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  • 60-Hz electromagnetic fields  (1)
  • Arenaria  (1)
  • Components analysis  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Plant ecology 37 (1978), S. 129-140 
    ISSN: 1573-5052
    Keywords: Bray-Curtis ; Coenocline ; Components analysis ; Non-linear ; Ordination ; Polynomial
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Recent studies suggest problems resulting from using essentially linear ordination techniques on non-linear ecological data. A new non-linear method, termed polynomial ordination, was developed in response to these problems. Its effectiveness was compared to that of two standard techniques, Bray-Curtis ordination and principal components analysis, by testing with both simulated and field data. The original species axes are resolved into their principal components. If significant curvilinear relationships between principal components are present, new axes are defined along these curves. The coordinates of positions of the sample points along the axes are then determined. Using simulated data, the coordinates of the sample points on the first axis were compared to their coordinates on the original simulated gradient. Two statistics were used to evaluate how well the gradient was recovered. Of the methods tested, polynomial ordination best placed the samples in the correct order, although principal components analysis better recovered their absolute positions. Ordinations of vegetation samples along a Sonoran Desert bajada by all three methods suggested that soil particle size is a major environmental gradient affecting the species composition of the vegetation.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Plant ecology 80 (1989), S. 25-35 
    ISSN: 1573-5052
    Keywords: Arenaria ; Competitive release ; Dominance shift ; Drought ; Sedum ; Senecio ; Southeastern USA ; Viguiera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Permanent quadrats in granite outcrop plant communities allowed us to monitor seasonal variation and annual fluctuation in community structure. Seasonal species turn-over was significant in communities on shallow soil, but not in communities on deeper soil where seasonal dominance shifts were common. Exceptional meteorological events appeared to mediate phenomena of competitive release in some island communities. A decrease in the abundance of Arenaria uniflora in Lichen-annual island communities, following a spring drought, was correlated with an increase in the abundance of Sedum smallii, a shallower-soil species. Richness in Annual-perennial island communities was higher in spring 1985 than in 1984 or 1986, and this occurred as the dominant species, Senecio tomentosus, temporarily declined in importance following a severe drought in late summer 1984. Significant annual fluctuation in the cover of Viguiera porteri could also be related to variations in the summer precipitation regime. Overall, plant responses to drought were individualistic and depended largely on the timing of these meteorological events in relation to the life-stages and/or the physiological status of the plants.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 11 (1990), S. 105-116 
    ISSN: 0197-8462
    Keywords: rats ; 60-Hz electromagnetic fields ; perinatal exposure ; conditioning ; altered operant behavior ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Rats were sham exposed or exposed perinatally to a 60-Hz electromagnetic field, 22 days in utero and the first 8 days post partum. Each of the 30 once-daily exposures was 20 h in duration. The electric component of the field was vertical 30 kV/m rms, and the magnetic field component was 100 μTG rms. Later, as adults, male rats were trained to emit an operant response when reinforced with food on a multiple, random-interval schedule. Exposed rats (N = 21) gradually came to respond at significantly lower rates than did sham-exposed controls (N = 20). This finding was confirmed and extended in a second, independently performed experiment. After a sequence including operant conditioning followed by experimental extinction of responding and then by a suspension of conditioning and finally by more than a month of reconditioning, slower rates of responding were found to persist in the adult animals. The evidence of altered behavior several months after combined, fetal-neonatal exposure to an electromagnetic field presents an interesting contrast with other findings: Field-exposed rats did not differ from sham-exposed rats in terms of body mass, physical appearance, grossly observed activity level, or incidence of disease.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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