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Greater Diameter (greater + diameter)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Geomorphic and riparian forest influences on characteristics of large wood and large-wood jams in old-growth and second-growth forests in Northern Michigan, USA

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2007
Arthur E. L. Morris
Abstract Large wood (LW; pieces with diameter greater than 10 cm and length greater than 1 m) and large-wood jams (LWJs; two or more pieces of LW in contact with each other) are important components of stream ecosystems that are often distributed along stream channels in response to geomorphic and riparian forest factors that interact hierarchically. As a result, information on these relationships is valuable for predicting patterns of wood accumulation and characteristics of individual pieces of wood. We studied relationships between geomorphic and riparian factors and LW and LWJ structure in different geomorphic settings associated with old-growth and second-growth settings in Upper Michigan. We used redundancy analysis (RDA) and regression tree analysis to evaluate changes in LW and LWJ structural characteristics among geomorphic and riparian forest settings. Geomorphic factors explained 38·5% of the variability in LW and LWJ characteristics, riparian forest factors uniquely explained 18·4% of the variance and the intersection of the two categories of environmental factors (i.e. the redundant portion) was 29·8%. At the landscape scale, our multivariate analyses suggest that the presence of rock-plane bedding was an important predictor of the number of LWJs and the percent of channel spanned by LWJs. Our analyses suggest differences in relationships between geomorphic factors and LW and LWJ structure. Channel width, distance from headwaters, gradient and sinuosity were identified by regression tree analyses as the most important variables for predicting LW characteristics, while channel width and confinement were the most important variables for predicting LWJ characteristics. Old-growth settings generally contained a higher proportion of conifer and LW (both in and out of LWJs) with greater diameter and volume than in second-growth settings. Our study supports the view that restoration of wood to streams will benefit from considering the associations of wood structure with landscape and reach-scale geomorphology. Copyright © 2007 John Wiley & Sons, Ltd. [source]

ADAPTIVE PLASTICITY OF THE PENIS IN A SIMULTANEOUS HERMAPHRODITE

EVOLUTION, Issue 8 2009
J. Matthew Hoch
Acorn barnacles are important model organisms for the study of sex allocation. They are sessile, nonselfing hermaphrodites that copulate with penises that have been suggested to be phenotypically plastic. On wave-exposed shores, Semibalanus balanoides develop penises with relatively greater diameter whereas in wave-protected sites they are thinner. A reciprocal transplant experiment between wave-exposed and protected sites tested whether these exposure-specific morphologies have adaptive value. Mating success was compared over a range of distances to compare the ability of barnacles to reach mates. Barnacles that grew in the wave-protected site and mated in the wave-protected site fertilized more broods at increasing distances than those transplanted to the wave-exposed site. For barnacles that developed in the wave-exposed site, there was no difference in the ability to fertilize neighbors between sites of differing exposure. This study demonstrates the adaptive value of plasticity in penis morphology. The results suggest a trade-off between development of a penis adapted to wave exposure and the ability to fertilize distant mates. Barnacles in different physical environments are limited by different factors, which may limit numbers of potential mates, constrain optimal sex allocation strategies and alter reproductive behavior. [source]

Biology of suckers: late-formed shoots in sugarcane

ANNALS OF APPLIED BIOLOGY, Issue 1 2001
G D BONNETT
Summary Suckers in sugarcane are tillers that form late in the growing season after the population of main stalks has been established. Their biology has rarely been studied, though unsubstantiated comments relating to their morphology, development and number are abundant. In this paper, the literature is reviewed and new experiments presented. Comparison of suckers, emerging plant and ratoon cane showed that suckers have a different leaf and stem morphology. Suckers have a greater diameter at their stem base and shorter and wider leaves than primary stalks of a similar age. In 1 -year-old crops, suckers have been demonstrated to decrease the net sucrose concentration of harvested material by diluting sucrose in the main stalks. By comparing main stalks without suckers to those that have initiated suckers, evidence is presented that suckers may also be decreasing the sucrose content of the stalks from which they are growing. Genotypic and environmental factors influence sucker number. Several experiments were designed to identify environmental stimuli for suckering. Increased nitrogen, through application late in the growing season, was found to increase the numbers of suckers present. Manipulation of the light environment of main stalks showed that a change in light quality (but not necessarily quantity) stimulated suckering. Further work is underway to define how these environmental stimuli lead to sucker initiation and growth. Major scientific questions that should be addressed are: the identification of other potential environmental stimuli, how the signals are perceived and translated into sucker initiation, and why suckers have different morphology. The practical challenge is to combine the new information about sucker biology and develop from it strategies to alter agronomy and select new cultivars that results in decreased suckering. [source]

Echocardiographic Study of Cardiac Morphological and Functional Changes before and after Parturition in Pregnancy-Induced Hypertension

ECHOCARDIOGRAPHY, Issue 3 2006
Lijun Yuan M.D.
Purpose: To investigate the cardiac morphological and functional changes by echocardiography, before and after parturition in patients with pregnancy-induced hypertension (PIH). Methods: The parameters related to cardiac morphology and left ventricular diastolic and systolic functions were compared before and after parturition in 32 patients with PIH and 24 normal pregnant (NP) women. Results: Compared with NP women, the PIH patients had greater diameters of left atrium and left ventricle in end-diastole (LAd: 38.9 ± 4.5 vs 34.6 ± 4.4 mm, P = 0.0015; LVEDd: 51.2 ± 5.8 vs 47.1 ± 4.2 mm, P = 0.036) and lower E/A (1.2 ± 0.2 vs 1.4 ± 0.2, P = 0.009) and greater fractional shortening (FS) (39.8 ± 6.5% vs 37.1 ± 6.9%, P = 0.042) and ejection fraction (EF) (0.72 ± 0.07 vs 0.66 ± 0.08, P = 0.040). Pericardial effusion (PE) occurred in 31.3% and 16.7% of PIH and NP, respectively. The LAd and LVEDd in 70% and 47% patients with PIH resolved and PE disappeared in 80% of PIH patients postpartum. E/A ratio in PIH significantly increased after parturition, while the two patients with cardiac systolic dysfunction did not improve very much. Conclusions: Compared with normal pregnancy, the most significant cardiac morphological changes in PIH are the greater diameters of left atrium and left ventricle, thicker inter-ventricular septum (IVS), more PE, impaired left ventricular diastolic function, and increased systolic function. The PE could disappear in PIH and about half of other abnormalities could recover to be the level of normal pregnancy postpartum within 2 months. [source]