1,423 research outputs found
Contrasting Global Patterns of Spatially Periodic Fairy Circles and Regular Insect Nests in Drylands
No full textNumerical analysis of spatial pattern is widely used in ecology to describe the characteristics of floral and faunal distributions. These methods allow attribution of pattern to causal mechanisms by uncovering the specific signatures of patterns and causal agents. For example, grassland-gap patterns called fairy circles (FCs) in Namibia and Australia are characterized by highly regular and homogenous distributions across landscapes that show spatially periodic ordering. These FCs have been suggested to be caused by both social insects and competitive plant interactions. We compared eight Namibian and Australian FC patterns and also modeled FCs to 16 patterns of social insect nests in Africa, Australia, and America that include the most regular termite mound patterns known. For pattern-process inference, we used spatial statistics based on both nearest-neighbor analysis and neighborhood-density functions. None of the analyzed insect-nest distributions attain the spatially periodic ordering that is typical of FCs. The inherently more variable patterns of termite and ant nests are commonly attributable to well documented aspects of the faunal life-history. Our quantitative evidence from drylands shows that the more variable insect-nest distributions in water-limited environments cannot explain the characteristic spatial signature of FCs. The analysis demonstrates the interpretation of scale-dependent neighborhood-density functions and that it is the identification of unique spatial signatures in regular patterns that need to be linked to process. While our results cannot verify a specific hypothesis, they support the hypothesis that FCs in these drylands are more likely an emergent vegetation pattern caused by strong plant competition for water
Supporting Data for “Why So Slow? Mechanistic Insights from Studies of a Poor Catalyst for Polymerization of ε-Caprolactone”
No full textThese files contain data along with associated output from instrumentation supporting all results reported in Stasiw, D. E.; Mandal, M.; Neisen, B. D.; Mitchell, L. A.; Cramer, C. J.; Tolman, W. B. Why so slow? Mechanistic insights from studies of a poor catalyst for polymerization of ε-caprolactone. Inorg. Chem., 2016, 56, 725–728. Polymerization of ε-caprolactone (CL) using an aluminum alkoxide catalyst (1) designed to prevent unproductive trans binding was monitored at 110 °C in toluene-d8 by 1H NMR and the concentration versus time data fit to a first-order rate expression. A comparison of t1/2 for 1 to values for many other aluminum alkyl and alkoxide complexes shows much lower activity of 1 toward polymerization of CL. Density functional theory calculations were used to understand the basis for the slow kinetics. The optimized geometry of the ligand framework of 1 was found indeed to make CL trans binding difficult: no trans-bound intermediate could be identified as a local minimum. Nor were local minima for cis-bound precomplexes found, suggesting a concerted coordination–insertion for polymer initiation and propagation. The sluggish performance of 1 is attributed to a high-framework distortion energy required to deform the “resting” ligand geometry to that providing optimal catalysis in the corresponding transition-state structure geometry, thus suggesting a need to incorporate ligand flexibility in the design of efficient polymerization catalysts..
Corresponding author for experimental data is William B. Tolman ([email protected]).
Corresponding author for computational data is Christopher J. Cramer ([email protected]).Funding for this project was provided by the Center for Sustainable Polymers at the University of Minnesota, a National Science Foundation (NSF)-supported Center for Chemical Innovation (Grant CHE-1413862). The X-ray diffraction experiments were performed using a crystal diffractometer acquired through NSF-MRI Award CHE-1229400. The authors acknowledge the MSI at the University of Minnesota for providing resources that contributed to the research results.Tolman, William, B; Cramer, Christopher, J; Stasiw, Daniel E; Mandal, Mukunda; Neisen, Benjamin D; Mitchell, Lauren A. (2017). Supporting Data for “Why So Slow? Mechanistic Insights from Studies of a Poor Catalyst for Polymerization of ε-Caprolactone”. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/D6F60H
N and P limitation of fynbos plants and the nutritional status of legume habitats in the Cape Floristic Region
No full textIn general, terrestrial ecosystems are limited by both N and P, but, as legumes fix atmospheric nitrogen, I hypothesized that fynbos legumes would be P limited and nonlegumes would be N limited, and that the degree to which these plants respond to N and P would depend on the levels of each of these two nutrients in the growth media. To test these hypotheses, three legumes and three non-legumes native to the fynbos were grown in a complete factorial arrangement of four levels of N and P in a glass house. Nitrogen was supplied at 20, 40, 80 and 150 mg kg-¹ soil and P at 0.8, 5, 15, and 31 mg kg-¹. Overall, the results showed that the responses of the legume and nonlegume species to N and P supply were species specific, but that the legume species seemed to be more limited by N supply than the non-legumes. There was no N x P interaction in this study, which implied that the plant response to N and P, did not depend on the levels of each other. Given the nitrogen fixing capabilities of legumes and high nutrient demanding lifestyle, I made the hypothesis that, on a given landscape, the soils on which the fynbos legumes occur were more nutrient rich than the bulk non-legume soils. Related to this hypothesis is the question of whether the more nutrient rich soils within the legume populations would be mirrored by leaves with both a higher specific leaf area and higher nutrient concentration, than the leaves of the non-legumes. To test these hypotheses, I determined the nutrient levels of both the soils and plants within both the legume- and non-legumes stands at eight different sites in the CFR. The data were subjected to multifactorial discriminant function analysis and Nested ANOVA analyses. The results of the analyses led to the conclusion that the soil on which legume stands occurred were rarely more fertile than the non-legumes on the landscape in the CFR, and, except for leaf N, there seemed to be no differences between leaf nutrient concentrations and the SLA of the legume and non-legume plants
The secretion of acid phosphatase by proteaceae as an adaptation to limited phosphate availability
No full textIncludes abstract.Includes bibliographical references (leaves 59-67).The Proteaceae are a distinctive component of South Africa’s Fynbos and Australia’s Kwongan vegetation and display a number of adaptations to the soils of these nutrientpoor regions, where availability of phosphate (P) is particularly limited. The Proteaceae are notable for the virtually family-wide ability to form cluster roots
The effects of attitudes about economic inequality on support for markets and democracy in Latin America, 1995-2010
No full textThe potential effects of economic inequality on markets and democracy have received significant attention in recent years. Less attention, however, has been devoted to empirically examining the attitudinal aspects of these relationships. In this dissertation, I examine the effects of attitudes about inequality on attitudes about government regulation of the economy, illiberal democracy, and civic engagement. I examine these effects with nine multilevel data sets spanning 1995-2010 and in the Latin America context. The statistical findings provide weak empirical support for the hypothesis that greater dissatisfaction with inequality is associated with greater support for a more government-regulated economy. They also suggest that dissatisfaction with inequality is not systematically related to support for illiberal democracy. Furthermore, the findings provide weak empirical evidence that dissatisfaction with inequality is systematically related to civic engagement. Moreover, the effects of dissatisfaction with inequality on support for these three individual-level outcomes do not appear to be systematically conditioned by various individual- and country-level factors. Therefore, the results suggest that attitudes about economic inequality are not consistently related to various attitudes about markets and democracy in the recent Latin American context. The findings help adjudicate between competing claims about the effects of economic inequality on markets and democracy, and they also shed light on the potential durability of markets and democracy in 21st century Latin America in the wake of widespread public dissatisfaction with economic inequality.Ph. D.Includes bibliographical referencesIncludes vitaby Brain D. Crame
Structure and carboxyl-terminal domain (CTD) binding of the Set2 SRI domain that couples histone H3 Lys36 methylation to transcription.
No full textDuring mRNA elongation, the SRI domain of the histone H3 methyltransferase Set2 binds to the phosphorylated carboxyl-terminal domain (CTD) of RNA polymerase II. The solution structure of the yeast Set2 SRI domain reveals a novel CTD-binding fold consisting of a left-handed three-helix bundle. NMR titration shows that the SRI domain binds an Ser2/Ser5-phosphorylated CTD peptide comprising two heptapeptide repeats and three flanking NH2-terminal residues, whereas a single CTD repeat is insufficient for binding. Residues that show strong chemical shift perturbations upon CTD binding cluster in two regions. Both CTD tyrosine side chains contact the SRI domain. One of the tyrosines binds in the region with the strongest chemical shift perturbations, formed by the two NH2-terminal helices. Unexpectedly, the SRI domain fold resembles the structure of an RNA polymerase-interacting domain in bacterial σ factors (domain σ2 in σ70)
Evaluating the importance of root abscission versus efflux to plant N-loss: consequences for plant N-isotope composition
No full textThe common observation that plant δ¹⁵N values are lower than those of associated soil is generally attributed to transporter-facilitated efflux of ¹⁵N-enriched N. N efflux tends to occur under specific conditions, for instance, when the external N concentration is high, when the external medium is acidic and when roots experience mechanical stress. While efflux is presumed to act as a regulator of cytoplasmic N concentrations, it is energetically costly for plants to take up N only to release it back into the rhizosphere. A link between root tissue loss (e.g. root turnover or rhizodeposition) and plant δ¹⁵N has not been suggested, although root abscission is likely to be more ubiquitous than N efflux. This thesis questions the extent to which N efflux and root abscission contribute to plant N-loss and plant δ¹⁵N values. I hypothesized that: (1) plants supplied with more N would have more negative δ¹⁵N relative to the source, and greater root abscission from a relatively larger root biomass (2) the aeration necessary for hydroponic culture can act as a mechanical stressor on roots, accentuating plant N-loss through root abscission and N efflux. Wheat was grown in sand with NO₃- supplied at five relative addition rates (RAR) and in hydroponics with three physical disturbance regimes (direct aeration, aeration constrained within a pipe and circulation of nutrient solution through sand). The δ¹⁵N of roots and shoots, as well as the plant-derived N accumulation in both growth mediums, were determined. When the N supply matched the plant N demand, as determined by the relative growth rate, there was no discrimination between plant and source δ¹⁵N. N-loss here, although negligible, was in the organic form, which implies root abscission. By contrast, when N supply exceeded plant N demand, plant δ¹⁵N values decreased (e.g. after 47 d, plant δ¹⁵N of RAR 0.075 d⁻¹ was 0.4‰ but was −4.1‰ at RAR 0.175 d⁻¹) because they lost ¹⁵N-enriched N. This N was largely inorganic and presumably lost through efflux. In disturbed hydroponic conditions (i.e. direct and pipe treatments), root 'fragments' were a major biomass- (six-fold greater than root dry weight) and N-loss (two-fold greater than plant net N uptake) pathway. Plants from all treatments lost more N within root fragments than through efflux, although the cumulative N-loss was significantly smaller from plants grown in relatively undisturbed hydroponic conditions (i.e. sand). This suggests that root abscission is likely to be an important N-loss pathway for plants and thus contributes to the global offset between plant and soil δ¹⁵N values. Moreover, efforts to improve nitrogen use efficiency of crop plants, though reduced efflux, need to take cognizance of root abscission because it is an unavoidable artefact of root growth
Testing the adaptive nature of morphological diversification in the hemiparasitic genus Thesium L. (Santalaceae)
No full textThis thesis tests the hypothesis that parasitism in Thesium represents a specialised foraging strategy for dealing with the nutrient poor soils found in the CFR
Ecological differentiation and the evolution and maintenance of fynbos diversity
No full textPreserving the structure and functioning of ecosystems and the benefits they provide to society depends on our understanding of how biodiversity influences ecosystem function and which processes determine the composition and diversity of biological assemblages. Ecological, evolutionary and biogeographical processes interact to determine the genesis, maintenance and spatio-temporal arrangement of biodiversity. Here I investigate these processes in the Cape fynbos of South Africa by examining the diversification, biogeography and community assembly of a clade of reticulate-sheathed Tetraria species (Cyperaceae:Schoeneae)
Association of retroplacental blood with basal plate myofibers
No full textObjectives: Diagnosed clinical abruption showing blood clot should be signed out in the pathology report as retroplacental hemorrhage with or without parenchymal indentation, and submitted clot separate from the placenta should be weighed. In our experience some cases sent as clinical abruptions have been cases of morbid adherence. This study was undertaken to evaluate the association of retroplacental blood with basal plate myofibers (BPMF).
Methods: 156 placentas reviewed by a board certified pediatric pathologist at a community hospital were evaluated for significant retroplacental blood. Basal plates were reviewed for deviations from normal.
Results: 33/156 placentas (21%) had significant retroplacental blood. 21/156 (13%) had a separate clot, of which 11/21 (52%) had basal plate myofibers (BPMF). 11 BPMF‐associated separate clots ranged from 10.5‐60 gms (average 23); while the clots of 10 cases with no demonstrated BPMF ranged from 19‐440 gms (average 82), tending to be larger (p<.03). Basal plate damage prior to delivery was noted in both sets of placentas. BPMF placentas could have myometrial damage prior to delivery.
Conclusions: Since BPMF may confer a risk for accreta in a subsequent pregnancy, submission of a separate clot with the placenta should lead the pathologist to evaluate for basal plate myofibers on H&E, and consider if there is an evidencebased indication to do an actin stain; before presuming a diagnosis of abruption.Peer reviewedAbstract published as Wyand, R. Cramer, S., Oshri, A., Heller, D. (2017). Association of retroplacental blood with basal plate myofibers. Placenta, 57, 280. http://dx.doi.org/10.1016/j.placenta.2017.07.18
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