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Sökning: WFRF:(O'Gorman Eoin J.)

  • Resultat 1-6 av 6
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  • Harper, G. M., et al. (författare)
  • SOFIA-EXES Mid-IR Observations of [Fe II] Emission from the Extended Atmosphere of Betelgeuse
  • 2017
  • Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X. ; 836:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a NASA-DLR SOFIA-Echelon Cross Echelle Spectrograph (EXES) and NASA Infrared Telescope Facility-Texas Echelon Cross Echelle Spectrograph (TEXES) mid-IR R ≃ 50,000 spectral study of forbidden Fe II transitions in the early-type M supergiants, Betelgeuse (α Ori: M2 Iab) and Antares (α Sco: M1 Iab + B3 V). With EXES, we spectrally resolve the ground term [Fe II] 25.99 μm ( a 6DJ= 7/2-9/2: Eup = 540 K) emission from Betelgeuse. We find a small centroid blueshift of 1.9 ± 0.4 km s-1 that is a significant fraction (20%) of the current epoch wind speed, with a FWHM of 14.3 ± 0.1 km s-1. The TEXES observations of [Fe II] 17.94 μm (a 4FJ= - 7/2 9/2: Eup = 3400 K) show a broader FWHM of 19.1 ± 0.2 km s-1, consistent with previous observations, and a small redshift of 1.6 ± 0.6 km s-1 with respect to the adopted stellar center-ofmass velocity of VCoM = 20.9 ± 0.3 km s-1. To produce [Fe II] 25.99 μm blueshifts of 20% wind speed requires that the emission arises closer to the star than existing thermal models for α Ori's circumstellar envelope predict. This implies a more rapid wind cooling to below 500 K within 10R∗ (q∗ = 44 mas, dist = 200 pc) of the star, where the wind has also reached a significant fraction of the maximum wind speed. The line width is consistent with the turbulence in the outflow being close to the hydrogen sound speed. EXES observations of [Fe II] 22.90 μm ( a 4DJ= 5/2-7/2: Eup = 11,700 K) reveal no emission from either star. These findings confirm the dominance of cool plasma in the mixed region where hot chromospheric plasma emits copiously in the UV, and they also constrain the wind heating produced by the poorly understood mechanisms that drive stellar outflows from these low variability and weak-dust signature stars.
  • O'Gorman, Eoin J., et al. (författare)
  • Impacts of Warming on the Structure and Functioning of Aquatic Communities : Individual-to Ecosystem-Level Responses
  • 2012
  • Ingår i: Advances in Ecological Research, Vol 47. - : Elsevier. - 9780123983152 ; , s. 81-176
  • Bokkapitel (refereegranskat)abstract
    • Environmental warming is predicted to rise dramatically over the next century, yet few studies have investigated its effects in natural, multi-species systems. We present data collated over an 8-year period from a catchment of geothermally heated streams in Iceland, which acts as a natural experiment on the effects of warming across different organisational levels and spatiotemporal scales. Body sizes and population biomasses of individual species responded strongly to temperature, with some providing evidence to support temperature size rules. Macroinvertebrate and meiofaunal community composition also changed dramatically across the thermal gradient. Interactions within the warm streams in particular were characterised by food chains linking algae to snails to the apex predator, brown trout These chains were missing from the colder systems, where snails were replaced by much smaller herbivores and invertebrate omnivores were the top predators. Trout were also subsidised by terrestrial invertebrate prey, which could have an effect analogous to apparent competition within the aquatic prey assemblage. Top-down effects by snails on diatoms were stronger in the warmer streams, which could account for a shallowing of mass-abundance slopes across the community. This may indicate reduced energy transfer efficiency from resources to consumers in the warmer systems and/or a change in predator-prey mass ratios. All the ecosystem process rates investigated increased with temperature, but with differing thermal sensitivities, with important implications for overall ecosystem functioning (e.g. creating potential imbalances in elemental fluxes). Ecosystem respiration rose rapidly with temperature, leading to increased heterotrophy. There were also indications that food web stability may be lower in the warmer streams.
  • Brose, Ulrich, et al. (författare)
  • Predicting the consequences of species lossusing size-structured biodiversity approaches
  • 2017
  • Ingår i: Biological Reviews. - : Wiley-Blackwell. - 1464-7931 .- 1469-185X. ; 92:2, s. 684-697
  • Forskningsöversikt (refereegranskat)abstract
    • Understanding the consequences of species loss in complex ecological communities is one of the great challenges in current biodiversity research. For a long time, this topic has been addressed by traditional biodiversity experiments. Most of these approaches treat species as trait-free, taxonomic units characterizing communities only by species number without accounting for species traits. However, extinctions do not occur at random as there is a clear correlation between extinction risk and species traits. In this review, we assume that large species will be most threatened by extinction and use novel allometric and size-spectrum concepts that include body mass as a primary species trait at the levels of populations and individuals, respectively, to re-assess three classic debates on the relationships between biodiversity and (i) food-web structural complexity, (ii) community dynamic stability, and (iii) ecosystem functioning. Contrasting current expectations, size-structured approaches suggest that the loss of large species, that typically exploit most resource species, may lead to future food webs that are less interwoven and more structured by chains of interactions and compartments. The disruption of natural body-mass distributions maintaining food-web stability may trigger avalanches of secondary extinctions and strong trophic cascades with expected knock-on effects on the functionality of the ecosystems. Therefore, we argue that it is crucial to take into account body size as a species trait when analysing the consequences of biodiversity loss for natural ecosystems. Applying size-structured approaches provides an integrative ecological concept that enables a better understanding of each species' unique role across communities and the causes and consequences of biodiversity loss.
  • O'Gorman, Eoin J., et al. (författare)
  • Interaction strength, food web topology and the relative importance of species in food webs.
  • 2010
  • Ingår i: Journal of Animal Ecology. - : Wiley-Blackwell Publishing Ltd.. - 0021-8790 .- 1365-2656. ; 79:3, s. 682-692
  • Tidskriftsartikel (refereegranskat)abstract
    • 1. We established complex marine communities, consisting of over 100 species, in large subtidal experimental mesocosms. We measured the strength of direct interactions and the net strength of direct and indirect interactions between the species in those communities, using a combination of theoretical and empirical approaches.2. Theoretical predictions of interaction strength were derived from the interaction coefficient matrix, which was parameterised using allometric predator–prey relationships. Empirical estimates of interaction strength were quantified using the ln-ratio, which measures the change in biomass density of species A in the presence and absence of species B.3. We observed that highly connected species tend to have weak direct effects and net effects in our experimental food webs, whether we calculate interaction strength theoretically or empirically.4. We found a significant correlation between our theoretical predictions and empirical estimates of direct effects and net effects. The net effects correlation was much stronger, indicating that our experimental communities were dominated by a mixture of direct and indirect effects.5. Re-calculation of the theoretical predictions of net effects after randomising predator and prey body masses did not affect the negative relationship with connectance.6. These results suggest that food web topology, which in this system is constrained by body mass, is overwhelmingly important for the magnitude of direct and indirect interactions and hence species importance in the face of biodiversity declines.
  • Plebani, Marco, et al. (författare)
  • Substratum-dependent responses of ciliate assemblages to temperature: a natural experiment in Icelandic streams
  • 2015
  • Ingår i: Freshwater Biology. - : Wiley-Blackwell. - 0046-5070. ; 60:8, s. 1561-1570
  • Tidskriftsartikel (refereegranskat)abstract
    • Ciliate assemblages play a significant role in the microbial food web. The effects of environmental temperature on assemblage composition may be influenced by abiotic factors such as seasonality and disturbance, but the effects of temperature on ciliate assemblages found on different substrata have not been explored. Sandy bottoms and submerged rocks harbour dissimilar ciliate assemblages, and it might be expected that their ciliate assemblages will respond differently to temperature. We studied how alpha diversity, beta diversity and total biomass of ciliate protist assemblages found on sandy bottoms and submerged rocks differed in 13 geothermally heated streams in Iceland whose mean temperatures range from 5 to 20 degrees C. We recorded number of operational taxonomic units (OTUs) and measured the size of cells in ciliate assemblages from both substrata. Effects of temperature on natural ciliate assemblages were substratum dependent. On rock surfaces, both total ciliate biomass and alpha diversity declined with increasing temperature, and beta diversity increased with increasing temperature difference due to OTU nestedness (assemblages from warm streams being composed chiefly of subsets of the OTUs found in colder streams). In sandy substrata, however, ciliate assemblage composition was independent of temperature. Substratum-specific responses may be due to differences in mechanical disturbance, nutrient availability or exposure to invertebrate grazers. Rock-surface assemblages may be more exposed to the flow and retain less nutrient than those of sandy substratum; thus, they may be more strongly resource limited and more responsive to direct effects of temperature on metabolism. Alternatively, rock-surface assemblages may be more exposed to grazing by invertebrates, which intensifies with temperature. Our study highlights the need to account for environmental context such as substratum type to fully understand the effect of temperature on microbial assemblages in streams. Future increases in global temperatures may affect fresh waters differently depending on their prevalent substratum. Those dominated by hard substrata may have their ciliate assemblages, and thus, food-web structures and ecosystem functioning more strongly affected by warming relative to systems dominated by soft substrata.
  • Warner, Emily, et al. (författare)
  • Impacts of soil temperature, phenology and plant community composition on invertebrate herbivory in a natural warming experiment
  • 2021
  • Ingår i: Oikos. - 0030-1299 .- 1600-0706. ; 130:9, s. 1572-1582
  • Tidskriftsartikel (refereegranskat)abstract
    • Species and community-level responses to warming are well documented, with plants and invertebrates known to alter their range, phenology or composition as temperature increases. The effects of warming on biotic interactions are less clearly understood, but can have consequences that cascade through ecological networks. Here, we used a natural soil temperature gradient of 5–35°C in the Hengill geothermal valley, Iceland, to investigate the effects of temperature on plant community composition and plant–invertebrate interactions. We quantified the level of invertebrate herbivory on the plant community across the temperature gradient and the interactive effects of temperature, plant phenology (i.e. development stage) and vegetation community composition on the probability of herbivory for three ubiquitous plant species, Cardamine pratensis, Cerastium fontanum and Viola palustris. We found that the percentage cover of graminoids and forbs increased, while the amount of litter decreased, with increasing soil temperature. Invertebrate herbivory also increased with soil temperature at the plant community level, but this was underpinned by different effects of temperature on herbivory for individual plant species, mediated by the seasonal development of plants and the composition of the surrounding vegetation. This illustrates the importance of considering the development stage of organisms in climate change research given the variable effects of temperature on susceptibility to herbivory at different ontogenetic stages.
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  • Resultat 1-6 av 6

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