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西藏日喀则恰布林剖面大竹卡组孢粉组合及其时代和古环境、古地理意义 总被引:1,自引:0,他引:1
西藏日喀则沿雅鲁藏布江分布的大竹卡组为一套杂色的砂砾岩沉积.与新生代印度-劳亚板块的碰撞和青藏高原的隆升具有密切的联系.迄今为止,其中尚未有可靠的化石发现用于指示时代.当前研究根据从大竹卡组中的一些粉、细砂岩中获得的较丰富的孢粉化石,首次探讨其沉积时期的古植物区系和陆地生态环境特征.孢粉组合以榆科和胡桃科具孔类和壳斗科三(拟孔)沟类被子植物花粉占优势,也见有较多的蕨类植物孢子和裸子植物两气囊花粉,其时代可能是渐新世-早中新世.孢粉组合反映大竹卡组沉积期间恰布林一带的气候比较温暖、湿润,揭示印度、劳亚大陆碰撞早期的热带-南亚热带低山丘陵环境.植物区系横向对比表明,恰布林自始新世末以来向北位移了大约500km. 相似文献
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In several areas of research on ecological assemblages, it is useful to be able to analyse patterns of spatial variation
at various scales. Multivariate analyses of dissimilarity or similarity in assemblages of species are limited by problems
of non-independence caused by repeated use of the sample-units. Where rank-order procedures are used, no comparative quantitative
measurements of dissimilarity at different scales are produced. An alternative method is described that uses the sample's
average assemblage (or centroid). These estimates are themselves averaged to give centroids for larger spatial scales. Dissimilarities
from the centroids at each scale are then calculated using independent replicates for each scale from those in each sample.
The dissimilarity measures can then be examined by analysis of variance to detect spatial scales of differences for each sample
at every level of a hierarchy of scales. The method is illustrated using data from mangrove forests and rocky shores, involving
up to 97 taxonomic groups (species, other taxa). Differences among assemblages at the scales of sites (tens of meters apart)
or locations at shores (hundreds of meters apart) were identified. Consequences of different numbers of replicates are discussed,
with some potential problems (and their solutions) in application.
Received: 14 November 1997 / Accepted: 14 September 1998 相似文献
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Summary The shallow marine subtropical Northern Bay of Safaga is composed of a complex pattern of sedimentary facies that are generally
rich in molluscs. Thirteen divertaken bulk-samples from various sites (reef slopes, sand between coral patches, muddy sand,
mud, sandy seagrass, muddy seagrass, mangrove channel) at water depths ranging from shallow subtidal to 40m were investigated
with regard to their mollusc fauna >1mm, which was separated into fragments and whole individuals.
Fragments make up more than 88% of the total mollusc remains of the samples, and their proportions correspond to characteristics
of the sedimentary facies. The whole individuals were differentiated into 622 taxa. The most common taxon,Rissoina cerithiiformis, represented more than 5% of the total mollusc content in the samples. The main part of the fauna consists of micromolluscs,
including both small adults and juveniles. Based on the results of cluster-, correspondence-, and factor analyses the fauna
was grouped into several associations, each characterizing a sedimentary facies: (1) “Rhinoclavis sordidula—Corbula erythraeensis-Pseudominolia nedyma association” characterizes mud. (2) “Microcirce sp.—Leptomyaria sp. association” characterizes muddy sand. (3)”Smaragdia spp.-Perrinia stellata—Anachis exilis—assemblage” characterizes sandy seagrass. (4) “Crenella striatissima—Rastafaria calypso—Cardiates-assemblage” characterizes muddy seagrass. (5) “Glycymeris spp.-Parvicardium sueziensis-Diala spp.-assemblage” characterizes sand between coral patches. (6) “Rissoina spp.-Triphoridae —Ostreoidea-assemblage” characterizes reef slopes. (7) “Potamides conicus—Siphonaria sp. 2—assemblage” characterizes the mangrove.
The seagrass fauna is related to those of sand between coral patches and reef slopes with respect to gastropod assemblages,
numbers of taxa and diversity indices, and to the muddy sand fauna on the basis of bivalve assemblages and feeding strategies
of bivalves. The mangrove assemblage is related to those of sand between coral patches and the reef slope with respect to
taxonomic composition and feeding strategies of bivalves, but has a strong relationship to those of the fine-grained sediments
when considering diversity indices. Reef slope assemblages are closely related to that of sand between coral patches in all
respects, except life habits of bivalves, which distincly separates the reef slope facies from all others. 相似文献
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通过对新疆克拉玛依地区吐孜阿克内沟剖面三工河组孢粉组合的研究,共鉴定孢粉23属32种,藻类化石2属4种,命名为Disacciatrileti-Monocolpates-Cyathidites组合(简称DMC组合)。描述了5种花粉Abietineaepollenites dunrobinensis Couper,Pseudopicea monstruosa Bolch.,Podocarpidites 相似文献
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M. J. Samways 《Oecologia》1990,84(4):482-490
Summary Ant assemblages in five closely-spaced point habitats were studied over a three-year period in a subtropical area of South Africa. A total of 20,746 individuals in 56 species were sampled with pitfall traps. Rapid species turnover occurred during short periods after longer intervals of relatively constant species composition. There was annual cycling of total numbers of individuals. The temporal variance for total number of individuals within each habitat increased significantly with mean population size by a logarithmic regression. This indicates that population fluctuations are dependent upon the mean, with a distinctive relationship. The total number of species was cyclical, with annual and approximately half-yearly cycles. Each habitat nevertheless carried a characteristic mean number of species. The temporal variance of species richness showed a highly significant positive logarithmic relationship with the mean number of species. Pheidole megacephala (F.) accounted for 45% of all individuals. Its overall population showed annual cycles. Ph. megacephala population trend was the main determinant for seasonal variation of the whole assemblage in most habitats. Percentage dominance was positively linearly correlated with the variance and with mean population level. Although Ph. megacephala population variance increased with the mean, proportionate variability did not, indicating that high populations are no more variable than low populations. Five variability measures were compared with each other on ant assemblages containing only the common species (1st quartile) and then including the increasingly rare species (1st and 2nd, 1st, 2nd and 3rd, and all quartiles). Williamson's Variability Measure, using logarithmic or inverse sine transformations, gave variable results depending whether or not the rarer species were included in the analysis. The Coefficient of Fluctuation also gave variable results depending on assemblage size. The Coefficient of Variation and Proportionate Variability Measure gave similar and consistent results, indicating that common species are not more variable than rare ones. The rarer species are stenotopic and tend always to be rare, whereas the common species are eurytopic, highly competitive and demographically volatile. Control measures for common ants, and conservation of rare ants, should take cognizance of these trends. 相似文献
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Riassunto La scheda morfopalinologica diSequoia sempervirens (Lamb.) Endl. continua lo studio sulle Pinohyta ornamentali più frequenti in Torino. È esaminato polline fresco ed acetolizzato proveniente da due stazioni e la provenienza non determina variazioni significative dei parametri morfometrici.
Summary The morphopalynological card ofSequoia sempervirens (Lamb.) Endl. is a new contribution to the comprehensive study on pollen of ornamental Pinophyta in Turin. Fresh and acetolysed grains from two stations are examined, and for all parameters no significative differences were observed in relation to the collection site.
Parole chiave: Sequoia sempervirens(Lamb.) Endl., Flora Palinologica Italina, Sezione Aeropalinologica. 相似文献
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Siphonophores are exclusively marine cnidaria and their predatory role in plankton food-webs is well recognised. In this study,
we analyse the structure and the spatial extent of siphonophore assemblages in relation to changes in freshwater outflows
and food availability in the southern Gulf of Mexico during a high (October) and a low (April) outflow periods. A total of
149 samples were collected using a 505 μm multiple closing net at 1–6 levels (0–100 m) of the water column, depending on the
bathymetry. Data on siphonophore species biovolumes (ml 100 m−3) were treated by means of the Bray-Curtis Dissimilarity Index, and two distinctive assemblages were identified: the ‘inner’
and the ‘outer’ assemblages, located over the inner and outer shelves. Temperature, salinity, zooplankton biomass, and siphonophore
species were included in a Principal Component Analysis (PCA) to identify the factors associated with each assemblage. Geographical
distribution of the assemblages practically remained the same during both seasons and its cross-shelf variability was stronger
than the vertical one. Seasonally, diversity values were higher in October, when the highest river discharges occur. Spatially,
the lowest diversity and mean siphonophore biovolumes values were registered in the ‘inner assemblage’, where the highest
and lowest salinity values were recorded. We suggest that even when extreme salinity values (>36.5 or <34) might depress siphonophore
populations in the coastal area, enough food availability in the concerned areas might mitigate the negative effect of salinity,
since a positive and significant (p < 0.05) relationship was found between siphonophores biovolume and zooplankton biomass. Bassia bassensis, Diphyes dispar and Enneanogum hyalinum, present in both assemblages during both seasons, were able to survive in a wide range of salinity values, following perhaps,
their prey. All the 23 species here registered were found in the ‘outer assemblage’; however, Abylopsis eschscholtzi, Chelophyes appendiculata and Diphyes bojani were more associated with the ‘outer’ group according to the PCA results. Enneagonum hyalinum was the only species frequently encountered and abundant in the ‘inner assemblage’ during both seasons and, supporting previous
observations, this species might be considered as an indicator of nearshore waters.
Handling editor: K. Martens 相似文献
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C. Granado-Lorencio J. Lobón Cerviá C. R. M. Araujo Lima 《Biodiversity and Conservation》2007,16(3):679-692
The Neotropical region is renowned for its high biodiversity, and the Amazon River basin contains the highest number of fish
species of any river system in the world. In recent years, habitat fragmentation and exploitation of biotic resources have
threatened biological integrity and provoked to need for sustainable management and conservation of the Amazon River system.
We studied 36 floodplain lakes along 2000 km of the Amazon River. The fish assemblages associated with flood forests are moderately
diverse, with low species dominance and reduced populations. To detect nestedness of fish assemblage composition in floodplain
lakes, a nested subset analysis was performed on species presence–absence. The incidence matrix (species × lakes) was maximally
packed using the Nestedness Temperature Calculator software. The results of ranking lakes and species allow us to establish
targets for conservation. Such strategy for sustainable management should be focused on maintaining the Amazonian biodiversity. 相似文献