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71.
Seabird associations in Pacific equatorial waters 总被引:2,自引:0,他引:2
Seabirds were counted along the same cruise tracks in the eastern tropical Pacific (10°øN-10°øS and 140°ø-90°øW) each spring and autumn for 8 years, 1984–1991. During spring, three species groups were apparent among eight species seen in five or more years: (1) Leach's Storm-petrel Oceanodroma leucorhoa and Wedge-rumped Storm-petrel Oceanodroma tethys , which feed on neuston by surface seizing; (2) Black-winged Petrel Pterodroma nigripennis and White-winged Petrel Pterodroma leucoptera , which feed on neuston and micronekton by surface seizing; (3) Juan Fernandez Petrel Pterodroma externa , Wedge-tailed Shearwater Puffinus pacificus and Sooty Tern Sterna fuscata , which feed on micronekton driven to the surface by foraging tuna. During autumn, only one group was identified from the seven species seen in five or more years: Leach's Storm-petrel associated with either Wedge-rumped Storm-petrel or Juan Fernandez Petrel and/or White-winged Petrel. Annual variability in assemblage composition was more extreme in the autumn and thus was similar to variation in physical and biological factors linked to the El Niño-Southern Oscillation cycle. 相似文献
72.
DAVID R. KOBLUK MICHAEL J. RISK 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1977,10(2):135-143
Algal borings in the shells of the articulate brachiopods Plaesiomys subquadrata (Hall) and Hebertella sinuata (Hall) from the Richmond Formation of Ohio are empty, or partially to entirely filled with pyrite. The pyrite occurs as single framboids and other crystal forms, or in chains filling the bores. The borings provide some insight into the early diagenetic history of the Richmond sediments near Cincinnati. Pyritization probably occurred within a few years, only a short distance (a few centimeters) below the sediment surface through the activities of sulfur-reducing bacteria. Pyrite precipitated around a nucleus such as a bacterium or algal cell, or developed within an organic structure such as an algal cell or organic membrane. 相似文献
73.
74.
DAVID A. BROCK 《Freshwater Biology》1980,10(3):239-250
SUMMARY. The pattern of cyclomorphosis of Bosmina longirostris was followed over a 21-month period in Lake Travis, Texas. Appreciable variation was observed in body size and in the lengths of antennules and mucrones. Electrophoresis of clonal isolates collected over the period of study showed a seasonal cycle in esterase phenotypes. A definite association was demonstrated between the esterase phenotypes and morphologies of these clonal isolates. Individuals of one esterase phenotype were usually large and long-featured, whereas individuals of the other esterase phenotypes were smaller, with short features. The association of morphology and esterase phenotypes from laboratory experiments corresponded to the association observed in field samples. These results support the hypothesis that the cyclomorphosis of Lake Travis Bosmina involves a succession of clones as well as phenotypic plasticity. 相似文献
75.
SUMMARY. A method is described for isolating and sterilizing fronds of Lemnà gibba, L. minor, L. trisulca, L. polyrrhiza and Wolffia arrhiza , employing enrichment followed by sodium hypochlorite treatment. The method enables about 4% of the total number of treated fronds to be used as initiators of clonal cultures in which bacteria responding to organic enrichment and algae are excluded. Appropriate growth media, culture vessels and culture conditions are detailed. 相似文献
76.
HEIMO G. POSAMENTIER STEVE S. CLARK DAVID L. HAIN HARRY F. RECHER 《Austral ecology》1981,6(2):165-175
Changes in coastal heath vegetation were measured for 6 years following a wildfire and the data compared with the pre-fire vegetation. For the first 2 years changes were related to time; after that environmental factors dominated the process of regeneration. During the first 4 years plant species spread rapidly and maximum species diversity per plot was reached 4 years after the fire. About the same time many species consolidated their position in the community; this being shown by cover levels greater than before the fire for some species. Six years after the fire the vegetation is still dynamic and very different when compared with the heath before burning. 相似文献
77.
Responses of seven Phaseolus genotypes to the four auxins picloram, 2,4-D, NAA and 1AA, in tissue cultures, were examined. Callus growth was promoted by picloram and the range of effective concentrations for most genotypes was broad. The auxin 2,4-D also enhanced callus growth, but the range of optimal concentrations was markedly narrower than that of picloram. NAA when supplied at relatively high concentrations gave good growth. IAA was ineffective in supporting callus growth. The differences in 2,4-D concentrations required for optimal growth and the differential responses to low concentrations (0.04–1.25 μM) of picloram between several genotypes tested were large. These genotypic variations in auxin responses were repeatable and may thus reflect genetic differences. 相似文献
78.
Radial estimates and the test for sphericity 总被引:1,自引:0,他引:1
79.
Partial residuals for the proportional hazards regression model 总被引:34,自引:0,他引:34
80.
DAVID J. PATTERSON 《The Journal of eukaryotic microbiology》1983,30(2):301-307
The ultrastructural organization of Nuclearia moebiusi is described. The organism has filose pseudopodia without supportive microtubules; it has mitochondria with flattened cristae, lacks extrusomes, microtubule-organizing centers, and cytoplasmic microtubules. During cell division, microtubules appear only within the nucleus, and reorganization of the nuclear envelope occurs late in the nuclear division cycle. Ultrastructural studies reveal that Nuclearia spp. have a pattern of cellular organization distinct from that of other amoebae. Comparison of ultrastructural features suggests that this organism is only distantly related to other rhizopod amoebae (including other filose amoebae) and to the heliozoa. 相似文献