The case for the multi-species ecological system, with special reference to succession and stability

Multi-species life support system based on ecological theor

Consequences of small storage capacity in nannoplankton pertinent to measurement of primary production in tropical waters

A theory based on the performance of an electrical analogue circuit for balanced ecosystems relates respiration to the storage of labile organic matter during daytime photosynthesis. A very small storage capacitance and time constant may be introduced into the circuit to simulate a nannoplanktonic sygtem. It is found that respiration approaches photosynthesis during the day and almost ceases at night. Consequently, the usual carbon14 measurements of net production, and the conventional light-and-dark-bottle oxygen measurements of net production and nighttime respiration greatly underestimate gross photosy~thesis of tropical seas. An example of this phenomenon is shown in a planktonic brine microcosm

Beyond connectedness: why pairwise metrics cannot capture community stability

The connectedness of species in a trophic web has long been a key structural characteristic for both theoreticians and empiricists in their understanding of community stability. In the past decades, there has been a shift from focussing on determining the number of interactions to taking into account their relative strengths. The question is: How do the strengths of the interactions determine the stability of a community? Recently, a metric has been proposed which compares the stability of observed communities in terms of the strength of three- and two-link feedback loops (cycles of interaction strengths). However, it has also been suggested that we do not need to go beyond the pairwise structure of interactions to capture stability. Here, we directly compare the performance of the feedback and pairwise metrics. Using observed food-web structures, we show that the pairwise metric does not work as a comparator of stability and is many orders of magnitude away from the actual stability values. We argue that metrics based on pairwise-strength information cannot capture the complex organization of strong and weak links in a community, which is essential for system stability

THE CAUTIOUS CRUSADER: HOW THE ATLANTA DAILY WORLD COVERED THE STRUGGLE FOR AFRICAN AMERICAN RIGHTS FROM 1945 TO 1985

Title of Dissertation: THE CAUTIOUS CRUSADER: HOW THE ATLANTA DAILY WORLD COVERED THE STRUGGLE FOR AFRICAN AMERICAN RIGHTS FROM 1945 TO 1985 Name: Maria E. Odum-Hinmon Doctor of Philosophy, 2005 Dissertation Directed By: Prof. Maurine Beasley, Ph. D. Philip Merrill College of Journalism This dissertation is a study of the Atlanta Daily World, a conservative black newspaper founded in 1928, that covered the civil rights struggle in ways that reflected its orientation to both democratic principles and practical business concerns. The World became the most successful black daily newspaper in the nation after becoming a daily in 1932 and maintaining that status for nearly four decades. This dissertation details how this newspaper chronicled the simultaneous push for civil rights, better conditions in the black community, and recognition of black achievement during the volatile period of social change following World War II. Using descriptive, thematic analysis and in-depth interviews, this dissertation explores the question: How did the Atlanta Daily World crusade for the rights of African Americans against a backdrop of changing times, particularly during the crucial forty-year period between 1945 and 1985? The study contends that the newspaper carried out its crusade by highlighting information and events important to the black community from the perspective of the newspaper’s strong-willed publisher, C. A. Scott, and it succeeded by relying on Scott family members and employees who worked long hours for low wages. The study shows that the World fought against lynching and pushed for voting rights in the 1940s and 1950s. The newspaper eschewed sit-in demonstrations to force eateries to desegregate in the 1960s because they seemed dangerous and counterproductive when the college students wound up in jail rather than in school. The World endorsed Republican Presidents and was not swayed to the other side when the Rev. Jesse Jackson ran for President in 1984. The newspaper, however, drew a line against the conservative agenda when the World wholeheartedly endorsed the merits of affirmative action. Now a weekly under more liberal leadership, the World continues to struggle to find its new role when blacks are more assimilated than ever into the fabric of American society. This dissertation, the first in-depth scholarly study of the newspaper, shows how it has managed to maintain itself as a voice of middle-class African American belief in the democratic process

Maximum Power Efficiency and Criticality in Random Boolean Networks

Random Boolean networks are models of disordered causal systems that can occur in cells and the biosphere. These are open thermodynamic systems exhibiting a flow of energy that is dissipated at a finite rate. Life does work to acquire more energy, then uses the available energy it has gained to perform more work. It is plausible that natural selection has optimized many biological systems for power efficiency: useful power generated per unit fuel. In this letter we begin to investigate these questions for random Boolean networks using Landauer's erasure principle, which defines a minimum entropy cost for bit erasure. We show that critical Boolean networks maximize available power efficiency, which requires that the system have a finite displacement from equilibrium. Our initial results may extend to more realistic models for cells and ecosystems.Comment: 4 pages RevTeX, 1 figure in .eps format. Comments welcome, v2: minor clarifications added, conclusions unchanged. v3: paper rewritten to clarify it; conclusions unchange

Assessing the importance of a self-generated detachment process in river biofilm models

1. Epilithic biofilm biomass was measured for 14 months in two sites, located up- and downstream of the city of Toulouse in the Garonne River (south-west France). Periodical sampling provided a biomass data set to compare with simulations from the model of Uehlinger, Bürher and Reichert (1996: Freshwater Biology, 36, 249–263.), in order to evaluate the impact of hydraulic disturbance. 2. Despite differences in application conditions (e.g. river size, discharge, frequency of disturbance), the base equation satisfactorily predicted biomass between low and high water periods of the year, suggesting that the flood disturbance regime may be considered a universal mechanism controlling periphyton biomass. 3. However modelling gave no agreement with biomass dynamics during the 7-month long low water period that the river experienced. The influence of other biomass-regulating factors (temperature, light and soluble reactive phosphorus) on temporal biomass dynamics was weak. 4. Implementing a supplementary mechanism corresponding to a temperature-dependent self-generated loss because of heterotrophic processes allowed us to accurately reproduce the observed pattern: a succession of two peaks. This case study suggests that during typical summer low water periods (flow stability and favourable temperature) river biofilm modelling requires self-generated detachment to be considered

Temporal Expectations in Delay of Gratification

We examined how temporal expectations influence preference reversals in a delay of gratification task for rats based on a hypothesis of Rachlin (2000), who suggested that preference for a larger-later reward may shift in favor of a smaller-immediate reward as a result of changes in when that larger reward is expected. To explore Rachlin’s hypothesis, we pre-exposed two groups of rats to the delays associated with a larger-later reinforcer from a delay of gratification task. One group experienced the delays as a function of their choices in an intertemporal choice task and the other group experienced delays yoked from the first group (independent of their behavior) in an exposure training procedure. In addition, we included a third group of rats that were not exposed to delays during pre-exposure training as a comparison to the other two groups. Overall, the two groups of rats that experienced delays during pre-exposure training tended to make fewer defection responses than the comparison group during the delay of gratification task. Consistent with Rachlin’s hypothesis, our results suggest that temporal learning may influence preference reversals in a delay of gratification task, providing a number of future directions for research in this area

African-American fathers’ perspectives on their children’s health education: a qualitative, exploratory study

Purpose: To investigate African-American fathers’ (AAF) perceptions regarding the applicability and need for their involvement as a health connection for their children and describe how participating fathers’ behavior was affected by their attitudes, knowledge, and perceptions of their influence on their children’s health. Methods: This exploratory study gathered data via semi-structured focus groups (n = 3) and thematically analyzed it utilizing a grounded theory approach. Participants included AAF (n = 20) with a mean age of 37 years (SD 11.79), with at least one child between 6 and 18 years old. Results: Four major themes were revealed: (1) appropriate health education for participants’ children (should first and foremost be delivered by parents); (2) participants’ paternal health-related guidance approach (reactive, rather than proactive); (3) participants’ perceived influences on health-related communication with their children (gender roles, efficacy constraints); and (4) paternal definitions of health (most often associated with diet). Conclusion: Understanding AAFs’ perceived and desired role in their children’s health edification can inform initiatives that actively engage these men, and nurture their level of involvement, to promote positive health behaviors among their children; this is necessary to realize their potential to actively improve the health of their children, families, and communities.The open access fee for this work was funded through the Texas A&M University Open Access to Knowledge (OAK) Fund