Global ecological success of Thalassoma fishes in extreme coral reef habitats

Phenotypic adaptations can allow organisms to relax abiotic selection and facilitate their ecological success in challenging habitats, yet we have relatively little data for the prevalence of this phenomenon at macroecological scales. Using data on the relative abundance of coral reef wrasses and parrotfishes (f. Labridae) spread across three ocean basins and the Red Sea, we reveal the consistent global dominance of extreme wave‐swept habitats by fishes in the genus Thalassoma, with abundances up to 15 times higher than any other labrid. A key locomotor modification—a winged pectoral fin that facilitates efficient underwater flight in high‐flow environments—is likely to have underpinned this global success, as numerical dominance by Thalassoma was contingent upon the presence of high‐intensity wave energy. The ecological success of the most abundant species also varied with species richness and the presence of congeneric competitors. While several fish taxa have independently evolved winged pectoral fins, Thalassoma appears to have combined efficient high‐speed swimming (to relax abiotic selection) with trophic versatility (to maximize exploitation of rich resources) to exploit and dominate extreme coral reef habitats around the world.     

Seasonal abundance and habitat use of bird species in and around Wondo Genet Forest,south‐central Ethiopia

The habitat use and seasonal migratory pattern of birds in Ethiopia is less explored as compared to diversity studies. To this end, this study aimed at investigating the patterns of distribution related to seasonality and the effect of habitat characteristics (elevation, slope, and average vegetation height) on habitat use of birds of Wondo Genet Forest Patch. A stratified random sampling design was used to assess the avian fauna across the four dominant habitat types found in the study area: natural forest, wooded grassland, grassland, and agroforestry land. A point transect count was employed to investigate avian species richness and abundance per habitat type per season. Ancillary data, such as elevation above sea level, latitude and longitude, average vegetation height, and percent slope inclination, were recorded with a GPS and clinometers per plot. A total of 33 migratory bird species were recorded from the area, of which 20 species were northern (Palearctic) migrants while 13 were inter‐African migrants. There was a significant difference in the mean abundance of migratory bird species between dry and wet seasons (t = 2.13, p = .038, df = 44). The variation in mean abundance per plot between the dry and wet seasons in the grassland habitat was significant (t = 2.35, p = .051, df = 7). In most habitat types during both dry and wet seasons, omnivore birds were the most abundant. While slope was a good predictor for bird species abundance in the dry season, altitude and average vegetation height accounted more in the wet season. The patch of forest and its surrounding is an important bird area for migratory, endemic, and global threatened species. Hence, it is conservation priority area, and the study suggests that conservation coupled with ecotourism development is needed for its sustainability.     

Photodegradation of DOC in a shallow prairie wetland: evidence from seasonal changes in DOC optical properties and chemical characteristics

Wetlands across the Canadian prairies are typically shallow (<1.0 m) and exhibit high dissolved organic carbon (DOC) concentrations (>10 mg l^–1). Studies have shown that DOC in such shallow wetlands is not as reliable an indicator of ultraviolet radiation (UVR) attenuation as it is in clearwater. Changes in DOC character and composition as a result of sunlight exposure might provide a reasonable explanation for this observation. To test this, we investigated seasonal changes in DOC optical and chemical properties in a shallow prairie wetland over a 2-year period. Although DOC concentration increased at least two-fold from spring until fall, DOC specific absorption (at 350 nm) and fluorescence decreased by 30 and 32%, respectively, for the same period. In both years, seasonal decreases in DOC molecular weight and size (from measurements of tangential filtration and mass electrospray mass spectrometry) were reflected in concomitant increases in spectral slope. ¹³C NMR analysis of DOC isolated on XAD-8 resins revealed a 49% decrease in aromatic moieties when spring values were compared to those in the fall. As well, ¹³C signatures of this isolated DOC became heavier seasonally. In a short term photodegradation experiment (6 days) we noted a 47% decline in DOC specific absorption coefficients at 350 nm and a 15% increase in spectral slope when water exposed to the total light spectrum was compared to that of a dark control. Taken together, all of these observations were consistent with the occurrence of seasonal DOC photodegradation in shallow prairie wetlands and underlined the importance of this process in shaping DOC character and composition in these hydrologically dynamic systems. Our data also indicates that constant mixing and shallow depths in these wetlands were factors which enhanced DOC photodegradation. Although the high DOC concentrations of prairie wetlands should theoretically offer protection for their biota, seasonal photodegradation of DOC means that these systems may not be as protected as their high DOC concentrations suggest.     

CO2对植物在光补偿点附近量子效率的影响

应用植物光合作用对光响应修正模型研究了CO2浓度分别为380和600 mol·mol-1时,栾树和辣椒在光补偿点附近光合量子效率的改变及Kok效应。结果表明:光响应修正模型可很好地拟合栾树和辣椒2种CO2浓度下的光响应曲线,且获得的光合参数与实测值相符合;2种不同CO2浓度条件下,栾树和辣椒总是存在初始量子效率(φ0)大于光补偿点处的量子效率(φc),光合量子效率在光补偿点附近不是常数,且与暗呼吸速率无关;CO2浓度的大小影响着栾树的Kok效应,但对辣椒的Kok效应影响不明显,分析认为,这是由于栾树在光补偿点附近光合量子效率的改变来自其净光合速率对光强的非线性响应,而辣椒不存在Kok效应。     

长白山南坡苔原植被的特殊性及坡向间差异性分析

以长白山苔原带南坡植被为对象,通过植被调查,与北坡和西坡植被进行比较,研究长白山苔原植被因坡向差异导致的不同植被变化模式。结果显示:(1)长白山苔原南坡植被中灌木处于优势地位,与北坡、西坡情况一致。但在物种组成上,各坡向差异明显,为中度不相似水平;(2)在生物多样性、多度、盖度等群落特征上,南坡与西坡的差异较大、与北坡相似性较强;(3)在物种多样性的空间分布上,南坡与北坡相同,即随海拔升高呈单峰变化且峰值出现在中部,与西坡物种多样性随海拔升高呈单调递减的趋势完全不同。表明不同群落抗干扰能力以及所受干扰程度存在差异,北坡处于演替中后期,较为稳定,抗干扰能力更强。南坡因受干扰强度较小,植被处于较稳定状态;(4)长白山苔原各坡向植被变化差异较大。南坡和北坡的植被相对稳定,与西坡草本植物强烈上侵明显不同。长白山苔原带植被的坡向差异源于各坡向的本底差异、环境差异以及对全球气候变化的差异性响应,是火山、强风干扰下植被演替与响应气候变化的植被变化共同作用的结果。     

黄土丘陵区香梨园土壤水分、养分分布特征及其与产量的关系

本研究以晋西黄土丘陵区玉露香梨种植下的3种不同坡位坡耕地土壤为对象,对不同坡位、不同生育期、不同深度的土壤水分、养分和产量进行观测分析。结果表明: 不同坡位中,香梨产量为高坡位>中坡位>低坡位,高坡位香梨产量与土壤含水量(SWC)、有机质(SOM)、速效钾(AK)显著相关,其中AK对产量的影响最显著,中、低坡位香梨产量与SWC、SOM、全氮(TN)显著相关,其中SWC对产量的影响最显著;高坡位SWC、SOM、速效磷(AP)和TN含量高于中、低坡位,而中坡位AK含量最高。不同土层深度中,土壤养分含量在0～20 cm最高,20～40 cm最低,而SWC在0～20 cm显著低于其他土层,在20～40 cm最高。不同生育期中,开花期SOM、AP和TN含量最高,结果期SWC最高,成熟期AK含量最高。建议该区域在今后香梨水肥管理中,开花期高坡位应加强对K肥的施用,结果期以N、P复合肥施用为主。在中、低坡位应增加灌溉量,灌溉量在300 m³·hm^-2可有效降低该区域水分对产量的限制。本研究可为黄土丘陵区香梨种植精准灌溉和科学施肥提供理论支持和数据参考。     

Trade-off between height and branch numbers in Stellera chamaejasme on slopes of different aspects in a degraded alpine grassland

权衡关系是生活史对策理论的基础, 株高和枝条数的权衡关系对理解植物在不同生境下的表型可塑性有重要意义。该研究选择祁连山北坡高寒退化草地, 利用ArcGIS建立研究区域的数字高程模型(DEM), 并提取样地坡向数据, 采用广义相加模型(GAM)与偏相关分析相结合的方法, 分析了不同坡向影响下狼毒(Stellera chamaejasme)种群株高和枝条数的关系。结果表明: 随着坡向由北坡转向东坡、南坡、西坡, 草地群落地上生物量和盖度呈“减小—增大—减小”的变化趋势, 群落高度则先增大后减小; 坡向是影响狼毒株高和枝条数空间分异的主要地形因子; 随着坡向由北、东转向西、南, 狼毒种群株高呈下降趋势, 而枝条数呈上升趋势, 二者表现出此消彼长的权衡关系, 狼毒植株比叶面积先增大后减小。不同坡向狼毒株高和枝条数的权衡关系, 反映了异质生境中资源多重竞争下狼毒生物量分配机制和提高种群适应性的种群更新策略。