西双版纳热带季节雨林自然和模拟积水树洞内水生生物多样性研究

积水树洞为丰富的水生生物类群提供特殊的栖息地。然而,我国积水树洞中的水生群落尚未得到充分记录,也没有模拟树洞试验。本研究在调查中国西双版纳热带季节雨林中的自然积水树洞的同时,也利用人工容器进行了积水树洞模拟试验,更加全面充分地了解水生群落类群的组成以及检测模拟树洞试验在国内森林生态系统内的可行性。结果表明,积水树洞内水生类群丰富,模拟树洞和自然树洞中双翅目幼虫都是主要类群。自然树洞内的多数物种在模拟树洞内被发现。模拟树洞能够为水生生物提供与自然树洞相似的生存环境,模拟树洞或将成为国内研究积水树洞内水生群落便利有效的工具。     

Miocene glaciomarine sediments from beneath the southern ross ice shelf, antarctica

Glaciomarine sediments with middle Miocene microfaunal assemblages are exposed at the sea floor below the southern Ross Ice Shelf. Plio-Pleistocene sediments are not present. Post-Miocene glacial sediments may have been deposited but removed by relatively recent ice shelf grounding. A meager Recent microfauna is present in some core tops.     

Flake tools stratified below paleo-Indian artifacts

In northwest Missouri, Lithic stage flake tools struck from prepared cores have been excavated underlying a Paleo-Indian fluted point assemblage. These assemblages were in two different loesses of the last glaciation. Thermoluminescent analysis of stone tools dates the Paleo-Indian occupations at 8690 +/- 1000 B.C. and 12,855 +/- 1500 B.C.; the Lithic stage occupations must be older than 13,000 B.C. on the basis of geologic correlation, lithic analysis, and cultural stratigraphy.     

Cretaceous cold-seep communities and methane-derived carbonates in the canadian arctic

Lower Cretaceous cold-seep fossil assemblages have been found in the Canadian Arctic Archipelago. Serpulid worm tubes and bivalves are most abundant in these communities; in contrast, fossils are scarce in the surrounding strata. The fossils are contained in an isotopically light (delta(13)C = -25 to -50 per mil) carbonate rock groundmass that is interpreted to have formed from bacterial oxidation of methane. The rocks were deposited at intermediate depth (相似文献   

Marked post-18th century environmental change in high-arctic ecosystems

Paleolimnological data from three high-arctic ponds on Cape Herschel, Ellesmere Island, Canada, show that diatom assemblages were relatively stable over the last few millennia but then experienced unparalleled changes beginning in the 19th century. The environmental factors causing these assemblage shifts may be related to recent climatic warming. Regardless of the cause, the biota of these isolated and seemingly pristine ponds have changed dramatically in the recent past and any hopes of cataloging natural assemblages may already be fruitless.     

Starch fossils and the domestication and dispersal of chili peppers (Capsicum spp. L.) in the Americas

Chili peppers (Capsicum spp.) are widely cultivated food plants that arose in the Americas and are now incorporated into cuisines worldwide. Here, we report a genus-specific starch morphotype that provides a means to identify chili peppers from archaeological contexts and trace both their domestication and dispersal. These starch microfossils have been found at seven sites dating from 6000 years before present to European contact and ranging from the Bahamas to southern Peru. The starch grain assemblages demonstrate that maize and chilies occurred together as an ancient and widespread Neotropical plant food complex that predates pottery in some regions.     

Abundance distributions imply elevated complexity of post-Paleozoic marine ecosystems

Likelihood analyses of 1176 fossil assemblages of marine organisms from Phanerozoic (i.e., Cambrian to Recent) assemblages indicate a shift in typical relative-abundance distributions after the Paleozoic. Ecological theory associated with these abundance distributions implies that complex ecosystems are far more common among Meso-Cenozoic assemblages than among the Paleozoic assemblages that preceded them. This transition coincides not with any major change in the way fossils are preserved or collected but with a shift from communities dominated by sessile epifaunal suspension feeders to communities with elevated diversities of mobile and infaunal taxa. This suggests that the end-Permian extinction permanently altered prevailing marine ecosystem structure and precipitated high levels of ecological complexity and alpha diversity in the Meso-Cenozoic.     

Refractory minerals in interplanetary dust

A newly studied interplanetary dust particle contains a unique set of minerals that closely resembles assemblages in the refractory, calcium- and aluminum-rich inclusions in carbonaceous chondrite meteorites. The set of minerals includes diopside, magnesium- aluminum spinel, anorthite, perovskite, and fassaite. Only fassaite has previously been identified in interplanetary dust particles. Diopside and spinel occur in complex symplectic intergrowths that may have formed by a reaction between condensed melilite and the solar nebula gas. The particle represents a new link between interplanetary dust particles and carbonaceous chondrites; however, the compositions of its two most abundant refractory phases, diopside and spinel, differ in detail from corresponding minerals in calcium- and aluminum-rich inclusions.     

A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs

It has generally been thought that the first dinosaurs quickly replaced more archaic Late Triassic faunas, either by outcompeting them or when the more archaic faunas suddenly became extinct. Fossils from the Hayden Quarry, in the Upper Triassic Chinle Formation of New Mexico, and an analysis of other regional Upper Triassic assemblages instead imply that the transition was gradual. Some dinosaur relatives preserved in this Chinle assemblage belong to groups previously known only from the Middle and lowermost Upper Triassic outside North America. Thus, the transition may have extended for 15 to 20 million years and was probably diachronous at different paleolatitudes.     

Parallel declines in pollinators and insect-pollinated plants in Britain and the Netherlands

Despite widespread concern about declines in pollination services, little is known about the patterns of change in most pollinator assemblages. By studying bee and hoverfly assemblages in Britain and the Netherlands, we found evidence of declines (pre-versus post-1980) in local bee diversity in both countries; however, divergent trends were observed in hoverflies. Depending on the assemblage and location, pollinator declines were most frequent in habitat and flower specialists, in univoltine species, and/or in nonmigrants. In conjunction with this evidence, outcrossing plant species that are reliant on the declining pollinators have themselves declined relative to other plant species. Taken together, these findings strongly suggest a causal connection between local extinctions of functionally linked plant and pollinator species.     

Effects of raw materials on biface manufacture

It has been suggested that the degree of refinement of trimming seen on Lower Paleolithic bifaces reflects the level of technical sophistication of the toolmaker. This has been tested by a series of experiments carried out at Olduvai Gorge, Tanzania, and related to some of the archeological assemblages there. It is concluded that advanced ideas and increased mastery over raw materials do not necessarily result in stone tools that are more refined in appearance.     

Radiocarbon dating of petroleum-impregnated bone from tar pits at Rancho La Brea, California

A liquid-chromatography method has been developed for the separation of amino acids with the same specific activity in radiocarbon from bones impregnated with isotopically dead petroleum compounds found in the La Brea tar pits. This technique permits the application of radiocarbon dating to such bone assemblages.     

Hoabinhian: a pebble-tool complex with early plant associations in southeast Asia

The term "Hoabinhian" has been applied to "mesolithic" assemblages from all parts of mainland Southeast Asia. Recent excavation in north Thailand has yielded the first associated carbon-14 dates and provided evidence for the early (about 7000 B. C.) domestication of plants in Southeast Asia.     

Precambrian columnar stromatolites in australia: morphological and stratigraphic analysis

The stratigraphic distribution in Australian Precambrian rocks of columnar stromatolites, organosedimentary structures formed by blue-green algae, has been investigated. Their morphology is being studied according to methods developed in Russia. The discovery of successive different assemblages supports not only regional but also intercontinental stratigraphic correlations which are in agreement with available isotopic datings.     

Precambrian age of the Boston basin: new evidence from microfossils

A Vendian (Late Proterozoic Z) age has been determined for the Boston Basin by comparison of a microflora from the Cambridge Argillite with other late Precambrian assemblages. The microfossils, which include Bavlinella cf. faveolata, are preserved as petrifactions in pyrite. This age designation for the sedimentary rocks of the Boston Basin should allow for the reinterpretation of the structure of the basin and its regional correlations.     

Angiosperm diversification and paleolatitudinal gradients in cretaceous floristic diversity

The latitudinally diachronous appearance of angiosperm pollen during the Cretaceous is well documented, but the subsequent diversification and accompanying significant changes in floristic dominance have not been assessed quantitatively for a wide range of paleolatitudes. Trend surfaces fitted to within-palynoflora diversity data from 1125 pollen and spore assemblages show that angiosperms first become floristically prominent in low paleolatitude areas( approximately 20 degrees N to 20 degrees S). Non-magnoliid dicotyledons show a similar but slightly delayed pattern of increase and are the principal component of angiosperm diversity from all areas sampled. Monocotyledons and magnoliid dicotyledons are significant primarily in low to middle paleolatitude palynofloras( approximately 50 degrees N to 20 degrees S) during the latest Cretaceous. As angiosperms become increasingly prevalent the importance of most non-angiosperm taxa either decreases or remains unchanged. The only apparent exception is a striking increase in gnetalean diversity concurrent with the initial angiosperm diversification at low paleolatitudes.     

Marine fossils at rancho la brea

Marine assemblages of foraminifera, ostracods, mollusks, and echinoids were recovered from deposits stratigraphically beneath the classic vertebrate assemblages from the tar pits at Rancho La Brea. The marine fossils indicate deposition in quiet, shallow water and suggest that accumulation of the type Rancholabrean material began during Wisconsin time.     

Scaling population density to body size in rocky intertidal communities

Interspecific comparisons of animal population density to body size has been the subject of active research in the last decade, especially for terrestrial animals when considering particular taxa or taxonomic assemblages. Studies of rocky intertidal communities showed that animal population density scales with body size to the -0.77 power. This relation held within local communities representing a broad array of animal taxa and was not affected by a dramatic alteration in the network of between-species interactions, as revealed by two long-term human exclusion experiments.     

Triassic vertebrates of gondwanan aspect from the richmond basin of virginia

A new locality of early Late Triassic age in the Richmond basin of east-central Virginia has yielded abundant remains of a diversified assemblage of small to medium-sized tetrapods that closely resembles Southern Hemisphere (Gondwanan) assemblages in the predominance of certain synapsids. Associated palynomorphs indicate an early middle Carnian age for the fossiliferous strata. The discovery suggests that previously recognized differences between tetrapod assemblages of early Late Triassic age from Gondwana and Laurasia at least in part reflect differences in stratigraphic age, rather than geographic separation.     

Ecology and catastrophic mortality in wild horses: implications for interpreting fossil assemblages

The identities, sexes, and reproductive status of groups of wild horses (Equus caballus) living in the Great Basin Desert of North America were known prior to their deaths on ridgelines. Another group of very young horses died on a quagmire. Snow accumulation or drought was apparently responsible for the mass deaths. These data have implications for reconstructing some aspects of the social structure of fossil mammals on the basis of skewed sex or age ratios in bone assemblages.