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91.
A preliminary study of aquatic insect communities and leaf decomposition in acid streams near Dorset,Ontario 总被引:10,自引:10,他引:0
Some streams near Dorset in south-central Ontario suffer from acid precipitation via run-off and seepage from thin soils with little buffering capacity. A spring-summer survey of eight headwater streams revealed some characteristics of their insect communities which could be correlated with pH. The streams could be divided into three groups according to pH and community structure. In the most acid group (annual pH range 4.3–4.8), Ephemeroptera were absent from two streams although mature Leptophlebia were collected just after spring thaw from the most acid one (pH 4.3–4.5). One of these three streams also lacked Plecoptera but the others had two or three genera, all shredders. The second group of three streams (pH 5.0–6.3), with one exception, did support Ephemeroptera (3–4 genera) and Plecoptera (1–4 genera), most of the latter being shredders. In all six of these acid streams, Trichoptera were more diverse and more dense than Ephemeroptera and Plecoptera; again, shredders were clearly dominant, especially the limnephilid caddisfly, Frenesia difficilis (Walker). These six streams also had similar chironomid communities (densities were an order of magnitude higher than other insects). Dominance by Chironomini and abundant Tanypodinae typified the most acid streams. In contrast, the two streams in the third group (pH 5.3–6.7) had richer and more balanced communities in general with relatively fewer shredders (no Frenesia), more collectors, and fewer Chironomini and Tanypodinae. As a field experiment showed that autumn-shed leaves decomposed more slowly in acid than in non-acid streams, summer-growing shredders may benefit from the pulse of acidity at snowmelt. 相似文献
92.
The hair density of free-ranging Japanese monkeys (Macaca fuscata fuscata) living in three different areas was investigated. The Japanese monkeys had thicker hair than other macaques. The hair density
in the Japanese monkeys varied with locality: the northern monkeys had thicker hair than the southern ones. The density did
not vary markedly with age up to 3 years of age, but then decreased gradually up to adult age (≧7 years old). The remarkable
growth of the trunk suggested that the total number of hairs increased with age, especially during the period as a juvenile. 相似文献
93.
Steinar Solberg Tor Larsen Leif Jørgensen 《In vitro cellular & developmental biology. Plant》1985,21(11):612-616
Summary This study examined whether nonconfluent endothelial cell cultures reacted differently than confluent ones toward thrombin-stimulated
platelets or a heparinized salt solution. The adherence to the endothelial cell cultures of51Cr-labeled human platelets stimulated at different thrombin concentrations was studied. There was significantly higher adherence
of stimulated platelets to nonconfluent cultures compared with confluent ones. This was confirmed by scanning electron microscopy,
which also revealed a tendency for the platelets to adhere at the cell periphery. Electron microscopy also showed that thrombin-stimulated
platelets induced endothelial cell contraction. Part of the peripheral endothelial cell surface toward the bottom of the culture
dish was inverted, facing the lumen of the dish. This phenomenon was particularly seen in nonconfluent cultures. When51Cr-labeled endothelial cultures were incubated with a mildly injurious fluid as heparinized sodium acetate and 20% serum,
at 20° C for 30 min, the nonconfluent cultures showed significantly more cell detachment and release of51Cr than the confluent ones. We conclude that under the conditions of the present experiments there are differences in the
reactivity of confluent and nonconfluent endothelial cell cultures. These differences probably reflect biological dissimilarities.
In experiments where properties of cultured endothelium are studied, care should be taken that the degree of confluency is
standardized. 相似文献
94.
The composition and distribution of the macroinvertebrate fauna of the shallow part of De Gijster, a medium sized water storage lake in The Netherlands, has been studied during 1984. The numerous individuals collected belong mainly to the Oligochaeta, Diptera (Chironomidae larvae) and Mollusca. Amongst them are elements of both the former polder fauna and the river fauna. A quantitative analysis revealed data on the horizontal distribution of several taxa within the lake as well as data on the influence of the lifecycle of some taxa on the annual composition of the fauna. 相似文献
95.
“Bulk density” and “dry-matter content” are useful indices of dry-matter accumulation in plant organs. A theoretical equation
describing the relationship between these two indices was put forward. To examine the reliability of this equation, the seasonal
changes of these two indices were investigated in the leaves and stems of different ages ofAucuba japonica. In each organ both indices varied seasonally almost parallel to each other, but the seasonal changes of dry-matter content
were less obvious than those of bulk density. The observed bulk density was always larger than that calculated from the observed
dry-matter content by the theoretical equation. A drying experiment showed that this discrepancy was caused by the decrement
of the volume of the plant material by water loss during the period from the weight measurement to the volume measurement.
When the water loss was negligible, the equation described well the relationships between the two indices of the experimental
materials. It was also shown that this equation was useful for the estimation of the amount of air space in plant materials. 相似文献
96.
97.
边缘性缺乏抗坏血酸之豚鼠,于三周内其肝脏及小肠粘膜3-羟-3-甲基戊二酰辅酶A还原酶(HMGR)活力均下降到原有水平的50%,但肝脏胆固醇7α-羟化酶活力尚无显著性改变。坏血病豚鼠(三周内)上述几种酶活力都下降至原有水平的50%左右。豚鼠摄取抗坏血酸不足,其血清总胆固醇浓度显著增加,而血清高密度脂蛋自胆固醇浓度显著减少,其改变程度与抗坏血酸缺乏状况一致。 相似文献
98.
Simple mathematical models are formulated to describe density independent and density dependent dispersal. These models clarify
hypotheses of density dependence and may be manipulated easily to suit particular applications. The models demonstrate that
the initial composition of a species aggregate must be controlled before valid conclusions can be drawn about the density
dependency of the aggregate's dispersal. Stochastic models of emigration are derived to assess the power of particular experimental
designs and statistical techniques to discriminate a known form of density dependent emigration.
Contribution No. 369, Great Lakes Research Division, University of Michigan
Contribution No. 369, Great Lakes Research Division, University of Michigan 相似文献
99.
100.
Teresa de Sa E Melo Patrice Morlière Sonia Goldstein René Santus Louis Dubertret Dominique Lagrange 《Biochemical and biophysical research communications》1984,120(2):670-676
5-methoxypsoralen (5-MOP) binds to human serum low density lipoproteins (LDL) according to a two-step process. Scatchard analysis of the first step yields K = 1.4 × 105 M?1 and 4 binding sites. It involves the LDL apoprotein. The second step corresponds to a solubilization, in the lipidic core, of ? 45 molecules of 5MOP per LDL molecule. It is accompanied by a large blue shift of the 5MOP fluorescence. The ability of LDL to bind 5MOP and to carry it into various cells may explain some biological effects sometimes encountered during PUVA therapy. 相似文献