Path selection and foraging efficiency in Argentine ant transport networks

We experimentally investigated both individual and collective behavior of the Argentine ant Linepithema humile as they crossed symmetrical and asymmetrical bifurcations in gallery networks. Ants preferentially followed the branch that deviated the least from their current direction and their probability to perform a U-turn after a bifurcation increased with the turning angle at the bifurcation. At the collective level, colonies were better able to find the shortest path that linked the nest to a food source in a polarized network where bifurcations were symmetrical from one direction and asymmetrical from the other than in a network where all bifurcations were symmetrical. We constructed a model of individual behavior and showed that an individual’s preference for the least deviating path will be amplified via the ants’ mass recruitment mechanism thus explaining the difference found between polarized and non-polarized networks. The foraging efficiency measured in the simulations was three times higher in polarized than in non-polarized networks after only 15 min. We conclude that measures of transport network efficiency must incorporate both the structural properties of the network and the behavior of the network users.     

Structure and resilience of the social network in an insect colony as a function of colony size

Social interactions are critical to the organization of worker activities in insect colonies and their consequent ecological success. The structure of this interaction network is therefore crucial to our understanding of colony organization and functioning. In this paper, I study the properties of the interaction network in the colonies of the social wasp Ropalidia marginata. I find that the network is characterized by a uniform connectivity among individuals with increasing heterogeneity as colonies become larger. Important network parameters are found to be correlated with colony size and I investigate how this is reflected in the organization of work in colonies of different sizes. Finally, I test the resilience of these interaction networks by experimental removal of individuals from the colony and discuss the structural properties of the network that are related to resilience in a social network. This contribution is part of the special issue “Social Networks: new perspectives” (Guest Editors: J. Krause, D. Lusseau, and R. James).     

Anaerobic treatment of fresh leachate from a municipal solid waste incinerator by upflow blanket filter reactor

This paper describes the feasibility of fresh leachate treatment by an upflow blanket filter (UBF). Through dilution and partial effluent recycling, the organic loading rates increased from 0.51 to 14.56 kg COD/(m³·d), meanwhile the corresponding hydraulic retention time decreased from 9.0 to 3.6 d. The reactor was able to achieve steady-state within 80 d. Based on the distribution of COD fluxes in the process, it was concluded that anabolism was the main pathway of COD removal in the initial phase (1–33 d), accounting for 57%–85% of total COD removed. As the anaerobic consortium of bacteria reached steady-state (after 70–86 d), the majority of COD removed was transformed into methane, because the specific methane yield was close to the theoretical value (0.36 L CH₄/(g COD_deg)).     

废塑料资源化产品对土壤中过氧化氢酶和脲酶活性的影响(Effect of Waste Plastics Recycling Products on Activities of Soil Catalase and Urease)

为探讨废塑料资源化产品对土壤酶活性的影响,通过室内培养试验研究了废塑料资源化产品暴露后土壤中过氧化氢酶和脲酶活性的变化.结果表明:废塑料资源化产品对土壤酶活性具有显著影响.250mg·kg-1、1250mg·kg-1、7250mg·kg-1废塑料资源化产品浓度处理对土壤中过氧化氢酶和脲酶影响明显不同.在土壤培养l～5d内,添加废塑料资源化产品的3个浓度处理土壤中过氧化氢酶活性显著低于对照(p<0.05),表现出明显的抑制作用,且浓度越高抑制作用越强.而后(5～35d),低浓度(250mg·kg-1)废塑料资源化产品对土壤过氧化氢酶一直表现为激活作用,但是,高浓度(1250mg·kg-1和7250mg·kg-1)处理对土壤过氧化氢酶活性则表现为激活-抑制-激活作用,且抑制、激活程度与处理浓度成呈相关.3个废塑料资源化产品浓度处理对脲酶活性影响在培养1～28d内主要是激活作用,且激活作用随着处理浓度的增大而增强,而后(28～35d)对脲酶活性表现为抑制作用.     

Least-inference methods for constructing networks of trophic flows

The construction of material and energy budgets within ecosystems has long been accomplished via manual calculation. Recently, optimization techniques have been adapted to automate the procedure, but these methods require assumptions that may not square with biological reality. Two algorithms are developed to construct ecosystem budgets under minimal inference. Although the methods do not recapitulate the model used to generate the input data, analysis reveals that the results do not differ statistically from networks that were constructed manually.     

Grasslands, People, and Conservation: Over-the-Horizon Learning Exchanges between African and American Pastoralists

Abstract:  The world's grasslands and large migratory populations of wildlife have been disproportionately lost or disrupted by human activities, yet are poorly represented in protected areas. The major threats they face are land subdivision and the loss of large-scale dynamic processes such as wildlife migrations and fire. The large-scale dynamical processes and ubiquity of livestock economies and cultures across the grasslands calls for an integrated ecosystem approach to conservation to make up the shortfall in protected-area coverage. Ranchers and pastoralists will be more inclined to adopt an integrated landscape approach to conservation if they also see the threats to wildlife and grassland ecosystems as affecting their livelihoods and way of life. We arranged a series of learning exchanges between African and American pastoralists, ranchers, scientists, and conservationists aimed at building the collaboration and consensus needed to conserve grasslands at a landscape level. There was broad agreement on the threat of land fragmentation to livelihoods, wildlife, and grasslands. The exchanges also identified weaknesses in prevailing public, private, and community modes of ownership in halting fragmentation. New collaborative approaches were explored to attain the benefits of privatization while keeping the landscape open. The African–U.S. exchanges showed that learning exchanges can anticipate over-the-horizon problems and speed up the feedback loops that underlie adaptive management and build social and ecological resilience.     

ARTIFICIAL NEURAL NETWORKS FOR SUBSURFACE DRAINAGE AND SUBIRRIGATION SYSTEMS IN ONTARIO,CANADA1

ABSTRACT: Artificial neural network (ANN) models were developed to simulate fluctuations in midspan water table depths (WTD) given rainfall, potential evapotranspiration, and irrigation inputs on a Brookston clay loam in Woodslee, Ontario, having a dual‐purpose subsurface drainage/subirrigation setup. Water table depths and meteorologic data collected at this site from 1992 to 1994 and from 1996 to 1997 were used to train the ANNs. The ANNs were then used for real‐time control and time series simulations. The lowest root mean squared errors (RMSE) for the various ANNs were 60.6 mm for real‐time control simulation, and 88.4 mm for time‐series simulation of water table depths. It was possible to simulate WTD for the different modes of water table management in one network by incorporating an indicator for switching from one to the other. The ANN simulations were quite good even though the training data sets had irregular measurement intervals. With fewer input parameters and small network structures, ANNs still provided accurate results and required little time for training and execution. ANNs are therefore easier and faster to develop and run than conventional models and can contribute to the proper management of subsurface drainage and subirrigation systems.     

醛类化合物分子结构与对鼠急性毒性关系

通过检索美国国立职业与卫生研究所化学物质毒性效应登录 ( RTECS) 1998年版光盘系统 ,搜集了 88种醛类化合物对大鼠急性毒性口服 LD₅₀ 数据 ,并利用遗传神经网络建立了醛类化合物分子结构与对大鼠急性毒性关系的 BP神经网络模式 ,模式的交互检验相关系数达 0.83～ 0.87,具有较强的预报能力 .遗传神经网络是由遗传算法和神经网络耦合而成 ,文章详细讨论了遗传神经网络的构造以及利用遗传神经网络建立 QSAR模型的方法 .     

垃圾填埋场渗滤液回流技术的研究

垃圾填埋场产生大量渗滤液,而一般渗滤液中含有很高浓度的有机物,特别是填埋场的初滤水COD_cr浓度可高达8×104mg/L,BOD₅浓度可高达5×104mg/L。因此,渗滤液必须得到处理。渗滤液回流可以利用垃圾填埋层中大量繁殖的微生物分解其中的有机物,使渗滤液得 到净化;同时利用回流控制填埋层含水量,加快有机物分解,提高沼气产生量。通过实验初步得出:渗滤液回流可以将渗滤液中有机物浓度大 大降低,COD_cr去除率最高可以达到95%以上,在半好氧状态下NH₃-N浓度可以降到10mg/L以下;沼气产生速率大大高于未回流的填埋层;同时填埋层渗滤液中有机物浓度大大降低。      

A Comparison of Waste Reduction Practices and the New Environmental Paradigm in Four Southern Chinese Areas

On domestic waste recycling, it was found that source separation of domestic waste in mainland China was supported by 85% of the urban population and about 11–13% of the household waste was recovered and sold by the householders for financial gains. It was also found that the lower income group tended to recover a greater portion of waste, indicating that voluntary waste recovery activities in mainland China were carried out largely due to economic reasons. Thus, the Western type of source separation program in which residents are requested to separate recyclables for the community may not be welcomed in mainland China. In Hong Kong, despite the presence of community waste recovery programs, the recovery of domestic waste is only about 6% and is therefore less than those of the mainland Chinese cities surveyed. On the choice of source separation programs, it was found that Hong Kong people ranked familiarity a more important criterion than convenience. Therefore, the collection frequency of recyclables and time and place for setting out recyclables should be as similar to those of normal waste collection as possible to attract high participation in source separation programs.