| 1. |
- Hunter, Lori M., et al.
(author)
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Rural Outmigration, Natural Capital, and Livelihoods in South Africa
- 2014
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In: Population, Space and Place. - : Wiley. - 1544-8444 .- 1544-8452. ; 20:5, s. 402-420
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Journal article (peer-reviewed)abstract
- Rural households across the globe engage in both migration and natural resource use as components of livelihood strategies designed to meet household needs. Yet, migration scholars have only recently begun to regularly integrate environmental factors into empirical modelling efforts. To examine the migration-environment association in rural South Africa, we use vegetation measures derived from satellite imagery combined with detailed demographic data from over 9000 households at the Agincourt Health and Demographic Surveillance Site. Results reveal that household-level temporary migration is associated with higher levels of local natural capital, although no such association exists for permanent migration. Further, more advantaged households exhibit a stronger association between migration-environment, in-line with the 'environmental capital' hypothesis, suggesting that natural resource availability can facilitate household income diversification. We argue that a focus on migration's environmental aspects is especially timely in the contemporary era of climate change and that natural capital availability and variability represent critical pieces of the empirical migration puzzle, especially regarding cyclical livelihood migration.
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| 2. |
- Leyk, Stefan, et al.
(author)
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Spatially and Temporally Varying Associations between Temporary Outmigration and Natural Resource Availability in Resource-Dependent Rural Communities in South Africa : A Modeling Framework.
- 2012
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In: Applied Geography. - : Elsevier. - 0143-6228 .- 1873-7730. ; 34, s. 559-568
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Journal article (peer-reviewed)abstract
- Migration-environment models tend to be aspatial within chosen study regions, although associations between temporary outmigration and environmental explanatory variables likely vary across the study space. This research extends current approaches by developing migration models considering spatial non-stationarity and temporal variation - through examination of the migration-environment association at nested geographic scales (i.e. whole-population, village, and subvillage) within a specific study site. Demographic survey data from rural South Africa, combined with indicators of natural resource availability from satellite imagery, are employed in a nested modeling approach that brings out distinct patterns of spatial variation in model associations derived at finer geographic scales. Given recent heightened public and policy concern with the human migratory implications of climate change, we argue that consideration of spatial variability adds important nuance to scientific understanding of the migration-environment association.
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| 3. |
- Mandt, Kathleen E., et al.
(author)
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Ion densities and composition of Titan's upper atmosphere derived from the Cassini Ion Neutral Mass Spectrometer : Analysis methods and comparison of measured ion densities to photochemical model simulations
- 2012
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. E10006-
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Journal article (peer-reviewed)abstract
- The Cassini Ion Neutral Mass Spectrometer (INMS) has measured both neutral and ion species in Titan's upper atmosphere and ionosphere and the Enceladus plumes. Ion densities derived from INMS measurements are essential data for constraining photochemical models of Titan's ionosphere. The objective of this paper is to present an optimized method for converting raw data measured by INMS to ion densities. To do this, we conduct a detailed analysis of ground and in-flight calibration to constrain the instrument response to ion energy, the critical parameter on which the calibration is based. Data taken by the Cassini Radio Plasma Wave Science Langmuir Probe and the Cassini Plasma Spectrometer Ion Beam Spectrometer are used as independent measurement constraints in this analysis. Total ion densities derived with this method show good agreement with these data sets in the altitude region (similar to 1100-1400 km) where ion drift velocities are low and the mass of the ions is within the measurement range of the INMS (1-99 Daltons). Although ion densities calculated by the method presented here differ slightly from those presented in previous INMS publications, we find that the implications for the science presented in previous publications is mostly negligible. We demonstrate the role of the INMS ion densities in constraining photochemical models and find that (1) cross sections having high resolution as a function of wavelength are necessary for calculating the initial photoionization products and (2) there are disagreements between the measured ion densities representative of the initial steps in Titan photochemistry that require further investigation.
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| 4. |
- Richards, Stephen, et al.
(author)
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Genome Sequence of the Pea Aphid Acyrthosiphon pisum
- 2010
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In: PLoS biology. - : Public Library of Science (PLoS). - 1544-9173 .- 1545-7885. ; 8:2, s. e1000313-
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Journal article (peer-reviewed)abstract
- Aphids are important agricultural pests and also biological models for studies of insect-plant interactions, symbiosis, virus vectoring, and the developmental causes of extreme phenotypic plasticity. Here we present the 464 Mb draft genome assembly of the pea aphid Acyrthosiphon pisum. This first published whole genome sequence of a basal hemimetabolous insect provides an outgroup to the multiple published genomes of holometabolous insects. Pea aphids are host-plant specialists, they can reproduce both sexually and asexually, and they have coevolved with an obligate bacterial symbiont. Here we highlight findings from whole genome analysis that may be related to these unusual biological features. These findings include discovery of extensive gene duplication in more than 2000 gene families as well as loss of evolutionarily conserved genes. Gene family expansions relative to other published genomes include genes involved in chromatin modification, miRNA synthesis, and sugar transport. Gene losses include genes central to the IMD immune pathway, selenoprotein utilization, purine salvage, and the entire urea cycle. The pea aphid genome reveals that only a limited number of genes have been acquired from bacteria; thus the reduced gene count of Buchnera does not reflect gene transfer to the host genome. The inventory of metabolic genes in the pea aphid genome suggests that there is extensive metabolite exchange between the aphid and Buchnera, including sharing of amino acid biosynthesis between the aphid and Buchnera. The pea aphid genome provides a foundation for post-genomic studies of fundamental biological questions and applied agricultural problems.
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