Different Patterns of Changes in the Dry Season Diameter at Breast Height of Dominant and Evergreen Tree Species in a Mature Subtropical Forest in South China

Information on changes in diameter at breast height （DBH） is important for net primary production （NPP） estimates, timing of forest inventory, and forest management. In the present study, patterns of DBH change were measured under field conditions during the dry season for three dominant and native tree species in a monsoon evergreen broad-leaved forest in the Dinghushan Biosphere Reserve. For each tree species, different patterns of DBH change were observed. In the case of the fast-growing tree species Castanopsis chinensis Hance, large diurnal fluctuations occur, with a peak DBH in the early morning （around 05：00 h） that decreases to a minimum by about 14：00 h. Both Schima superba Gardn. et Chemp and Cryptocarya chinensis （Hance） Hemsh exhibited less diurnal swelling and shrinkage. Diurnal fluctuations for these species were observed on a few occasions over the period of observation. Graphical comparisons and statistical analysis of changes in DBH with meteorological variables indicate that for different trees, the different changes in DBH observed responded to different meteorological variables. Large stem changes were found to occur for Ca. chinensis trees that were associated with variations in solar radiation. However, both S. superba and Cr. chinensis were found to be less sensitive to solar radiation. Changes in the DBH of these two species were found to be controlled mainly by soil temperature and soil moisture. During the later dry season, with a lower soil temperature and soil moisture, all three tree species stopped growing and only negligible shrinkage, expansion, or fluctuation occurred, suggesting that the optimum time to measure tree growth in the Dinghushan Biosphere Reserve is the later dry season.     

Factors influencing the seed source and sink functions of a floodplain nature reserve in the Netherlands

Question: How do species traits and abiotic factors influence the extent of hydrochorous dispersal into and out of a small floodplain area along a free‐flowing river in The Netherlands? Location: The Kappersbult nature reserve (53°07′28″N, 6°37′14″E), which is a floodplain along the Dutch River Drentsche Aa. Methods: Seeds transported by the river were collected in fine mesh nets for 24 consecutive hours once or twice a week for 1 year, upstream and downstream of the studied floodplain. Data on the captured seeds were related to species traits and abiotic factors and species composition in the floodplain. Results: The floodplain functioned both as a seed source and sink. High levels of river water seemed to promote seed transport to or from the floodplain. Seeds of riverbank species occurred significantly more often in the river water than expected. Net source species had significantly higher seed production, taller stature and higher seed buoyancy, but lower site elevation than net sink species. Seed weight was significantly higher for sink species than for other species. Conclusion: Our study found that inundation, and therefore more natural river water management, is a prerequisite for seed transport to and from a floodplain. The restoration of target floodplain vegetation may be successful for common species that produce many seeds and grow in proximity to the river. Consequently, it is expected that the probability of restoring vegetation types that occur further from the river, such as wet grasslands, by hydrochorous dispersal is low.     

不同类群水生昆虫群落间的一致性以及空间和环境因子的相对作用

生物多样性监测和保护过程中通常用到指示类群,然而对于这些指示类群有效性的测度仍然十分欠缺.为探讨不同类群水生昆虫群落的一致性及空间因子、环境变量的相对影响,作者于2010年4月对东苕溪流域源头溪流21个采样点进行了调查.共记录水生昆虫7目44科92属130种.我们将水生昆虫群落划分成鞘翅目(C)、蜉蝣目+襀翅目+毛翅目(EPT)和双翅目+广翅目+蜻蜒目(DMO)3个类群.一致性分析结果表明:3个类群的群落一致性(r)较高,分别为C对EPTr=0.65 (P＜0.001)、C对DMO r=0.67 (P＜0.001)、EPT对DMO r=0.82 (P＜0.001).方差分解表明环境变量是影响不同类群水生昆虫群落结构的主要因素,空间因子的影响相对较小.环境因子中影响不同类群水生昆虫群落的关键变量大体相似,其中海拔、pH、平均流速和化学需氧量是最主要的驱动因子.我们的结果表明该研究区域不同类群的水生昆虫群落一致性很高,且对环境变量的响应也相似;因此,在水生昆虫生物多样性保护中可考虑利用其中的某一类群,如蜉蝣目+襀翅目+毛翅目(EPT)类群,作为有效的指示类群.     

基于MaxEnt模型的甘肃安西极旱荒漠国家级自然保护区北山羊生境评估

明晰甘肃安西极旱荒漠国家级自然保护区珍稀濒危物种北山羊的分布格局,并阐释气候变化和人类活动对北山羊的影响,对今后北山羊生境管理和物种保护具有重要意义。基于北山羊实测分布点记录和环境变量数据,结合MaxEnt模型和ArcGIS空间分析功能,利用CMIP6的8个气候模式均值预测中度发展路径（SSP2-4.5）下,基准期（1970-2000年）和未来气候（2041-2060年、2081-2100年）变化情景下,甘肃安西极旱荒漠国家级自然保护区北山羊的潜在适生区分布范围及变化,并综合贡献率和置换重要性值对北山羊生境选择关键环境因子进行了分析。研究结果表明：（1） MaxEnt模型的预测精度较高,三种气候条件下ROC曲线下面积（AUC,Area Under Curve）>0.97,且真实技巧统计（TSS,True Skill Statistic）>0.90,模拟结果可靠。（2）影响北山羊生境选择的主要环境因子为气候条件（降水量季节性变异系数和等温性）、海拔和人为干扰（距泉和居名点距离）。水是保护区北山羊生存的最基本要素,气候条件共同控制北山羊生境条件。此外,北山羊习性决定其生境宜选择高海拔和远离人类活动影响地区。（3）基准期保护区北山羊主要分布在北片和南片高海拔山区,面积365.77 km²（占整个保护区的4.31%）,北山羊适生区面积北片>南片、中高等适生区主要位于保护区北片。（4） CMIP6未来气候变化情景下,随着保护区生态环境改善和濒危物种保护措施的实施,北山羊潜在适生区面积呈增加趋势,但是受北山羊近亲繁殖的影响,整体上北山羊数量和适生区面积增加并不显著且有向南部及高海拔地区转移趋势。     

Molecular confirmation of Enterococcus faecalis and E. faecium from clinical, faecal and environmental sources

AIMS: The genus Enterococcus includes opportunistic pathogens such as E. faecalis and E. faecium, and is also used to assess water quality. Speciation of enterococci in environmental studies can be particularly problematic, therefore protocols for unambiguous, DNA-based analysis could receive wide use in applications ranging from water quality monitoring to microbial source tracking. The goal of this work was to investigate the usefulness of PCR for speciation of putative, biochemically identified E. faecalis and E. faecium isolated from water, faeces and sewage. METHODS AND RESULTS: Putative enterococci (n = 139) were isolated on mEI agar from dog, human, gull and cow faeces, and from sewage, freshwaters and marine waters. A total of 128 isolates passed standard physiological tests for the genus, and were speciated by the API 20 Strep (APIStrep) biochemical test system. 42.2% were identified as E. faecalis, and all were confirmed by PCR. 19.5% were biochemically identified as E. faecium, but only seven were PCR-positive. CONCLUSIONS: The 16S rDNA of PCR-positive and PCR-negative E. faecium, including isolates that were inconclusively identified by APIStrep, was sequenced. All formed a monophyletic clade with E. faecium sequences in Genbank. SIGNIFICANCE AND IMPACT OF THE STUDY: Biochemical identification of E. faecalis agreed 100% with PCR assays, therefore a simple protocol of isolation on mEI followed by PCR should be useful for environmental studies. Discrepancies among biochemical identification, PCR confirmation and DNA sequencing were noted for E. faecium, indicating that routine isolation/identification of E. faecium from environmental samples is a much more difficult task.     

环境因子对海南岛野生兰科植物物种组成与分布格局的影响

海南岛是中国兰科植物物种丰富度较高的地区, 了解环境因子对海南岛野生兰科植物物种组成和分布格局的影响, 对于该地区野生兰科植物的保护管理和相关研究具有重要指导意义。基于海南岛野生兰科植物调查分布样方的植被类型、海拔、坡向、坡度、年平均气温、年降水量的数据, 采用典范相关分析探索了环境因子对物种组成的影响, 并计算各个环境因子对物种组成的总效应与净效应, 同时分析了6个环境因子对野生兰科植物分布格局的影响。结果表明, 所选的6个环境因子共解释了海南岛野生兰科植物组成变异的3.7%; 植被类型、海拔、年平均气温、年降水量、坡向、坡度这6个环境因子的总效应与净效应均达显著水平, 但其解释率依次减小。所选的6个环境因子对海南岛野生兰科植物的分布均有影响, 野生兰科植物在海南岛主要分布在中海拔段、5°-35°的坡度范围、阴坡与半阴坡、年平均气温较低且年降水量较高的环境, 并且于原生植被中分布最多。     

Influence of thermal conditions on habitat use by a rare spring‐emerging butterfly Euphydryas editha taylori

We may expect butterflies as ectotherms to have particularly active life‐history stages that occur in the warmest and lightest times of the year; however, there are temperate species that are active when climatic conditions seem unfavourable and photoperiod short, such as the Taylor's checkerspot (Euphydryas editha taylori). For such species, studies suggest that even subtle changes to microclimate can potentially impact populations. Thus, understanding how in situ variations in microclimate influence the Taylor's checkerspot butterfly could provide much needed insights into more effective management. We conducted a series of surveys that explored (i) adult habitat use, (ii) final instar larval distribution and (iii) adult movement up to and across site boundaries at two sites in Oregon, USA, in 2010 and 2011. We found that in situ habitat use by the Taylor's checkerspot butterfly was strongly influenced by microclimate. Both adult activities and final instar larvae distribution were clustered within the warmest areas of the sites. Moreover, adults did not use up to 59% and larva up to 90% of their sites, despite vegetation structure and composition being uniform. More specifically, butterfly habitat use increased with increasing ground temperatures, and we found that areas with the highest ground temperatures were more exposed to direct sunlight. Similarly, we found that butterflies tended to only move through sunlit site boundaries. We conclude that the Taylor's checkerspot is sensitive to changes in its thermal environment at fine spatial scales. Our results highlight the importance of microclimate as an indicator of habitat quality, and establishing the thermal criteria in which species of concern exists may provide valuable insights into the implications of climate change.     

Estimating treatment effects with partially observed covariates using outcome regression with missing indicators

Missing data is a common issue in research using observational studies to investigate the effect of treatments on health outcomes. When missingness occurs only in the covariates, a simple approach is to use missing indicators to handle the partially observed covariates. The missing indicator approach has been criticized for giving biased results in outcome regression. However, recent papers have suggested that the missing indicator approach can provide unbiased results in propensity score analysis under certain assumptions. We consider assumptions under which the missing indicator approach can provide valid inferences, namely, (1) no unmeasured confounding within missingness patterns; either (2a) covariate values of patients with missing data were conditionally independent of treatment or (2b) these values were conditionally independent of outcome; and (3) the outcome model is correctly specified: specifically, the true outcome model does not include interactions between missing indicators and fully observed covariates. We prove that, under the assumptions above, the missing indicator approach with outcome regression can provide unbiased estimates of the average treatment effect. We use a simulation study to investigate the extent of bias in estimates of the treatment effect when the assumptions are violated and we illustrate our findings using data from electronic health records. In conclusion, the missing indicator approach can provide valid inferences for outcome regression, but the plausibility of its assumptions must first be considered carefully.     

Forest vascular plants as indicators of plant species richness: A data analysis of a flora atlas from northwestern Germany

Abstract

Our study had the objective to examine whether the number of forest vascular plants in a forest-poor region may be indicative of total plant species richness and of the number of threatened plant species. We also related forest plant species richness to geological and soil variables. The analysis was based on a regional flora atlas from the Weser-Elbe region in northwestern Germany including incidence data of species in a total of 1109 grid cells (each ca. 2.8 × 2.8 km²). All taxa were classified either as forest or non-forest species. Total species richness in the grid cells ranged from 65 to 597, with a mean value of 308. The number of forest species varied between 20 and 309 (mean 176). Grid cells with or without particular geological units differed in total and forest species richness, with those containing peatland and marshland being particularly species-poor. Indicator value analysis showed that both total and forest species richness in the grid cells were related to soil acidity and nitrogen in a hump-backed manner, with the highest number of species found at moderately low values for nitrogen and at intermediate values of pH. Forest species richness was highly positively correlated with the number of non-forest species and threatened non-forest species. Indicators for high species richness were primarily those species that are confined to closed semi-natural forests with a varied topography and relatively base- and nutrient-rich soils. Grid cells including historically ancient forest exhibited a higher species richness than grid cells lacking ancient forest, indicating the importance of a long habitat continuity for a high phytodiversity. The “habitat coincidence” of high species richness is best explained by similar responses of forest species and species of other habitats to the main environmental gradients. It is suggested that the regional patterns found for the Weser-Elbe region can be transferred also to other forest-poor regions in Central Europe.     

Artificial Feeding Systems for Plant-Parasitic Nematodes

Feeding of an "obligate" plant-parasitic nematode (nonfungal feeder), Pratylenchus scribneri, in the absence of plant tissue was demonstrated in an artificial system consisting of liquid media and indicator dyes including amaranth and various nontoxic food colors. Among the compounds tested, sucrose, dextrose, Gamborg''s B5 medium, and DL-methionine stimulated a small percentage of feeding (12-36%). A high percentage of feeding (90-100%) occurred in a filtrate from excised corn roots cultured in Gamborg''s B5 medium. This feeding system has the potential to develop an artificial medium for plant-parasitic nematodes and to screen novel nematicides that are stomach poisons.