311 research outputs found
Using Anthropogenic Risks to Inform Salmonid Conservation at the Landscape Scale
The expansion and industrialization of humanity has caused many unforeseen consequences to the natural world. Due to the importance of freshwater for people, rivers have been particularly altered to meet human needs, often at the expense of the natural world. Supplying water for farms, industries, and cities has reshaped the natural state of rivers by altering river paths, chemistry, and species compositions. These changes have harmed many species that prospered before widespread human alterations, including the native trout and salmon of western North America. As human populations continue to grow, new threats will surface for rivers, and the trout and salmon that call rivers home. As a result, many scientists have considered how to assess and counter-act threats to trout and salmon. Often, efforts focus around rehabilitating stretches of river, but do not consider large-scale watershed conditions,which may be responsible for chronic stream degradation. Tools have been developed to guide decision making for coordinating conservation efforts that consider the multitude of risks facing trout and salmon. In this thesis I implemented these tools to help managers and decision makers understand how risks affect their conservation efforts. Two examples are provided, with the first considering development and resource extraction risks to Pacific salmon spawning habitat in Alaska. The second example considers climate, development, and competition risks for cutthroat trout, throughout Utah. Results from both examples clarify that managers who consider risks while conducting conservation yield greater results than managers who attempt to avoid risks. The findings here intend to inform future conservation effort for trout and salmon, and also clarify the importance of risk management in conservation
Using Systematic Conservation Planning to Establish Management Priorities for Freshwater Salmon Conservation, Matanuska-Susitna Basin, AK, USA
1- The Alaskan Matanuska-Susitna Basin (MSB) provides habitat for all five Pacific salmon species, and their large seasonal spawning runs are important both ecologically and economically. However, the encroachment of human development through urbanization and extractive industries poses a serious risk to salmon habitat in the MSB.
2- Using systematic conservation planning techniques, different methods of incorporating anthropogenic risks were assessed to determine how to cost-effectively conserve salmon habitat in the area.
3- The consequences of four distinct conservation scenarios were quantified: no consideration of either urbanization or extractive industries (âRisk ignoredâ scenario); accounting for the risk of urbanization, and avoiding conservation in all fossil fuel rich areas (âUrbanization accounted, all extraction avoidedâ scenario); accounting for urbanization and oil and gas development, but avoiding conservation in coal rich areas (âUrbanization accounted, coal areas avoidedâ scenario); and accounting for all anthropogenic risks to habitat, and allowing conservation in oil, gas, or coal rich areas (âAll risks accountedâ scenario). To compare conservation success and resiliency, the impact of these risks were estimated using Monte Carlo simulations. The final cost of each solution was then divided by the number of conservation targets met to determine a return on investment.
4- Results from scenarios that avoided all extractive activities, or just coal, suggest that conservation targets cannot be met by simply avoiding fossil fuel rich areas, and these scenarios resulted in lower returns on investment than when risks from extraction were incorporated into the solution.
5- By providing economically rooted conservation prioritization, this study provides a method for local managers and conservation groups to identify conservation opportunities in MSB river basins
Global Patterns in Marine Sediment Carbon Stocks
To develop more accurate global carbon (C) budgets and to better inform management of human activities in the ocean, we need high-resolution estimates of marine C stocks. Here we quantify global marine sedimentary C stocks at a 1-km resolution, and find that marine sediments store ⌠3117 (3006â3209) Pg C in the top 1 m (more than twice that of terrestrial soils). Sediments in abyss/basin zones account for 75% of the global marine sediment C stock, and 52% of that stock is within the 200-mile Exclusive Economic Zones of countries. Currently, only âŒ2% of sediment C stocks are located in highly to fully protected areas that prevent the disturbance of the seafloor. Our results show that marine sediments represent a large and globally important C sink. However, the lack of protection for marine C stocks makes them highly vulnerable to human disturbances that can lead to their remineralization to CO2, further aggravating climate change impacts
Ultraviolet Imaging of the Globular Cluster 47 Tucanae
We have used the Ultraviolet Imaging Telescope to obtain deep far-UV (1620
Angstrom), 40' diameter images of the prototypical metal-rich globular cluster
47 Tucanae. We find a population of about 20 hot (Teff > 9000 K) objects near
or above the predicted UV luminosity of the hot horizontal branch (HB) and
lying within two half-light radii of the cluster center. We believe these are
normal hot HB or post-HB objects rather than interacting binaries or blue
stragglers. IUE spectra of two are consistent with post-HB phases. These
observations, and recent HST photometry of two other metal-rich clusters,
demonstrate that populations with rich, cool HB's can nonetheless produce hot
HB and post-HB stars. The cluster center also contains an unusual diffuse
far-UV source which is more extended than its V-band light. It is possible that
this is associated with an intracluster medium, for which there was earlier
infrared and X-ray evidence, and is produced by C IV emission or scattered
light from grains.Comment: 13 pages AASLaTeX including one postscript figure and one bitmapped
image, JPEG format. Submitted to the Astronomical Jorunal. Full Postscript
version available at http://www.astro.virginia.edu/~bd4r
Reliable Identification of Binary Supermassive Black Holes from Rubin Observatory Time-Domain Monitoring
Periodic signatures in time-domain observations of quasars have been used to
search for binary supermassive black holes. These searches, across existing
time-domain surveys, have produced several hundred candidates. The general
stochastic variability of quasars, however, can masquerade as a false-positive
periodic signal, especially when monitoring cadence and duration are limited.
In this work, we predict the detectability of binary supermassive black holes
in the upcoming Rubin Observatory Legacy Survey of Space and Time (LSST). We
apply computationally inexpensive sinusoidal curve fits to millions of
simulated LSST Deep Drilling Field light curves of both single, isolated
quasars and binary quasars. Period and phase of simulated binary signals can
generally be disentangled from quasar variability. Binary amplitude is
overestimated and poorly recovered for two-thirds of potential binaries due to
quasar accretion variability. Quasars with strong intrinsic variability can
obscure a binary signal too much for recovery. We also find that the most
luminous quasars mimic current binary candidate light curves and their
properties: false positive rates are 60\% for these quasars. The reliable
recovery of binary period and phase for a wide range of input binary LSST light
curves is promising for multi-messenger characterization of binary supermassive
black holes. However, pure electromagnetic detections of binaries using
photometric periodicity with amplitude greater than 0.1 magnitude will result
in samples that are overwhelmed by false positives. This paper represents an
important and computationally inexpensive way forward for understanding the
true and false positive rates for binary candidates identified by Rubin.Comment: 21 pages, 14 figures, 3 table
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
Applications of Microlensing to Stellar Astrophysics
Over the past decade, microlensing has developed into a powerful tool to
study stellar astrophysics, especially stellar atmospheres, stellar masses, and
binarity. I review this progress. Stellar atmospheres can be probed whenever
the source in a microlensing event passes over the caustic (contour of infinite
magnification) induced by the lens because the caustic effectively resolves the
source. Broad-band observations of four events have yielded limb-darkening
measurements, which in essence map the atmospheric temperature as a function of
depth. And now, for the first time, spectroscopic observations of one event
promise much richer diagnostics of the source atmosphere. In the past two
years, a practical method has finally been developed to systematically measure
the lens masses in microlensing events. This will permit a census of all
massive objects, both dark and luminous, in the Galactic bulge, including
low-mass stars, brown dwarfs, white dwarfs, neutron stars, and black holes. The
method combines traditional ground-based photometry with astrometric and
photometric measurements by the Space Interferometry Mission (SIM) in solar
orbit. Using a related technique SIM can also obtain accurate (>~ 1%) mass
measurement of a dozen or so nearby stars, thus enabling precision tests of
stellar models. Binary lenses can give rise to dramatic and easily detectable
microlensing signatures, even for large mass ratios. This makes microlensing a
potentially powerful probe of the companion mass distribution, especially in
the Galactic bulge where this function is difficult to probe by other
techniques.Comment: PASP Invited Review, in press (August 2001). 33 pages including 5
fig
Altered Risk-Based Decision Making following Adolescent Alcohol Use Results from an Imbalance in Reinforcement Learning in Rats
Alcohol use during adolescence has profound and enduring consequences on decision-making under risk. However, the fundamental psychological processes underlying these changes are unknown. Here, we show that alcohol use produces over-fast learning for better-than-expected, but not worse-than-expected, outcomes without altering subjective reward valuation. We constructed a simple reinforcement learning model to simulate altered decision making using behavioral parameters extracted from rats with a history of adolescent alcohol use. Remarkably, the learning imbalance alone was sufficient to simulate the divergence in choice behavior observed between these groups of animals. These findings identify a selective alteration in reinforcement learning following adolescent alcohol use that can account for a robust change in risk-based decision making persisting into later life
Ancient DNA suggests modern wolves trace their origin to a late Pleistocene expansion from Beringia.
Grey wolves (Canis lupus) are one of the few large terrestrial carnivores that have maintained a wide geographic distribution across the Northern Hemisphere throughout the Pleistocene and Holocene. Recent genetic studies have suggested that, despite this continuous presence, major demographic changes occurred in wolf populations between the late Pleistocene and early Holocene, and that extant wolves trace their ancestry to a single late Pleistocene population. Both the geographic origin of this ancestral population and how it became widespread remain unknown. Here, we used a spatially and temporally explicit modelling framework to analyse a dataset of 90 modern and 45 ancient mitochondrial wolf genomes from across the Northern Hemisphere, spanning the last 50,000Â years. Our results suggest that contemporary wolf populations trace their ancestry to an expansion from Beringia at the end of the Last Glacial Maximum, and that this process was most likely driven by Late Pleistocene ecological fluctuations that occurred across the Northern Hemisphere. This study provides direct ancient genetic evidence that long-range migration has played an important role in the population history of a large carnivore, and provides an insight into how wolves survived the wave of megafaunal extinctions at the end of the last glaciation. Moreover, because late Pleistocene grey wolves were the likely source from which all modern dogs trace their origins, the demographic history described in this study has fundamental implications for understanding the geographical origin of the dog.L.L., K.D. and G.L. were supported by the Natural Environment Research Council, UK (grant numbers NE/K005243/1, NE/K003259/1); LL was also supported by the European Research Council grant (339941âADAPT); A.M. and A.E. were supported by the European Research Council Consolidator grant (grant number 647787âLocalAdaptation); L.F. and G.L. were supported by the European Research Council grant (ERCâ2013âStG 337574âUNDEAD); T.G. was supported by a European Research Council Consolidator grant (681396âExtinction Genomics) & Lundbeck Foundation grant (R52â5062); O.T. was supported by the National Science Center, Poland (2015/19/P/NZ7/03971), with funding from EU's Horizon 2020 programme under the Marie SkĆodowskaâCurie grant agreement (665778) and Synthesys Project (BETAF 3062); V.P., E.P. and P.N. were supported by the Russian Science Foundation grant (N16â18â10265 RNF); A.P. was supported by the Max Planck Society; M.LâG. was supported by a Czech Science Foundation grant (GAÄR15â06446S)
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Ancient DNA suggests modern wolves trace their origin to a late Pleistocene expansion from Beringia.
Grey wolves (Canis lupus) are one of the few large terrestrial carnivores that have maintained a wide geographic distribution across the Northern Hemisphere throughout the Pleistocene and Holocene. Recent genetic studies have suggested that, despite this continuous presence, major demographic changes occurred in wolf populations between the late Pleistocene and early Holocene, and that extant wolves trace their ancestry to a single late Pleistocene population. Both the geographic origin of this ancestral population and how it became widespread remain unknown. Here, we used a spatially and temporally explicit modelling framework to analyse a dataset of 90 modern and 45 ancient mitochondrial wolf genomes from across the Northern Hemisphere, spanning the last 50,000Â years. Our results suggest that contemporary wolf populations trace their ancestry to an expansion from Beringia at the end of the Last Glacial Maximum, and that this process was most likely driven by Late Pleistocene ecological fluctuations that occurred across the Northern Hemisphere. This study provides direct ancient genetic evidence that long-range migration has played an important role in the population history of a large carnivore, and provides an insight into how wolves survived the wave of megafaunal extinctions at the end of the last glaciation. Moreover, because late Pleistocene grey wolves were the likely source from which all modern dogs trace their origins, the demographic history described in this study has fundamental implications for understanding the geographical origin of the dog.L.L., K.D. and G.L. were supported by the Natural Environment Research Council, UK (grant numbers NE/K005243/1, NE/K003259/1); LL was also supported by the European Research Council grant (339941âADAPT); A.M. and A.E. were supported by the European Research Council Consolidator grant (grant number 647787âLocalAdaptation); L.F. and G.L. were supported by the European Research Council grant (ERCâ2013âStG 337574âUNDEAD); T.G. was supported by a European Research Council Consolidator grant (681396âExtinction Genomics) & Lundbeck Foundation grant (R52â5062); O.T. was supported by the National Science Center, Poland (2015/19/P/NZ7/03971), with funding from EU's Horizon 2020 programme under the Marie SkĆodowskaâCurie grant agreement (665778) and Synthesys Project (BETAF 3062); V.P., E.P. and P.N. were supported by the Russian Science Foundation grant (N16â18â10265 RNF); A.P. was supported by the Max Planck Society; M.LâG. was supported by a Czech Science Foundation grant (GAÄR15â06446S)
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