Photo-dependent population dynamics of Stentor coeruleus and its consumption of Colpidium striatum

The predatory protozoan Stentor coeruleus Ehrenberg, 1830 is known to show photosensitivity and photodispersion, avoiding regions of high light intensity as an antipredation strategy. This physiological and behavioral response to light likely has demographic consequences. We manipulated light intensity to determine population responses of S. coeruleus and the resulting effects on its prey Colpidium striatum Stokes, 1886. We show that S. coeruleus maintained the highest population density under ambient light levels and low densities under both high and no light treatments. The results from the no light treatment were surprising because little work has been done on possible important behavioral and physiological processes cued by light. These results add power to the use of S. coeruleus as a model predator system to test ecological dynamics and processes associated with predation.

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Substrate Acidification by Geranium: Light Effects and Phosphorus Uptake

Journal of the American Society for Horticultural Science ◽

10.21273/jashs.133.4.515 ◽

2008 ◽

Vol 133 (4) ◽

pp. 515-520 ◽

Cited By ~ 2

Author(s):

Matthew D. Taylor ◽

Paul V. Nelson ◽

Jonathan M. Frantz

Keyword(s):

Light Intensity ◽

Phosphorus Uptake ◽

Dry Weight ◽

P Uptake ◽

High Light Intensity ◽

High Light ◽

P Deficiency ◽

Light Levels ◽

Direct Light ◽

Substrate Ph

Sudden pH decline (SPD) describes the situation where crops growing at an appropriate pH rapidly (within 1–2 weeks) cause the substrate pH to shift downward one to two units. ‘Designer Dark Red’ geraniums (Pelargonium ×hortorum Bailey) were grown in three experiments to assess possible effects of light on SPD and phosphorous (P) uptake. The first experiment tested the effect of four light intensities (105, 210, 575, and 1020 ± 25 μmol·m−2·s−1) on substrate acidification. At 63 days, substrate pH declined from 6.0 to 4.8 as light intensity increased. Tissue P of plants grown at the highest two light levels was extremely low (0.10%–0.14% of dry weight). P stress has been reported to cause acidification. Because plants in the two lowest light treatments had adequate P, it was not possible to determine if the drop in substrate pH was a direct light effect or a combination of light and P. The second experiment used a factorial combination of the three highest light levels from Expt. 1 and five preplant P rates (0, 0.065, 0.13, 0.26, or 0.52 g·L−1 substrate) to assess this question. When tissue P concentrations were deficient, pH decreased by 0.6 to 1.0 pH units within 2 weeks and deficiency occurred more often with high light intensity. These data indicated that P deficiency caused substrate acidification and indicated the possibility that P uptake was suppressed by high light intensity. The third experiment was conducted in hydroponics to determine the direct effect of high light intensity on P uptake. In this experiment, cumulative P uptake per gram root and the rate of P uptake per gram root per day both decreased 20% when light intensity increased from 500 to 1100 μmol·m−2·s−1. It is clear from this study that P deficiency causes geraniums to acidify the substrate and that high light suppresses P uptake.

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f. The pattern reversed between irrdiances 475 to 810 jimol m s" with a definite increase in cytochrome f and no change in rubisco. In fact, such a relationship between growth light intensity and cytochrome f content was shown by Reddy et al., (1983) in Sorghum cultivars, where the high levels of cytochrome f were associated with high light intensity between 900 and 1800 |iE m-s-, while it decreased in low light levels. The study

Photosynthesis ◽

10.1201/9781482294446-16 ◽

2004 ◽

pp. 111-112

Keyword(s):

Light Intensity ◽

High Light Intensity ◽

High Light ◽

Cytochrome F ◽

Low Light ◽

Light Levels

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Time Estimation in Humans: Effects of Ambient Illumination and Sex

Perceptual and Motor Skills ◽

10.2466/pms.1981.53.3.747 ◽

1981 ◽

Vol 53 (3) ◽

pp. 747-750 ◽

Cited By ~ 26

Author(s):

Eugene R. Delay ◽

Maryjo A. Richardson

Keyword(s):

College Students ◽

Light Intensity ◽

Analysis Of Variance ◽

Time Estimation ◽

High Light Intensity ◽

High Light ◽

Female College Students ◽

Ambient Illumination ◽

Light Levels ◽

Arousal Theory

7 male and 7 female college students made estimations of 15-sec. intervals in conditions of dark, low and high ambient illumination. Analysis of variance showed significant effects of illumination and illumination by sex. Increased light levels shortened time estimation except for males under high light intensity. Results are discussed in terms of arousal theory and the relevance of these factors in research on time estimation.

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