Public and professional views on invasive non-native species – A qualitative social scientific investigation

The potential of invasive non-native species to modify ecosystems is well established. Yet, the resulting visibility of the field of invasion biology and its growing influence on policy decisions has led to the development of persistent critique. In addition, public opposition to the removal of non-native species has repeatedly delayed interventions, sometimes to the point where eradication has become impossible. Understanding the views of the lay-public is thus of crucial importance. Our study investigated views on invasive non-native species as held by both the general public and ecologists. We chose an in-depth qualitative social scientific approach to identify species attributes that people draw on to evaluate biological invasions and potential management options. Interviews and focus group discussions (n = 79 participants) were conducted in the North-east of Scotland, and included members of the public from a wide range of backgrounds, as well as research ecologists and professionals dealing with invasive non-native species. Two key arguments, namely (i) harmfulness of a species and (ii) human responsibility for its spread, shaped both ecologists’ and lay-people’s discussions. Non-nativeness was understood by our participants in various ways and did not necessarily raise concerns about a species. Our results indicate that for information campaigns on species management to be effective, values inherent to the debate about invasive non-native species need addressing in a more explicit and transparent manner. Arguments such as human responsibility that are currently neglected in the scientific discourse, but that were important criteria for a wide range of participants, should be made explicit.     

The influence of disturbance and habitat on the presence of non-native plant species along transport corridors

The impact from transportation corridors on surrounding habitat often reaches far beyond the edge of the corridor. The altered disturbance regime in plant communities along corridor edges and vehicle traffic facilitate the spread and establishment of invasive non-native plant species. We compared the frequency of non-native plant species along highways and railways and the ability of these species to invade grasslands and dense forests along these corridors. We measured the frequency of several non-native plant species along transects 0-150 m from the edge of highways and railways in grasslands and forests, as well as at control sites away from corridors. Both transportation corridors had higher frequency of non-native species than respective control sites. Grasslands had higher frequency of non-native species than forested habitats, but the frequency did not differ between the highways and the railways. The frequency of non-native species in grasslands along highways and railways was higher than at grassland control sites up to 150 m from the corridor edge, whereas the frequency in forested habitats along corridors was higher than at forested control sites up to only 10 m from the corridor edge. There was a significant decrease in the frequency of non-native species with increasing distance from both corridors in the forest, while grasslands showed no significant change in non-native species frequency with distance from corridors. This suggests that corridor edges and grassland habitats act as microhabitats for non-native species and are more prone to invasion than forests, especially if disturbed. Our results emphasize the importance of minimizing the disturbance of adjacent plant communities along highways and railways during construction and maintenance, particularly in grassland habitats and in areas sensitive to additional fragmentation and habitat loss.     

Regional differences in patterns of fish species loss with changing land use

Human-centered land use causes ecosystem degradation and loss of biodiversity in streams, yet such processes may be highly heterogeneous among species and regions. We quantified fish species sensitivity to several classes of land use and determined if trends varied among three geoclimatic regions of Maryland, USA. Our approach compares the cumulative frequency distribution (CFD) of sites where a species was expected to occur to the CFD of those where it was collected to estimate the species-specific maximum degree of land use tolerated and the minimal amount that may induce an impact. Fishes were most vulnerable to urban land use gradients, though trends were region-specific with heightened sensitivity in the Piedmont (64-72% of species negatively affected) relative to the Coastal Plain (45-52% negatively affected). Species found in both regions exhibited greater vulnerability to urbanization in the Piedmont. Responses to agricultural land use were less severe though trends were region-specific as well with the least sensitive in the Piedmont and the greatest negative impact in the Highlands region. In many cases, reduced population abundances were detected at lower levels of land use relative to the range where the species was apparently extirpated. Our results demonstrate that population reduction and species loss due to land use change differs substantially among regions, even within a single species. Greater sensitivity observed in abundance-weighted analyses implies that further loss of fish diversity may be impending in impacted streams. Our results have direct application to prioritize conservation resources and forecast future declines in species distributions and biodiversity.     

Relative contributions of domestic and foreign sourced ballast water to propagule pressure in Puget Sound, Washington, USA

The movement and release of non-indigenous species (NIS) in ship ballast water is a global threat to the conservation of native aquatic species and habitats. One key to successful NIS establishment in coastal waters is propagule pressure - the size and frequency of NIS inoculations. We estimated propagule pressure of high-risk coastal zooplankton delivered in ballast water to Puget Sound, Washington, USA, which receives 7.5 × 10⁶ m³ of ballast water annually. We weighed the relative propagule pressure from domestic and foreign ballast water, in terms of propagule size (number of individuals), frequency of NIS occurrences, and diversity (number of known NIS species). Ship discharge volume was not a good predictor of propagule pressure. Instead route type (domestic or foreign) and ballast water exchange status (exchanged in mid-ocean vs. unexchanged) were much better predictors of propagule supply. Overall, while the diversity of non-indigenous zooplankton was higher in trans-oceanic ballast, the annual discharge of coastal zooplankton propagules to Puget Sound was much greater for ships conducting domestic voyages. These results suggest that intra-coastal ballast water must be further scrutinized as a pathway for NIS introduction, and calls into question regional “common waters” agreements that allow vessels to move ballast without conducting ballast water treatment.     

The suitability of weed risk assessment as a conservation tool to identify invasive plant threats in East African rainforests

We tested the ability of an international Weed Risk Assessment (WRA) protocol to predict invasion status of 230 alien plant species introduced via a botanical garden to tropical rainforest in Tanzania. The reliability and accuracy of WRA in discriminating between invaders and non-invaders was independently assessed using field data on species demography and distribution. The WRA rejected 83% of known invaders, and accepted 74% of non-invaders. Only 1% of accepted species were known invaders at the site. WRA performance varied among different growth forms, and underestimated the risks arising from palm species. Among those species that had naturalised, the WRA was better at identifying invaders of open rather than forest habitats. The WRA score was significantly correlated with how widespread species had become at the site, suggesting some capacity to predict spatial spread at a landscape scale. Knowledge of propagule pressure and residence time did not increase explanatory power. These results indicate that the WRA was able to discriminate between invaders and non-invaders with accuracy comparable to similar assessments in temperate and sub-tropical regions. It could be made more effective by weighting traits important in tropical forests e.g. certain growth forms, shade tolerance etc. more heavily. Such a modified WRA could be used successfully elsewhere in the palaeotropics as a screening tool to identify the risk of invasion arising from plants introduced for agroforestry, horticulture or landscaping. Given the increasing pressures on tropical forests and importance of agroforestry to local economies, the WRA protocol represents a useful conservation tool.     

Indicator species and the problem of spatial inconsistency in nestedness patterns

The potential as indicators of species richness were investigated for 178 species belonging to six ecologically defined species groups (epiphytic bryophytes on nutrient-rich bark, epiphytic macrolichens on nutrient rich bark, pendant lichens on conifer trees, bryophytes on siliceous rocks, bryophytes on dead conifer wood, and polypore fungi on dead conifer wood), using species data from 0.25 ha plots from three different coniferous forest areas (ca. 200 ha each). A species was defined as a potential indicator species for a species group within a study area if its distribution was statistically significantly nested within the species-plot matrix ranked according to species richness, and if the plot frequency of the species was less than 25%.Only two species were identified as potential indicators within all three areas and on average ≈80% of the potential indicator species were lost from one area to another. The results indicate that inconsistency between areas in the species’ frequency distributions and their position in nested hierarchies may strongly reduce the general predictive power of indicator species of species richness, even if significantly nested patterns are found at the community level. We suggest that indicators related to amount and quality of habitats may be an alternative to lists of indicator species of species richness.     

重庆市茶园蚂蚁物种多样性及空间分布格局

为筛选茶园害虫的蚂蚁类天敌,采用样地调查法研究了重庆主要产茶区(海拔371~1 068 m)茶园蚂蚁物种多样性特征与空间分布格局。在重庆主要产茶区茶园,设置3条垂直带,每条垂直带划分为低海拔(300~500 m)、中海拔(500~700 m)和高海拔(700 m以上)3个水平带,每个水平带设置3~4块样地,调查茶园的蚂蚁物种组成、群落多样性及空间分布特点。在物种多样性方面:共采集到蚁科昆虫4亚科,39种。各水平带物种丰富度为7~13种,Shannon-Wiener多样性指数0.55~1.25,Pielou均匀度指数0.08~0.16,Simpson优势度指数为0.26~0.65;各水平带蚂蚁群落多样性指数差异不显著,表明其多样性水平比较一致。群落相似性指数为0.22~0.48,多数处于中等不相似水平。在群落优势种方面:不同海拔茶园蚂蚁优势种数目1~3种,常见种最多达6种,最少仅1种;稀有种最多17种,最少5种;从重庆范围来看,重庆主要产茶区茶园蚂蚁群落共有7种优势种。在蚂蚁空间分布方面:有17种蚂蚁具有较宽的垂直空间分布,活动范围涵盖土壤、地表和树冠,有作为天敌昆虫资源的可能。仅有9种蚂蚁在不同水平带的茶园中均有分布。结合群落相似性与多样性分析结果,重庆茶园生境破碎,蚂蚁群落间物种交流受阻,不利于茶园生物多样性水平的稳定与提高。     

Environmental effects related to the local absence of exotic fish

Given the extent of biological invasions in industrialized countries, our understanding of the determinants of overall patterns of biological invasions could gain most from consideration of why exotic species are absent from some areas, rather than from distribution patterns of exotic species. Fish communities were sampled at 381 sites representing 221 rivers in the Adour-Garonne stream system (116 000 km², SW France). Very few rivers were not colonized by exotic fish species, however, on a local basis, only 33% of the sampling sites hosted exotics. Using General Linear Modelling, we found that patterns of exotic fish (occurrence, number of species, proportion within assemblage) responded to both land-use and physical variables, whereas patterns of native fish only responded to the local meso-scale characteristics of each stream reach from headwaters to mouth. All fish communities were susceptible to invasion regardless of native species richness, and higher native species richness did not decrease the opportunity for establishment by exotic species. The likelihood that exotic fish are absent primarily increased with elevation and with lower human influence upon the land cover, while human-impacted landscapes (agricultural and urban areas) were more likely to host exotic fish and higher numbers of exotic species. In light of urban and agricultural development, our ability to detect responses of exotic species to landscape alterations using a combination of simple physical and land cover variables exemplifies a cost-effective technique for assessing areas at greater invasion risk in large stream systems.     

运用双液相系统进行三氯苯的生物降解

Due to easy volatilization of volatile organic compounds from water,it is difficult to monitor their aerobic biodegradation in the traditional single water system.Whether a two-liquid-phase system(TLPS) could overcome this obstacle and enhance the degradation of volatile contaminants? In this study,a TLPS composed of silicone oil and water was employed to investigate the biodegradation of volatile compounds,trichlorobenzenes(TCBs),by the adapted microorganisms in an activated soil.The degradation and volatilization of TCBs in TLPS and in a single water system were compared.The results showed that due to volatilization losses of TCBs,the mass balance of TCBs in a single water system was very low.In contrast,using TLPS could effectively inhibit the volatilization losses of TCBs and achieved a very good mass balance during the biodegradation process.Meanwhile,the TLPS could increase microbial activity and microbial growth during the degradation process.With TLPS,the TCB degradation was in descending order of 1,2,4-TCB> 1,2,3-TCB>> 1,3,5-TCB,which was related to the exposed concentration of the contaminants in soil.This study showed that TLPS could be employed as an effective tool to evaluate the biodegradation of volatile hydrophobic organic compounds,which could not be achieved with the traditional single water system.     

The role of life-history and location of barriers to migration in the spatial distribution and conservation of fish assemblages in a coastal river system

Water resource development in coastal river catchments contributes to poor fish assemblage health due to the effects of barriers to migration and altered flow regimes. Impacts of migration barriers on fish assemblages depend primarily on the location of each barrier within the river network and migration needs of regional fish fauna. This study examined how temporal and spatial patterns in the distribution and composition of fish assemblages was associated with varying estuarine connectivity and migration barriers in higher altitude reaches in the eastern Hunter River catchment, temperate Australia. Species richness and abundances of diadromous species were expected to be greater in a tributary catchment with unrestricted connectivity to the Hunter River estuary when compared to a neighbouring tributary catchment with restricted connectivity. Six diadromous species were sampled only, or in greater abundances, in the unrestricted tributary when compared to the restricted tributary. As a consequence, assemblage composition in the restricted tributary was dominated by non-diadromous species. Greater abundances of the amphidromous Cox’s gudgeon (Gobiomorphus coxii) were sampled in the unrestricted tributary following their estuarine-freshwater upstream juvenile migration period when compared to the restricted tributary. Differences in the accumulations of migratory species immediately downstream of upland barriers between the two levels of estuary connectivity indicate that migration barriers in lowland reaches have significant effects throughout the entire catchment. Results of this study indicate that the location of each barrier to migration within river networks has varying consequences for catchment-scale connectivity loss and assessing the impacts of multiple barriers. Determining the effects and most appropriate management of migration barriers requires that all obstructions within a river network are recognised, as multiple barriers can have cumulative and interacting consequences for freshwater fish fauna, especially diadromous species.     

Food for thought: Risks of non-native species transfer to the Antarctic region with fresh produce

To understand fully the risk of biological invasions, it is necessary to quantify propagule pressure along all introduction pathways. In the Antarctic region, importation of fresh produce is a potentially high risk, but as yet unquantified pathway. To address this knowledge gap, >11,250 fruit and vegetables sent to nine research stations in Antarctica and the sub-Antarctic islands, were examined for associated soil, invertebrates and microbial decomposition. Fifty-one food types were sourced from c. 130 locations dispersed across all six of the Earth’s inhabited continents. On average, 12% of food items had soil on their surface, 28% showed microbial infection resulting in rot and more than 56 invertebrates were recorded, mainly from leafy produce. Approximately 30% of identified fungi sampled from infected foods were not recorded previously from within the Antarctic region, although this may reflect limited knowledge of Antarctic fungal diversity. The number of non-native flying invertebrates caught within the Rothera Research Station food storage area was linked closely with the level of fresh food resupply by ship and aircraft. We conclude by presenting practical biosecurity measures to reduce the risk of non-native species introductions to Antarctica associated with fresh foods.     

基于自组织神经网络的耕地自然质量评价方法及其应用

耕地质量各构成要素的特点和相互间的影响,决定了耕地质量的外在表现,客观地确定耕地自然质量,对耕地分等定级具有重要的意义。该文通过对已有耕地质量评价方法的优势与不足的分析,提出在空间数据库基础上应用自组织神经网络的耕地自然质量评价方法,并应用该方法对吉林省九台市耕地自然质量进行了评价,通过步长为1 000次训练,自动生成13个类别,在13个类别基础上按照九台市的指定作物的光温生产潜力指数、作物的产量比系数,进行了耕地自然质量评价。根据评价分值的大小分为3等,其中质量等级Ⅰ级占全市耕地面积42.13%,Ⅱ级占全市耕地面积30.40%,Ⅲ级占全市耕地面积27.47%。评价结果与《九台市耕地质量更新成果》比较,图斑重合率为80.78%,面积重合率为79.42%。2种评价方法可能出现差异的原因:该文评价方法增加了坡度因子,且《九台市耕地质量更新成果》采用的是全省统一的指标权重;2种方法对于一些定性描述指标均通过信息赋权值法进行量化,而2种方法中量化方法不同,赋值不同。该方法将自组织神经网络和地理信息系统相结合,有效地集成影响耕地质量相关的土壤及土壤环境信息,利用自组织神经网络在没有教师信号时自动连接权值向着更利于竞争方向调整,通过度量评价单元的相似程度,使类间差异最大而类内差异最小,逐步将评价单元划分类别。根据每个类别中图斑自然质量指数的大小进行耕地质量等别评价,提高了评价结果的可信度,为耕地质量评价提供了新思路。     

利用GGE双标图和综合选择指数划分棉花品种生态区

为提高农作物品种多性状选育和应用的可靠性,本研究基于品种选择指数,应用GGE双标图进行了棉花品种生态区划分。首先依据国家棉花品种审定标准构建通用性强的品种选择指数(SI),即SI=0.40×皮棉产量+0.13×纤维比强度+0.09×(纤维长度+马克隆值)+0.11×枯萎病+0.09×黄萎病+0.10×霜前花率。然后,采用GGE双标图方法对2000—2013年期间39组(含585个单点试验)长江流域国家棉花区域试验中品种选择指数的基因型与环境互作效应及环境间关系进行综合评价与分析。研究结果将长江流域棉区划分为四川盆地生态区、南襄盆地生态区、浙江省沿海生态区和长江中下游生态区。其中,长江中下游生态区为长江流域的主要品种生态区,对长江流域的总体环境代表性最强,涵盖了湖南省环洞庭湖棉区、湖北省江汉平原和鄂东南岗地棉区、江西省环鄱阳湖棉区、安徽省沿江棉区、江苏省宁镇丘陵及沿江和沿海棉区;四川盆地生态区、南襄盆地生态区和浙江省沿海生态区均为特殊生态环境条件下的品种生态区,对总体环境代表性较差。因此,将以长江流域棉区为广谱适应性育种目标环境的棉花品种综合性状选择试验优先安排在长江中下游生态区中,有利于提高育种的总体选择效果,而其余品种生态区不适宜作为以长江流域为目标环境的品种综合性状选择环境,可侧重于特殊适应性品种选育。本研究充分展示了GGE双标图在品种生态区划分方面的应用效果,合理划分了长江流域基于选择指数的棉花品种生态区,可为长江流域棉区的品种多性状选择和推荐策略提供决策依据,也为其他棉区和作物品种生态区划分提供参考。     

A semi-empirical model to assess uncertainty of spatial patterns of erosion

Distributed erosion models are potentially good tools for locating soil sediment sources and guiding efficient Soil and Water Conservation (SWC) planning, but the uncertainty of model predictions may be high. In this study, the distribution of erosion within a catchment was predicted with a semi-empirical erosion model that combined a semi-distributed hydrological model with the Morgan, Morgan and Finney (MMF) empirical erosion model. The model was tested in a small catchment of the West Usambara Mountains (Kwalei catchment, Tanzania). Soil detachability rates measured in splash cups (0.48–1.16 g J^− 1) were close to model simulations (0.30–0.35 g J^− 1). Net erosion rates measured in Gerlach troughs (0.01–1.05 kg m^− 2 per event) were used to calibrate the sediment transport capacity of overland flow. Uncertainties of model simulations due to parameterisation of overland flow sediment transport capacity were assessed with the Generalized Likelihood Uncertainty Estimation (GLUE) methodology. The quality of the spatial predictions was assessed by comparing the simulated erosion pattern with the field-observed erosion pattern, measuring the agreement with the weighted Kappa coefficient of the contingency table. Behavioural parameter sets (weighted Kappa > 0.50) were those with short reinfiltration length (< 1.5 m) and ratio of overland flow power α to local topography power γ close to 0.5. In the dynamic Hortonian hydrologic regime and the dissected terrain of Kwalei catchment, topography controlled the distribution of erosion more than overland flow. Simulated erosion rates varied from − 4 to + 2 kg m^− 2 per season. The model simulated correctly around 75% of erosion pattern. The uncertainty of model predictions due to sediment transport capacity was high; around 10% of the fields were attributed to either slight or severe erosion. The difficult characterisation of catchment-scale effective sediment transport capacity parameters poses a major limit to distributed erosion modelling predicting capabilities.     

基于多时相遥感信息的中国农业种植制度空间格局研究

多熟种植是中国重要的种植制度,对保持和增加粮食产量和促进农村经济发展有重要意义。复种指数受自然条件和农村社会状况的影响处于不断变化之中,及时获取其变化信息对估计粮食产量变化及其原因和农业发展科学决策有非常重要的意义。中国地域辽阔,作物种植制度复杂多样,传统的统计方法不能及时满足政府获取种植制度变化的要求。卫星遥感是探测大尺度土地覆被格局及变化最有效手段,因此可以作为获取区域和全国尺度作物复种指数的一个重要途径。该研究探讨了应用多时相遥感数据定量表达全国种植制度信息提取的方法及可行性,采用峰值特征点检测法结合作物生长季相特征及农田管理特点(播种和收获)提取了中国农田的多熟种植信息,并与统计数据的复种指数进行比较验证,为进一步进行农业种植制度变化研究奠定了基础。     

土壤水流模式染色剂示踪及优先流程度评估

优先流是结构性土壤水分入渗的主要方式。为了直接利用土壤水流模式分析其优先流程度,该文采用亮蓝染色剂示踪原状与扰动土柱的土壤水运移,定量评估优先流的相对发育程度。研究结果表明原状土柱优先流发育,空间变异性强,受优先流通道的特征控制,其优先流水流模式以蚯蚓大孔隙流和土块裂隙优先流为主。扰动土柱的水流模式为活塞流,无优先流发育。该文提出了随深度变化的染色面积比的变异系数指示原状土柱优先流相对程度的评价准则:变异系数越低,优先流程度越高。变异系数≥0.5%为优先流程度一般发育,0.25%~0.5%之间为发育,≤0.25%为非常发育。并通过原状和扰动土柱灌溉模拟试验验证了评价准则的可靠性。     

Using Moran's I and geostatistics to identify spatial patterns of soil nutrients in two different long‐term phosphorus‐application plots

The spatial variation of soil nutrients especially the soil test phosphorus (STP) in grassland soils is becoming important because of the use of soil‐nutrients information as a basis for policies such as the recently EU‐introduced Nitrates Directive. Up to now, the small‐scale spatial variation of soil nutrients in grassland has not been studied. The main aim of this study was to investigate the spatial patterns of soil nutrients in two grazed grassland plots with a long‐term (38 y) P‐application experiment, in order to better understand the spatial variation of soil nutrients and the correlation among soil nutrients in grasslands. Two small areas (one from a high‐P background and the other from a medium‐P background) were selected. Soil samples (304 per study area) were collected based on a 1 m × 1 m grid system. The samples were analyzed for STP, Mg, K, pH, and lime requirement (LR). The results were analyzed using conventional statistics, Moran's I, geostatistics, and a GIS. Based on the global Moran's I values, significant positive spatial autocorrelations were found for STP, Mg, pH, and LR in both study areas. Spatial clusters and spatial outliers were detected using the local Moran's I index. Clear linear‐shaped high‐high or low‐low value clusters of the studied variables except K were observed in the study areas due to long‐term usage of machine spreader or other agricultural‐management methods in the past. The corresponding linear patterns were further found in the spatial‐distribution maps. Small spatial patches were found for soil K revealing that it had a random spatial distribution related to the relatively uniform K fertilizer in the study areas. The spatial clusters revealed by local Moran's I were in line with the spatial patterns in the distribution maps.     

Host-status and host-sensitivity of wild Cucumis species to Meloidogyne incognita race 4

Abstract

Wild watermelon (Cucumis africanus) and wild cucumber (Cucumis myriocarpus), which are highly resistant to the southern root-knot nematode (Meloidogyne incognita) race 2, have the potential for serving as seedling rootstocks for the highly nematode-susceptible watermelon (Citrullus lanatus) cultivars. In South Africa, due to high labour costs, most cotton farmers are turning to watermelon production. In these regions, there is high incidence of M. incognita race 4. A pot experiment in the greenhouse was, therefore, initiated to investigate the host-status and host-sensitivity of Cucumis africanus and Cucumis myriocarpus to M. incognita race 4, when inoculated with 0, 200, 600, 100, 1400, 1800 and 2200 eggs and second-stage juveniles (J2s). At harvest, 56 days after inoculation, the reproductive factor values at all levels of inoculation were less than one. Penetration indices on both plant species were greater than one, suggesting that the resistance was post-infectional and therefore, introgressible. Sex (male: female) ratios of M. incognita race 4 on the two Cucumis species were greater than one, suggesting that more J2s were converted into males. Infection of Cucumis species by the test nematode had no effect on yield components of the two plant species due to poor feeding sites. The two Cucumis species were, therefore, resistant to M. incognita race 4, with post-infectional resistance, where the sex ratio was skewed towards maleness. Thus, the two Cucumis species have the potential to be used as nematode-resistant rootstocks in watermelon production.     

Hypotheses to explain patterns of population change among breeding bird species in England

Population declines are now evident across many taxa, but within each assemblage there is often considerable variation in constituent population trends. We used bird population trends produced from the BTO/JNCC Common Birds Census (CBC) and the RSPB/BTO/JNCC Breeding Bird Survey (BBS), to test five main hypotheses to explain population changes of 59 breeding species in England (1967-2006): (1) breeding habitat, (2) predation risk to nest sites, (3) species climatic niche, (4) migration strategy, and (5) over-wintering bioclimatic zones of migrants, accounting for additional demographic and ecological traits. In absence of phylogenetic inter-relatedness, farmland species declined more than woodland species, most pronounced prior to 1986, probably reflecting agricultural intensification (1). We found limited support that ground nesters have declined more than above-ground or cavity nesters (2), and there was some indication that species with more northerly European distributions showed larger declines than more southerly-distributed species (3). Larger population declines were recorded for Afro-tropical migrants than species wintering in Europe or in the UK, most notable prior to 1986 (4). However, declines were not uniform across all migrants (5) - species over-wintering in the arid savannah bioclimatic zone of Africa decreased in population between 1967 and 1976, whereas species wintering in humid West African forest and savannah declined more after 1987. These results suggest both breeding and over-wintering factors influenced population trends. European countries signed to the Convention on the Conservation of Migratory Species of Wild Animals are required to protect and conserve populations of migrants. Understanding connectivity between breeding and over-wintering populations, and similar environmental pressures experienced within over-wintering areas may be a useful step towards mitigating against further declines in migrants.     

Factors contributing to temporal stability in spatial patterns of water content in the tillage zone

The rates of many biological processes vary across an agricultural landscape in response to the spatial patterns of water content in the tillage zone. Although, water content varies temporally through the growing season, the combined effects of soil properties, landscape attributes, tillage or position relative to the crop row on the temporal variation in the spatial pattern in soil water content are not well understood. We measured the soil water content (0–0.20 m) regularly through three growing seasons at 32 positions along each of two transects in a side-by-side comparison of corn under conventional tillage (plowing and secondary tillage) and no till in order to identify factors with the strongest influence on the spatial patterns in water content. The tillage comparison traversed a landscape in which the clay content (cl) varied from 5.8 to 37.4% and the organic carbon content (OC) varied from 0.9 to 3.9%. The spatial pattern in water contents during wetting and drying events were temporally stable, as reflected in R²>0.7 of correlation analysis of water contents on successive measurement dates. Multiple regression analyses indicated that the water contents, averaged over all measurement dates, were positively correlated with cl and ln(OC) and were smaller in the row than the inter-row position. The reduction in water content due to conventional tillage was diminished with increasing OC. However, application of multiple regression analyses to each set of water contents measured on a given day for each year indicated that the impact of soil properties, tillage and position relative to the row varied within and among seasons.