discuss the different patterns of extra-pair mating. Received: 11 July 1997 / Accepted after revision: 23 May 1998     

保护性耕作下小麦田土壤呼吸及碳平衡研究

为了研究小麦农田生态系统土壤碳排放与作物碳蓄积特征,采用LI6400-09在重庆北碚西南大学教学试验农场对平作(T)、垄作(R)、平作+覆盖(TS)、垄作+覆盖(RS)这4种处理下的西南紫色土丘陵区小麦/玉米/大豆套作体系中小麦生长季节的土壤呼吸及植株生长动态进行了观测.利用根系生物量外推法(root biomass regression,RBR)和根排除法(root exclusion,RE)这2种方法比较分析根系呼吸对土壤总呼吸的贡献,并估算小麦农田碳收支状况.结果表明,土壤呼吸介于0.62~2.91μmol·(m2·s)-1,平均值为1.71μmol·(m2·s)-1.T、R、TS、RS各处理日均土壤呼吸速率分别为1.29、1.59、1.99、1.96μmol·(m2·s)-1,表现为T相似文献   

Seeds and rights: new approaches to post-war agricultural rehabilitation in Sierra Leone

Based on preliminary findings of ongoing 'action research' in the war zone in central Sierra Leone, this paper shows how more equitable seed distribution could contribute to fostering a culture of human rights as well as to agricultural rehabilitation. Assessment of seeds-and-toosl programmes in 19 villages found that aid agency targeting and distribution modalities channelled inputs through village committees which denied assistance to intended beneficiary groups. Such distribution inequalities constitute violations of fundamental human rights, exacerbate grievance and division and maintain the threat of social disorder. The benefits and disadvantages of an alternative, more inclusive, rights-based approach to seed distribution are discussed, and preliminary results from the pilot phase of CARE's Rights-based Approach to Food Security Project are presented. Under this project, village-level peace and rights days are held to allow villagers to debate the vulnerabilities that facilitated the war and to elaborate on local notions of human rights. In symbolising new beginnings, seed can be seen as a useful medium through which to debate a more inclusive--and ultimately less vulnerable--society.     

Wind energy potential analysis for Thailand: Uncertainty from wind maps and sensitivity to turbine technology

Rapid development of wind energy has been witnessed in Thailand. However, different wind resource maps (over land) have brought great uncertainty to wind energy planning. Here, four important mesoscale wind maps were considered: DEDP (2001), World Bank (2001), Manomaiphiboon et al. (2010) of JGSEE, and DEDE (2010). The wind maps were first harmonized to a common grid at 100 m and then compared. The earlier wind maps (DEDP and World Bank) are shown to represent the lower and upper limits of predicted speed, respectively, while JGSEE and DEDE tend to be more moderate with predictions statistically closer to observations. A consolidated wind map was constructed based on their median and shown to have the best prediction performance. It was then used for the technical potential analysis, in which three large (2-MW) turbine models (two conventional and one designed for low wind speed) were considered. By GIS techniques, any land areas not feasible for large wind turbines were excluded, and the corresponding overall onshore technical potential ranges between 50 and 250 GW, depending on map and turbine model. Considering only economically feasible turbines (with capacity factors of 20%) and the median-based map, the final technical potential equals 17 GW when using the low-wind-speed model but is reduced to 5 GW with the conventional models, adequately meeting the national wind energy target of 3 GW by the year 2036. The results suggest a strong sensitivity of estimated technical potential to turbine technology and a suitability of low-wind-speed turbines for wind conditions in Thailand.     

Sustained dynamic transience in a Lotka-Volterra competition model system for grassland species

Theoretical approaches, such as the Lotka-Volterra framework, enable predictions about long term species coexistence based on stability criteria, but generally assume temporal constancy of system equations and parameters. In real world systems, temporal variability may interfere with the attainment of stable states. Managed grassland ecosystems in Northwestern Europe experience structural periodic fluctuations in environmental conditions: the seasons. In addition, periodic disturbances such as cutting are very common. Here we show, using a Lotka-Volterra system applied to grassland species with empirically derived parameters, that seasonal variability can result in a time dependent equilibrium and redirection of displacement processes.Parameter estimates differed between species and - in most cases - between the seasons. As a result, five of the fifteen tested species combinations had different outcomes of species interactions between seasons. This indicates that systems remain in dynamic transience over the year as the equilibrium changes and the species composition of the system follows the equilibrium without ever attaining it. The non-attainment of the steady state enables coexistence of species even if there is competitive exclusion in one of the seasons. For three of the fifteen species combinations, cutting frequency affected the long-term coexistence patterns. Cutting resets the biomass of competing species and favours during regrowth those species that have a high growth rate, which can alter species coexistence in comparison to a Lotka-Volterra model without cutting. The Lotka-Volterra framework with seasonally changing empirical parameters predicts coexistence as a possible outcome of systems that in component seasons are characterised by exclusion, and vice versa.     

水环境中天然溶解有机质分子量的研究现状及意义

溶解有机质存在于所有的水环境中,它是组成不均匀、结构复杂和分子量分布很宽的有机化合物混合体。本文综述了测量溶解有机质分子量的主要方法,各种方法的原理和优缺点,其中详细介绍了高效体积排阻色谱法的原理,平均分子量和分散系数的计算,以及分子量的校正;同时介绍了可能影响分子量分布的主要地球化学因素,以及天然水中溶解有机质的分子量分布的特征。