排序方式: 共有28条查询结果,搜索用时 15 毫秒
1.
Outbreaks of bark beetles in forests can result in substantial economic losses. Understanding the factors that influence the development and spread of bark beetle outbreaks is crucial for forest management and for predicting outbreak risks, especially with the expected global warming. Although much research has been done on the ecology and phenology of bark beetles, the complex interplay between beetles, host trees, beetle antagonists and forest management makes predicting beetle population development especially difficult. Using the recent infestations of the European Spruce Bark Beetle (Ips typographus L. Col. Scol.) in the Bavarian Forest National Park (Germany) as a case study, we developed a spatially explicit agent-based simulation model (SAMBIA) that takes into account individual trees and beetles. This model primarily provides a tool for analysing and understanding the spatial and temporal aspects of bark beetles outbreaks at the stand scale. Furthermore, the model should allow an estimation of the effectiveness of concurrent impacts of both antagonists and management to confine outbreak dynamics in practice. We also used the model to predict outbreak probabilities in various settings. The simulation results indicated a distinct threshold behaviour of the system in response to pressure by antagonists or management of the bark beetle population. Despite the different scenarios considered, we were able to extract from the simulations a simple rule of thumb for the successful control of an outbreak: if roughly 80% of individual beetles are killed by antagonists or foresters, outbreaks will rarely take place. Our model allows the core dynamics of this complex system to be reduced to this inherent common denominator. 相似文献
2.
We sampled 240 wadeable streams across Wisconsin for different forms of phosphorus and nitrogen, and assemblages of macroinvertebrates
and fish to (1) examine how macroinvertebrate and fish measures correlated with the nutrients; (2) quantify relationships
between key biological measures and nutrient forms to identify potential threshold levels of nutrients to support nutrient
criteria development; and (3) evaluate the importance of nutrients in influencing biological assemblages relative to other
physicochemical factors at different spatial scales. Twenty-three of the 35 fish and 18 of the 26 macroinvertebrate measures
significantly correlated (P < 0.05) with at least one nutrient measure. Percentages of carnivorous, intolerant, and omnivorous fishes, index of biotic
integrity, and salmonid abundance were fish measures correlated with the most nutrient measures and had the highest correlation
coefficients. Percentages of Ephemeroptera–Plecoptera–Trichoptera individuals and taxa, Hilsenhoff biotic index, and mean
tolerance value were macroinvertebrate measures that most strongly correlated with the most nutrient measures. Selected biological
measures showed clear trends toward degradation as concentrations of phosphorus and nitrogen increased, and some measures
showed clear thresholds where biological measures changed drastically with small changes in nutrient concentrations. Our selected
environmental factors explained 54% of the variation in the fish assemblages. Of this explained variance, 46% was attributed
to catchment and instream habitat, 15% to nutrients, 3% to other water quality measures, and 36% to the interactions among
all the environmental variables. Selected environmental factors explained 53% of the variation in macroinvertebrate assemblages.
Of this explained variance, 42% was attributed to catchment and instream habitat, 22% to nutrients, 5% to other water quality
measures, and 32% to the interactions among all the environmental variables. 相似文献
3.
Threshold values for domino effects caused by blast wave interaction with process equipment 总被引:6,自引:0,他引:6
Valerio Cozzani Ernesto Salzano 《Journal of Loss Prevention in the Process Industries》2004,17(6):437-447
The present study focuses on the definition and assessment of overpressure threshold values for the damage to equipment caused by blast waves originated by primary accidental scenarios. A revision of literature data and of the available damage probability models was carried out. Threshold values were proposed for different categories of process equipment, taking into account either damage levels or release intensities following the loss of containment. Specific threshold values for domino effect were also proposed. 相似文献
4.
Raphaël Jeanson Jennifer H. Fewell Root Gorelick Susan M. Bertram 《Behavioral ecology and sociobiology》2007,62(2):289-298
Empirical evidence suggests that division of labor in insect societies is positively related to group size both within and
across taxa. Response threshold models (RTM) have been commonly used to analyze patterns of division of labor. However, these
models have been explored empirically and theoretically for only a limited number of tasks, and few studies have examined
predictions of the model as colony size and work availability change. We theoretically examine how group size influences division
of labor using a fixed response-threshold model. We simultaneously explore how expected by-products of increased colony size,
including demand (total work need relative to total work force available) and task number, affect this relationship. Our results
indicate that both low demand and high task number positively influence division of labor. We suggest that these changes parallel
what is observed within social groups as their size increases, and that, in part, the commonly observed increased division
of labor with increasing group size is emergent. 相似文献
5.
环境监测数据是环境保护工作的基础,监测仪器设备的精良及监测方法的科学性则是获得优质数据的保障工具.本文运用数学方法对目前广泛使用的采样仪器进行了采样误差的分析研究,指出了改善仪器和改善监测方法去获取更精确数据的途径. 相似文献
6.
7.
Sunggyu Lee Sunmi Kim Hyun-Kyung Lee In-Seok Lee Jeongim Park Hai-Joong Kim Jeong Jae Lee Gyuyeon Choi Sooran Choi Sungjoo Kim Su Young Kim Kyungho Choi Sungkyoon Kim Hyo-Bang Moon 《Chemosphere》2013
Breast milk is a noninvasive specimen to assess maternal and infant exposure to polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs). In this study, 206 breast milk samples were collected from 87 participants during lactation, at <7, 15, 30, or 90 days postpartum in four cities in Korea. The total concentrations of PCBs (ΣPCB) and OCPs (ΣOCP) ranged from <LOQ to 84.0 (median: 12.1) ng g−1 lipid weight and from <LOQ to 559 (median: 144) ng g−1 lipid weight, respectively. The residue levels of these contaminants measured in our study were relatively lower than those reported for European, African and Asian populations. Within a month postpartum typically after day seven the levels of ΣPCB and ΣOCP significantly increased. Some OCP compounds were correlated with maternal age, BMI, parity, and delivery mode. Certain types of dietary habits such as seafood and noodle consumption were significantly associated with ΣPCB and ΣOCP. The estimated daily intakes (EDIs) of ΣPCB and ΣOCP were 45.2–127 ng kg−1 bw day−1 and 625–1259 ng kg−1 bw day−1 during lactation, respectively, which are lower than the threshold values proposed by the US EPA and Health Canada. The exposure of Korean infants to chlordanes via breast milk had a potential health risk which deserves further investigation. 相似文献
8.
9.
Flowrate targeting for threshold problems and plant-wide integration for water network synthesis 总被引:3,自引:0,他引:3
Foo DC 《Journal of environmental management》2008,88(2):253-274
Water reuse/recycle has gained much attention in recent years for environmental sustainability reasons, as well as the rising costs of fresh water and effluent treatment. Process integration techniques for the synthesis of water network have been widely accepted as a promising tool to reduce fresh water and wastewater flowrates via in-plant water reuse/recycle. To date, the focus in this area has been on water network synthesis problems, with little attention dedicated to the rare but realistic cases of so-called threshold problems. In this work, targeting for threshold problems in a water network is addressed using the recently developed numerical tool of water cascade analysis (WCA). Targeting for plant-wide integration is then addressed. By sending water sources across different geographical zones in plant-wide integration, the overall fresh water and wastewater flowrates are reduced simultaneously. 相似文献
10.
Landscape Planning for Agricultural Nonpoint Source Pollution Reduction I: A Geographical Allocation Framework 总被引:1,自引:1,他引:0
Agricultural nonpoint source pollution remains a persistent environmental problem, despite the large amount of money that
has been spent on its abatement. At local scales, agricultural best management practices (BMPs) have been shown to be effective
at reducing nutrient and sediment inputs to surface waters. However, these effects have rarely been found to act in concert
to produce measurable, broad-scale improvements in water quality. We investigated potential causes for this failure through
an effort to develop recommendations for the use of riparian buffers in addressing nonpoint source pollution in Wisconsin.
We used frequency distributions of phosphorus pollution at two spatial scales (watershed and field), along with typical stream
phosphorus (P) concentration variability, to simulate benefit/cost curves for four approaches to geographically allocating
conservation effort. The approaches differ in two ways: (1) whether effort is aggregated within certain watersheds or distributed
without regard to watershed boundaries (dispersed), and (2) whether effort is targeted toward the most highly P-polluting
fields or is distributed randomly with regard to field-scale P pollution levels. In realistic implementation scenarios, the
aggregated and targeted approach most efficiently improves water quality. For example, with effort on only 10% of a model
landscape, 26% of the total P load is retained and 25% of watersheds significantly improve. Our results indicate that agricultural
conservation can be more efficient if it accounts for the uneven spatial distribution of potential pollution sources and the
cumulative aspects of environmental benefits. 相似文献