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41.
Summary Despite extensive discussions during the last 20 years stromatolites are still used by many geologists as unequivocal indicators
of very shallow-water conditions. We investigated four stratigraphic units from the Lower and Middle Jurassic of southern
Germany (Posidonien-Schiefer, Amaltheen-Ton) and of the Northern Calcareous Alps (Adneter Kalk, Klauskalk), which were formerly
interpreted as shallow marine sediments by some authors due to the occurrence of stromatolites. Our interpretations of the
macro-, micro- and ultrafacies of these sediments are not compatible with shallow-water settings. We therefore propose a deep-marine,
aphotic origin of these stromatolites.
Former interpretations of the Posidonien-Schiefer as a shallow-water deposit are mainly based on the occurrence of stromatolites.
We favour the model of a temporarily stagnant, deep, aphotic basin for these planktonrich sediments. Particles resembling
ooids, but lying within mudstones cannot be taken as evidence for shallow agitated water. They either formed within the mud
or are allochthonous.
The deep-water setting of the red limestone of the Alpine Early and Middle Jurassic is indicated by a lack of platform-typical
components like coated grains and phototrophic benthos and by shells of plankton and nekton forming a major part of the sediment.
Stromatolites occur on the steep slope of a drowned Rhaetian reef with an estimated relief of 50–100 m and immediately below
and within radiolarian limestones, deposited below the aragonite compensation depth (ACD).
The aphotic stromatolites show some morphological differences to their shallow water counterparts. In all of our sections
they occurred during intervals of reduced sedimentation. They form only thin horizons and probably grew very slowly. Mineralizations
by Fe−Mn oxides and phosphate are very common. The presence of a microbial film is evident from binding of sedimentary particles,
but the nature of the microbes is not known. Growth habits within the very distinct environments of red limestone and black
shales show some common features, but also clear differences.
The microproblematicumFrutexites
Maslov is a very common component in deep-water stromatolites, but may also itself form small crusts or dendrolites. It occurs in
two different forms. Opaque, slender forms with indistinct outlines probably grew within the weakly lithified sediment. Thicker,
transparent forms with well defined outlines are found in cavities and probably also grew on the seafloor. Well preserved
specimens display an internal fabric of radially arranged fibres of Fe−Mn oxides and calcite. It is suggested that calcite
or aragonite were one original mineralogy ofFrutexites, which was later replaced by Fe−Mn oxides or phosphate.
It is not certain whetherFrutexites is an organic, biomineralized structure or an inorganic mineralization, but the variable mineralogy and growth forms in different
environments point to an organic origin. But even if organic, the occurrence in cryptic habitats and negative phototactic
growth-directions make it clear thatFrutexites was not phototrophic. 相似文献
42.
为在PrinceRupert林区的“亚北方”部分建立生态立地质量与森林生产力的联系,对从93个小杆松林分和77个白云杉林分获得的数据进行了分析.所研究的林分处于两个气候状况、8个土壤水分状况以及5个土壤养分状况.这些气候、土壤水分和养分状况被视为等级变量用于林地分类和回归分析.小杆松和白云杉的立地指数随土壤水分和养分状况变化而变化,但不依赖于气候变化.与土壤水分相关的变化格局对两个种来说很相似,但与土壤养分相关的变化格局则全然不同.在所建立的5类回归模型中,土壤小区模型对于两个种都显示出立地指数与土壤水分和养分状况具有很强的相互关系(R2>0.80,SEE≤1.6m).可以认为土壤水分和养分的等级度量在大范围内可作为小杆松和白云杉立地指数的预测预报因子. 相似文献
43.
P. Slurink 《Human Evolution》1993,8(4):265-273
In contrast to many other models of human evolution the “balance of power” theory of Alexander has a clear answer to the question
why a runaway selection process for unique social and moral capacities occurred in our ancestry only and not in other species:
“ecological dominance” is hypothesized to have diminished the effects of “extrinsic” forces of natural selection such that
withinspecies, intergroup competition increased (Alexander, 1989). Alexander seems to be wrong, however, in his claim that
already the common HUCHIBO (Humans, Chimps, Bonobo's)-ancestor has crossed the ecological dominance barrier. In this paper
an adapted version of Alexander's model is presented and several different ways are proposed to make this adapted version
testable. A preliminary survey of the available paleontological and paleoecological data suggests that there is some evidence
of a less vulnerable position towards predators in earlyHomo and that there are clear signs related to a crossing of the ecological dominance barrier inHomo sapiens sapiens. 相似文献
44.
Ephedra sinica is a rare and vulnerable species in China, and the habitat of Ephedra sinica is seriously threatened (by climate change and human activities). Predicting the suitable growth areas and constructing ecological corridors for Ephedra sinica in China will help to protect it scientifically. Based on 306 valid distribution records and 13 selected environmental factors, the maximum entropy (MaxEnt) model was used to simulate the potential current habitat zones and future (2050 and 2070) habitat zones of Ephedra sinica under four climate change scenarios. The minimum cumulative resistance (MCR) model was applied to extract important ecological corridors of Ephedra sinica. The results indicate that: (1) Under the current environment, the total area of the suitable habitat for Ephedra sinica in China is 42.24 × 105 km2, mainly distributed in Northwest China and North China. (2) Suitable area increases as the RCP rises. The center of mass of the habitat zone moved northward from Shaanxi Province to Ordos City in Inner Mongolia Autonomous Region. (3) Of the 13 environmental factors selected, the primary factor was elevation (20.8 %), followed by wettest month precipitation (18.2 %) and temperature seasonality (15.2 %). (4) Built 19 ecological corridors, with a total corridor length of 430.2 km, including seven long-distance passages and 12 short-distance corridors. All corridors are far from the artificial surface, mostly near high-altitude areas. The 19 ecological corridors constructed using the MCR model will also provide considerable importance for the survival of Ephedra sinica on a longer time scale in the future. 相似文献
45.
桃儿七分布格局与生态适应的初步研究 总被引:10,自引:0,他引:10
以云南产桃儿七Sinopodophyllum hexandrum(Royle)Ying为研究材料,分析了它的分布格局及生态适应。指出桃儿七是一个分布范围较广、生态适应幅度大的物种;在分布区内它主要出现在具有次生植被的山谷中,个体在居群内的分布格局,由于受到放牧活动的影响而呈聚群式分布,植株常出现在灌木丛下和树根附近。它适应夏秋湿润凉爽,冬季及早春寒冷干燥的气候条件,并具有相应的生长与发育节律。人类 相似文献
46.
47.
48.
The field metabolic rates (FMR) and rates of water flux were measured in two species of varanid lizards over five periods of the year in tropical Australia. The energetics of these species were further investigated by directly measuring activity (locomotion) and body temperatures of free-ranging animals by radiotelemetry, and by measuring standard metabolic rate (over a range of body temperatures) and activity metabolism in the laboratory. Seasonal differences in the activity and energetics were found in these goannas despite similar, high daytime temperatures throughout the year in tropical Australia. Periods of inactivity were associated with the dry times of the year, but the onset of this period of inactivity differed with respect to habitat even within the same species. Varanus gouldii, which inhabit woodlands only, were inactive during the dry and late dry seasons. V. panoptes that live in the woodland had a similar seasonal pattern of activity, but V. panoptes living near the floodplain of the South Alligator River had their highest levels of activity during the dry season when they walked long distances to forage at the receding edge of the floodplain. However, during the late dry season, after the floodplain had dried completely, they too became inactive. For V. gouldii, the rates of energy expenditure were 196 kJ kg–1 day–1 for active animals and 66 kJ kg–1 day–1 for inactive animals. The rates of water influx for these groups were respectively 50.7 and 19.5 ml kg–1 day–1. For V. panoptes, the rates of energy expenditure were 143 kJ kg–1 day–1 for active animals and 56 kJ kg–1 day–1 for inactive animals. The rates of water influx for these two groups were respectively 41.4 and 21.0 ml kg–1 day–1. We divided the daily energy expenditure into the proportion of energy that lizards used when in burrows, out of burrows but inactive, and in locomotion for the two species during the different seasons. The time spent in locomotion by V. panoptes during the dry season is extremely high for a reptile (mean of 3.5 h/day spent walking), and these results provide an ecological correlate to the high aerobic capacity found in laboratory measurements of some species of varanids. 相似文献
49.
Synopsis The ecological and evolutionary forces maintaining genetic polymorphism within populations is of continuing interest to evolutionary biologists. Male pygmy swordtails,Xiphophorus pygmaeus, are polymorphic at a Y-linked locus controlling body color. Fish with the + and cp alleles have blue bodies; those with the con allele have bright gold bodies. Male and female fish were tested in the laboratory to determine if there were any preferences for association with groups of male fish based on color. Single test fish were presented with two groups of males of different phenotypes, and times in which the test fish spent in proximity to each group were recorded. Males of different phenotypes showed no differences in preference, nor did phenotype of the males in the groups affect the behavior of the test fish. Females also showed no preference for males of a particular phenotype. Finally, female test fish showed no preference for groups containing a male with the rare phenotype compared to a group containing all males of the same phenotype. 相似文献
50.
Weed species and weed communities 总被引:3,自引:0,他引:3
Wolfgang Holzner 《Plant Ecology》1978,38(1):13-20
Summary With weeds as with many plant species the main or first level factor determining the area of distribution is a (complex) climatic one. As they have an artificially enlarged area of distribution, they have a huge border area (in an ecological sense), where the climate is not optimal for them, and where they have a narrow ecological and sociological amplitude and are especially sensitive to some measures of modern intensified agriculture. In their northern border areas species of southern origin are restricted to calcarcous substrates and to agrestal and finally ruderal communities, while in their optimal climate they are indifferent to that soil factor and able to compete with other species even in natural vegetation types. Species presumably of origin in atlantic areas are restricted with increasing continentality to very poor and acid soils, as they cannot compete with other species on better sites any more, because of their physiological properties. Thus weed distribution demonstrates the complicated reaction of plant species to the complexes of soil-climatic factors and to the competition of other species. As far as weeds are concerned, species may be only relatively calciphilous, but genuinely calcifuge species, the control being climatic in the former case and physiological in the second.The measures of modern agriculture bring about a gradual extinction of sensitive species from the limit of their range towards their centre of distribution, where they can find refuge habitats in the natural vegetation. The sensitivity of such species (also against herbicides) seems to increase towards their limits. Resistant species occur with increasing densities after the removal of their competitors. In addition, they are able to enlarge their area and to invade sites, where they had not been able to compete before, or sites where they could not previously bear the environmental conditions together with the competition of the rich weed flora.As the complex climatic gradients responsible for the ranges of weed species show smooth transitions, the alteration of species composition in weed communities is also a gradual one. This is one of the problems of weed phytosociology briefly discussed.Nomenclature follows Ehrendorfer (1973), Phytosociological units according to Westhoff & Den Held (1969).Contribution to the Symposium on Plant Species and Plant communities, held at Nijmegen, 11–12 November 1976, on the occasion of the 60th birthday of Professor Victor Westhoff.Field studies were partly supported by a grant of the Austrian Federal Ministry of Agriculture and Forestry. 相似文献