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121.
122.
FRANK CLARK DEREK DEADMAN MALCOLM GREENWOOD KIM SøHOLT LARS EN 《Medical and veterinary entomology》1997,11(3):213-216
Abstract Circadian rhythm in newly emerged individuals of the Red Squirrel ( Scuirus vulgaris ) flea C.s. sciurorum was studied in a constant environment, using an insect activity monitor. Trials were run over 7 days using two start times (08.00 and 17.00 hours). The results show that, regardless of start time, the fleas display a 24 h activity rhythm. The presence of a rhythm under constant conditions gives a strong indication that C. s.sciurorum has a self-sustaining clock which is started by disturbance and is most likely to be linked to host activity patterns. 相似文献
123.
LARS BERN 《Freshwater Biology》1994,32(1):105-112
1. Preferences for particles over a broad size range were assessed in four crustacean zooplankton species under field conditions. The particles employed were six spherical algae with diameters of 2, 6, 13, 19, 38 and 61 μm. 2. Diaphanosoma brachyurum and Daphnia cucullata preferred the two smallest particles, Chydorus sphaericus the three smallest and Eudiaptomus gracilis the 19 μm particle. 3. These size preferences agree well with earlier determinations based on seston particles in the same lake, indicating consistent size preferences by these species over a broad size range. 相似文献
124.
LARS KAMP-NIELSEN 《Physiologia plantarum》1971,24(3):556-561
The effect of mercury ions on the photosynthesis and growth of Chlorella pyrenoidosa in a balanced medium has been studied and compared with the effect of copper. In many ways Hg treated algae behave like algae treated with Cu in concentrations of the same molarity, but important deviations occur. Hg acts at a lower and in a more narrow range of concentrations than does Cu due to a more specific binding. The depressing effect of Hg is not counteracted by other cations such as potassium and sodium, and iron has only a slight effect. Cell division is stopped after Hg addition and there is no accumulation of assimilation products. On the contrary the cells become pale yellow. Preliminary studies indicate a light-independent leakage in the cytoplasmatic membrane leading to an outflow of potassium ions. This is the primary action of both Hg and Cu poisoning, but the leakage does not seem to be correlated with the decrease of photosynthesis. After a lapse of time — dependent on the mercury/cell concentration ratio — a detoxication takes place probably due to the binding of Hg to “insensitive sites” in the cells. Probable mechanisms for the action of Hg on photosynthesis and growth are discussed. 相似文献
125.
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127.
CHRISTOPHER R. BARNES LARS E. FAHREUS 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1975,8(2):133-149
Ordovician conodontophorid distribution, paleogeography, paleoclimate, and global tectonics strongly support the existence of one biogeographic conodontophorid province, largely restricted to equatorial regions and characterized by raised salinity and temperature. This Midcontinent Province is recognized in North America, Australia, and Siberia. The same data indicate that in other areas the North Atlantic Province represents a normal-marine, virtually cosmopolitan fauna. In both provinces, communities are recognized that show a lateral segregation, strongly indicating that the majority of Ordovician conodontophorids were benthic or nektobenthic. The only Ordovician pelagic forms we recognize are the simple cone genera that either lack, or have a simple, symmetry transition series. It appears possible to correlate certain evolutionary changes in the conodont apparatus with changes in preferred habitat. 相似文献
128.
LARS WERDELIN 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1994,27(2):110-110
Review of Smith, A. B. 1994: Symstematics and the Fossil Record: Documenting Evolutionary Patterns. 223 pp. Blackwell Scienfific Publications, Oxford 相似文献
129.
LARS BERN 《Freshwater Biology》1987,17(1):151-159
SUMMARY. 1. The grazing of [methyl-3 H]thymidine-labelled bacteria by zooplankton was studied in Lake Norrviken. Sweden.
2. Animals did not ingest bacteria attached to large colonies of the cyanobacterium Microcystis wesenbergii Kom. but small aggregates of hacteria and free bacteria were readily consumed.
3. Diaphanosoma brachyurum (Liévin). Daphnia cucullata Sars. and Daphnia galeata Sars grazed free bacteria more quickly than aggregates, but Endiaptomus gracilis (Sars), Chydorus sphaericus Müll. and Bosmi- na coregoni s.l. Baird grazed the aggregates more readily.
4. Filtering rate determinations varied from LA to 123 μl ind.−1 h − 1 for various species. 相似文献
2. Animals did not ingest bacteria attached to large colonies of the cyanobacterium Microcystis wesenbergii Kom. but small aggregates of hacteria and free bacteria were readily consumed.
3. Diaphanosoma brachyurum (Liévin). Daphnia cucullata Sars. and Daphnia galeata Sars grazed free bacteria more quickly than aggregates, but Endiaptomus gracilis (Sars), Chydorus sphaericus Müll. and Bosmi- na coregoni s.l. Baird grazed the aggregates more readily.
4. Filtering rate determinations varied from LA to 123 μl ind.
130.
LARS WERDELIN 《Journal of Zoology》1987,211(2):259-266
Supernumerary dental elements have been reported in Lynx lynx by several authors. These features have been given different evolutionary interpretations by different commentators. I note here that, since these features are absent in the plesiomorphic sister-groups of L. lynx , they represent a true evolutionary reversal. If they were simply a retention of an evolutionarily older phenotype, we should expect to see them developed in at least one plesiomorphic sister-group. Such development of a previously hidden character can occur if it is genetically linked to features selected for, until it becomes phenotypically expressed, whereupon selection can act on the character itself. Since Dollo's law, which is the theoretical issue behind the present discussion, is not a law, but a rule, and, like all rules based on probabilities, we should expect to find exceptions in the fossil record. Such exceptions are not rare, but few are as spectacular as the present one, in which the redeveloped feature is at least phenotypically identical with one which has been lost in the Felidae since the Miocene. 相似文献