2,201 research outputs found
Modelling the impacts of an invasive species across landscapes: a step-wise approach
We estimate the extent of ecological impacts of the invasive Asian paper wasp across different landscapes in New Zealand. We used: (i) a baseline distribution layer (modelled via MaxEnt); (ii) Asian paper wasp nest density (from >460 field plots, related to their preferences for specific land cover categories); and (iii) and their foraging intensity (rates of foraging success, and the time available to forage on a seasonal basis). Using geographic information systems this information is combined and modelled across different landscapes in New Zealand in a step-wise selection process. The highest densities of Asian paper wasps were in herbaceous saline vegetation, followed closely by built-up areas, and then scrub and shrubland. Nest densities of 34 per ha, and occupancy rates of 0.27 were recorded for herbaceous saline vegetation habitats. However, the extent of impacts of the Asian paper wasp remains relatively restricted because of narrow climate tolerances and spatial restriction of preferred habitats. A step-wise process based on geographic information systems and species distribution models, in combination with factors such as distribution, density, and predation, create a useful tool that allows the extent of impacts of invasive species to be assessed across large spatial scales. These models will be useful for conservation managers as they provide easy visual interpretation of results, and can help prioritise where direct conservation action or control of the invader are required
The death of massive stars - II. Observational constraints on the progenitors of type Ibc supernovae
The progenitors of many type II core-collapse supernovae have now been
identified directly on pre-discovery imaging. Here we present an extensive
search for the progenitors of type Ibc supernovae in all available
pre-discovery imaging since 1998. There are 12 type Ibc supernovae with no
detections of progenitors in either deep ground-based or Hubble Space Telescope
archival imaging. The deepest absolute BVR magnitude limits are between -4 and
-5. We compare these limits with the observed Wolf-Rayet population in the
Large Magellanic Cloud and estimate a 16 per cent probability we have failed to
detect such a progenitor by chance. Alternatively the progenitors evolve
significantly before core-collapse or we have underestimated the extinction
towards the progenitors. Reviewing the relative rates and ejecta mass estimates
from lightcurve modelling of Ibc SNe, we find both incompatible with Wolf-Rayet
stars with initial masses >25Msun being the only progenitors. We present binary
evolution models that fit these observational constraints. Stars in binaries
with initial masses <20Msun lose their hydrogen envelopes in binary
interactions to become low mass helium stars. They retain a low mass hydrogen
envelope until approximately 10,000 years before core-collapse; hence it is not
surprising that galactic analogues have been difficult to identify.Comment: Accepted by MNRAS. 31 pages, 12 figures, 8 table
Readiness of Congregate Nutrition Sites to Deliver Nutrition Education to Older Adults
Title III of the Older Americans Act requires congregate nutrition sites (CNSs) to provide nutrition education. In 2015, we assessed 19 CNSs in Appalachian South Carolina for nutrition education readiness. Nutrition education readiness and general education readiness were both low. Overall, the CNSs were not ready to deliver education interventions due to lack of training/education, funds, drivers, and communication technologies. Addressing these problems could improve the likelihood that education would be effective. The readiness concepts described here can be used by Extension educators to determine whether delivery sites are ready to effectively provide education programs
Invasive Impacts of the Asian Paper Wasp Across Different Landscapes
Dissertação de Mestrado em Evolução e Biologia Humanas, apresentada ao Departamento de Ciências da Vida da Faculdade de Ciências e Tecnologia da Universidade de Coimbr
Time varying Na I D absorption in ILRTs as a probe of circumstellar material
Intermediate-Luminosity Red Transients (ILRTs) are a class of observed
transient posited to arise from the production of an electron-capture supernova
from a super-asymptotic giant branch star within a dusty cocoon. In this paper,
we present a systematic analysis of narrow Na I D absorption as a means of
probing the circumstellar environment of these events. We find a wide diversity
of evolution in ILRTs in terms of line strength, time-scale, and shape. We
present a simple toy model designed to predict this evolution as arising from
ejecta from a central supernova passing through a circumstellar environment
wherein Na II is recombining to Na I over time. We find that while our toy
model can qualitatively explain the evolution of a number of ILRTs, the
majority of our sample undergoes evolution more complex than predicted. The
success of using the Na I D doublet as a diagnostic tool for studying
circumstellar material will rely on the availability of regular high-resolution
spectral observations of multiple ILRTs, and more detailed spectral modelling
will be required to produce models capable of explaining the diverse range of
behaviours exhibited by ILRTs. In addition, the strength of the Na I D
absorption feature has been used as a means of estimating the extinction of
sources, and we suggest that the variability visible in ILRTs would prevent
such methods from being used for this class of transient, and any others
showing evidence of variabilityComment: 14 pages, 10 figures, submitted to MNRA
Crystal structure of geranylgeranyl pyrophosphate synthase (CrtE) involved in cyanobacterial terpenoid biosynthesis
Cyanobacteria are photosynthetic prokaryotes that perform oxygenic photosynthesis. Due to their ability to use the photon energy of sunlight to fix carbon dioxide into biomass, cyanobacteria are promising hosts for the sustainable production of terpenoids, also known as isoprenoids, a diverse class of natural products with potential as advanced biofuels and high-value chemicals. However, the cyanobacterial enzymes involved in the biosynthesis of the terpene precursors needed to make more complicated terpenoids are poorly characterized. Here we show that the predicted type II prenyltransferase CrtE encoded by the model cyanobacterium Synechococcus sp. PCC 7002 is homodimeric and able to synthesize C20-geranylgeranyl pyrophosphate (GGPP) from C5-isopentenyl pyrophosphate (IPP) and C5-dimethylallyl pyrophosphate (DMAPP). The crystal structure of CrtE solved to a resolution of 2.7 Å revealed a strong structural similarity to the large subunit of the heterodimeric geranylgeranyl pyrophosphate synthase 1 from Arabidopsis thaliana with each subunit containing 14 helices. Using mutagenesis, we confirmed that the fourth and fifth amino acids (Met-87 and Ser-88) before the first conserved aspartate-rich motif (FARM) play important roles in controlling chain elongation. While the WT enzyme specifically produced GGPP, variants M87F and S88Y could only generate C15-farnesyl pyrophosphate (FPP), indicating that residues with large side chains obstruct product elongation. In contrast, replacement of M87 with the smaller Ala residue allowed the formation of the longer C25-geranylfarnesyl pyrophosphate (GFPP) product. Overall, our results provide new structural and functional information on the cyanobacterial CrtE enzyme that could lead to the development of improved cyanobacterial platforms for terpenoid production
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