Bioacoustic analysis of frog calls from northeast India

Mating calls of three frog species abundant in northeast IndiaRana tigerina,Rana cyanophlyctis andRana limnocharis were recorded in the fields of Assam and Meghalaya during their breeding season (July-August, 1991). The calls were analysed for their temporal and spectral characters. They were species specific, with distinct call duration and call period, number of pulses per call and interpulse interval, and dominant frequency and frequency domain. A comparison of the mating calls ofRana cyanophlyctis with those of the siblingRana ehrenbergi from Yemen showed differences in their temporal and spectral characters, supporting the suggestion that these two species are distinct species, rather than subspecies of the same species. Differences in the temporal and spectral pattern were found in the mating calls of morphologically alike specimens ofRana limnocharis, indicating that the present morphotypeRana limnocharis in northeast India is composed of several species.     

渔山岛岩礁基质潮间带大型底栖动物优势种生态位

2009年3月至2010年1月期间对渔山岛岩礁基质潮间带大型底栖动物进行定量采样调查,并获得大型底栖动物85种,筛选出全年取样获得优势种30种,隶属5门7纲24科。对获得的30个优势种以Shannon—Wiener指数为基础进行了生态位宽度测定,以Pianka重叠指数为基础进行了生态位重叠值分析,结果显示：潮间带大型底栖动物群落中优势种生态位宽度变化范围为0.18~1.94,值较高的有条纹隔贻贝、覆瓦小蛇螺、角偏顶蛤、日本笠藤壶、鳞笠藤壶和马氏毛粒蟹,均大于1.00,它们对环境适应的能力较强;各优势种的生态位重叠程度不均匀,在0~0.97之间,它们对群落环境资源的利用存在着交叉,潜在的种间竞争压力较大。以密度数据四次开方为基础,利用欧氏距离进行群落物种的系统聚类分析和非度量多维标度排序分析,结果均表明30个优势种可以分为三大类,即狭布种、泛化种和特有种。优势种生态位宽度、优势种之间的生态位重叠值与物种的分布与数量密切相关,生境相似程度高的物种聚类和排序距离就小,大型底栖动物主要通过在资源位上的分布、摄食类群和生活型等的差异缓解竞争。     

海南霸王岭五唇兰两种生态型生态位特征

东亚特有种五唇兰自然状态下存在叶背红色和绿色两种生态型。对海南岛霸王岭地区的五唇兰群落中草本层生态位特征进行测定和分析,探讨两种生态型五唇兰在群落中的地位和作用以及彼此间的竞争关系。结果表明: 狭穗草、叶背红色型五唇兰和毛俭草在该层占据较大的重要值。叶背红色型五唇兰较叶背绿色型具有更广的生态位宽度; 拟金草和叶背红色型五唇兰以相似的生态位宽度值居该层物种生态位宽度的首位。两种生态型五唇兰均与该层其他大部分物种具有较大生态位重叠值,两者间的生态位重叠亦很大。这说明五唇兰对其生境有很好的适应性,两种生态型间可能存在较大的竞争。     

Niche properties of Central European spiders: shading, moisture and the evolution of the habitat niche

Aim  Niche theory emphasizes the importance of environmental conditions for the distribution and abundance of species. Using a macroecological approach our study aimed at identifying the important environmental gradients for spiders. We generated numerical values of niche position and niche width. We also investigated relationships between these niche properties as well as the degree of phylogenetic conservatism in order to draw conclusions about the evolution of the habitat niche.
Location  Central Europe: lowlands of Austria, Belgium, Germany, Luxembourg, the Netherlands and Switzerland.
Methods  We analysed 244 published spider communities from 70 habitat types by correspondence analysis. The resulting community scores were used to test for correlations with habitat characteristics. Species scores were used to derive niche position (mean scores) and niche width (standard deviation of scores). To test for niche conservatism we estimated variance components across the taxonomic hierarchy.
Results  The first two axes of the correspondence analysis were correlated with shading and moisture, respectively. Niche width had a hump-shaped relationship to both environmental gradients. β-diversity was strikingly higher in open habitats than in forests. Habitat niche conservatism was lower than phylogenetic conservatism in body size.
Main conclusions  Environmental factors are important drivers for the β-diversity of spiders, especially across open habitats. This underlines the importance of preserving the whole range of moisture conditions in open habitats. Narrow niches of species occurring at the ends of both environmental gradients indicate that adaptations to extreme habitats lead to constraints in ecological flexibility. Nevertheless, the habitat niche of species seems to evolve much faster than morphological or physiological traits.     

北部湾北部生态系统结构与功能——浮游动物空间生态位及其分化

根据2006—2007年北部湾北部海域4个航次调查资料,采用K-优势度曲线法对浮游动物种(类)群进行排序分析,运用Levins公式和Pianka指数分析了主要优势种(类)群的生态位宽度值和生态位重叠程度,并通过除趋势典范对应分析(DCCA)研究生态位分化状况。结果表明,该海区浮游动物优势种(类)群按生态位宽度值可划分为广生态位、中生态位和窄生态位三大类型。其中,广生态位的种(类)群如肥胖软箭虫、亚强次真哲水蚤、长尾类幼体等具有较强的生态适应性,生活范围较广;窄生态位的种(类)群,对环境的适应性较差,对海流和水团等环境因素的变化具有指示意义。生态位宽度能够反映种(类)群丰度季节变化,但不能反映具体丰度大小。北部湾北部全年主要优势种(类)群的生态位宽度值介于0.08—0.77之间,并且各优势种(类)群的生态位宽度差异较大,种对间生态位重叠值介于0.02—0.89之间,平均生态位重叠指数为0.45,种(类)群之间利用资源环境的互补性较强,这与海域内生境多样化并且各优势种对环境适应能力的差异存在一定联系。DCCA分析表明,影响浮游动物分布的主要因子是水深、温度和盐度,其次是叶绿素a和溶解氧。     

Regional occupancy in unicellular eukaryotes: a reflection of niche breadth,habitat availability or size‐related dispersal capacity?

1. The distribution patterns of unicellular and multicellular organisms have recently been shown to differ profoundly, with the former probably being mostly cosmopolitan, whereas the latter are mostly restricted to certain regions. However, the within‐region distribution patterns of these two organism groups may be rather similar. 2. We predicted that the degree of regional occupancy in unicellular eukaryotes would be related to niche characteristics, dispersal ability and size, as has been found previously for multicellular organisms. The niche characteristics we considered were niche position, that measures marginality in species habitat distribution, and niche breadth, that measures amplitude in species habitat distribution. Niche characteristics were determined using Outlying Mean Index (OMI) analysis. 3. We found that the regional occupancy in our model group of unicellular eukaryotes, stream diatoms, was primarily a reflection of the niche position of a species or, more generally, habitat availability. Thus, non‐marginal species (i.e. species that occupied common habitat conditions across the region) tended to be more widely distributed than marginal species (i.e. species that were restricted to a limited range of rare habitat conditions). This finding was further supported by the general linear model, with niche position, niche breadth, maximum size and attachment mode as explanatory variables: niche position was by far the most important variable accounting for variability in regional occupancy, with significant amounts of additional variation related to niche breadth and maximum size of diatoms. 4. Thus, the degree of regional occupancy among unicellular eukaryotes may be primarily governed by habitat availability, supporting former findings for multicellular organisms.     

神农架川金丝猴栖息地优势树种生态位及食源植物

该文采用定量分析法, 研究了湖北神农架千家坪地区川金丝猴 (Rhinopithecus roxellana) 现生栖息地优势树种的生态位宽度、生态位重叠和生态位相似比例, 分析了优势树种生态位对神农架川金丝猴生存的影响。结果如下:1) 在64000m2的样方中, 木本植物255种, 隶属于44科105属, 其中乔木23科51属129种, 灌木22科49属113种, 木质藤本7科9属13种。优势科主要有蔷薇科、樟科、槭树科、忍冬科、壳斗科和四照花科等。2) 生态位宽度在栖息地森林群落乔木层中最高的为红桦 (Betula albo-sinensis) (5.261), 华山松 (Pinus armandii) (4.545) 、巴山冷杉 (Abiesfargesii) (4.289) 和糙皮桦 (Betula utilis) (3.256) 次之;灌木层中最高的为红晕杜鹃 (Rhododendron erubescens) (2.245), 多枝柳 (Salixpolyclona) (2.064) 、华中山楂 (Crataegus wilsonii) (1.508) 和陇东海棠 (Malus kansuensis) (1.453) 次之。3) 主要树种生态位宽度大于1的有30种, 占总数的11.67%, 其中21种是川金丝猴食源植物, 占神农架川金丝猴食源植物总数的10.40%;重要值排名前25位的树种中, 18种为食源植物, 占重要值总和的74.50%。4) 优势种的生态位重叠值在0.4以上的有7对种群;大部分种群的生态位相似性比值在0~0.3之间, 占全部种对的83.82%。结果表明, 神农架川金丝猴栖息地植物组成复杂, 优势种多为食源植物;优势种的生境高度相似、生态位多有重叠、种间竞争较为激烈, 将导致现有栖息地森林群落结构及植物组成发生变化, 食源植物短缺, 甚至栖息地面积缩减等现象, 这些都会影响川金丝猴的生存。因此, 加强保护神农架千家坪川金丝猴现生栖息地森林为川金丝猴创造适宜生存空间迫在眉睫。     

新疆阜康绿洲荒漠过渡带主要植物种的生态位分析

采用Levins公式和王刚生态重叠计测方法,对新疆阜康绿洲荒漠过渡带中的7个植物种,分别从群落梯度和3个单一生态因子（土壤水分维,土壤盐分维,土壤酸碱度维）上对其生态位分化进行了定量分析。结果如下：（1）在群落梯度上,生态位大小依次为红砂（0.7010）,梭梭（0.6434）,角果藜（0.4774）,雾冰藜（0.3745）,盐爪爪（0.3541）,叉毛蓬（0.3354）和碱蓬（0.2769）;（2）红砂在土壤水分、土壤盐分、土壤酸碱度维上的生态位分别为0.5274,0.6039和0.3620,梭梭在这3维上分别为03320,0.3083和0.5103,从生态位宽度看,红砂和梭梭处于优势种地位,其余为非优势种;（3）每个物种在群落梯度上的生态位宽度基本大于在上述3个资源轴上的平均生态位;（4）红砂与梭梭在土壤盐分维上的生态位重叠最大（0.4203）。表明了这两个优势种在利用土壤盐分方面有相似的特性。     

滇西北高原藏区小型兽类体表寄生蚤的生态位特征

为探讨云南西北高原藏区小型兽类体表寄生蚤的生态位特征,根据海拔和地形等自然环境特点,在德钦县选取42个调查样点,划分为5个垂直带,4种生境,采用铗夜法和笼日法捕获小兽,梳捡其体表寄生蚤,运用生态位宽度指数（B_i）和生态位重叠指数（NO）对其生态位特征进行分析。结果：共梳捡寄生蚤1275头,隶属4科9亚科17属33种,其中迪庆额蚤和云南栉眼蚤为优势种,常见种12种,稀有种19种。在海拔资源轴上,B_i值前三分别是特新蚤德钦亚种0.698、棕形额蚤0.690、斯氏新蚤川滇亚种0.667;生境资源轴上,B_i值前三分别是：无值大锥蚤0.630、特新蚤指名亚种0.57、特新蚤德钦亚种0.537;寄主资源轴上,B_i值前三为绒鼠怪蚤0.584、迪庆额蚤0.567、棕形额蚤0.553;多维生态位宽度来看,特新蚤德钦亚种和迪庆额蚤B_i值较大,分别为1.031、1.019。海拔、生境、寄主生态位重叠指数中,有意义的重叠种对分别占比35.6%、39.39%、9.28%;完全不重叠的种对分别占比26.89%、18.56%、51.14%;完全重叠的种对分别占比2.27%、13.26%和0.19%。三种生态因子中,优势种和常见种的生态位宽度值较大,对资源的利用能力和竞争能力较强。不同生态因子的生态位重叠指数格局不同,与资源轴本身有关。有意义的重叠和完全不重叠的种对占比较多,前者多为优势种、常见种、稀有种两两之间重叠,重叠指数越高,竞争关系越激烈;完全不重叠的种对多为稀有种之间,无资源利用竞争关系。总体来说,德钦县小兽体表寄生蚤种类丰富,生态位分化较为均匀,本研究可为该地蚤传疾病的监测防控提供生态学依据。     

Intra- und interspezifische Crowding-Effekte bei Kaulquappen der Kreuzkröte,Bufo calamita Laur.

Summary Tadpoles ofBufo calamita, a species that spawns in little temporary pools, were tested on intra- and interspecific crowding-effects. Water was conditioned by tadpoles of the following species:Bufo calamita (tadpoles of different age),Alytes obstetricans, Bombina variegata, Bufo bufo, Hyla arborea, Rana lessonae, R. ridibunda andR. temporaria. Tadpoles ofBufo calamita are most sensitive to water conditioned by older tadpoles of the own species during the first 2–3 weeks of development. They are also strongly inhibited by tadpoles ofRana temporaria andBufo bufo (that, as a rule, do not occur in the same habitat). Relative little effects are observed in water conditioned by tadpoles of the two species that occur very often in ecological sympatry withBufo calamita: Hyla arborea andBombina variegata. Young tadpoles ofBufo calamita are most tolerant of tadpoles of the same age of the own species. The crowding-effect increases with the number and weight of tadpoles/volume conditioning the water. In the age of 2–3 weeks the sensibility to intra- and interspecific crowding-effects fades. Thus inBufo calamita the age specific sensibility to crowding-effects in tadpoles may act as a density regulation mechanism in temporary pools.

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Mit Unterstützung des Schweizerischen Nationalfonds zur Förderung der wissenschaftlichen Forschung (Beitrag Nr. 3.256.69).     

茂兰喀斯特森林不同地形部位优势乔木种群的生态位研究

为了解茂兰喀斯特森林优势乔木种群的生态位特征,该研究对茂兰国家级喀斯特森林自然保护区三种地形(坡地、槽谷、漏斗)进行了群落调查,并计算三种地形部位优势乔木种群的生态位宽度、生态位重叠等特征。结果表明:不同地形部位的优势乔木种群的生态位宽度Bi和Ba值的排列顺序虽稍有差异,但总体上是一致的。轮叶木姜子(Litsea verticillata)在坡地、槽谷地形中的生态位宽度较大,其Bi/Ba分别为0.782 4/0.415 7、0.891 3/0.703 0;齿叶黄皮(Clausena dunniana)在坡地、漏斗地形中有较大的生态位宽度,其Bi/Ba分别为0.788 0/0. 518 3、0. 962 7/0. 826 0。生态位重叠值(Lhi)最大的是漏斗中的朴树(Celtis sinensis)和云贵鹅耳枥(Carpinus pubescens)(0.138 2),最小的是坡地中的圆叶乌桕(Triadica rotundifolia)和巴东荚蒾(Viburnum henryi)(0.001 5)、槽谷中的轮叶木姜子和青冈(Cyclobalanopsis glauca)(0.001 5)。生态学特性和对生境需求相似的物种,生态位重叠值通常较大,反之则小;物种的生态位宽度较大,则其生态位重叠值亦较大,反之则小。这说明三种地形中群落优势种群间的生态位重叠程度较小,茂兰喀斯特森林处于稳定的顶极群落阶段,但群落内种群因环境资源有限而产生的竞争较为激烈,在不同地形生境中的竞争激烈程度表现为漏斗>槽谷>坡地,光照的差异是影响各地形部位优势乔木种群天然分布的主要因子。     

昆承湖优势种鱼类时空-营养生态位

为了解昆承湖优势种鱼类资源利用情况,首先利用生态位方法计算了时间、空间及营养三个资源维度的生态位宽度及重叠值,然后根据时空-营养生态位宽度值将优势种鱼类划分为广位种、中位种和窄位种,最后讨论了生态位宽度及重叠的可能原因。结果显示：刀鲚Coilia nasus、蒙古鲌Chanodichthys mongolicus、似鱎Toxabramis swinhonis、似鳊Pseudobrama simoni、鳙Hypophthalmichthys nobilis、鲢Hypophthalmichthys molitrix、花鱼骨Hemibarbus maculatus、似刺鳊鮈Paracanthobrama guichenoti、大鳍鱊Acheilognathus macropterus和鲫Carassius auratus为优势种。在时间维度：鲢的生态位宽度最大,似鳊的最小;生态位重叠具有显著意义的有24对,占总的53.33%。在空间维度,似刺鳊鮈最大,鲢最小;生态位重叠具有显著意义的有36对,占总的80%。在营养维度,最大的为鲫,最小的为花鱼骨;生态位重叠具有显著意义的有8对,占17.78%...     

Macroecology meets macroevolution: evolutionary niche dynamics in the seaweed Halimeda

Aim Because of their broad distribution in geographical and ecological dimensions, seaweeds (marine macroalgae) offer great potential as models for marine biogeographical inquiry and exploration of the interface between macroecology and macroevolution. This study aims to characterize evolutionary niche dynamics in the common green seaweed genus Halimeda, use the observed insights to gain understanding of the biogeographical history of the genus and predict habitats that can be targeted for the discovery of species of special biogeographical interest. Location Tropical and subtropical coastal waters. Methods The evolutionary history of the genus is characterized using molecular phylogenetics and relaxed molecular clock analysis. Niche modelling is carried out with maximum entropy techniques and uses macroecological data derived from global satellite imagery. Evolutionary niche dynamics are inferred through application of ancestral character state estimation. Results A nearly comprehensive molecular phylogeny of the genus was inferred from a six‐locus dataset. Macroecological niche models showed that species distribution ranges are considerably smaller than their potential ranges. We show strong phylogenetic signal in various macroecological niche features. Main conclusions The evolution of Halimeda is characterized by conservatism for tropical, nutrient‐depleted habitats, yet one section of the genus managed to invade colder habitats multiple times independently. Niche models indicate that the restricted geographical ranges of Halimeda species are not due to habitat unsuitability, strengthening the case for dispersal limitation. Niche models identified hotspots of habitat suitability of Caribbean species in the eastern Pacific Ocean. We propose that these hotspots be targeted for discovery of new species separated from their Caribbean siblings since the Pliocene rise of the Central American Isthmus.     

洮河自然保护区大峪沟林区紫果云杉群落木本植物种群生态位特征

基于群落调查数据,以样地代表多种资源的综合状态,物种重要值作为生态位的计测指标,利用Levins和Shannon生态位宽度,Schoener生态位相似和Pianka生态位重叠对洮河自然保护区大峪沟林区的紫果云杉群落木本植物种群生态位进行定量研究。结果表明：紫果云杉群落乔木层共有树种8种,隶属于4科6属,紫果云杉占绝对优势,岷江冷杉为次优势种;灌木层共有植物50种,隶属于16科25属,忍冬科的蓝靛果、葱皮忍冬和唐古特忍冬等以及蔷薇科的峨眉蔷薇和银露梅等构成了灌木层的主体,紫果云杉幼苗优势不明显,但生态位宽度最大。本研究表明,生态位宽度受物种生态特性及其分布和生境共同影响,重要值大的物种生态位宽度一般较大,生态位宽度大的物种之间生态位相似性和重叠性一般较大,并与其它物种重叠的概率高、重叠程度大,生态位宽度小的物种集中出现时也会出现较大的生态位重叠,同科或同属的物种间常有较大生态位相似和重叠。生态位宽度反映着种群的扩散潜力,生态位相似反映着群落的稳定性,生态位重叠反映着物种间存在或潜在的竞争程度。紫果云杉在乔、灌木层均有最大的生态位宽度,生态适应性最强,群落结构稳定,具有进一步扩散的可能。     

浙江省檫木林生境与生态位研究

植被生境是群落乃至整个生态系统的物质基础,生态位宽度、生态位重叠、种间关系在群落生态学研究领域也具有重要地位,因此在植被生境基础之上展开的生态位、种间关系研究对了解生态系统功能具有重要意义。主成分分析表明:土壤养分和海拔因子对檫木生长分布起着重要的限制性作用;通过重要值对环境因子趋势拟合得出檫木在浙江省的典型生境为:海拔400—800 m,坡度20°—40°,阴坡半阴坡,土壤厚度大且肥沃的区域;在出现檫木的189个监测样地中,共出现的乔木树种有149种,主要优势树种(以重要值排序)为杉木Cunninghamia lanceolata、马尾松Pinus massoniana Lamb.、木荷Schima superba、枫香Liquidambar formosana Hance、青冈Cyclobalanopsis glauca (Thunb) Oerst、苦槠Castanopsis sclerophylla、石栎Lithocarpus glaber(Thunb.) Nakai、檫木Sassafras tzumu (Hemsl.) Hemsl.等。生态位宽度大小依次为杉木、檫木、马尾松、木荷、枫香、青冈、苦槠、板栗Castanea mollissima等,可见杉木、檫木、马尾松、木荷对外部环境有较强的适应能力,在各个资源位中出现较多,对资源的利用优势比较明显,檫木的生态位宽度达到了61.65,仅次于杉木的89.64,甚至大于马尾松的57.28,也说明檫木能在研究区拥有较好的群落地位;檫木与野樱桃Cerasus serrula (Franch.) Yüet L的生态位重叠值高达0.9以上,和浙江楠Phoebe chekiangensisC. B. Shang、构树Broussonetia papyrifera、鸡爪槭Acer palmatum Thunb.的生态位重叠值分别达0.831、0.785、0.531,说明檫木和野樱桃、浙江楠、构树、鸡爪槭对生境要求比较相近,在生态资源充足的情况下可尝试混交造林;通过监测样地中11个优势树种的种间联结分析,显示檫木与杉木、马尾松、木荷的种间具有显著的正联结关系,与枫香、苦槠和青冈也存在正联结关系,可见在研究区内檫木能够与这些树种互相吸引。     

On humans and wildlife in Mediterranean islands

Aim To investigate the effects of human‐induced landscape changes in Mediterranean islands on the ecological and evolutionary responses of bird communities and populations. The combination of mass extinction of large mammals and massive deforestation by humans was hypothesized to produce new selection regimes to which organisms were likely to respond. Habitat selection and niche breadth have been investigated at the scale of species, and phenotypic variation at the scale of local populations. Location The study was carried out along habitat gradients and in habitat mosaics at different spatial scales on the island of Corsica and in areas of similar size and structure in continental France. Methods Two sets of gradients have been used for investigating habitat selection and niche breadth: gradients of altitude, and gradients of vegetation structure. Population studies focused on the blue tit, Cyanistes caeruleus. Large samples of breeding attempts by this species in 10 habitats provided detailed data on phenotypic variation of fitness‐related traits both on Corsica and on the mainland. Results The extent of niche space used by birds differed substantially depending on which habitat gradient was considered. Many species have been found to contract their habitat niche along the elevation gradient on Corsica compared with the mainland, whereas all species in the vegetation gradient broadened their niche on the island. Breeding patterns of the blue tit differed considerably depending on whether they settle in deciduous oaks (Quercus humilis) or in evergreen sclerophyllous oaks (Quercus ilex). Phenotypic variation of breeding traits was much higher on the island, where more populations were correctly timed for the best breeding period than on the mainland, a pattern that is likely to result from lower dispersal of organisms on the island. Main conclusions The differences in observed niche breadth between the two series of habitat gradients is explained both by the species‐specific ecology of the species and the human‐induced environmental history of Corsica. Large‐scale landscape changes provided new opportunities for island colonization by non‐forest species, which are isolated as small, ‘fugitive’ local populations. In both gradients, forest species that are typical components of the Corsican bird fauna definitely expanded their niche and occupied a wider range of habitats on Corsica than on the mainland. At the population scale, landscapes included habitat patches with contrasted selection regimes, which resulted in high phenotypic variation for many fitness‐related traits. Reduced dispersal of birds on the island resulted in a much higher degree of local differentiation on Corsica than on the mainland.     

Geographical and ecological distributions of frog hemiclones suggest occurrence of both 'General-Purpose Genotype' and 'Frozen Niche Variation' clones

Asexuals often occupy broad geographical and ecological ranges. Two models have been proposed to explain the ubiquity of asexuals: the General‐Purpose Genotype (GPG) and the Frozen Niche Variation (FNV) model. According to these models, asexuals differ in their ecological niche width and may occupy narrow specialist niches or ubiquitous niches. A thousand water frogs from 37 different populations located in France in different habitats were studied, and two (hemi)clonal hybrid types were identified genetically, Rana esculenta and R. grafi. Altogether, 13 hemiclones were identified both in R. grafi and R. esculenta. Three of these were geographically and ecologically widely distributed, and usually very common in populations. In contrast, the remaining 10 hemiclones had small geographical ranges and were restricted to special habitat types, suggesting ecological niche specialization. The results suggest that in hybridogenetic water frogs GPG and FNV hemiclones coexist.     

福建三明钩栲种群与主要伴生树种生态位研究

采用Levins生态位宽度及重叠、Shannon-Wiener生态位宽度测度式,定量分析福建三明钩栲群落8个主要伴生树种的生态位宽度、生态位重叠。结果表明,该群落中优势种的生态位宽度值均普遍较大;生态位宽的种群对生态位窄的种群可能有较大的重叠值,反之则低;揭示钩栲的生态位特征及空间分布格局,对今后生产实践具有一定的参考价值。     

Nest site availability and niche differentiation between two cavity‐nesting birds in time and space

Niche differentiation is a key concept in the field of ecology and refers to the process by which competing species within an ecological community partition utilization of environmental resources to achieve coexistence. The existence of niche differentiation is uniquely difficult to prove on account of the fact that historical interaction among species, which plays a key role in elucidating the current state of coexistence among species, is not well known. We created continuous niche gradients in nest‐site resources between two sympatric secondary cavity‐nesting birds, the green‐backed tit (Parus monticolus) and the russet sparrow (Passer cinnamomeus), and investigated whether nesting site is a factor contributing to limiting breeding overlap by regular inspection and 388,160 min of film recording. Our results indicate that although we manipulated nest site availability to be uniformly high along the habitat gradient, the two bird species have little overlap in nest sites and rarely compete for them. Furthermore, the green‐backed tit possessed a wide range of fundamental niche that covered that of the russet sparrow, while their reproductive time was largely segregated. The sparrow was more aggressive and outcompeted the tit in their overlapped range. These results suggest that even though nesting sites are crucial to the reproduction of cavity‐nesting birds, some other factor plays a more important role in limiting niche overlap between sparrows and tits in space and time. Given that these two cavity‐nesting birds continued to use different habitats and breed in segregated time after our manipulation, their relationship is better explained by the ghost of competition past theory.     

Variation in niche parameters along the diversity gradient of unicellular eukaryote assemblages

We examined the relationship between average niche parameters and species richness of benthic diatom assemblages of boreal streams. We hypothesized that diverse assemblages should be typified by small average niche breadth of species, whereas low-diversity assemblages should be typified by broad average niche breadth. We also hypothesized that low-diversity sites should be dominated by either non-marginal species only or marginal species only, depending on the degree to which these sites could be categorized to range from environmentally typical sites to atypical sites. Niche breadth and niche position for each species were determined via Outlying Mean Index analysis. As hypothesized, we found that median niche parameters were significantly related to species richness. Median niche breadth showed both significant linear (R(2)=0.328, p<0.001) and unimodal (R(2)=0.354, p<0.001) relationship to species richness. The relationship between median niche position and species richness was best approximated by a unimodal model (R(2)=0.214, p=0.005). The underlying gradient in species richness was best accounted for by a regression model including moss cover, iron, and nitrogen, and explained 32% of variability in species richness. Our results showed that sites with high-diversity assemblages are likely to be occupied by specialists with a narrow niche breadth, whereas low diversity assemblages are dominated by generalists. Furthermore, the unimodal relationship between niche position and species richness suggested that species-poor sites may be typified by either non-marginal or marginal species.