scholarly journals Disentangling the Relative Strength of Niche Competition from Grazing-Induced Phytoplankton Mortality

2016 ◽  
Author(s):  
Stephen J. Beckett ◽  
Joshua S. Weitz
Keyword(s):  
Relative Strength ◽  
Dilution Method ◽  
Mortality Process ◽  
Grazing Mortality ◽  
Dilution Experiments ◽  
Principal Tool ◽  
Niche Competition ◽  
Mortality Estimates ◽  
Microzooplankton Grazing

AbstractThe dilution method is the principal tool used to infer in situ microzooplankton grazing rates. However, grazing is the only mortality process considered in the theoretical model underlying the interpretation of dilution method experiments. Here we evaluate the robustness of mortality estimates inferred from dilution experiments when there is concurrent niche competition amongst phytoplankton. Using a combination of mathematical analysis and numerical simulations, we find that grazing rates may be overestimated – the degree of overestimation is related to the importance of niche competition relative to microzooplankton grazing. In response, we propose a conceptual method to disentangle the effects of niche competition and grazing by diluting out microzooplankton, but not phytoplankton. Our theoretical results suggest this revised “Z-dilution” method can robustly infer grazing mortality, regardless of the dominant phytoplankton mortality driver in our system. Further, we show it is possible to independently estimate both grazing mortality and niche competition if the classical and Z-dilution methods can be used in tandem. We discuss the significance of these results for quantifying phytoplankton mortality rates; and the feasibility of using the Z-dilution method in practice.

scholarly journals Microzooplankton grazing rate in Ensenada of La Paz, B.C.S., Mexico

2017 ◽  
Vol 41 (3) ◽  
pp. 545-557
Author(s):  
Gabriela María Esqueda-Escárcega ◽  
Sergio Hernández-Trujillo ◽  
Gerardo Aceves-Medina ◽  
Sonia Futema-Jiménez ◽  
José Reyes Hernández-Alfonso
Keyword(s):  
Spatial Scales ◽  
Grazing Rate ◽  
Grazing Pressure ◽  
Phytoplankton Growth ◽  
Dilution Method ◽  
Sampling Station ◽  
La Paz ◽  
The Relationship ◽  
Microzooplankton Grazing

Phytoplankton growth and microzooplankton grazing rates in situ, were studied in a fixed sampling station from October 2007 to August 2008, at the Ensenada de La Paz, Mexico, using the dilution method. The apparent growth rate of phytoplankton was higher in December (1.33 d-1) and lower in October (0.35 d-1). The grazing rate was highest in April (0.86 d-1) and minimum in February and August (0.38 d-1). Grazing pressure, measured as the percentage of potential production removed (% PPR) varied between 28 and 76%. The relationship between phytoplankton growth and grazing rate indicates that chlorophyll-a production is consumed by approximately 50%, involving other processes that cause mortality of phytoplankton, as sedimentation rate and mesozooplankton grazing. The finding of moderate grazing in autumn and a clear growth and consumption in the winter are features that require monitoring in larger temporal and spatial scales.

scholarly journals Strength and Cost Analysis of New Steel Sets as Roadway Support Project in Coal Mines

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Qinghai Li ◽  
Renshu Yang ◽  
Jingkai Li ◽  
He Wang ◽  
Zhijie Wen
Keyword(s):  
Coal Mines ◽  
High Strength ◽  
Relative Strength ◽  
Relative Cost ◽  
Soft Rocks ◽  
Deformation Control ◽  
Geological Conditions ◽  
Roadway Support ◽  
Critical Challenge

Roadway support in swelling soft rocks in coal mines has become a critical challenge in recent years. For deformation control in swelling soft rocks, high strength sets are preferred in sites. But high strength always means high costs. Therefore, higher strength sets with not too much cost will be more welcomed in situ. Based on this, three new sets, including a floor beam set, a roof + floor beams set, and a roof + floor beams + braces set, have been developed in the present research. Strength comparisons and costs comparisons have been conducted in this research. Results illustrate that compared with the original set, in the floor beam set, the relative strength of bottom corners reaches 2.964, while the relative cost reaches 1.294; compared with the original set, in the roof + floor beams set, the relative strength of the top arch reaches 2.345, while the relative strength of bottom corners reaches 2.964, and the relative cost reaches 1.568; and compared with the original set, in the roof + floor beams + braces set, the relative strength of the top arch reaches 2.635, and the relative strength of bottom corners reaches 5.905, but the relative cost reaches 1.930. Floor beam set and roof + floor beams set illustrate higher strength and not too higher costs than the original set. Although the roof + floor beams + braces set exhibit much higher strength, they also demonstrate much higher costs than the original set. These new sets can be chosen according to different geological conditions in situ.

scholarly journals Estimating microzooplankton grazing half-saturation constants from dilution experiments with nonlinear feeding kinetics

2014 ◽  
Vol 59 (3) ◽  
pp. 639-644 ◽  
Author(s):  
Bingzhang Chen ◽  
Edward A. Laws ◽  
Hongbin Liu ◽  
Bangqin Huang
Keyword(s):  
Dilution Experiments ◽  
Microzooplankton Grazing

scholarly journals Growth rates of common pelagic ciliates in a highly eutrophic lake measured with a modified dilution method

2016 ◽  
Vol 45 (2) ◽  
Author(s):  
Krzysztof Rychert
Keyword(s):  
Growth Rates ◽  
Eutrophic Lake ◽  
Dilution Method ◽  
Size Fractionation ◽  
Natural Conditions ◽  
Fractionation Method ◽  
Dilution Experiments

AbstractThe growth rates of ciliates estimated under natural conditions with the widely used size fractionation method are much lower than those observed in cultures. However, recent studies performed with a modified dilution method demonstrated that the size fractionation method underestimates the ciliate growth, because it does not remove predators of the same size as the organisms studied. Thus, it is still unresolved whether ciliates are food-limited in different systems and whether their growth rates are indeed lower than those in cultures. This study was conducted in highly eutrophic Lake Gardno using a modified dilution method. Each time, two dilution experiments were performed (around noon and around midnight). Four small, common ciliates from the genera

scholarly journals Reality checks on microbial food web interactions in dilution experiments: Responses to the comments of Dolan and McKeon

2004 ◽  
Vol 1 (1) ◽  
pp. 65-76 ◽  
Author(s):  
M. R. Landry ◽  
A. Calbet
Keyword(s):  
Direct Evidence ◽  
Nutrient Recycling ◽  
Grazing Rate ◽  
Open Ocean ◽  
Food Web Interactions ◽  
Resource Limited ◽  
Dilution Experiments ◽  
Dilution Effects ◽  
Microzooplankton Grazing ◽  
Global Extrapolation

Abstract. Microzooplankton grazing rate estimates by the dilution approach have recently been criticized as systematically biased in the direction of being overestimates of actual rates in nature, and particularly in the open oceans. This argument is based on observed mortality responses of ciliated protozoa to reduced food in several coastal experiments and a global extrapolation which assumes that all grazing in all ocean systems scales to the abundance of ciliates. We suggest that these conclusions are unrealistic on several counts: they do not account for community differences in open ocean and coastal systems; they ignore experimental direct evidence supporting dilution rate estimates in the open oceans, and they discount dilution effects on mortality as well as growth in multi-layered, open-ocean food webs. High microzooplankton grazing rates in open-ocean systems are consistent with current views on export fluxes and trophic transfers. More importantly, significantly lower rates would fail to account for the efficient nutrient recycling requirements of these resource-limited and rapid-turnover communities.

Progression of an inductive signal activates sporulation in Dictyostelium discoideum

Development ◽  
1994 ◽  
Vol 120 (10) ◽  
pp. 2891-2900 ◽  
Author(s):  
D.L. Richardson ◽  
W.F. Loomis ◽  
A.R. Kimmel
Keyword(s):  
Transcriptional Start Site ◽  
Relative Strength ◽  
Spatial Gradient ◽  
Intracellular Camp ◽  
Promoter Strength ◽  
Dependent Protein ◽  
Early Developmental ◽  
Beta Galactosidase ◽  
Inductive Signal

spiA, a marker for sporulation, is expressed during the culmination stage of Dictyostelium development, when the mass of prespore cells has moved partly up the newly formed stalk. Strains containing a full-length spiA promoter/lacZ fusion were stained for beta-galactosidase activity at intervals during development. The results indicate that expression of spiA initiates in prespore cells at the prestalk/prespore boundary (near the apex) and extends downward into the prespore mass as culmination continues. A spatial gradient of staining expands from the top of the prespore mass and intensifies until the front of activation reaches the bottom, whereupon the entire region stains darkly. The spiA promoter can be deleted to within 301 bp of the transcriptional start site with no effect on the relative strength, timing or spatial localization of expression. Further 5′ deletions from −301 to −175 reduce promoter strength incrementally, although timing and spatial expression are not affected. Deletions to −159 and beyond result in inactive promoters. Treatment of early developmental structures with 8-Br-cAMP in situ activates the intracellular cAMP-dependent protein kinase (PKA) and precociously induces spiA expression and sporulation. The absence of an apparent gradient of staining in these structures suggest that PKA is equivalently activatable throughout the prespore region and that all prespore cells are competent to express spiA. Thus, we postulate that the pattern of expression of spiA reveals the progression of an inductive signal for sporulation and suggest that this signal may originate from the prestalk cells at the apex.

scholarly journals Conserving original in situ diversity in microzooplankton grazing set-ups

2010 ◽  
Vol 3 ◽  
Author(s):  
Martin Günter Joachim Löder ◽  
Nicole Aberle ◽  
Christine Klaas ◽  
Alexandra Claudia Kraberg ◽  
Karen Helen Wiltshire
Keyword(s):  
Microzooplankton Grazing

scholarly journals Effect of Relative Strength of Two Networks on the Internal Fracture Process of Double Network Hydrogels As Revealed by in Situ Small-Angle X-ray Scattering

2020 ◽  
Vol 53 (4) ◽  
pp. 1154-1163 ◽  
Author(s):  
Kazuki Fukao ◽  
Tasuku Nakajima ◽  
Takayuki Nonoyama ◽  
Takayuki Kurokawa ◽  
Takahiko Kawai ◽  
...  
Keyword(s):  
Small Angle ◽  
Fracture Process ◽  
Relative Strength ◽  
Double Network ◽  
X Ray ◽  
X Ray Scattering ◽  
Internal Fracture ◽  
Ray Scattering
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