79 research outputs found

    Ecology of the Black-faced sheathbill on Marion Island

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    Thesis (PhD)--Stellenbosch University, 2013.ENGLISH ABSTRACT: As the pace of climate change has begun to accelerate so too has it become clear that the direct impacts thereof are likely to have profound consequences for many island systems. Moreover, it has also been suggested that climate change will exacerbate the effects of many invasive species, so further impacting both diversity and ecosystem functioning. Forecasts for such interactions have been most pronounced for the Southern Ocean islands, which are home to a wide variety of endemic species. This thesis is about such interactions and their specific impacts on a key endemic, the black-faced sheathbill (Chionis minor) on the Prince Edward Islands. Of increasing concern is how invasive rodent populations in the Southern Ocean may be responding to global climate change, as ameliorating conditions on these islands are forecast to decrease thermal and resource restrictions on rodents. However, firm evidence for changing rodent populations in response to climate change, and demonstrations of associated impacts on the terrestrial environment, are entirely absent for the region. In Chapter 2 of this thesis, these relationships are explored for invasive house mice (Mus musculus) on Marion Island. Using spatially explicit capture-recapture modeling, it is determined that mouse populations across a range of habitats have increased over time. Owing to an extended breeding season, made possible by ameliorating conditions brought on by climate change, the total number of mice on the island at annual peak density more than doubled over the past decade. It is also demonstrated that mice directly reduce invertebrate densities, with biomass losses up to two orders of magnitude in some habitats. Because of the importance of invertebrates to nutrient cycling on the island, such changes are likely to have significant ecosystem-level impacts. In Chapter 3 the focus expands to examine how increasing mouse impacts and other outcomes of climate change are affecting the ecology of the black-faced sheathbill. It has been established that invasive house mice are capable of suppressing the populations of several seabird species in the Southern Ocean. However, mouse impacts on the region’s few island endemic land-birds remain largely unexplored. Further, a significant effect of climate change may be realized by altering interspecific interactions, specifically food webs. A significant portion of sheathbill diets is derived from rockhopper penguins, a species currently under a climate-change-driven decline, which may have significant effects on sheathbills. The study found that terrestrial invertebrates are no longer a significant prey resource for sheathbills on Marion Island, and that sheathbills have effectively been displaced from a formerly important winter food resource by mice. In response, the number of sheathbills foraging in king penguin colonies increased. Moreover, a reduced rockhopper penguin population lead to significant declines in both the number and proportion of sheathbills foraging in rockhopper penguin colonies. The sum result was a significant decline in the body condition of female sheathbills. Rather than decrease reproductive output, sheathbills responded by decreasing clutch size and producing significantly fewer male nestlings. While population estimates did not detect a reduction in the number of sheathbills, population projections suggest that the population is in decline, with the reproductive population declining faster than the absolute population. There is need for greater study of island species, as for even relatively well-studied taxa such as birds many aspects of ecology remain significantly less studied when compared to species occurring on continents. For example, basal metabolic rate (BMR) is a fundamental characteristic of all endotherms, yet only a handful of island birds have had their BMR measured, and fewer still to a level that allows intraspecific analysis. In Chapter 4 the BMR of black-faced sheathbills on Marion Island was measured to determine whether the unique phylogenetic position and ecology of sheathbills equate to a unique BMR when allometrically compared to other birds. It was found that the BMR of sheathbills is typical for a bird of its size. However, significant intraspecific variation was found to occur, with differences in habitat quality a likely driver. The results of the study show that the combined effects of climate change and invasive species can have significant consequences for terrestrial endemics in the Southern Ocean. Further, the long-term changes observed in sheathbills make clear the need for improved documentation and study of island species in general, as many of the responses observed in this study are significant but subtle and would not have been evident without detailed knowledge of species ecology and vital rates. Giving greater focus to insular biota is imperative to understanding their current status and ecology as well as establishing a barometer against which further global change can be measured and mitigation measures evaluated. Specific conservation responses for the black-faced sheathbill on Marion Island include the provision of nest boxes at king penguin colonies, and eradication of house mice. The latter would have long-term benefits for the species, invertebrates, ecosystem functioning generally, and likely also for important seabirds such as several species of albatrosses whose chicks are being increasingly preyed on by mice. Eradication would, however, be difficult and expensive, and with substantial potential non-target effects, including on sheathbills, that would have to be carefully managed. In the absence of local mouse eradication, and with ongoing climate change, specific management of the sheathbill population through the provision of supplementary nesting sites seems the most appropriate conservation action. It should therefore be examined in small-scale trials to ascertain the likelihood of unintended consequences. Importantly, the maintenance of Prince Edward Island as largely free of invasive species is key to the conservation of the local black-faced sheathbill subspecies, Chionis minor marionensis, endemic to the Prince Edward Island group.AFRIKAANSE OPSOMMING: Soos die tempo van klimaatsverandering begin om te versnel, het dit ook duidelik geword dat die direkte impak daarvan waarskynlik ernstige gevolge vir baie eilande gaan hê. Verder word dit is ook voorgestel dat klimaatsverandering die gevolge van baie indringerspesies sal vererger, so ʼn verdere impak het op beide diversiteit en die funksionering van die ekosisteem. Voorspellings vir sulke interaksies is die meeste uitgespreek vir die Suidelike Oseaan-eilande, wat ook die tuiste van 'n wye verskeidenheid van endemiese spesies is. Hierdie tesis is oor sulke interaksies en hul spesifieke impak op 'n sleutel endemiese spesie is, die swart gesig skedebek (Chionis minor) op die Prince Edward-eilande. ʼn Groter bron van bekommernis is hoe uitheemse knaagdier bevolkings in die Suidelike Oseaan kan reageer teenoor globale klimaatsverandering, aangesien toestande op die eilande voorspel word om hitte en hulpbron beperkings vir knaagdiere te verminder. Maar, ferm bewyse vir die verandering van knaagdier bevolkings in reaksie op klimaatsverandering, en demonstrasies van gepaardgaande impakte op die terrestriële omgewing, is heeltemal afwesig vir die streek. In Hoofstuk 2 van hierdie tesis, word hierdie verhoudings ondersoek vir indringende huis muise (Mus musculus) op Marion-eiland. Ruimtelik vang-terugvang modelle word gebruik om vas te stel dat die muis bevolkings oor 'n verskeidenheid van habitatte mettertyd toegeneem het. As gevolg van 'n uitgebreide broeiseisoen as gevolg van die verligting van toestande gebring deur klimaatsverandering, het die totale aantal muise op die eiland by die jaarlikse hoogtepunt digtheid meer as verdubbel oor die afgelope dekade. Dit is ook getoon dat muise die digtheid van ongewerweldes direk verminder het, met biomassa verliese tot twee ordes in sommige habitatte. As gevolg van die belangrikheid van die ongewerweldes vir voedingstof sirkulering op die eiland, behoort sulke veranderinge waarskynlik 'n beduidende ekosisteem-vlak impak te hê. In Hoofstuk 3 word die fokus verbreed om te sien hoe die verhoging van die muis impakte en ander uitkomste van klimaatsverandering die ekologie van die swart gesig skedebek beïnvloed. Daar is vasgestel dat indringende huis muise in staat is om die bevolkings van verskeie spesies seevoëls te onderdruk in die Suidelike Oseaan. Maar die muis impak op die streek se paar eiland endemiese land voëls bly grootliks onverken. Verder kan 'n beduidende uitwerking van klimaatsverandering verwesenlik word deur die wysiging van interspesifieke interaksies, veral voedselwebbe. 'n Beduidende gedeelte van skedebek dieet word gekry van Geelkuifpikkewyne, 'n spesie wat tans onder 'n klimaat-veranderinggedrewe agteruitgang is, wat ook 'n beduidende uitwerking het op die skedebek. Die studie het gevind dat terrestriële ongewerweldes nie meer 'n beduidende prooi hulpbron vir die skedebek op Marion-eiland is nie, en dat die skedebek effektief is verplaas uit 'n voorheen belangrike winter kos hulpbron deur muise. In reaksie hierop het die aantal skedebekke wat kos soek in die koning pikkewyn kolonies toegeneem. Verder, 'n verlaagde Geelkuifpikkewyn bevolking lei tot 'n beduidende afname in beide die aantal en persentasie van skedebekke wat kos soek in Geelkuifpikkewyn kolonies. Die gevolg was 'n beduidende afname in die liggaamstoestand van die vroulike skedebekke. Eerder as ʼn afname van reproduksie, het skedebekke gereageer deur 'n vermindering in die aantal eiers en produseer aansienlik minder manlike kuikens. Terwyl bevolking skattings nie 'n afname in die aantal skedebekke kan vind nie, dui bevolking projeksies daarop dat die bevolking besig is om af te neem, met die voortplanting bevolking wat vinniger daal as die absolute bevolking. Daar is 'n behoefte vir 'n groter studie van eiland spesies, omdat selfs vir betreklik goed bestudeerde groepe soos voëls baie aspekte van die ekologie aansienlik minder bestudeer bly in vergelyking met spesies op die vastelande. Byvoorbeeld, basale metaboliese tempo (BMT) is 'n fundamentele kenmerk van alle endotermiese diere, maar net 'n handjievol van die eiland voëls het hul BMT laat meet, en nog minder tot 'n vlak wat dit moontlik maak intraspesifieke analise. In Hoofstuk 4 was die BMT van die swart gesig skedebek op Marion-eiland gemeet om te bepaal of die unieke filogenetiese posisie en ekologie van skedebekke gelyk aan 'n unieke BMT wanneer allometries vergelyk word met ander voëls. Daar is gevind dat die BMT van skedebekke tipies is vir 'n voël van sy grootte. Daar is egter belangrike intraspesifieke variasie gevind, met verskille in habitat kwaliteit as 'n waarskynlike verduideliking. Die resultate van die studie toon dat die gekombineerde effek van klimaatsverandering en indringerspesies beduidende gevolge vir terrestriele inheemse spesies in die Suidelike Oseaan kan hê. Verder maak die lang-termyn veranderinge waargeneem in skedebekke dit duidelik dat die behoefte aan verbeterde dokumentasie en studie van die eiland spesies in die algemeen, omdat baie van die reaksies waargeneem in hierdie studie betekenisvol is, maar subtiel en sou nie gewees het sonder gedetailleerde kennis van die spesies ekologie van die spesie nie. Om ʼn groter fokus op die insulêre biota te plaas is noodsaaklik om hul huidige status en die ekologie te begryp, sowel as om 'n barometer waarteen verdere globale verandering gemeet kan word en versagtende maatreëls geëvalueer. Spesifieke bewaring antwoorde vir die swart gesig skedebek op Marion-eiland sluit in die voorsiening van nes bokse by koning pikkewyne, en die uitwissing van huis muise. Laasgenoemde sou lang-termyn voordele vir die spesie en ongewerweldes hê, asook funksionering van die ekosisteem in die algemeen, en waarskynlik ook vir belangrike seevoëls soos verskeie spesies van albatrosse wie se kuikens toenemend geëet word deur muise. Uitwissing sou egter moeilik en duur wees, en het 'n aansienlike potensiaal vir nieteiken effekte, insluitend op skedebekke, wat sal versigtig moet bestuur word. In die afwesigheid van plaaslike muis uitwissing, en met voortdurende verandering van die klimaat, spesifieke bestuur van die skedebek bevolking deur die voorsiening van aanvullende broeiplekke blyk die mees geskikte bewaringsaksie. Dit moet dus ondersoek word in 'n kleinskaal proewe om die waarskynlikheid van onbedoelde gevolge te bepaal. Wat belangrik is die instandhouding van Prince Edward Eiland as grootliks vry van indringerspesies en is die sleutel tot die bewaring van die plaaslike swart gesig skedebek subspesie, Chionis minor marionensis, endemies aan die Prince Edward Eiland groep

    Upper limits on the strength of periodic gravitational waves from PSR J1939+2134

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    The first science run of the LIGO and GEO gravitational wave detectors presented the opportunity to test methods of searching for gravitational waves from known pulsars. Here we present new direct upper limits on the strength of waves from the pulsar PSR J1939+2134 using two independent analysis methods, one in the frequency domain using frequentist statistics and one in the time domain using Bayesian inference. Both methods show that the strain amplitude at Earth from this pulsar is less than a few times 102210^{-22}.Comment: 7 pages, 1 figure, to appear in the Proceedings of the 5th Edoardo Amaldi Conference on Gravitational Waves, Tirrenia, Pisa, Italy, 6-11 July 200

    Improving the sensitivity to gravitational-wave sources by modifying the input-output optics of advanced interferometers

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    We study frequency dependent (FD) input-output schemes for signal-recycling interferometers, the baseline design of Advanced LIGO and the current configuration of GEO 600. Complementary to a recent proposal by Harms et al. to use FD input squeezing and ordinary homodyne detection, we explore a scheme which uses ordinary squeezed vacuum, but FD readout. Both schemes, which are sub-optimal among all possible input-output schemes, provide a global noise suppression by the power squeeze factor, while being realizable by using detuned Fabry-Perot cavities as input/output filters. At high frequencies, the two schemes are shown to be equivalent, while at low frequencies our scheme gives better performance than that of Harms et al., and is nearly fully optimal. We then study the sensitivity improvement achievable by these schemes in Advanced LIGO era (with 30-m filter cavities and current estimates of filter-mirror losses and thermal noise), for neutron star binary inspirals, and for narrowband GW sources such as low-mass X-ray binaries and known radio pulsars. Optical losses are shown to be a major obstacle for the actual implementation of these techniques in Advanced LIGO. On time scales of third-generation interferometers, like EURO/LIGO-III (~2012), with kilometer-scale filter cavities, a signal-recycling interferometer with the FD readout scheme explored in this paper can have performances comparable to existing proposals. [abridged]Comment: Figs. 9 and 12 corrected; Appendix added for narrowband data analysi

    Search for gravitational wave bursts in LIGO's third science run

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    We report on a search for gravitational wave bursts in data from the three LIGO interferometric detectors during their third science run. The search targets subsecond bursts in the frequency range 100-1100 Hz for which no waveform model is assumed, and has a sensitivity in terms of the root-sum-square (rss) strain amplitude of hrss ~ 10^{-20} / sqrt(Hz). No gravitational wave signals were detected in the 8 days of analyzed data.Comment: 12 pages, 6 figures. Amaldi-6 conference proceedings to be published in Classical and Quantum Gravit

    Quantum state preparation and macroscopic entanglement in gravitational-wave detectors

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    Long-baseline laser-interferometer gravitational-wave detectors are operating at a factor of 10 (in amplitude) above the standard quantum limit (SQL) within a broad frequency band. Such a low classical noise budget has already allowed the creation of a controlled 2.7 kg macroscopic oscillator with an effective eigenfrequency of 150 Hz and an occupation number of 200. This result, along with the prospect for further improvements, heralds the new possibility of experimentally probing macroscopic quantum mechanics (MQM) - quantum mechanical behavior of objects in the realm of everyday experience - using gravitational-wave detectors. In this paper, we provide the mathematical foundation for the first step of a MQM experiment: the preparation of a macroscopic test mass into a nearly minimum-Heisenberg-limited Gaussian quantum state, which is possible if the interferometer's classical noise beats the SQL in a broad frequency band. Our formalism, based on Wiener filtering, allows a straightforward conversion from the classical noise budget of a laser interferometer, in terms of noise spectra, into the strategy for quantum state preparation, and the quality of the prepared state. Using this formalism, we consider how Gaussian entanglement can be built among two macroscopic test masses, and the performance of the planned Advanced LIGO interferometers in quantum-state preparation

    Searching for a Stochastic Background of Gravitational Waves with LIGO

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    The Laser Interferometer Gravitational-wave Observatory (LIGO) has performed the fourth science run, S4, with significantly improved interferometer sensitivities with respect to previous runs. Using data acquired during this science run, we place a limit on the amplitude of a stochastic background of gravitational waves. For a frequency independent spectrum, the new limit is ΩGW<6.5×105\Omega_{\rm GW} < 6.5 \times 10^{-5}. This is currently the most sensitive result in the frequency range 51-150 Hz, with a factor of 13 improvement over the previous LIGO result. We discuss complementarity of the new result with other constraints on a stochastic background of gravitational waves, and we investigate implications of the new result for different models of this background.Comment: 37 pages, 16 figure

    The state of the Martian climate

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    60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

    Status Update and Interim Results from the Asymptomatic Carotid Surgery Trial-2 (ACST-2)

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    Objectives: ACST-2 is currently the largest trial ever conducted to compare carotid artery stenting (CAS) with carotid endarterectomy (CEA) in patients with severe asymptomatic carotid stenosis requiring revascularization. Methods: Patients are entered into ACST-2 when revascularization is felt to be clearly indicated, when CEA and CAS are both possible, but where there is substantial uncertainty as to which is most appropriate. Trial surgeons and interventionalists are expected to use their usual techniques and CE-approved devices. We report baseline characteristics and blinded combined interim results for 30-day mortality and major morbidity for 986 patients in the ongoing trial up to September 2012. Results: A total of 986 patients (687 men, 299 women), mean age 68.7 years (SD ± 8.1) were randomized equally to CEA or CAS. Most (96%) had ipsilateral stenosis of 70-99% (median 80%) with contralateral stenoses of 50-99% in 30% and contralateral occlusion in 8%. Patients were on appropriate medical treatment. For 691 patients undergoing intervention with at least 1-month follow-up and Rankin scoring at 6 months for any stroke, the overall serious cardiovascular event rate of periprocedural (within 30 days) disabling stroke, fatal myocardial infarction, and death at 30 days was 1.0%. Conclusions: Early ACST-2 results suggest contemporary carotid intervention for asymptomatic stenosis has a low risk of serious morbidity and mortality, on par with other recent trials. The trial continues to recruit, to monitor periprocedural events and all types of stroke, aiming to randomize up to 5,000 patients to determine any differential outcomes between interventions. Clinical trial: ISRCTN21144362. © 2013 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved
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