Finding the appropriate level of complexity for a simulation model: An example with a forest growth model

The topic of model complexity is fundamental to model developers and model users. In this study, we investigate how over- and under-fitting of a driving function in a simulation model influences the predictive ability of the model. Secondly, we investigate whether model selection approaches succeed in selecting driving functions with the best predictive ability. We address these issues through an example with the forest simulator SORTIE-ND. Utilizing maximum likelihood methods and individual tree growth data we parameterize five growth functions of increasing complexity. We then incorporate each growth function into the simulation model SORTIE-ND and test predicted growth against independent data. Compared to the independent data, the simplest and the most complex growth functions had the poorest predictive ability while functions of intermediate complexity had the best predictive ability. The poor predictive ability of the simplest model is caused by poor approximation of the system while the poor predictive ability of the most complex model is caused by biased parameter estimates. A growth function of intermediate complexity was the most parsimonious model where error due to approximation and error due to estimation were simultaneously minimized. The model selection criteria AIC and BIC were found to select complex functions that were over-fitted according to the independent data comparison. BIC was closer to choosing the model that minimized prediction error than AIC. In this example, BIC is the more appropriate model selection criterion. It is important that both model developers and models users remember that more complex models do not always result in better predictive models.     

Advances in remote sensing of freshwater fish habitat: A systematic review to identify current approaches,strengths and challenges

Remote sensing technology offers the ability to derive information on freshwater fish habitats across broad geographic areas and has the potential to transform approaches to monitoring. However, the numerous platforms, sensors and analytical software that are available may overwhelm those interested in utilizing this important technology and thus limit its broad application and uptake. Our review is intended to shed light on the capacity of this technology to transform freshwater fish habitat monitoring by examining the fundamental characteristics of the major remote sensing technologies that have been used for characterizing freshwater habitats, conducting a systematic literature review of studies that have used remote sensing technologies to characterize freshwater fish habitats and, highlighting some of the key habitat features, fish species and regions, that have been examined. Lastly, we identify the relative strengths and weaknesses of the various remote sensing technologies that can be used, recommend future research that could help improve the use of these technologies, and, provide a series of important considerations for those who are interested in utilizing these technologies for freshwater fish habitat characterization.     

凸二次规划的一个Mehrotra型预估-校正算法

将Salahi等人对线性规划的优化算法推广到凸二次规划,证明了推广后的算法在最坏情况下,至多经过0(n2log(x0)Ts0/ε)次迭代后终止,其中n是问题的规模,(x0,s0)是算法的初始可行点,ε是精度最后给出了Matlab仿真实验,验证了算法的可行性.     

Variability in movement dynamics of topminnow (Fundulus notatus and F. olivaceus) populations

Abstract – Movement and dispersal patterns are key biological processes across a range of organisational levels. The Fundulus notatus species complex includes several species with similar ecological niches that exhibit broadly overlapping ranges. We conducted a mark–recapture study on two of the most widely distributed members of this species complex to improve our understanding of their movement and habitat use. A population of F. notatus was studied between June and August of 2008 and 2009 in Cahokia Creek, a small tributary of the Mississippi River in Illinois, along with a parallel study of Fundulus olivaceus between May and July of 2009 in Big Creek, a tributary of the Pascagoula River in Mississippi. Fish were recaptured approximately weekly, and habitat variables were measured. Estimated daily movement rates varied significantly both between locations and between years. Fundulus olivaceus in Big Creek moved <1 m per day, while F. notatus in Cahokia Creek in 2009 moved nearly 23 m per day. The distribution of movements was strongly leptokurtic in all three data sets. Differences in movement rates were attributed to significant differences in population size and habitat characteristics. Our data did not support the hypothesis that populations consist of distinct mobile and resident components. Instead, individual fish went through periods of little or no movement followed by extensive movement (consistent with the home range shift model of fish movement). We discuss the implications these results have for contact zone dynamics between these two species.     

Artificial structures as tools for fish habitat rehabilitation in a neotropical reservoir

• 1. Since most of the natural habitats critical for freshwater fish survival have been adversely affected by human disturbance, the effectiveness of artificial structures in providing new and suitable habitats for fish has been increasingly investigated.
• 2. This paper evaluates the role of artificial structures as fish habitat in a structureless 30 km² Brazilian reservoir, through underwater surveys conducted monthly from April 1999 to March 2000.
• 3. In total, 5759 fish in nine species were recorded, but only three cichlid species—one native, Geophagus brasiliensis and two non‐native, Cichla kelberi and Tilapia rendalli—showed consistent association with the artificial habitats, suggesting that this family reacts to submerged structures.
• 4. The absence of fish at control sites compared with high occurrences in sites provided with a physically complex structure suggests that artificial structures can play an important ecological role for cichlids smaller than 150 mm TL, probably related to shelter and/or feeding benefits.
• 5. The level of structural complexity and position in the water column influenced fish use of artificial structures. C. kelberi was associated with highly complex structures, whereas moderately complex bottom structures were more effective in harbouring G. brasiliensis. Bottom structures are apparently more important than midwater structures in harbouring T. rendalli, but structural complexity seemed to play a secondary role.
• 6. This study is the first in demonstrating that adding complex artificial structures can expand habitats for small fish (<150 mm TL), especially cichlids, in a neotropical impoundment. It seems reasonable to expect that deploying physically complex structures in other oligotrophic, structureless and cichlid‐dominated impoundments in Brazil will lead to similar results to those found in this work.

Copyright © 2008 John Wiley & Sons, Ltd.     

转变科学观念,促进“减抗”行稳致远

鉴于2019年我国兽用抗菌药使用量的反弹与2015—2019年兽用中药市场规模（销售额）总体处于萎缩的趋势等情况,在对抗生素滥用的简单化认识误区及其不可替代性进行分析探讨的基础上,提出了转变科学观念,正确认识与合理应用抗生素的看法。同时提出在抗生素使用方面的辨证与辨病相结合、促进“减抗”行稳致远的3点建议：⑴走出单一禁限与替代的误区,通过合理应用来“减抗”;⑵重视辨证与辨病相结合,让抗生素合理应用有法可依;⑶加强新观念人才培养与培训,促进“减抗”行稳致远。     

祁连山水源林经营模式研究

水源林经营系统是一个复杂系统，关系着中国的水资源和生态安全，意义重大。为适应祁连山水源林经营管理实践和西部生态建设的需要．在实地调查的基础上．采用复杂性科学的新理论与新方法提出了一个有科学依据的、定量化、可操作的祁连山水源林经营模式，创新了原来的经营模式。该模式融合了水源林经营理论、水源林目标体系、水源林经营原则、水源林目标结构体系和水源林经营技术体系。该模式通过改善水源林结构，实践水源林的可持续经营．逐步实现水源林经营的生态效益、社会效益和经济效益目标，从而提供中国河西走廊地区稳定的优质水资源。促进该地区可持续发展和应对全球气候变化。根据该模式．对祁连山水源林区现有青海云杉Picencrassifolia林经营提出了经营建议。该模式对提高该区水源林的经营水平和经营效益具有现实指导意义。表1参30     

基于小波消噪和符号动力学的参考作物腾发量变化的复杂性研究

提出了基于小波消噪的符号动力学途径研究参考作物腾发量(ET0)变化的复杂度,以辽宁省的锦州、北镇、义县、黑山4个站为例,对各气象因素(1957～2006年)及ET0序列进行小波消噪,运用Lempel-Ziv算法计算其复杂度。结果表明:整个锦州市由于噪声影响ET0的平均复杂度为9.25,较真实序列平均复杂度大;义县ET0变化比其他3个站复杂;从时间上分析,锦州4个站中有3个站(锦州、义县、黑山)近20年呈现下降趋势。从符号动力学的角度研究ET0系统的复杂性,为ET0研究提供了新的工具。     

关系复杂性对关系类别间接性学习分类的影响

以252名大学生为被试,使用3种复杂性不同的关系类别,创设个人关系类别的间接性学习条件和参照性交流关系类别的间接性学习条件,通过限定分类和自由分类2种任务,探查关系复杂性对关系类别间接性学习分类的影响特点.结果发现:关系复杂性对关系类别间接性学习分类中学习条件具有显著影响作用,随着关系复杂性的增高参照条件的分类成绩逐渐降低,个人条件的分类成绩逐渐增高;关系复杂性对关系类别间接性学习中分类方式具有显著影响作用,关系复杂性较低时分类方式间无显著差异,关系复杂性较高和高时限定分类显著高于自由分类.     

Landscape-moderated importance of hedges in conserving farmland bird diversity of organic vs. conventional croplands and grasslands

Hedges provide important nesting, feeding and sheltering sites for birds in agricultural areas, while organic farming also enhances farmland birds. However, it is little known how the interaction of these local variables (amount of hedges and organic management) with landscape scale variables affects birds. We selected paired conventional and organic winter wheat fields and meadows in each of 10 landscapes in Germany. Birds were surveyed in the fields and in the adjoining hedges. More bird species occurred in organic than in conventional fields regardless of land-use type (wheat fields and meadows). However, hedge length had a much stronger effect on bird richness than organic farmland management. We found an interaction of landscape complexity and hedge length in that hedge length enhanced bird richness only in case of simple landscapes (<17% semi-natural areas within a 500 m radius around the centre of bird survey plots). In more complex landscapes the local effect of hedge length levelled off because bird richness was high even without local hedges. Therefore, adding hedges or introducing organic farming practices should be primarily promoted in simple landscapes, where it really makes a difference for biodiversity.