Pattern-oriented modeling of bird foraging and pest control in coffee farms

We develop a model of how land use and habitat diversity affect migratory bird populations and their ability to suppress an insect pest on Jamaican coffee farms. Bird foraging—choosing which habitat patch and prey to use as prey abundance changes over space and time—is the key process driving this system. Following the “pattern-oriented” modeling strategy, we identified nine observed patterns that characterize the real system's dynamics. The model was designed so that these patterns could potentially emerge from it. The resulting model is individual-based, has fine spatial and temporal resolutions, represents very simply the supply of the pest insect and other arthropod food in six habitat types, and includes foraging habitat selection as the only adaptive behavior of birds. Although there is an extensive heritage of bird foraging theory in ecology, most of it addresses only the individual level and is too simple for our context. We used pattern-oriented modeling to develop and test foraging theory for this across-scale problem: rules for individual bird foraging that cause the model to reproduce a variety of patterns observed at the system level. Four alternative foraging theories were contrasted by how well they caused the model to reproduce the nine characteristic patterns. Four of these patterns were clearly reproduced with the “null” theory that birds select habitat randomly. A version of classical theory in which birds stay in a patch until food is depleted to some threshold caused the model to reproduce five patterns; this theory caused lower, not higher, use of habitat experiencing an outbreak of prey insects. Assuming that birds select the nearby patch providing highest intake rate caused the model to reproduce all but one pattern, whereas assuming birds select the highest-intake patch over a large radius produced an unrealistic distribution of movement distances. The pattern reproduced under none of the theories, a negative relation between bird density and distance to trees, appears to result from a process not in the model: birds return to trees at night to roost. We conclude that a foraging model for small insectivorous birds in diverse habitat should assume birds can sense higher food supply but over short, not long, distances.     

Separability,functional structure and aggregation for a class of models in environmental economics

The purpose of this paper is to provide a theoretical bridge between the many-commodity general equilibrium models and the simpler one good-one pollutant models used in environmental economics. The interest is in determining the conditions that will permit a vector of pollutants (or goods) to be treated as if it were only one quantity, the amount of environmental pollution (or consumption). A general equilibrium model is constructed and the concepts of separability and functional structure are applied to examine the requirements for consistent aggregation. It is shown that this aggregation process may in general produce two entirely different sets of aggregate measures of pollution and consumption. This result is of theoretical and empirical significance. Alternative criteria for aggregation suggest that the aggregation depends upon very stringent features of the economy concerned.     

Prospects for repellent in pest control: current developments and future challenges

The overall interest in environmentally safe pest control methods and the rise of insecticide resistance in pest populations have prompted medical and agricultural entomology research on insect repellents in recent years. However, conducting research on repellent is challenging for several reasons: (1) the different repellent phenomena are not well defined; (2) it is difficult to test for and quantify repellent; (3) the physiological mechanisms are poorly known; (4) the field efficacy appears to be highly variable. Here, we identified five different types of repellent: expellency, irritancy, deterrency, odor masking and visual masking, and described behavioral bioassays to differentiate between them. Although these categories are currently defined by their behavioral response to different stimuli, we suggest new definitions based on their mechanism of action. We put forward three main hypotheses on the physiological mechanism: (1) a dose effect that modifies the behavior, (2) a repellent mechanism with specific receptors, or (3) inhibition of the transduction of neural information.     

The choice of efficient pollution policies: Technology and economics in the control of sulphur dioxide

This article reexamines the choice between charges and regulations to control pollution, by concentrating on the example of sulphur dioxide. A summary of the technology of this pollutant is followed by a discussion of the informational requirements of alternative policies. Particular attention is paid to the distinction between continuous monitoring and spot checks, to the number of polluters, and to the relationship between inputs to the polluting process and emissions. The final section considers how the issues dealt with would apply to water pollution and concludes that charges are not a priori always preferable to regulations.     

Graphical evaluation of environmental management options: Examples from a forest-insect pest system

A graphical technique is demonstrated which, when combined with any resource simulation model, permits the resource manager to explore the effects of different management options. Also, this technique (nomogram or response surface) permits derivation of “optimal solutions” given particular objectives. Examples of the methodology are given for the spruce budworm—forest system in eastern Canada. Effects of several kinds of uncertainties are dicussed, including uncertainties in model assumptions, management precision, future objectives and system evolution. The graphical nature of nomograms helps managers and analysts to grasp more easily the complicated behavior of ecological systems models. Finally, the role of computer models in decision-making is discussed.     

Biological and environmental influences on the trophic ecology of leatherback turtles in the northwest Atlantic Ocean

Understanding the causes and consequences of variability in trophic status is important for interpreting population dynamics and for identifying important habitats for protected species like marine turtles. In the northwest Atlantic Ocean, many leatherback turtles (Dermochelys coriacea) from distinct breeding stocks throughout the Wider Caribbean region migrate to Canadian waters seasonally to feed, but their trophic status during the migratory and breeding cycle and its implications have not yet been described. In this study, we used stable carbon and nitrogen isotope analyses of bulk skin to characterize the trophic status of leatherbacks in Atlantic Canadian waters by identifying trophic patterns among turtles and the factors influencing those patterns. δ¹⁵N values of adult males and females were significantly higher than those of turtles of unknown gender (i.e., presumed to be subadults), and δ¹⁵N increased significantly with body size. We found no significant differences among average stable isotope values of turtles according to breeding stock origin. Significant inter-annual variation in δ¹⁵N among cohorts probably reflects broad-scale oceanographic variability that drives fluctuations in stable isotope values of nutrient sources transferred through several trophic positions to leatherbacks, variation in baseline isotope values among different overwintering habitats used by leatherbacks, or a combination of both. Our results demonstrate that understanding effects of demographic and physiological factors, as well as oceanographic conditions, on trophic status is key to explaining observed patterns in population dynamics and for identifying important habitats for widely distributed, long-lived species like leatherbacks.     

Biological responses to environmental forcing: the linear tracking window hypothesis

Determining the relative contributions of intrinsic and extrinsic processes to the regulation of biological populations has been a recurrent ecological issue. Recent discussions concerning ecosystem "regime shifts" again raise the question of whether population fluctuations are mainly controlled by external forcing. Results of nonlinear time series analyses indicate that pelagic populations typically do not passively track stochastic environmental variables. Rather, population dynamics are better described as nonlinear amplification of physical forcing by biological interactions. However, we illustrate that in some cases populations do show linear tracking of the physical environment. To explain why population dynamics can sometimes be linear, we propose the linear tracking window hypothesis: populations are most likely to track the stochastic environmental forcing when their generation time matches the characteristic time scale of the environmental signal. While our observations follow this hypothesis well, our results indicate that the linear tracking window is a necessary but not a sufficient condition.     

高氯酸盐环境行为与生态毒理研究进展

高氯酸盐是一种无机污染物质,其特点是扩散速度快、稳定性高、难降解,较低浓度的高氯酸盐可干扰甲状腺的正常功能,从而影响人体正常的新陈代谢,阻碍人体正常的生长和发育,其环境污染问题已引起了人们高度关注,成为近年环境科学和医学的研究热点.文章在介绍高氯酸盐的理化性质和用途的基础上,综述了各地水体环境、饮用水以及牛奶、蔬菜等食品中高氯酸盐的污染现状,发现很多国家境内都存在不同程度的高氯酸盐污染,高氯酸盐在中国环境中也是普遍存在的,在污水淤泥、水稻、瓶装饮用水和牛奶中均能检测到;初步探讨了高氯酸盐在土壤和水体中的环境行为,认为环境中高氯酸根离子的降解主要是生化降解,微生物在其降解过程中起主要作用;综述了高氯酸盐对植物、动物、微生物和人体的急慢性毒性效应,指出自然环境中的高氯酸盐浓度很有可能具有慢性毒性;最后就高氯酸盐在生态环境中的检测方法和生物降解等研究前沿进行了展望,为今后高氯酸盐的使用、污染预防及治理提供参考.     

Genetic and environmental effects on the growth rate of Littorina saxatilis

Transfer experiments with two morphs of Littorina saxatilis Olivi (=L. rudis) typically inhabiting exposed and sheltered localities, showed a between-morph difference in shell growth in the same type of habitat, and a withinmorph difference between exposed and sheltered environments. The former indicates a genetic difference between the two morphs, although growth rate has an environmental component as shown by the latter. Juvenile snails of the exposed morph were on average slightly larger than sheltered morph juveniles on hatching, but at 20 wk, when raised in identical environments, the sheltered morph juveniles had grown significantly larger than the exposed ones. A rise in temperature from 5° to 10°C enhanced growth rate for snails raised in the laboratory. Temperature alone could not however explain increased growth during the spring and summer in natural populations.     

Integrated versus chemical pest management: The case of rice field mosquito control

We compare pesticide use and total cost of mosquito control under integrated and chemical control strategies using data from the San Joaquin Valley, California. The analysis shows that the use of biological control allows substantial cuts in chemical treatments, inspection effort and control costs required to meet mosquito control targets. Thus, integrated pest management in this case is clearly superior economically as well as preferable from an ecological perspective. These results suggest the desirability of public action to augment mosquitofish supplies, the lack of which currently constitutes a key obstacle to broader application of the integrated strategy.     

中国快速城镇化的边际环境污染效应变化实证分析

通过建立模型并实际测算城镇化每增长1个百分点引起的污染物产排放变化量,来分析我国城镇化发展的边际环境污染效应。结果显示,我国城镇化发展与环境污染之间的矛盾仍十分突出,1996-2009年期间,城镇化每增长1个百分点带来的城镇生活污水排放量、COD产生量、NH3-N产生量、NOx排放量、CO2排放量、城镇生活垃圾产生量仍呈上升趋势。由于近年来城镇污水处理率明显提升,城镇化每增长1个百分点带来的COD和NH3-N排放量由＂十五＂的增加逐步转为＂十一五＂的减少;由于城镇生活用煤的减少,城镇化每增长1个百分点带来的SO2排放量在＂十五＂＂十一五＂期间都呈减少趋势。为减少环境污染,我国应选择有中国特色的城镇化发展道路,合理把握城镇化发展速度和节奏,促进城镇与环境协调发展。     

硝基苯环境效应的研究综述

硝基苯污染威胁着人类和生态系统健康,国外有关硝基苯的环境毒理的研究已经广泛展开,但我国仍处于起步阶段.文章综述了国内外硝基苯环境效应的研究进展,介绍了其基本理化性质、用途、环境基准和标准值、污染的生态毒理效应以及其在生态系统中的迁移转化规律.研究认为环境中的硝基苯属于低毒污染物,但难溶于水,易溶于有机溶剂,难以降解,造成水体和土壤污染的持续时间长,且能够在生物体内积累,产生生物放大效应,因此,高浓度的硝基苯对生态系统和人体健康造成较大的生态风险;不过,阳光中的近紫外线、γ射线、声波振荡以及生物分解等作用可自然环境中硝基苯有降解作用,而生物和物理吸附能降低其浓度,从而降解其毒性.目前,有关自然生态系统中硝基苯迁移转化过程之间协同作用与相互影响的研究还有待于进一步深入.     

The environmental effects of trade within and across sectors

This paper presents a model that combines within and across sector channels through which trade affects our environment by embedding heterogeneous firms and fixed costs into a two-sector framework with an endogenous response to environmental policy. In contrast to existing literature that tends to examine these channels separately, the combined framework developed here shows how cross-sector comparative advantage and within-sector responses to trade and environmental policy or factor endowments interact to affect our environment through three channels: changes in output, cross-sector market share, and emissions intensity. In contrast to a single-sector model with neutral productivity, consideration of two sectors allows for trade liberalization to affect the allocation of inputs in each sector and thereby affect total pollution output. The additional consideration of heterogeneous firm responses to falling trade costs will generate endogenous increases in productivity that increase output, reduce aggregate emissions intensity, and moderate the cross-sector resource adjustment, relative to a representative-firm model. Simulation results show how the combined framework can replicate existing empirical outcomes, and provide concise ceteris paribus insights regarding the potential role of trade and environmental policy changes and factor expansion in driving observed outcomes and their contribution to each of the three channels.