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Mean Elevation (mean + elevation)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Use of latanoprost to reduce acute intraocular pressure rise following neodymium: Yag laser iridotomy

ACTA OPHTHALMOLOGICA, Issue 3 2002
Catherine J. Liu
ABSTRACT. Purpose: To evaluate the efficacy of latanoprost in reducing acute intraocular pressure (IOP) elevation after neodymium:Yag laser iridotomy (LI). Methods: Primary angle-closure glaucoma (PACG) eyes were randomized to receive premedication with latanoprost and pilocarpine or with pilocarpine only before LI. Postoperative IOP changes were compared with Wilcoxon signed-ranks test using the fellow eyes of 47 patients who had one eye in each group. Results: Postoperative pressure spikes were significantly lower (p =,0.010) in the latanoprost group (4.1 ± 5.0 mmHg) than in the control group (6.7 ± 7.0 mmHg). Mean elevation of IOP was less in the latanoprost group than in the control group at 1 hour (2.5 ± 4.8 versus 4.1 ± 4.7 mmHg, p = 0.013) and 2 hours (0.8 ± 5.6 versus 4.4 ± 8.1 mmHg, p = 0.003) postoperatively. Eleven eyes in the latanoprost group (23.4%) and 20 eyes in the control group (42.6%) developed a rise in IOP ,,6 mmHg (p =,0.048). Conclusion: Latanoprost may reduce the pressure rise following LI in PACG eyes, but its application is limited by a late onset of effect. [source]

High resolution quantification of gully erosion in upland peatlands at the landscape scale

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2010
Martin Evans
Abstract The upland peatlands of the UK are severely eroded, with large areas affected by gully erosion. The peatlands are important areas of carbon storage and provide a range of other ecosystem services including water supply and biodiversity all of which are negatively impacted by erosion of the upland surface. The magnitude of the gully erosion, and consequent adjustment of the peatland morphology, is such that in degraded peatlands the extent and magnitude of erosion is a major control on peatland function. Accurate mapping of gully form is therefore a necessary precondition to the understanding and management of these systems. This paper develops an approach to extracting gully maps from high resolution digital elevation models (DEMs). Gully maps of the Bleaklow Plateau in northern England were derived from a 2,m LiDAR DEM by combining areas of low difference from mean elevation and high positive plan curvature. Gully depth was modelled by interpolating between gully edges. Testing of the gully mapping and depth modelling against aerial photography, manual interpretation of the DEM and ground survey revealed that gully plan form is well represented and gully width and depth are modelled with tolerances close to the horizontal and vertical resolution of the LiDAR imagery. Estimates of gully width and depth were less reliable for gullies with total width of less than four pixels. The approach allows for the first time the derivation of accurate estimates of gully extent and magnitude over large areas and provides the basis for modelling a range of processes controlled by gullying. The approach has wider applicability to mapping gully erosion in a wide range of environments. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Poleward shifts in breeding bird distributions in New York State

GLOBAL CHANGE BIOLOGY, Issue 8 2009
BENJAMIN ZUCKERBERG
Abstract Like other regions of the northern hemisphere, the northeastern United States has experienced a general increase in regional temperatures over the past 20 years. Quantifying the ecological implications of these changing temperatures has been severely constrained by a lack of multispecies distributional data by which to compare long-term changes. We used the New York State Breeding Bird Atlas, a statewide survey of 5332 25 km2 blocks surveyed in 1980,1985 and 2000,2005, to test several predictions that the birds of New York State are responding to climate change. Our objective was to use an information-theoretic approach to analyze changes in three geographic range characteristics, the center of occurrence, range boundaries, and states of occurrence to address several predictions that the birds of New York State are moving polewards and up in elevation. As expected, we found all bird species (n=129) included in this analysis showed an average northward range shift in their mean latitude of 3.58 km [Prob(Ha|data)=0.87)]. Past studies have found that northern range boundaries are more likely to be influenced by climatic factors than southern range boundaries. Consequently, we predicted that northward shifts would be more evident in northern as opposed to southern range boundaries. We found, however, that the southern range boundaries of northerly birds moved northward by 11.4 km [n=43, Prob(Ha|data)=0.92], but this pattern was less evident in northern range boundaries of southerly birds. In addition, we found that bird species demonstrated a general shift downhill in their mean elevation, but demonstrated little change in their elevational boundaries. The repeated pattern of a predicted northward shift in bird ranges in various geographic regions of the world provides compelling evidence that climate change is driving range shifts. [source]

Can differences in autonomous selfing ability explain differences in range size among sister-taxa pairs of Collinsia (Plantaginaceae)?

NEW PHYTOLOGIST, Issue 3 2009
An extension of Baker's Law
Summary ,,Species with greater selfing ability are predicted to be better adapted for colonizing new habitats (Baker's Law). Here, we tested an expansion of this hypothesis: that species proficient at autonomous selfing have larger range sizes than their less proficient sister taxa. We also tested competing hypotheses regarding seed production and niche breadth on range size. ,,Floral traits affecting the proficiency of autonomous selfing were measured and seed production was calculated for six sister-taxa pairs in the clade Collinsia. We tested for the hypothesized effects of these variables on elevational distribution and range size. ,,We found that species most proficient at selfing had significantly larger range sizes than their sister-taxa that were less proficient at selfing. Species proficient at autonomous selfing occupied a higher mean elevation than their sister taxa, but they did not differ in their total elevational range. Species with greater seed production did not have larger range sizes. ,,Our results extend Baker's Law, suggesting that species proficient at autonomous selfing are better adapted to establish new populations and thus can more readily expand their range. Autonomous selfing ability may play a vital role in explaining variance in range size among other species. [source]