Effect of size-dependent muskrat (Ondatra zibethica) predation on the spatial distribution of a freshwater clam, Anodonta piscinalis Nilsson (Unionidae, Bivalvia)

1995 ◽  
Vol 73 (6) ◽  
pp. 1085-1094 ◽  
Author(s):  
Jukka Jokela ◽  
Pia Mutikainen
Keyword(s):  
Spatial Distribution ◽  
Central Place ◽  
Selection Gradient ◽  
Freshwater Clam ◽  
Size Dependent ◽  
Evolutionary Response ◽  
Spatial Refuge ◽  
Mean Size ◽  
Study Sites ◽  
Anodonta Piscinalis

We studied the effect of central-place foraging by muskrats on the spatial distribution of freshwater clam Anodonta piscinalis. We also analysed the prey-size preference of muskrats. We collected A. piscinalis shells from four muskrat middens representing different prey populations and sampled the clam populations quantitatively. Muskrats had clear effects on the spatial distribution of the clams. At all study sites the area close to shore had no clams. The width of the empty area was correlated with the number of shells found in the muskrat midden. The density of clams decreased and their mean size increased with the distance from muskrat midden at two of the sites. Muskrats did not prey on clams smaller than 50 mm. Muskrats preferred 60- to 70-mm clams at three of the sites and 85- to 90-mm clams at the fourth. In an analysis conducted using ages, a selection gradient on the growth rate of clams was found for three of the study populations. However, spatial refuge from predation and inconsistency of selection may slow down or counterbalance the evolutionary response to predation.

scholarly journals Scaling gene expression for cell size control and senescence in Saccharomyces cerevisiae

2020 ◽  
Author(s):  
Yuping Chen ◽  
Bruce Futcher
Keyword(s):  
Gene Expression ◽  
Cell Size ◽  
Size Control ◽  
Gene Expression Program ◽  
Set Point ◽  
Size Dependent ◽  
Large Size ◽  
Mean Size ◽  
Almost All ◽  
Expression Program

Abstract Cells divide with appropriate frequency by coupling division to growth—that is, cells divide only when they have grown sufficiently large. This process is poorly understood, but has been studied using cell size mutants. In principle, mutations affecting cell size could affect the mean size (“set-point” mutants), or they could affect the variability of sizes (“homeostasis” mutants). In practice, almost all known size mutants affect set-point, with little effect on size homeostasis. One model for size-dependent division depends on a size-dependent gene expression program: Activators of cell division are over-expressed at larger and larger sizes, while inhibitors are under-expressed. At sufficiently large size, activators overcome inhibitors, and the cell divides. Amounts of activators and inhibitors determine the set-point, but the gene expression program (the rate at which expression changes with cell size) determines the breadth of the size distribution (homeostasis). In this model, set-point mutants identify cell cycle activators and inhibitors, while homeostasis mutants identify regulators that couple expression of activators and inhibitors to size. We consider recent results suggesting that increased cell size causes senescence, and suggest that at very large sizes, an excess of DNA binding proteins leads to size induced senescence.

Theoretical and Experimental Study of Shunt Effects in Thin-film Photovoltaics

2001 ◽  
Vol 668 ◽  
Author(s):  
V. G. Karpov ◽  
G. Rich ◽  
D. H. Rose ◽  
A. V. Subashiev ◽  
G. Dorer
Keyword(s):  
Thin Film ◽  
Experimental Study ◽  
Spatial Distribution ◽  
Electrical Potential ◽  
Screening Length ◽  
System Parameters ◽  
Size Dependent ◽  
Thin Film Photovoltaics ◽  
The Relationship ◽  
Good Agreement

ABSTRACTWe present an analytical model that quantitatively describes the physics behind shunting in thin-film photovoltaics and predicts size-dependent effects in the I/V characteristics of solar cells. The model consists of an array of micro-diodes and shunt in parallel between the two electrodes, one of which mimics the TCO and has a finite resistance. We introduce the concept of the screening length L, over which the shunt affects the electrical potential of the system. The nature of this screening is that the system generates currents in response to the point perturbation caused by the shunt. L is expressed explicitly in terms of the system parameters. We find the spatial distribution of the electrical potential in the system and its I/V characteristics. The measured I/V characteristics depend on the relationship between the cell size l and L, being markedly different for the cases of small (l<<L) and large (l>>L) cells. This model is verified experimentally; good agreement is obtained.

Synthesis of Ferrite Nanoparticle and Ferrite-Gold Heterostructures

2010 ◽  
Vol 123-125 ◽  
pp. 251-255 ◽  
Author(s):  
Fang Hsin Lin ◽  
Reuy An Doong
Keyword(s):  
Au Nanoparticles ◽  
Reaction Conditions ◽  
Gold Nanocrystals ◽  
Size Dependent ◽  
Synthetic Procedure ◽  
Mean Size ◽  
Ferrite Nanoparticle ◽  
High Boiling Point ◽  
The Mean ◽  
Magnetite Nanocrystals

The synthesis of uniform and monodispersed magnetic and optical nanocrystals has received much attention in recent years due to the size-dependent physicochemical properties. In this study, we have demonstrated a general approach for the synthesis of size-tunable ferrite and gold nanocrystals and their nanocomposite. The monodispersed magnetite nanocrystals were obtained by thermal decomposition of iron-oleate complex in a high boiling point solvent in presence of oleylamine and oleic acid. The size of magnetite nanocrystal can be tuned from 7 – 11nm by changing the amount of iron-oleate complex. The other key parameters such as temperature, amount of capping agents, types of solvent were also discussed. This synthetic procedure could also apply to synthesis other type of ferrite nanocrystals. When Mn-acetate was partially substituted for iron-oleate in a 1:2 ratio in the same reaction conditions as in the synthesis of Fe3O4, monodispersed MnFe2O4 nanocrytals with 14nm could be obtained. Except those magnetic nanocrystals, we also synthesized various sizes of monodispersed gold nanocrystals by reducing HAuCl4 in presence of t-butylamine-borane and oleylamine. By varying the reaction temperature, the particle size could be well-tuned from 2nm to 8nm with the characteristic surface plasmon absorption between 510 and 520 nm. For Fe3O4/Au composite, it was prepared via the decomposition of iron-oleate over the surface of the Au nanoparticles. The mean size of the Fe3O4/Au nanocomposite was ∼17 nm which shows a saturation magnetization of 46.92 emu/g and absorption peak at 512nm. These composites with both magnetic and optical properties would make them very promising in the fields of biomedine and environment.

Structure and regeneration dynamics of three subtropical midmontane moist evergreen broad-leaved forests in southwestern China, with special reference to bamboo in the forest understories

2007 ◽  
Vol 37 (12) ◽  
pp. 2701-2714 ◽  
Author(s):  
Cindy Q. Tang ◽  
Tianxing Li ◽  
Xiaohong Zhu
Keyword(s):  
Tree Regeneration ◽  
Southwestern China ◽  
Structure And Dynamics ◽  
Seedling Bank ◽  
Canopy Trees ◽  
Mean Size ◽  
Bamboo Flowering ◽  
The Mean ◽  
Study Sites ◽  
Survival Of Seedlings

Two midmontane moist evergreen broad-leaved forests on the Ailao Mountains, Yunnan, and one on Mount Emei, Sichuan, southwestern China were studied to characterize the forest structure and dynamics as manifested in size, age, canopy gaps, regeneration modes, and the survival of seedlings. The most dominant canopy trees were species of Lithocarpus and Castanopsis of Fagaceae along with species of Machilus of Lauraceae and of Schima of Theaceae. The vertical structures of the forests were multilayered. All the canopy species had multimodal-shaped size and age distributions. In each forest of the study sites, the mean size of a canopy gap, caused mainly by the death of canopy trees, was smaller than 65 m2. No surviving seedlings of Fagaceae species were found in understories having bamboo with a coverage greater than 25% in any quadrat of the three forests. The poor seedling bank in the study forests is apparently due to the presence of bamboo in the understory. The tree regeneration may be synchronously related to the bamboo flowering event (interval approximately 55–60 years).

scholarly journals Spatial Patterns of Snow Distribution for Improved Earth System Modelling in the Arctic

2021 ◽  
Author(s):  
Katrina E. Bennett ◽  
Greta Miller ◽  
Robert Busey ◽  
Min Chen ◽  
Emma R. Lathrop ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Random Forest ◽  
Vegetation Index ◽  
Snow Water Equivalent ◽  
The Arctic ◽  
System Modelling ◽  
Earth System ◽  
Snow Distribution ◽  
Study Sites ◽  
Earth System Modelling

Abstract. The spatial distribution of snow plays a vital role in Arctic climate, hydrology, and ecology due to its fundamental influence on the water balance, thermal regimes, vegetation, and carbon flux. However, for earth system modelling, the spatial distribution of snow is not well understood, and therefore, it is not well modeled, which can lead to substantial uncertainties in snow cover representations. To capture key hydro-ecological controls on snow spatial distribution, we carried out intensive field studies over multiple years for two small (2017–2019, ~2.5 km2) sub-Arctic study sites located on the Seward Peninsula of Alaska. Using an intensive suite of field observations (> 22,000 data points), we developed simple models of spatial distribution of snow water equivalent (SWE) using factors such as topographic characteristics, vegetation characteristics based on greenness (normalized different vegetation index, NDVI), and a simple metric for approximating winds. The most successful model was the random forest using both study sites and all years, which was able to accurately capture the complexity and variability of snow characteristics across the sites. Approximately 86 % of the SWE distribution could be accounted for, on average, by the random forest model at the study sites. Factors that impacted year-to-year snow distribution included NDVI, elevation, and a metric to represent coarse microtopography (topographic position index, or TPI), while slope, wind, and fine microtopography factors were less important. The models were used to predict SWE at the locations through the study area and for all years. The characterization of the SWE spatial distribution patterns and the statistical relationships developed between SWE and its impacting factors will be used for the improvement of snow distribution modelling in the Department of Energy’s earth system model, and to improve understanding of hydrology, topography, and vegetation dynamics in the Arctic and sub-Arctic regions of the globe.

scholarly journals Ultrastructure of cells after reversible dark-induced blocking of mitotic divisions in antheridial filaments of Chara vulgaris L.

2014 ◽  
Vol 49 (3) ◽  
pp. 169-186 ◽  
Author(s):  
Maria Kwiatkowska ◽  
Janusz Maszewski ◽  
Maria M. Maszewska
Keyword(s):  
Cell Cycle ◽  
Endoplasmic Reticulum ◽  
Spatial Distribution ◽  
Cell Growth ◽  
Golgi Apparatus ◽  
Lipid Droplets ◽  
Continuous Darkness ◽  
Mean Size ◽  
Dense Matrices ◽  
The Mean

As compared with the control plants cultured under photoperiodic L : D = =14 : 10 conditions (K w i a t k o w s k a, M a s z e w s k i, 1978), the ultrastructure of nuclei -in cells blocked by a 5 day exposure to continuous darkness is characterized by homogenous arrangement. This homogeneity is maintained in all generations of antheridial filaments irrespective of cell length, which in the controls, being directly correlated with particular type of nuclear structure, may serve as a precise indicator of a given stage of interphase. From similarities in both the spatial distribution and content of condensed chromatin in is concluded that the block of the cell cycle is imposed at the beginning of the G<sub>2</sub> phase. On comparing these cells with the early G<sub>2</sub> period (stage VII) in the control plants, marked changes in the structure of nucleoli were found. They decrease in size by half owing to the complete decline of granular component. The area occupied by endoplasmic reticulum undergoes a 50% reduction. The decrease in the activity of Golgi apparatus expressed by a drop in number of smooth vesicles surrounding a single dictyosome is found to parallel the limited rate of cell growth. The number of coated vesicles and cisterns of dictyosome slightly increases. Mitochondria show typical condensed configuration with dense matrices and swollen cristae, while in the control orthodox forms are prevailing. The mean size of mitochondria is smaller, but their number exceeds that of the control plants. The surface area of mitochondrial profiles is found to remain constant proportion of the cytoplasm section, e.g., about 3%. Dark-cultured antheridial filaments show absolute decline of lipid droplets. No differences were found in structure of plastids and vacuols, as well as in number of ribosomes in cytoplasm surface unit.

Understorey predicts the spatial distribution of Ixodes hirsti in South Australia

2008 ◽  
Vol 56 (2) ◽  
pp. 123 ◽  
Author(s):  
Margot Oorebeek ◽  
Sonia Kleindorfer
Keyword(s):  
Spatial Distribution ◽  
Mortality Rate ◽  
Reproductive Success ◽  
Preliminary Investigation ◽  
South Australia ◽  
Saturation Deficit ◽  
Questing Ticks ◽  
Tick Survival ◽  
Vegetation Characteristics ◽  
Study Sites

Ticks reduce the fitness of their host by increasing mortality rate and reducing reproductive success. Understanding the distribution of ticks is therefore crucial in assessing the vulnerability of host populations. The distribution of ticks is dependent on the dispersal capabilities of their hosts as well as the suitability of the new habitat. In this study, we examine the spatial distribution of Ixodes hirsti in South Australia and investigate the influence of vegetation characteristics on the presence of ticks. Additionally, we conducted a preliminary investigation into the effects of vegetation characteristics on the microclimate experienced by questing ticks. Ticks were present in six of the nine study sites. We found that the number of shrubs and the percentage of ground covered by shrubs were significant predictors of the presence of ticks: ticks were present only at sites with a dense cover of shrubs. Additionally, our preliminary data showed that dense understorey was associated with a low saturation deficit and, as such, provided a suitable microclimate for tick survival.

scholarly journals Tasa de captura y composición de tamaños de Anadara spp. en Puerto El Morro, Ecuador

2018 ◽  
pp. 01
Author(s):  
Luis Alfredo Flores Vera ◽  
Maribel Morales-Escalante
Keyword(s):  
Spatial Distribution ◽  
Size Composition ◽  
Fishing Effort ◽  
Catch Rate ◽  
Biological Information ◽  
Small Scale ◽  
Population Status ◽  
Short Term ◽  
Palabras Clave ◽  
Mean Size

Catch rate and size composition of mangrove cockles Anadara spp. in Puerto El Morro, Ecuador Resumen Un análisis de la tasa de captura [captura por unidad de esfuerzo (CPUE)] y la composición de tamaños del desembarque de concha en la localidad de Puerto El Morro, fue realizado entre los años 2011 y 2013 a partir de información colectada en base a una bitácora de pesca. La CPUE promedio para el año 2011 fue de 115 conchas.conchero-1.día-pesca-1, mientras que para el 2012 y 2013 fue de 122 y 126 conchas.conchero-1.día-pesca-1, respectivamente. La captura estuvo compuesta principalmente por la especie A. tuberculosa en los tres años (>99 %). La longitud promedio de captura para A. tuberculosa oscilo entre 48,8 mm y 49,2 mm para el periodo de estudio. Un bajo porcentaje de tallas no comerciales caracterizó la pesquería del recurso. Se infiere un ligero incremento en la CPUE entre el 2011 y 2013, provocado quizás por la reducción observada en la población operativa de concheros y la distribución espacial del esfuerzo de pesca a zonas de mayor productividad. Se sugiere a corto plazo la evaluación directa de las principales áreas de pesca para conocer el estado actual de las mismas y relacionarla con indicadores pesqueros. Palabras clave: captura por unidad de esfuerzo (cpue); estructura poblacional; pesquería artesanal; recurso concha; Refugio de Vida Silvestre Manglares El Morro. Abstract Catch rate [catch per unit of effort (CPUE)] and size composition of the mangrove cockle fishery were analyzed in Puerto El Morro from 2011 to 2013 based on a fishing logbook to register the fishery and biological information. The average CPUE in 2011 was 115 cockles.cockle-collector-1.fishing-day-1, whereas 122 cockles.cockle-collector-1.fishing-day-1 for 2012 and 126 cockles.cockle-collector-1.fishing-day-1 for 2013. A high percentage of the specie A. tuberculosa was observed in the catch in all years (>99%). It was estimated for A. tuberculosa a mean size between 48,8 mm and 49,2 mm. Also, a low percentage of non-commercial sizes were observed in the catch. The slight increase of the CPUE between 2011 and 2013 is perhaps a result of the reduction in fishing effort and its spatial distribution to fishing areas of higher yield. It is suggested in a short term to assess the most important fishing areas to know the population status of this, and related to indicators of the fishery. Keywords: catch per unit of effort (CPUE); population structure; small-scale fishery; mangrove cockle; Refugio de Vida Silvestre Manglares El Morro.

scholarly journals Case studies of particle formation events observed in boreal forests: implications for nucleation mechanisms

2008 ◽  
Vol 8 (20) ◽  
pp. 6085-6102 ◽  
Author(s):  
F. Yu ◽  
R. Turco
Keyword(s):  
Case Studies ◽  
Boreal Forests ◽  
Forest Site ◽  
Air Masses ◽  
Size Dependent ◽  
Stable Clusters ◽  
Nucleation Model ◽  
Nucleation Mechanisms ◽  
Mean Size ◽  
Physical And Chemical

Abstract. Aerosol nucleation events observed worldwide may have significant climatic and health implications. However, the specific nucleation mechanisms remain ambiguous. Here, we report case studies of eight nucleation events observed during an intensive field campaign at a boreal forest site (Hyytiälä, Finland) in spring 2005. The present analysis is based on comprehensive kinetic simulations using an ion-mediated nucleation (IMN) model in which the key physical and chemical parameters are constrained by a variety of recent measurements. Out of the 22 days of the campaign on which nucleation events were observed, eight major events were selected for detailed analysis on the basis of indications that the observed air masses were relatively homogeneous. In most of these cases, reasonable agreement is found between IMN predictions and field data for a range of variables, including critical nucleation sizes, size-dependent overcharging ratios, and the concentrations of 1.8–3 nm stable clusters and 3–6 nm particles, and their diurnal variations. The possible reasons leading to substantial differences between observation and theory in some cases are also explored. Statistically, roughly 80% of the nucleation events recorded during the Hyytiälä campaign exhibited mean size-dependent particle overcharging ratios within the range of, or exceeding, those predicted by the IMN model, suggesting that ion nucleation processes were significant during these events. The nucleation rates calculated using the IMN modeling approach are contrasted with those predicted by other theories/models, and key differences between the results are discussed. In particular, it is concluded that the ion nucleation model originally developed by Lovejoy et al. (2004) significantly under-predicts ion nucleation rates, and cannot explain the new observations from Hyytiälä regarding the electrical properties of nanoparticles. We also show that, for the well documented conditions of the Hyytiälä project, the binary and ternary homogeneous nucleation rates calculated using the most current theories would fall well below ~10−7 cm−3 s−1, and thus would be negligible.

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