126 research outputs found
Recommended from our members
Ecological survey and interpretation of the Willamette Floodplain Research Natural Area, W.L. Finley National Wildlife Refuge, Oregon
The purpose of this study was to: (1) evaluate land
use and vegetation history of the Willamette Floodplain
Research Natural Area; (2) characterize present day
vegetation; (3) evaluate the relation of vegetation to
environment, and (4) establish a baseline dataset for future
trend analysis in order that response of different plant
species to fire frequencies may be assessed.
I used historical records, aerial photographs,
interviews, and literature to ascertain land use and
vegetation history. I assumed that the RNA had been
maintained as prairie by periodic aboriginal burning. Fire
ignited by settlers continued as a management tool into the
late 19th century. Grazing was a major disturbance in the
late 19th and early 20th centuries, and plowing or some
other soil disturbance on the raised elongated mounds may
have occurred. With removal of livestock grazing in the early 1960s and only a sporadic burning program, shrub cover
increased markedly over the past several decades.
I surveyed vegetation in the summer of 1991 in 36
random permanent plots. 1 classified species cover with
two-way indicator species analysis, identifying two major
communities. One is dominated by tall dense Rosa
eg'lanteria, Hypericum perforatum, and many alien weedy
species located on slightly elevated mounds, and the other
is dominated by shorter but also dense Rosa eglanteria,
Deschampsia cespitosa, and many species with wetland
affinity on intermounds. Monotypic patches of Spiraea
douglasii also occur on intermounds.
Species composition strongly correlates with
raicrotopography related to an indirect soil moisture index
based on wetland status of individual species. Composition
correlates less strongly with year since last burn. I
confirmed vegetation-environment relations by null
hypothesis analysis, tested by multi-response permutation
procedure. Vegetation significantly differs on mounds vs.
intermounds and vegetation significantly reflects burning
history. I ordinated floristic data by non-metric scaling.
I also tallied nested frequency data as a baseline for
future trend analysis in order to assess change in
vegetation in response to fire frequency. Frequency change
of Rosa eglanteria will best be detected by change in a 0.01
m2 plot size, Holcus lanatus by a 0.10 m2 plot, and
remaining species by a 1.00 m2 plot
The economic impact of sight loss and blindness in the UK adult population
Background: To quantify the economic impact of sight loss and blindness in the United Kingdom (UK) population, including direct and indirect costs, and its burden on health.
Methods: Prevalence data on sight loss and blindness by condition, Census demographic data, data on indirect costs, and healthcare cost databases were used. Blindness was defined as best corrected visual acuity (BCVA) of < 6/60, and sight loss as BCVA < 6/12 to 6/60, in the better-seeing eye.
Results: Sight loss and blindness from age-related macular degeneration (AMD), cataract, diabetic retinopathy, glaucoma and under-corrected refractive error are estimated to affect 1.93 (1.58 to 2.31) million people in the UK. Direct health care system costs were £3.0 billion, with inpatient and day care costs comprising £735 million (24.6%) and outpatient costs comprising £771 million (25.8%). Indirect costs amounted to £5.65 (5.12 to 6.22) billion. The value of the loss of healthy life associated with sight loss and blindness was estimated to be £19.5 (15.9 to 23.3) billion or £7.2 (5.9 to 8.6) billion, depending on the set of disability weights used. For comparison with other published results using 2004 disability weights and the 2008 estimates, the total economic cost of sight loss and blindness was estimated to be £28.1 (24.0 to 32.5) billion in 2013. Using 2010 disability weights, the estimated economic cost of sight loss and blindness was estimated to be £15.8 (13.5 to 18.3) billion in 2013.
Conclusions: The large prevalence of sight loss and blindness in the UK population imposes significant costs on public funds, private expenditure, and health. Prevalence estimates relied on dated epidemiological studies and may not capture recent advances in treatment, highlighting the need for population-based studies that track the prevalence of sight-impairing eye conditions and treatment effects over time
The rise of drug dealing in the life of the North American street gang
Historical gang literature traditionally perceived street gangs as boisterous outfits occasionally engaged in delinquency. In recent decades however, street gang behavior has come to be seen ever more as encroaching upon criminality, primarily due to its involvement in drug supply. This article aims to provide a brief historical review as to how the practice of drug supply entered into the life of the street gang, with specific emphasis on The War on Drugs in the 1970s and the rise of the crack cocaine economy in the 1980s
A redox switch in angiotensinogen modulates angiotensin release.
Blood pressure is critically controlled by angiotensins, which are vasopressor peptides specifically released by the enzyme renin from the tail of angiotensinogen-a non-inhibitory member of the serpin family of protease inhibitors. Although angiotensinogen has long been regarded as a passive substrate, the crystal structures solved here to 2.1 Å resolution show that the angiotensin cleavage site is inaccessibly buried in its amino-terminal tail. The conformational rearrangement that makes this site accessible for proteolysis is revealed in our 4.4 Å structure of the complex of human angiotensinogen with renin. The co-ordinated changes involved are seen to be critically linked by a conserved but labile disulphide bridge. Here we show that the reduced unbridged form of angiotensinogen is present in the circulation in a near 40:60 ratio with the oxidized sulphydryl-bridged form, which preferentially interacts with receptor-bound renin. We propose that this redox-responsive transition of angiotensinogen to a form that will more effectively release angiotensin at a cellular level contributes to the modulation of blood pressure. Specifically, we demonstrate the oxidative switch of angiotensinogen to its more active sulphydryl-bridged form in the maternal circulation in pre-eclampsia-the hypertensive crisis of pregnancy that threatens the health and survival of both mother and child
The effects of habitat fragmentation on the demography and population genetic structure of Uromys Caudimaculatus
Habitat fragmentation can have an impact on a wide variety of biological processes including abundance, life history strategies, mating system, inbreeding and genetic diversity levels of individual species. Although fragmented populations have received much attention, ecological and genetic responses of species to fragmentation have still not been fully resolved. The current study investigated the ecological factors that may influence the demographic and genetic structure of the giant white-tailed rat (Uromys caudimaculatus) within fragmented tropical rainforests. It is the first study to examine relationships between food resources, vegetation attributes and Uromys demography in a quantitative manner. Giant white-tailed rat densities were strongly correlated with specific suites of food resources rather than forest structure or other factors linked to fragmentation (i.e. fragment size). Several demographic parameters including the density of resident adults and juvenile recruitment showed similar patterns. Although data were limited, high quality food resources appear to initiate breeding in female Uromys. Where data were sufficient, influx of juveniles was significantly related to the density of high quality food resources that had fallen in the previous three months. Thus, availability of high quality food resources appear to be more important than either vegetation structure or fragment size in influencing giant white-tailed rat demography. These results support the suggestion that a species’ response to fragmentation can be related to their specific habitat requirements and can vary in response to local ecological conditions. In contrast to demographic data, genetic data revealed a significant negative effect of habitat fragmentation on genetic diversity and effective population size in U. caudimaculatus. All three fragments showed lower levels of allelic richness, number of private alleles and expected heterozygosity compared with the unfragmented continuous rainforest site. Populations at all sites were significantly differentiated, suggesting restricted among population gene flow. The combined effects of reduced genetic diversity, lower effective population size and restricted gene flow suggest that long-term viability of small fragmented populations may be at risk, unless effective management is employed in the future. A diverse range of genetic reproductive behaviours and sex-biased dispersal patterns were evident within U. caudimaculatus populations. Genetic paternity analyses revealed that the major mating system in U. caudimaculatus appeared to be polygyny at sites P1, P3 and C1. Evidence of genetic monogamy, however, was also found in the three fragmented sites, and was the dominant mating system in the remaining low density, small fragment (P2). High variability in reproductive skew and reproductive success was also found but was less pronounced when only resident Uromys were considered. Male body condition predicted which males sired offspring, however, neither body condition nor heterozygosity levels were accurate predictors of the number of offspring assigned to individual males or females. Genetic spatial autocorrelation analyses provided evidence for increased philopatry among females at site P1, but increased philopatry among males at site P3. This suggests that male-biased dispersal occurs at site P1 and female-biased dispersal at site P3, implying that in addition to mating systems, Uromys may also be able to adjust their dispersal behaviour to suit local ecological conditions. This study highlights the importance of examining the mechanisms that underlie population-level responses to habitat fragmentation using a combined ecological and genetic approach. The ecological data suggested that habitat quality (i.e. high quality food resources) rather than habitat quantity (i.e. fragment size) was relatively more important in influencing giant white-tailed rat demographics, at least for the populations studied here . Conversely, genetic data showed strong evidence that Uromys populations were affected adversely by habitat fragmentation and that management of isolated populations may be required for long-term viability of populations within isolated rainforest fragments
- …