鄂尔多斯高原北缘水分梯度下天然植被分布格局初探

以鄂尔多斯高原杭锦旗北部独贵塔拉镇的过渡带为研究对象,通过样线调查,研究了水分梯度下天然植被的空间分布规律.TWINSPAN的分类结果表明,群落以中生和旱生为主,一些耐盐的植物散布其中;相邻样方间相似性指数的变化反映了不同类型群落在研究区内的镶嵌分布,从而形成了该区域内群落的多样性和复杂性.对植被样方与地形地貌因子的CCA排序结果显示,植被群落空间格局的形成更多地取决于区域内的水分变化梯度.在本文的研究尺度上,这种水分变化梯度主要由微地形地貌的变化来决定,而不是由与黄河的距离因子来决定.因此,在本区域的土地开发利用过程中,应充分考虑目前已经形成的相对稳定的地形地貌单元特点,在缺乏完善的风沙防护措施和排水除盐措施的情况下,不宜采取大规模平整土地进行综合开发.     

永德大雪山中山湿性常绿阔叶林植物区系的初步研究

中山湿性常绿阔叶林是永德大雪山亚热带山地植被垂直带上最具特征性的植被类型,也是该地区面积最大、保存最为完整、最有保护价值的植被类型。从该类型植被中219种常见和优势植物的种类结构分析看,只有热带亚洲成分、中国-喜马拉雅成分及中国特有成分能够贯穿于乔木Ⅰ、Ⅱ、Ⅲ层,灌木层,草本层和层外植物各层次之中;其区系成分以中国-喜马拉雅和中国特有成分占优势,同时热带亚洲成分也占有相当的比例,说明其区系具有亚热带向温带过渡的性质;而中国特有种的进一步分析亦表明其区系的过渡性质。这表明永德大雪山处于中国-喜马拉雅森林植物区系和热带亚洲植物区系的分界面上,其植物区系的过渡特征非常明显。通过永德大雪山中山湿性常绿阔叶林与邻近地区同类型植被的优势种和主要伴生种的比较,我们初步认为该地此类森林植被环境更“温湿”。     

Biochemical variation to determine phylogenetic relationships betweenHordeum chilense and other American species of the genusHordeum (Poaceae)

Slab gel electrophoresis techniques have been applied to the study of isozyme and kernel protein patterns in 20 accessions ofHordeum chilense and related species in order to elucidate their phylogenetic relationships. On the basis of our results we can conclude that: (1) Conventional classification based on morphological characters does not totally agree with biochemical data. (2) Sectt.Anisolepis andCritesion seem to be clearly differentiated. (3) The accessions classified asH. compressum present biochemical phenotypes quite different from the rest of the species. (4)H. stenostachys, H. muticum andH. chilense constitute a group of variable species with many biochemical similarities and close phylogenetic relationships. (5) The evolutionary pattern of these American species seems to follow a model of reticulate evolution.     

Early post‐fire succession in northwestern Patagonia grasslands

Abstract. Large‐scale disturbances, notably fire and grazing, structure grass and shrubland dynamics in semi‐arid environments. We studied early post‐fire succession in two burned grasslands, one unburned grassland, and one shrubland near the burned area. We observed three processes: (1) establishment of a ‘phantom’ community comprised of fugitive species. Although transient, these species increase diversity and recharge the seed bank before the next disturbance; (2) regeneration of the original community by persistence of resprouter species and by auto‐replacement; (3) early stages of invasion by seedlings of the shrub Fabiana imbricata, which germinate next to shrubland and create new F. imbricata patches. Weed invasion was principally due to the ruderal exotic species Verbascum thapsus from the nearby road verge and by rapid increase of Rumex acetosella cover, another exotic species present before the fire. Although post‐fire climatic conditions are particularly important in semi‐arid environments, succession depends greatly on the regeneration strategies and dispersal abilities of the species present in the burned area. The phantom community occurs only at the first stage of succession when there is little competition for resources. We could call this process ‘the race for occupation of the area’. The second stage, when competition for resources becomes progressively more important, could be called ‘the effort to maintain space’.     

Precopulatory behaviour and the evolutionary relationships of Discoglossidae

The phylogenetic relationships among primitive anurans remain controversial, even when several morphological and molecular approaches have been used in an attempt to resolve them. Nevertheless, very little effort has been made to study these relationships with behavioural data. We studied the relation between some precopulatory behaviour characters (male call characteristics and call recognition by females) and the different proposed phylogenies among the anuran genera Alytes, Discoglossus and Bombina . Different acoustic variables were analysed from male calls of different species of these genera; Alytes cisternasii females were used in recognition tests with calls from those species. A phenetic tree generated from male call characteristics grouped Bombina with Discoglossu s and separated these two genera from Alytes, although the tree generated from female response data did not show such a clear result. A. cisternasii females are mostly using some features that are absent in Alytes calls in order to recognize male calls. The two characters, mapped onto the three alternative phylogenetic proposals, did not resolve the trichotomy among the three genera, but suggested that the studied behavioural characters have a clear phylogenetic load.     

Modern pollen–vegetation relationships along transects on the Whangapoua Estuary, Great Barrier Island, northern New Zealand

Aims To quantify pollen–vegetation relationships from saline to freshwater in an estuarine gradient from surface samples of the modern pollen rain, to allow more accurate interpretations of the stratigraphic palynological record. Location Whangapoua Estuary, Great Barrier Island, northern New Zealand. Methods Six transects were laid out along a vegetation sequence running from estuarine mud to freshwater swamp. Along these transect lines, 108 plots were sampled for vegetation and surface sediments from wet sand, mud, plant litter or moss (sand and mud sites are inundated by most tides, other sites less frequently). All sediment samples were analysed for pollen. The relationships between plant species frequency and pollen representation were examined at a community scale using twinspan and ordination analyses, and for individual species using fidelity and dispersibility indices, regression and box‐plot analyses. Results The quantitative relationships between source taxon vegetation frequency and its pollen representation varied between species due to differential pollen production and dispersal. twinspan of the surface pollen samples suggests five vegetation types: (A) mangrove (Avicennia marina); (C) Leptocarpus similis salt meadow; (D) Baumea sedges; (E) Leptospermum shrubland; and (F) Typha/Cordyline swamp forest. The (B) Juncus kraussii community is not represented palynologically owing to the destruction of its delicate pollen grains during acetolysis of samples. Detrended correspondence analysis places these communities on an estuarine‐to‐freshwater gradient. However, pollen assemblages at the seaward end of the salinity gradient are less clearly representative of the associated vegetation than those at the landward end, probably because the open vegetation at the former allows the influx of wind‐ and water‐dispersed pollen from surrounding vegetation. Main conclusions The vegetation pattern (zonation) at Whangapoua is reflected in the pollen rain. When the long‐distance and over‐represented pollen types are excluded, five out of six of the broad vegetation communities can be identified by their pollen spectra. Species with high fidelity and low‐to‐moderate dispersibility indices can be used to identify the vegetation types in the sedimentary sequences. The more open vegetation types at the ‘marine end’ of the sequence tend to be ‘overwhelmed’ by regional pollen, but the nature of the sediments and the presence of discriminatory species (e.g. A. marina, Plagianthus divaricatus, Cordyline australis), even in small amounts, will allow correct identification of the local vegetation represented in sedimentary palynological sequences. A box‐plot analysis indicates that the pollen and spore types A. marina (mangroves), Sarcocornia quinqueflora (salt meadow), P. divaricatus (sedges), Gleichenia (shrubland) and C. australis (swamp forest) are highly discriminatory in relation to vegetation type. These discriminatory palynomorphs help with the interpretation of stratigraphic pollen studies. However, salt marsh vegetation communities in the sediments must be interpreted with caution as the marine sediments are easily affected by erosion, bioturbation and tidal inundation effects.     

Celebrities: From Teachers to Friends

In this paper we present two compatible hypotheses to explain interest in celebrity gossip. The Learning Hypothesis explains interest in celebrity gossip as a by-product of an evolved mechanism useful for acquiring fitness-relevant survival information. The Parasocial Hypothesis sees celebrity gossip as a diversion of this mechanism, which leads individuals to misperceive celebrities as people who are part of their social network. Using two preliminary studies, we tested our predictions. In a survey with 838 respondents and in-depth interviews with 103 individuals, we investigated how interest in celebrity gossip was related to several dimensions of the participants’ social lives. In support of the Learning Hypothesis, age proved to be a strong predictor of interest in celebrities. In partial support of the Parasocial Hypothesis, media exposure, but not social isolation, was a strong predictor of interest in celebrities. The preliminary results support both theories, indicate that across our life span celebrities move from being teachers to being friends, and open up a list of future research opportunities.