5,006 research outputs found
Predators, Prey Refuges, and the Spatial Scaling of Density-Dependent Prey Mortality
We tested the biological cause of density-dependent mortality in the bridled goby (Coryphopterus glaucofraenum), a small coral reef fish, and evaluated whether this knowledge allowed us to detect density dependence at different spatial scales in natural habitats. To identify the biological cause of density dependence, we manipulated both population density and the availability of shelter (crevices used as refuges from predators) in small plots of continuous reef. We detected strong density-dependent mortality in plots with few refuges, but mortality was density independent in plots with abundant refuges, indicating that limited shelter causes density dependence. Predator density was unrelated to the density of gobies and refuges, suggesting that predators displayed a type III functional response in patches with few refuges. In a second experiment, we manipulated goby density within replicate plots of three sizes (4, 16, and 64 m2) that varied naturally in the availability of refuges. If refuge availability was ignored, mortality appeared to be density independent at all scales. If, however, plots were grouped by refuge availability, mortality was density dependent in plots with few refuges, but low and density independent in plots with many refuges at all spatial scales. Understanding the mechanism of density dependence (refuge shortage) was thus required to measure the strength of density dependence in natural, spatially variable, habitat. We suggest that density dependence was detectable in plots of different sizes because the relationships between the densities of gobies, refuges, and goby predators were similar across the spatial scales we studied. Our work demonstrates that identifying the biological interactions that cause density dependence, and characterizing the spatial domains at which those interactions operate, will be important to accurately assess the effects of density dependence on population dynamics
Small-scale field experiments accurately scale up to predict density dependence in reef fish populations at large scales
Field experiments provide rigorous tests of ecological hypotheses but are usually limited to small spatial scales. It is thus unclear whether these findings extrapolate to larger scales relevant to conservation and management. We show that the results of experiments detecting density-dependent mortality of reef fish on small habitat patches scale up to have similar effects on much larger entire reefs that are the size of small marine reserves and approach the scale at which some reef fisheries operate. We suggest that accurate scaling is due to the type of species interaction causing local density dependence and the fact that localized events can be aggregated to describe larger-scale interactions with minimal distortion. Careful extrapolation from small-scale experiments identifying species interactions and their effects should improve our ability to predict the outcomes of alternative management strategies for coral reef fishes and their habitats
Prosomal-width-to-weight relationships in American horseshoe crabs (Limulus polyphemus): examining conversion factors used to estimate landings
Horseshoe crabs (Limulus polyphemus) are valued by many
stakeholders, including the commercial fishing industry, biomedical companies, and environmental interest groups. We designed a study to test the accuracy of the conversion factors that were used by NOAA Fisheries and state agencies to estimate horseshoe crab landings before mandatory
reporting that began in 1998. Our results indicate that the NOAA Fisheries conversion factor consistently overestimates the weight of male horseshoe crabs, particularly those from New England populations. Because of the inaccuracy of this and other conversion factors, states are now mandated to report the number (not biomass) and sex of landed horseshoe
crabs. However, accurate estimates of biomass are still necessary for use in prediction models that are being developed to better manage the horseshoe crab fishery. We recommend that managers use the conversion factors presented in this study to convert current landing data from numbers to biomass of harvested horseshoe crabs
for future assessments
Diagnosis and Management of COVID-19 Disease
SARS-CoV-2 is a novel coronavirus that was identified in late 2019 as the causative agent of COVID-19 (aka coronavirus disease 2019). On March 11, 2020, the World Health Organization (WHO) declared the world-wide outbreak of COVID-19 a pandemic. This document summarizes the most recent knowledge regarding the biology, epidemiology, diagnosis, and management of COVID-19
Wideband outdoor MIMO channel model derived from directional channel measurements at 2 GHz
This paper describes the use of directional channel measurements to derive a MIMO channel model. The measurements were obtained using a wideband channel sounder and eight element circular array in a metropolitan area in central Bristol, U.K. The raw measurements were processed using SAGE to extract the parameters of multipath components. The analysis of these parameters revealed several interesting features, notably that their amplitude distribution was well modelled as log-normal, and that there was little evidence of clustering in the angles of arrival. Hence a MIMO channel based on the assumption of finite scattering was derived, using the distributions obtained. The model allows the channel matrix H to be derived in the narrow-band case, and a tapped delay line model is also obtained for wideband systems. While the model derived is based on only a small set of measurements, it provides a case study for MIMO modelling based on measurements
Estimating Pasture Land Cover in the New England Region of Northern New South Wales
Land cover across the southern Australian temperate agricultural region comprises primarily of native pasture, introduced improved pastures and crops for livestock production and also perennial remnant vegetation. A feed-base pasture audit was carried out throughout southern Australia commencing mid-year 2011 (Donald and Burge 2012; Donald et al. 2012). The purpose of the audit was to map and analyse information obtained about the pasture feed-base for livestock production by surveying Statistical Local Areas (SLAs) across the southern states. The purpose of this Feed-Base audit was to survey pastures within agricultural NSW, Victoria, Tasmania, South Australia and South-Western Australia, collate these data into an organised database, and prepare a short report and summarise by tabulating and mapping pasture species abundance and distribution. Data collected were based on “desk-top estimates” by state district agronomists and agricultural consultants. In this paper a method using satellite imagery is described on how more objective assessments of pasture types can be provided as a means to discriminate between the SLA’s major pasture classes far more objectively than by visual assessment. Satellite remote sensing may be used to define landcover classes for large regional areas. A number of procedures have been developed to discriminate between pastures, crop and woody vegetation (for example Hill et al. 1997, Emelyanova et al. 2008). In the Hill study (Hill et al. 1997) NOAA AVHRR NDVI provided spatial land cover maps of pasture cover at 1 km resolution. The classifications results in that study showed that satellite information may be used to help in the interpretation of pasture survey results, and in turn, the survey data can provide some validation data for the pasture types ascribed to the remotely sensed classes.
In this study daily temporal continental scale imagery from 250 m2 resolution TERRA and AQUA satellite Moderate Resolution Imaging Spectroradiometer (MODIS) normalised difference vegetation index (NDVI) composited into weekly continental images provided a means to assess temporal profile of spectral greenness over the growing season
High population density recruitment and survival of a harvested coral reef fish
A negative relationship between population growth and population density (direct density dependence) is necessary for population regulation and is assumed in most models of harvested populations. Experimental tests for density dependence are lacking for large-bodied, harvested fish because of the difficulty of manipulating population density over large areas. We studied a harvested coral reef fish, Lutjanus apodus (schoolmaster snapper), using eight large, isolated natural reefs (0.4–1.6 ha) in the Bahamas as replicates. An initial observational test for density dependence was followed by a manipulation of population density. The manipulation weakened an association between density and shelter-providing habitat features and revealed a positive effect of population density on recruitment and survival (inverse density dependence), but no effect of density on somatic growth. The snappers on an individual reef were organized into a few shoals, and we hypothesize that large shoals on high-density reefs were less vulnerable to large piscivores (groupers and barracudas) than the small shoals on low-density reefs. Reductions in predation risk for individuals in large social groups are well documented, but because snapper shoals occupied reefs the size of small marine reserves, these ecological interactions may influence the outcome of management actions
Assessing Recognition of Sexist Language: Development and Use of the Gender-Specific Language Scale
Teaching effective writing in the social sciences includes teaching recognition of sexist language. The development and teaching uses of the Gender-Specific Language Scale (GSLS), an instrument designed to assess recognition of sexist language, are described. Three experiments with predominantly European-American male and female students provide support for the reliability and validity of the GSLS, and suggest that it measures a different construct than an essay questionnaire used in previous studies of sexist language. Implications for teaching are discussed
First scattered light images of debris disks around HD 53143 and HD 139664
We present the first scattered light images of debris disks around a K star
(HD 53143) and an F star (HD 139664) using the coronagraphic mode of the
Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST). With
ages 0.3 - 1 Gyr, these are among the oldest optically detected debris disks.
HD 53143, viewed ~45 degrees from edge-on, does not show radial variation in
disk structure and has width >55 AU. HD 139664 is seen close to edge-on and has
belt-like morphology with a dust peak 83 AU from the star and a distinct outer
boundary at 109 AU. We discuss evidence for significant diversity in the radial
architecture of debris disks that appears unconnected to stellar spectral type
or age. HD 139664 and possibly the solar system belong in a category of narrow
belts 20-30 AU wide. HD 53143 represents a class of wide disk architecture with
characteristic width >50 AU.Comment: 7 pages, 3 figure
Constraining the Progenitor Companion of the Nearby Type Ia SN 2011fe with a Nebular Spectrum at +981 Days
We present an optical nebular spectrum of the nearby Type Ia supernova
2011fe, obtained 981 days after explosion. SN 2011fe exhibits little evolution
since the +593 day optical spectrum, but there are several curious aspects in
this new extremely late-time regime. We suggest that the persistence of the
~\AA\ feature is due to Na I D, and that a new emission feature at
~\AA\ may be [Ca II]. Also, we discuss whether the new emission
feature at ~\AA\ might be [Fe I] or the high-velocity hydrogen
predicted by Mazzali et al. The nebular feature at 5200~\AA\ exhibits a linear
velocity evolution of per 100 days from at least
+220 to +980 days, but the line's shape also changes in this time, suggesting
that line blending contributes to the evolution. At days after
explosion, flux from the SN has declined to a point where contribution from a
luminous secondary could be detected. In this work we make the first
observational tests for a post-impact remnant star and constrain its
temperature and luminosity to and
. Additionally, we do not see any evidence for narrow H
emission in our spectrum. We conclude that observations continue to strongly
exclude many single-degenerate scenarios for SN 2011fe.Comment: 11 pages, 10 figures, published by MNRA
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