建阳市农村生态建设的工程与效益

建阳市位于闽北中心，属亚热带季风气候，光热资源丰富，境内多年平均降水量１７４６２ｍｍ，全市森林２３４７８０２×１０５ｈａ，覆盖率达６９４％。土地总面积３３８３×１０５ｈａ，其中耕地３０４４×１０４ｈａ，林地２７６４８７×１０５ｈａ。全市土...     

Characterizing and predicting species distributions across environments and scales: Argentine ant occurrences in the eye of the beholder

Aim Species distribution models (SDMs) or, more specifically, ecological niche models (ENMs) are a useful and rapidly proliferating tool in ecology and global change biology. ENMs attempt to capture associations between a species and its environment and are often used to draw biological inferences, to predict potential occurrences in unoccupied regions and to forecast future distributions under environmental change. The accuracy of ENMs, however, hinges critically on the quality of occurrence data. ENMs often use haphazardly collected data rather than data collected across the full spectrum of existing environmental conditions. Moreover, it remains unclear how processes affecting ENM predictions operate at different spatial scales. The scale (i.e. grain size) of analysis may be dictated more by the sampling regime than by biologically meaningful processes. The aim of our study is to jointly quantify how issues relating to region and scale affect ENM predictions using an economically important and ecologically damaging invasive species, the Argentine ant (Linepithema humile). Location California, USA. Methods We analysed the relationship between sampling sufficiency, regional differences in environmental parameter space and cell size of analysis and resampling environmental layers using two independently collected sets of presence/absence data. Differences in variable importance were determined using model averaging and logistic regression. Model accuracy was measured with area under the curve (AUC) and Cohen's kappa. Results We first demonstrate that insufficient sampling of environmental parameter space can cause large errors in predicted distributions and biological interpretation. Models performed best when they were parametrized with data that sufficiently sampled environmental parameter space. Second, we show that altering the spatial grain of analysis changes the relative importance of different environmental variables. These changes apparently result from how environmental constraints and the sampling distributions of environmental variables change with spatial grain. Conclusions These findings have clear relevance for biological inference. Taken together, our results illustrate potentially general limitations for ENMs, especially when such models are used to predict species occurrences in novel environments. We offer basic methodological and conceptual guidelines for appropriate sampling and scale matching.     

中国主要农产品虚拟要素贸易网络结构特征分析

据虚拟水概念定义虚拟要素,并将其划分为虚拟资源要素和虚拟生态要素两类,选取虚拟资源要素中的耕地要素和虚拟生态要素中的化肥/农药要素为研究对象,定量分析2002—2016年以粮食贸易为载体的虚拟耕地、虚拟化肥/农药要素的贸易量,构建虚拟要素贸易网络,通过复杂网络的研究方法,结果表明:2002—2016年我国主要农产品虚拟耕地、化肥/农药要素的贸易总量呈下降趋势,降幅分别约25.51%、8.01%;虚拟耕地要素网络节点入度较大的为长江中下游、华南、西南地区,出度较大的为黄淮海和东北地区,虚拟化肥/农药要素网络与之相反;地区间节点强度的差异性大,虚拟耕地要素差值最大可达1459.56万hm~2,虚拟化肥/农药要素达61.38万t;二者网络节点度和强度的累积分布均符合幂律分布规律,其尾部的"重尾"现象揭示了节点度和强度的高可变性以及网络结构的脆弱性;虚拟耕地要素的输入区网络同配,输出区网络异配,揭示了地区间耕地要素的流动既呈集聚又有分散的态势,虚拟化肥/农药要素网络节点相关性皆为减函数,网络异配,揭示了虚拟化肥/农药要素在八大区域间联通的状况。网络结构特征分析为研究网络抗毁性特征和网络的优化调控机制奠定基础,为中国粮食贸易格局和粮价制定以及各个地区的农业种植结构调整提供理论依据。     

Biodiversity assessment in ecological restoration above the timberline

Ecological restoration trials in high-alpine sites require sampling of indigenous plant populations. This problem is discussed briefly in relation to initial genetic diversity in the restoration material. The further part of the paper deals with restoration trials in the Swiss Alps and their assessment.The plots, set in machine-graded downhill ski runs, were revegetated with transplants of alpine species used in various combinations. Safe-site conditions were simulated with biodegradable wood-fibre mats. Surveys carried out in plots aged four to seven years focused on plant species inventory and age-state structure of mixed stands. The alpha diversity assessment included speices number and the associated aspects. The consistent increase in species number, the number of plant families represented, and range of life-forms was apparently independent of the restoration timing. The age-state structure of the mixed stands was characterized by a considerable increase in the range of age-state classes and, in particular, a regular appearance of younger variants. These changes clearly indicate development of self-sustaining plant communities influenced by reproduction of the transplants and extensive immigration. It is proposed that age-state structure be called delta diversity and included in a routine assessment of post-restoration status of both single plant populations and mixed stands.     

Sexual selection and ecological generalism are correlated in antbirds

Sexual selection is thought to counteract natural selection on the grounds that secondary sexual traits are inherently costly and evolve at the expense of naturally selected traits. It is therefore commonly predicted that increased sexual selection is associated with decreased physiological tolerance or ecological plasticity. Using phylogenetic comparative methods, we test this prediction by exploring relationships between traits assumed to be sexually selected (plumage dichromatism and song structure) and traits assumed to be naturally selected (altitudinal range and habitat range) in a diverse family of tropical birds. Contrary to expectations, we find that taxa with higher levels of dichromatism, and lower song pitch, occupy a wider variety of habitats and elevations. In other words, indices of sexual selection are positively related to two standard measures of ecological generalism. One interpretation of this pattern is that sexual selection combines synergistically with natural selection, thereby increasing physiological tolerance or the propensity to adapt to novel environments. An alternative possibility is that ecological generalism increases population density, which in turn promotes sexual selection in the form of greater competition for mates. Overall, our results suggest that a synergism between natural selection and sexual selection may be widespread, but the processes underlying this pattern remain to be investigated.     

Butterfly Response to Microclimatic Conditions Following Ponderosa Pine Restoration

Efforts to restore ponderosa pine ecosystems to open, park‐like conditions that predominated prior to European‐American settlement result in altered stand structure and increased landscape heterogeneity, potentially altering habitat suitability for invertebrates and other forest organisms. We examined the responses of two butterfly species, Colias eurytheme and Neophasia menapia, to microclimatic changes at structural edges created by experimental restoration treatments in northern Arizona. We monitored microclimate, including air temperature, light intensity, and vapor pressure deficit (VPD), on several mornings during butterfly releases. We placed adult butterflies at east‐ and west‐facing edges approximately one half‐hour before dawn to determine their behavioral response to microclimatic differences between east‐ and west‐facing edges. After sunrise, all three microclimatic variables were higher at east‐facing edges, and the difference in microclimate between the two edge orientations increased through early morning. For both species, butterflies placed at east‐facing edges flew earlier than butterflies at west‐facing edges. Colias eurytheme, an open‐habitat species, tended to move toward the treated forest during initial flight, while movements of Neophasia menapia, a forest‐dwelling species, did not differ from random flight. Our results indicate that butterflies respond to microclimatic factors associated with restoration treatments, while responses to structural changes in habitat vary among species, based on habitat and food plant preferences. These changes in forest structure and microclimate may affect the distribution of many mobile invertebrates in forested landscapes undergoing restoration treatments.     

A comparison of the wood anatomy of 11 species from two cerrado habitats (cerrado s.s. and adjacent gallery forest)

A comparative study of the secondary xylem (wood) anatomy of 11 species (38 specimens) occurring in cerrado s.s. and the adjacent gallery forest (both cerrado s.l. habitat) was made with the aim of identifying the anatomical characteristics of ecological value and correlating them with the environmental conditions. The anatomical features that vary, in general, between the two habitats are: growth ring distinctness (well or poorly defined); tyloses and deposits (more abundant in cerrado specimens); gelatinous fibres (more evident in cerrado specimens and in different patterns between habitats); variation in paratracheal and banded parenchyma (more abundant in cerrado); and more cells per parenchyma strand in cerrado. In general, gallery forest specimens have wider vessels, fewer vessels per square millimetre and larger intervessel pits, indicating more efficient water conduction, whereas cerrado s.s. specimens are the opposite, with low vulnerability and mesomorphy indices, demonstrating greater safety under conditions of water stress. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, ?? , ??–??.     

Long-term exclosure of sheep-grazing from an ancient wood: Vegetation change after a sixty-year experiment

Question: An ancient woodland site with a long history of coppicing and heavy grazing was protected from domesticated stock in 1955. Results of a vegetation-monitoring experiment were subsequently published in 1983. This study followed up the original research to investigate whether observed trends were as predicted. These included a shift in tree species composition in favour of shade-tolerant species, beech (Fagus sylvatica) and rowan (Sorbus aucuparia), at the expense of light-demanding birch (Betula spp.) and oak (Quercus petraea agg.), and progress towards a typical woodland ground flora. Location: Peak District National Park, United Kingdom. Methods: The mixed oak–birch woodland was re-surveyed in 2011. Two enclosures (1955 and 1980s) and an unenclosed control area were investigated. Overstorey structure and composition was assessed by measuring canopy openness and the girths of all trees and saplings. Herb layer species composition was also recorded in 28 vegetation plots. Results: We demonstrated a progressive decline in the number of mature oaks and birch in the old enclosure although they still regenerated successfully. Only a few individuals of beech and rowan appeared. Herb layer species composition differed between the subareas but since the 1980s, the temporal change in the old enclosure was negligible. The new enclosure followed a similar pattern in both canopy and herb layer as observed in the early years in the old enclosure. However, the control subarea had no regeneration of woody species and limited ground flora. Conclusions: After nearly 60 years, the replacement of light-demanding dominants by shade-tolerant trees was still limited, probably by low pH and stable light conditions. The findings are pertinent to the impacts of large herbivore grazing (domestic stock or wild) on woodland dynamics.