长山列岛邻近海域鱼类群落种类组成和多样性时空变化

为了解黄、渤海生态系统交错带长山列岛邻近水域鱼类群落种类组成和多样性,根据2016年10月,2017年1月、5月及8月进行的鱼类资源底拖网调查数据,应用相对重要性指数、物种多样性指数、k优势度曲线等方法,研究了长山列岛邻近海域鱼类群落种类组成、物种多样性时空变化及其与环境因子的关系。结果表明: 该海域共计捕获鱼类77种,以温水性、底层、洄游性鱼类为主,优势种组成季节变化明显,春季、冬季主要优势种为黄鮟鱇,夏季以日本鲭、鳀等中上层鱼类为主。全年共计出现洄游性鱼类46种,季节间物种迁移指数均在100以上,其中秋季物种迁移指数最大。鱼类群落物种丰富度指数在春季最高、Shannon多样性指数和均匀度指数在秋季最高。夏季物种丰富度指数与表层水温呈显著负相关;冬季物种丰富度指数与水深、底层水温呈极显著正相关,Shannon多样性指数与底层水温呈极显著正相关。长山列岛邻近海域作为黄、渤海两大生态系统的交错带,鱼类群落表现出高物种多样性、洄游种多以及明显的时空异质性。     

Habitat differentiation among three Nigeria–Cameroon chimpanzee (Pan troglodytes ellioti) populations

Ecological niche models (ENMs) are often used to predict species distribution patterns from datasets that describe abiotic and biotic factors at coarse spatial scales. Ground‐truthing ENMs provide important information about how these factors relate to species‐specific requirements at a scale that is biologically relevant for the species. Chimpanzees are territorial and have a predominantly frugivorous diet. The spatial and temporal variation in fruit availability for different chimpanzee populations is thus crucial, but rarely depicted in ENMs. The genetic and geographic distinction within Nigeria–Cameroon chimpanzee (Pan troglodytes ellioti) populations represents a unique opportunity to understand fine scale species‐relevant ecological variation in relation to ENMs. In Cameroon, P. t. ellioti is composed of two genetically distinct populations that occupy different niches: rainforests in western Cameroon and forest–woodland–savanna mosaic (ecotone) in central Cameroon. We investigated habitat variation at three representative sites using chimpanzee‐relevant environmental variables, including fruit availability, to assess how these variables distinguish these niches from one another. Contrary to the assumption of most ENM studies that intact forest is essential for the survival of chimpanzees, we hypothesized that the ecotone and human‐modified habitats in Cameroon have sufficient resources to sustain large chimpanzee populations. Rainfall, and the diversity, density, and size of trees were higher at the rainforest. The ecotone had a higher density of terrestrial herbs and lianas. Fruit availability was higher at Ganga (ecotone) than at Bekob and Njuma. Seasonal variation in fruit availability was highest at Ganga, and periods of fruit scarcity were longer than at the rainforest sites. Introduced and secondary forest species linked with anthropogenic modification were common at Bekob, which reduced seasonality in fruit availability. Our findings highlight the value of incorporating fine scale species‐relevant ecological data to create more realistic models, which have implications for local conservation planning efforts.     

绿洲-荒漠过渡带土壤蓄水量的空间分布及其时间稳定性

掌握土壤水分动态变化规律是绿洲地区水资源管理与生态建设的关键.本文在黑河中游绿洲与荒漠交错地带设置面积约50 km²的研究区域,持续监测2012—2014年间植被生长季节土壤水分含量,利用地统计分析与时间稳定性分析探索土壤水分的时空分布特征.结果表明: 黑河北岸绿洲-荒漠过渡带土壤蓄水量8月最大、10月最小,0～2 m土层土壤平均蓄水厚度约367 mm.绿洲-荒漠过渡带土壤水分梯度除受河流影响外,还与土地利用方式密切相关.不同土地利用类型土壤蓄水量依次为农地>乔木林地>灌木林地>荒漠,农地土壤蓄水量平均高出外围荒漠土壤蓄水量300%以上.研究区内各采样点土壤水分时间稳定性具有明显的空间差异,不同土地利用类型土壤水分稳定程度依次为灌木林地>荒漠>农地>乔木林地.河流对沿岸绿洲土壤水分的直接影响集中在3 km以内,在河岸绿洲与新垦沙地农田之间存在一条土壤水分较为稳定的样带,可以用于指示绿洲生态系统的发展与演变.     

水分胁迫对蒺藜光合作用、生物量和药材质量的影响

通过盆栽试验,分析了水分胁迫对蒺藜光合特性、生物量形成和主要药用成分积累的影响.结果表明:水分胁迫改变了蒺藜的光合日进程,使蒺藜的净光合速率和蒸腾速率显著降低,植株光合能力减弱,同化能力下降,最终导致干物质积累受阻,生物量降低.但水分胁迫促进了蒺藜总皂苷类物质积累.灌水量为150和450 mm处理下,蒺藜总皂苷含量分别为13.26和12.47 mg·g^-1,与其余处理(250、350 mm)总皂苷含量差异显著.总皂苷和总黄酮类物质动态积累趋势与生物量积累趋势相反,生物量积累高峰期,次生代谢产物含量反而降低生物量积累受外界环境因子的直接影响较大,而次生代谢产物除受外界环境因子的影响外,还受到生物量积累等内部因素影响.     

Stand history is more important than climate in controlling red maple (Acer rubrum L.) growth at its northern distribution limit in western Quebec,Canada

Aims We examined growth of red maple (Acer rubrum L.) to evaluate environmental controls of its northern distributional limit in Eastern North America and its potential response to future climate change.Methods We collected growth data from nine sites located along a 300-km transect (47–49°N), which included frontier population of red maple and covered three bioclimatic domains in western Quebec. We analyzed three growth variables: growth rates during the first 30 years of maple lifespan, cumulative basal area increment (BAI) over the most recent decade (2000–2009) and annual growth rate over the whole tree lifespan ranging from 58 to 112 years. We also examined growth sensitivity to climate by using response function analysis.Important findings Three different proxies of maple absolute growth (initial growth rate, BAI during 2000–09 and mean diameter growth rate) indicated a better growth with an increase in latitude. We speculate that stand history effectively overrode the direct effects of colder climate on maple growth along the S-N gradient. Regeneration of maple in the southern sites likely occurred in canopy gaps, whereas in the north it was contingent upon large disturbances such as stand-replacing fires, which apparently provided more favorable light environment for maple growth than canopy gaps. The annual growth variability, which reflects effects of annual weather on growth and is largely independent from the absolute growth rate, was significantly affected by monthly climate, suggesting a positive effect of higher summer temperature in the northern part of the transect (48–49°N) and a negative effect of summer drought in the south (47–48°N). In the future, the natural and human disturbance regimes will be dominant controls of the actual biomass productivity of red maple at the northern limit of its present distribution range. Direct effects of climate on maple growth would likely be less important in this context, and will likely entail negative effect of increased summer drought in the southern part of the study area and positive effects of increased temperatures in the north.     

Inhibitory effects of Artemisia herba-alba on the germination of the gypsophyte Helianthemum squamatum

The potential allelopathic role of Artemisia herba-alba has been evaluated in order to explain the community pattern of the gypsum semiarid environments of central Spain. This pattern shows a sharp ecotone between a gypsophile sparse shrubby community dominated by Helianthemum squamatum, which grows on slopes with gypsum surface crusts, and a nitrohalophilous community on the gypsum alluvial soils of piedmont dominated by Artemisia herba-alba. In order to explain this pattern, resource limitation was discarded because no significant differences in several soil parametrers, but fine earth fraction and organic matter content, had been detected in a previous study. Results confirm the inhibitory effect of aqueous extracts on the final germination percentage of scarified seeds of Helianthemum squamatum and also on the shape of the germination curves, which indicate delay of germination for the aqueous extracts. Assays with soil of the Artemisiacommunity (three types) showed that germination was strongly inhibited in soils obtained below the canopy of mature plants (litter maintained) and retarded in the other treatments. We suggest that the spatial community pattern detected in this gypsum environment and characterised by a sharp ecotone could be at least partially controlled by interference through allelopathy. This determines the excliusion of Helianthemum squamatum plants from alluvial soils.     

The role of local and regional processes in shaping dung beetle communities in tropical forest plantations in Borneo

We examine whether rain forest dung beetle species found in plantations in Sabah, northern Borneo, tend to be endemic or geographically widespread. In addition, linear regressions of abundance vs. distance from a major river in primary rain forest are calculated to see if species found in plantation forest show affinity to one specific biotope (riverine vs. interior forest) in their natural habitat. Results show that 14 of the 40 species recorded from plantations are endemic to Borneo. Only edge‐specialist endemic species are found in plantation forest, with no interior‐forest specialists recorded. Data suggest that endemic species that are adapted to more exposed conditions in primary rain forest, such as riverine species, can in some instances tolerate man‐made habitats. Twenty‐nine species (±SE 4.0) per transect are recorded from plantation transects, whereas 44.2 (±1.7 SE) are recorded in primary rain forest. As species richness is much lower in plantations than natural forest, implying loss of biodiversity, we conclude that measures of biogeographic distinctiveness, whereby endemic species confer higher values, may be misleading unless they take into account edge‐affinity. Local‐ as well as regional‐distributional data may therefore be needed to interpret correctly patterns of species assemblages in derived forest ecosystems.     

Water availability as driver of birch mortality in Hustai National Park,Mongolia

Trees in the forest-steppe ecotones face stress due to reduced water availability as a consequence of more extreme seasonal fluctuations in precipitation and temperature. Together with browsing pressure this can hinder tree growth, tree regeneration and competition between trees and grasses. We studied the impact of both stress factors on the mortality of birch trees in two forest sites at Hustai National Park, Mongolia, by applying tree-ring research to determine growth-limiting factors and assessing browsing pressure on young and adult birch. We expected warm and dry summer conditions as main growth limiting factor. Moreover, we expected a positive relation between deer density and tree mortality with browsing mainly affecting smaller trees with a low diameter at breast height (DBH). We found that the growth in both birch populations is mainly driven by winter precipitation and – to a lesser extent – negatively affected by high summer temperature. This suggests that water availability as defined by soil moisture, especially at the beginning of the growing season is crucial for birch growth in our study area. For mortality we found significant differences between both populations, but no significant relationship with deer density. In plots with high mortality rates mean tree height of the remaining living trees decreased. These results suggest that under expected climate change with declining annual precipitation rates, the birch forest of Hustai National Park is converting into a steppe ecosystem, like described for other forest ecosystems in this ecotone.