Showing 3431 - 3440 of 5831 Items
Vulnerability of eelgrass (Zostera marina) to green crab (Carcinus maenas) invasion
Date: 2014-08-01
Creator: Sabine Y Berzins
Access: Open access
- Eelgrass (Zostera marina) is a perennial seagrass that is widely distributed among the shallow subtidal and intertidal Atlantic coastline of the United States and Canada. A highly productive keystone species, eelgrass helps maintain healthy estuarine and ecosystem functions by stabilizing sediments, regulating water flow, absorbing nutrients, and providing critical habitat for animals including commercially important species like soft-shell clams, blue mussels, and migrating waterfowl. Loss of eelgrass beds can therefore result in degraded water quality, shoreline erosion, and reduced fish and wildlife populations. Historically, the Maine coast supported extensive eelgrass beds. However, between 2010 and 2013, eelgrass distribution in Casco Bay declined in area by over 55%. This decline in eelgrass distribution coincides with a regional population explosion of green crabs (Carcinus maenas), an invasive species that physically disturbs eelgrass while foraging for prey. This summer, I collaborated with several Casco Bay Eelgrass Partners including individuals from the Fish and Wildlife Service, Maine Department of Environmental Protection, and the Friends of Casco Bay. Led by U.S. Geological Survey biologist Dr. Hilary Neckles, this project identifies factors that make eelgrass more or less resilient to invasion by green crabs. In June, we established permanent eelgrass survey transects at five locations spanning eastern Casco Bay. Where possible, two transects were established in different types of sediment (fine or coarse/sandy). Most of the eelgrass loss observed over the past decade has been in fine sediments. The question remains; is eelgrass in coarse sediments prone to similar levels of damage? In addition to differences in substrate type, each site also exhibited varying degrees of eelgrass density, shoot height, green crab density and population structure, and other environmental stressors including light availability, temperature, nutrient availability, and natural physical disturbance. I made biweekly measurements of green crab densities at one site, Widgeon Cove in Harpswell. Crap trapping indicated few green crabs occurred near the Widgeon Cove transect, but traps at the other four Casco Bay sites collected as many as 300 crabs within a 24-hour period. Final measurements in the eelgrass transects will be taken in September and data collection will be completed in October. Data gathered this summer will provide information to help move forward with a plan to protect and potentially restore eelgrass in Casco Bay. Additionally, I identified patches of eelgrass in the Kennebec Estuary that might be viable sites for replanting next summer. I hope to continue working on this project next year, thinking about ways to restore eelgrass to the system while identifying ways to increase trapping pressure on green crabs such that their numbers might be reduced. Final Report of research funded by the Rusack Coastal Studies fellowship.
Making predictions in an uncertain world: Environmental structure and cognitive maps
Date: 1999-01-01
Creator: Eric Chown
Access: Open access
- This article examines the relationship between environmental and cognitive structure. One of the key tasks for any agent interacting in the real world is the management of uncertainty; because of this the cognitive structures which interact with real environments, such as would be used in navigation, must effectively cope with the uncertainty inherent in a constantly changing world. Despite this uncertainty, however, real environments usually afford structure that can be effectively exploited by organisms. The article examines environmental characteristics and structures that enable humans to survive and thrive in a wide range of real environments. The relationship between these characteristics and structures, uncertainty, and cognitive structure is explored in the context of PLAN, a proposed model of human cognitive mapping, and R-PLAN, a version of PLAN that has been instantiated on an actual mobile robot. An examination of these models helps to provide insight into environmental characteristics which impact human performance on tasks which require interaction with the world. Copyright 1999 International Society for Adaptive Behavior.
Accelerating change: The power of faculty change agents to promote diversity and inclusive teaching practices
Date: 2019-10-02
Creator: R. Heather Macdonald, Rachel J. Beane, Eric M.D. Baer, Pamela L. Eddy, Norlene R., Emerson, Jan Hodder, Ellen R. Iverson, John R. McDaris, Kristin O’Connell, Carol J. Ormand
Access: Open access
- Faculty play an important role in attracting students to the geosciences, helping them to thrive in geoscience programs, and preparing them for careers. Thus, faculty have the responsibility to work toward broadening participation in the geosciences by implementing equitable and inclusive practices in their teaching and their programs. Faculty professional development that promotes diversity and inclusion is one way to move evidence-based practices into wider use. The adoption of these practices may be accelerated through a professional development diffusion model that amplifies the impacts through the work of faculty change agents. An example of this approach is the SAGE 2YC professional development program, in which faculty change agents learn and practice strategies during workshop sessions, implement changes in their own teaching, and then work in teams to lead workshops in their region under the auspices of the national program. Although this example focuses on two-year colleges, the model is applicable to faculty professional development more broadly. The success of the model is due in large part to a suite of leader-developed workshop sessions and curated resources that change agent teams may select and adapt for the regional workshops they lead. Furthermore, change agents are trusted colleagues, which makes adoption of the evidence-based practices by regional workshop participants more likely. Increased adoption of a change agent approach to faculty development will support the creation and sharing of additional resources, leading to wider diffusion and implementation of inclusive teaching practices.
Reflections questionnaire response by Anonymous on April 1, 2021
Date: 2021-01-01
Creator: Anonymous
Access: Open access
- This is a response to the Documenting Bowdoin & COVID-19 Reflections Questionnaire. The questionnaire was created in March 2021 by staff of Bowdoin's George J. Mitchell Department of Special Collections & Archives. The author is from the class of 2022.
Green Icebergs Revisited
Date: 2019-02-01
Creator: Stephen G. Warren, Collin S. Roesler, Richard E. Brandt, Mark Curran
Access: Open access
- Ice crystals form in supercooled seawater beneath several Antarctic ice shelves; as they rise to the ice-shelf base they scavenge particles from the water and incorporate them into the growing basal ice. The resulting marine ice can be ~100 m thick; it differs from sea ice in that it is clear, desalinated, and bubble-free. Icebergs of marine ice vary in color from blue to green, depending on the nature and abundance of foreign constituents in the seawater that became trapped in the ice as it grew. A red or yellow material (i.e., one that absorbs blue light), in combination with the blue of ice, can shift the wavelength of minimum absorption to green. Previously, dissolved organic carbon (DOC) had been proposed to be responsible for the green color. Subsequent measurements of low DOC values in green icebergs, together with the recent finding of large concentrations of iron in marine ice from the Amery Ice Shelf, suggest that the color of green icebergs is caused more by iron-oxide minerals than by DOC. These icebergs travel great distances from their origin; when they melt they can deliver iron as a nutrient to the Southern Ocean.
Methods for Modernism: American Art, 1876-1925
Date: 2010-01-01
Creator: Diana K. Tuite, Linda J. Docherty
Access: Open access
Projecting global land-use change and its effect on ecosystem service provision and biodiversity with simple models
Date: 2010-12-01
Creator: Erik Nelson, Heather Sander, Peter Hawthorne, Marc Conte, Driss, Ennaanay, Stacie Wolny, Steven Manson, Stephen Polasky
Access: Open access
- Background: As the global human population grows and its consumption patterns change, additional land will be needed for living space and agricultural production. A critical question facing global society is how to meet growing human demands for living space, food, fuel, and other materials while sustaining ecosystem services and biodiversity [1]. Methodology/Principal Findings: We spatially allocate two scenarios of 2000 to 2015 global areal change in urban land and cropland at the grid cell-level and measure the impact of this change on the provision of ecosystem services and biodiversity. The models and techniques used to spatially allocate land-use/land-cover (LULC) change and evaluate its impact on ecosystems are relatively simple and transparent [2]. The difference in the magnitude and pattern of cropland expansion across the two scenarios engenders different tradeoffs among crop production, provision of species habitat, and other important ecosystem services such as biomass carbon storage. For example, in one scenario, 5.2 grams of carbon stored in biomass is released for every additional calorie of crop produced across the globe; under the other scenario this tradeoff rate is 13.7. By comparing scenarios and their impacts we can begin to identify the global pattern of cropland and irrigation development that is significant enough to meet future food needs but has less of an impact on ecosystem service and habitat provision. Conclusions/Significance: Urban area and croplands will expand in the future to meet human needs for living space, livelihoods, and food. In order to jointly provide desired levels of urban land, food production, and ecosystem service and species habitat provision the global society will have to become much more strategic in its allocation of intensively managed land uses. Here we illustrate a method for quickly and transparently evaluating the performance of potential global futures.
The parasexual cycle in Candida albicans provides an alternative pathway to meiosis for the formation of recombinant strains
Date: 2008-05-01
Creator: Anja Forche, Kevin Alby, Dana Schaefer, Alexander D. Johnson, Judith, Berman, Richard J. Bennett
Access: Open access
- Candida albicans has an elaborate, yet efficient, mating system that promotes conjugation between diploid a and α strains. The product of mating is a tetraploid a/α cell that must undergo a reductional division to return to the diploid state. Despite the presence of several "meiosis-specific" genes in the C. albicans genome, a meiotic program has not been observed. Instead, tetraploid products of mating can be induced to undergo efficient, random chromosome loss, often producing strains that are diploid, or close to diploid, in ploidy. Using SNP and comparative genome hybridization arrays we have now analyzed the genotypes of products from the C. albicans parasexual cycle. We show that the parasexual cycle generates progeny strains with shuffled combinations of the eight C. albicans chromosomes. In addition, several isolates had undergone extensive genetic recombination between homologous chromosomes, including multiple gene conversion events. Progeny strains exhibited altered colony morphologies on laboratory media, demonstrating that the parasexual cycle generates phenotypic variants of C. albicans. In several fungi, including Saccharomyces cerevisiae and Schizosaccharomyces pombe, the conserved Spo11 protein is integral to meiotic recombination, where it is required for the formation of DNA double-strand breaks. We show that deletion of SPO11 prevented genetic recombination between homologous chromosomes during the C. albicans parasexual cycle. These findings suggest that at least one meiosis-specific gene has been re-programmed to mediate genetic recombination during the alternative parasexual life cycle of C. albicans. We discuss, in light of the long association of C. albicans with warm-blooded animals, the potential advantages of a parasexual cycle over a conventional sexual cycle. © 2008 Forche et al.
Taming the giant within
Date: 2019-01-01
Creator: Jack R. Bateman, David J. Anderson
Access: Open access