Faculty Scholarship
Showing 31 - 40 of 733 Items
The initiation and development of small peat-forming ecosystems adjacent to lakes in the north central Canadian low arctic during the Holocene
Date: 2017-07-01
Creator: Philip Camill, Charles E. Umbanhowar, Christoph Geiss, Mark B. Edlund, Will O., Hobbs, Allison Dupont, Catherine Doyle-Capitman, Matthew Ramos
Access: Open access
- Small peat-forming ecosystems in arctic landscapes may play a significant role in the regional biogeochemistry of high-latitude systems, yet they are understudied compared to arctic uplands and other major peat-forming regions of the North. We present a new data set of 25 radiocarbon-dated permafrost peat cores sampled around eight low arctic lake sites in northern Manitoba (Canada) to examine the timing of peat initiation and controls on peat accumulation throughout the Holocene. We used macrofossils and charcoal to characterize changes in the plant community and fire, and we explored potential impacts of these local factors, as well as regional climatic change, on rates of C accumulation and C stocks. Peat initiation was variable across and within sites, suggesting the influence of local topography, but 56% of the cores initiated after 3000 B.P. Most cores initiated and remained as drier bog hummock communities, with few vegetation transitions in this landscape. C accumulation was relatively slow and did not appear to be correlated with Holocene-scale climatic variability, but C stocks in this landscape were substantial (mean = 45.4 kg C m ), potentially accounting for 13.2 Pg C in the Taiga Shield ecozone. To the extent that small peat-forming systems are underrepresented in peatland mapping, soil organic carbon (SOC) stocks may be underestimated in arctic regions. Mean fire severity appeared to be negatively correlated with C accumulation rates. Initiation and accumulation of soil C may respond to both regional and local factors, and substantial lowland soil C stocks have the potential for biogeochemical impacts on adjacent aquatic ecosystems. −2
Prototypes, location, and associative networks (PLAN): Towards a unified theory of cognitive mapping
Date: 1995-01-01
Creator: Eric Chown, Stephen Kaplan, David Kortenkamp
Access: Open access
- An integrated representation of large-scale space, or cognitive map, colled PLAN, is presented that attempts to address a broader spectrum of issues than has been previously attempted in a single model. Rather than examining way-finding as a process separate from the rest of cognition, one or the fundamental goals of this work is to examine how the wayfinding process is integrated into general cognition. One result of this approach is that the model is "heads-up," or scene-based, because it takes advantage of the properties of the human visual system and, particularly, the visual system's split into two pathways. The emphasis on the human location or "where" system is new to cognitive mapping and is port of an attempt to synthesize prototype theory, associative networks and location together in a connectionist system. Not all of PLAN is new, however. Many of its parts have analogues in one or another preexisting theory. What makes PLAN unique is integrating the various components into a coherent whole, and the capacity of this resulting system to speak to a wide range of constraints. Our approach emphasizes adaptiveness; thus, our focus on such issues as ease of use and efficiency of learning. The result is a model that has a stronger relationship both to the environment, and to the ways that humans interact with it, compared with previous models. The resulting model is examined in some detail and compared to other systems. © 1995.
The efficiency of voluntary incentive policies for preventing biodiversity loss
Date: 2011-01-01
Creator: David J. Lewis, Andrew J. Plantinga, Erik Nelson, Stephen Polasky
Access: Open access
- Habitat loss is a primary cause of loss of biodiversity but conserving habitat for species presents challenges. Land parcels differ in their ability to produce returns for landowners and landowners may have private information about the value of the land to them. Land parcels also differ in the type and quality of habitat and the spatial pattern of land use across multiple landowners is important for determining the conservation value of parcels. This paper analyzes the relative efficiency of simple voluntary incentive-based policies in achieving biodiversity conservation objectives. This topic is important not just for biodiversity conservation but for any effort to provide a public good requiring coordination across multiple decision-makers who have some degree of private information. We develop a method that integrates spatially explicit data, an econometric model of private land-use decisions, landscape simulations, a biological model of biodiversity as a function of landscape pattern, and an algorithm that estimates the set of efficient solutions. These methods allow us to simulate landowner responses to policies, measure the consequences of these decisions for biodiversity conservation, and compare these outcomes to efficient outcomes to show the relative efficiency of various policy approaches. We find substantial differences in biodiversity conservation scores generated by simple voluntary incentive-based policies and efficient solutions. The performance of incentive-based policies is particularly poor at low levels of the conservation budget where spatial fragmentation of conserved parcels is a large concern. Performance can be improved by encouraging agglomeration of conserved habitat and by incorporating basic biological information, such as that on rare habitats, into the selection criteria. © 2010 Elsevier B.V.
Religion and science in the Eastern mediterranean
Date: 2016-09-01
Creator: Robert Morrison
Access: Open access
- “Science and Orthodox Christianity: An Overview” is an ambitious survey that reminds scholars of science in Islamic societies that the conversation between Islam and science is really a conversation between Islam and science in different contexts and that conversations between Islam and science can be found with less renowned scientific developments such as prophetic medicine. This response points out parallels in how Greek Orthodox and Ottoman Muslim scholars mediated new developments in Western European science and in how both Greek Orthodox and some Ottoman Muslim scholars propounded a mathematical humanism. Finally, it argues that the account of post-1453 scientific exchange is more complex than “Science and Orthodox Christianity” intimates. At the least, if there was no scholarly exchange between Greek Orthodox Christians, on the one hand, and, on the other hand, Muslims and Jews—who, in turn, enjoyed scholarly exchange with the West well after 1453—there are clearly two different Easts.
Conical wave propagation and diffraction in two-dimensional hexagonally packed granular lattices
Date: 2016-01-25
Creator: C. Chong, P. G. Kevrekidis, M. J. Ablowitz, Yi Ping Ma
Access: Open access
- Linear and nonlinear mechanisms for conical wave propagation in two-dimensional lattices are explored in the realm of phononic crystals. As a prototypical example, a statically compressed granular lattice of spherical particles arranged in a hexagonal packing configuration is analyzed. Upon identifying the dispersion relation of the underlying linear problem, the resulting diffraction properties are considered. Analysis both via a heuristic argument for the linear propagation of a wave packet and via asymptotic analysis leading to the derivation of a Dirac system suggests the occurrence of conical diffraction. This analysis is valid for strong precompression, i.e., near the linear regime. For weak precompression, conical wave propagation is still possible, but the resulting expanding circular wave front is of a nonoscillatory nature, resulting from the complex interplay among the discreteness, nonlinearity, and geometry of the packing. The transition between these two types of propagation is explored.
Fgf signaling is required for zebrafish tooth development
Date: 2004-10-01
Creator: William R. Jackman, Bruce W. Draper, David W. Stock
Access: Open access
- We have investigated fibroblast growth factor (FGF) signaling during the development of the zebrafish pharyngeal dentition with the goal of uncovering novel roles for FGFs in tooth development as well as phylogenetic and topographic diversity in the tooth developmental pathway. We found that the tooth-related expression of several zebrafish genes is similar to that of their mouse orthologs, including both epithelial and mesenchymal markers. Additionally, significant differences in gene expression between zebrafish and mouse teeth are indicated by the apparent lack of fgf8 and pax9 expression in zebrafish tooth germs. FGF receptor inhibition with SU5402 at 32 h blocked dental epithelial morphogenesis and tooth mineralization. While the pharyngeal epithelium remained intact as judged by normal pitx2 expression, not only was the mesenchymal expression of lhx6 and lhx7 eliminated as expected from mouse studies, but the epithelial expression of dlx2a, dlx2b, fgf3, and fgf4 was as well. This latter result provides novel evidence that the dental epithelium is a target of FGF signaling. However, the failure of SU5402 to block localized expression of pitx2 suggests that the earliest steps of tooth initiation are FGF-independent. Investigations of specific FGF ligands with morpholino antisense oligonucleotides revealed only a mild tooth shape phenotype following fgf4 knockdown, while fgf8 inhibition revealed only a subtle down-regulation of dental dlx2b expression with no apparent effect on tooth morphology. Our results suggest redundant FGF signals target the dental epithelium and together are required for dental morphogenesis. Further work will be required to elucidate the nature of these signals, particularly with respect to their origins and whether they act through the mesenchyme. © 2004 Elsevier Inc. All rights reserved.
Rapid mechanisms for generating genome diversity: Whole ploidy shifts, aneuploidy, and loss of heterozygosity
Date: 2014-01-01
Creator: Richard J. Bennett, Anja Forche, Judith Berman
Access: Open access
- Human fungal pathogens can exist in a variety of ploidy states, including euploid and aneuploid forms. Ploidy change has a major impact on phenotypic properties, including the regulation of interactions with the human host. In addition, the rapid emergence of drug-resistant isolates is often associated with the formation of specific supernumerary chromosomes. Pathogens such as Candida albicans and Cryptococcus neoformans appear particularly well adapted for propagation in multiple ploidy states with novel pathways driving ploidy variation. In both species, heterozygous cells also readily undergo loss of heterozygosity (LOH), leading to additional phenotypic changes such as altered drug resistance. Here, we examine the sexual and parasexual cycles that drive ploidy variation in human fungal pathogens and discuss ploidy and LOH events with respect to their far-reaching roles in fungal adaptation and pathogenesis.
Two modes of transvection at the eyes absent gene of Drosophila demonstrate plasticity in transcriptional regulatory interactions in cis and in trans
Date: 2019-01-01
Creator: Katherine Tian, Rachel E. Henderson, Reyna Parker, Alexia Brown, Justine E., Johnson, Jack R. Bateman
Access: Open access
- For many genes, proper gene expression requires coordinated and dynamic interactions between multiple regulatory elements, each of which can either promote or silence transcription. In Drosophila, the complexity of the regulatory landscape is further complicated by the tight physical pairing of homologous chromosomes, which can permit regulatory elements to interact in trans, a phenomenon known as transvection. To better understand how gene expression can be programmed through cis- and trans-regulatory interactions, we analyzed transvection effects for a collection of alleles of the eyes absent (eya) gene. We find that trans-activation of a promoter by the eya eye-specific enhancers is broadly supported in many allelic backgrounds, and that the availability of an enhancer to act in trans can be predicted based on the molecular lesion of an eya allele. Furthermore, by manipulating promoter availability in cis and in trans, we demonstrate that the eye-specific enhancers of eya show plasticity in their promoter preference between two different transcriptional start sites, which depends on promoter competition between the two potential targets. Finally, we show that certain alleles of eya demonstrate pairing-sensitive silencing resulting from trans-interactions between Polycomb Response Elements (PREs), and genetic and genomic data support a general role for PcG proteins in mediating transcriptional silencing at eya. Overall, our data highlight how eya gene regulation relies upon a complex but plastic interplay between multiple enhancers, promoters, and PREs.
Economic-based projections of future land use in the conterminous United States under alternative policy scenarios
Date: 2012-04-01
Creator: V. C. Radeloff, E. Nelson, A. J. Plantinga, D. J. Lewis, D., Helmers, J. J. Lawler, J. C. Withey, F. Beaudry, S. Martinuzzi
Access: Open access
- Land-use change significantly contributes to biodiversity loss, invasive species spread, changes in biogeochemical cycles, and the loss of ecosystem services. Planning for a sustainable future requires a thorough understanding of expected land use at the fine spatial scales relevant for modeling many ecological processes and at dimensions appropriate for regional or national-level policy making. Our goal was to construct and parameterize an econometric model of land-use change to project future land use to the year 2051 at a fine spatial scale across the conterminous United States under several alternative land-use policy scenarios. We parameterized the econometric model of land-use change with the National Resource Inventory (NRI) 1992 and 1997 land-use data for 844 000 sample points. Land-use transitions were estimated for five land-use classes (cropland, pasture, range, forest, and urban). We predicted land-use change under four scenarios: business-as-usual, afforestation, removal of agricultural subsidies, and increased urban rents. Our results for the business-as-usual scenario showed widespread changes in land use, affecting 36% of the land area of the conterminous United States, with large increases in urban land (79%) and forest (7%), and declines in cropland (\-16%) and pasture (\-13%). Areas with particularly high rates of land-use change included the larger Chicago area, parts of the Pacific Northwest, and the Central Valley of California. However, while land-use change was substantial, differences in results among the four scenarios were relatively minor. The only scenario that was markedly different was the afforestation scenario, which resulted in an increase of forest area that was twice as high as the business-as-usual scenario. Land-use policies can affect trends, but only so much. The basic economic and demographic factors shaping land-use changes in the United States are powerful, and even fairly dramatic policy changes, showed only moderate deviations from the business-as-usual scenario. Given the magnitude of predicted land-use change, any attempts to identify a sustainable future or to predict the effects of climate change will have to take likely land-use changes into account. Econometric models that can simulate land-use change for broad areas with fine resolution are necessary to predict trends in ecosystem service provision and biodiversity persistence. © 2012 by the Ecological Society of America.
Tempered, invariant, positive-definite distributions on SU(1, 1)/{± 1}
Date: 1984-01-01
Creator: William H. Barker
Access: Open access