The Effects of Intraspecific Variation of Crayfish Behavior on Nutrient Cycling in Aquatic Environments

Human activities are rapidly altering species traits at a global scale. Yet, there remains a critical need to determine whether trait variation within species affects ecosystem responses to global change. In particular, intraspecific variation in feeding behavior can have strong effects on ecosystem processes, such as nutrient cycling in streams. Crayfish are dominant consumers in streams and play key roles in controlling important stream dynamics such as nutrient cycling. We hypothesized that within-population, individual variation in crayfish foraging behavior is associated with differences in nutrient excretion. The objectives of this study were to (i) to quantify individual differences in foraging behavior and boldness of crayfish using a giving up density (GUD) approach. (ii) to quantify individual differences in nutrient excretion of crayfish. (iii) to test whether foraging rate, boldness, and excretion rate are repeatable traits in the laboratory setting and (iv) to examine whether there is a relationship between individual variation in foraging rate, boldness, and excretion. These objectives were explored with both behavioral and excretion assays, and general linear and nonlinear mixed models as well as ANOVA tests. We found that behavior and excretion were repeatable and that behavior is associated with ammonium excretion. The finding that crayfish foraging behavior is associated with differences in nutrient excretion has important implications for invasion ecology and nutrient cycling. It is known that behavioral changes occur along with invasion. These behavioral changes can significantly impact the nutrient excretion, and therefore nutrient dynamics within invaded environments.No embargoAcademic Major: Environmental Scienc

Optimal Control Prediction Method for Control Allocation

This paper proposes a novel prediction method for online optimal control allocation that extends the volume of moments achievable with the Moore-Penrose generalized inverse to the entire Attainable Moment Set. This method formulates the control allocation problem using selected basis vectors and associated gains which reduces the optimization problem dimensions and provides physical insight into the resulting optimal solutions. The proposed algorithm finds the entire family of unique optimal control solutions along the desired moment vector from the origin to the boundary of the Attainable Moment Set. Numerical results for the Moore-Penrose prediction method show that the unique minimal controls obtained yield the desired moment with near machine precision accuracy while maintaining control effectors within specified position limits. This method has been fully validated against the unique solution obtained on the boundary of the Attainable Moment Set using the Durham Direct Allocation method. Minimal control solutions obtained for moments in the interior of the Attainable Moment Set, similarly yield the desired moment to near machine precision while providing control solutions that are smaller (i.e. 2-norm) than solutions found with traditional control allocation algorithms (e.g. interior point methods) applied to the minimal control problem. Numerical simulations using a Matlab autocoded executable (MEX) for the representative real world problem of 3-moments with 20 individual control effectors and prescribed control position limits show a mean computation speed of approximately 125 Hz which is sufficient to enable real-time flight allocation

Affine Generalized Inverse for Optimal Control Allocation

This research is a follow on to the "Optimal Control Prediction Method for Control Allocation" paper in which the Prediction Method iterative algorithm was introduced. Previously, the Prediction Method was shown to provide optimal control allocation solutions over the entire Attainable Moment Set for the Moore-Penrose and the generalized (weighted) inverse. As an extension to the Prediction Method, this paper introduces a family of Moore Penrose Affine Generalized Inverses, applicable for all moments, which compute control allocation solutions using a constant matrix and fixed null-space vector. The Moore-Penrose Affine Generalized Inverse is proven to yield equivalent solutions to those of the Prediction Method and therefore is guaranteed to yield Moore-Penrose optimal control allocation solutions. While the Prediction Method is applicable for any moment along an a priori specified moment direction, the Affine Generalized Inverse is shown to yield optimal control allocation solutions in a neighborhood of the given moment which is not restricted to a specified moment direction. Furthermore, the Affine Generalized Inverse is shown to provide the time derivative of optimal control allocation solutions and to facilitate maintaining solutions within control effector rate limitations. The Moore-Penrose Affine Generalized Inverse is broadened to encompass any arbitrary (weighted) Affine Generalized Inverse. Finally, a method of creating a moment lookup table is outlined to utilize the Affine Generalized Inverse as an offline control allocation solution for all moments in the Attainable Moment Set

Changes in soil characteristics under different aged plantations of Corsican pine (pinus nigra) at Chopwell Woodland Park, Gateshead, UK

This study examines the pedogenic processes and temporal changes occurring in soils across six different aged plantations of Corsican pine (Pinus nigra), which were otherwise similar in their environmental characteristics, including geology, slope angle and aspect, altitude and land use history. A representative soil profile was sampled, on a horizon basis, and a further 10 topsoil samples were collected, on a grid basis, from each plantation. Properties determined in the laboratory included pH, organic carbon content, particle size distribution, exchangeable base content (Ca, Mg, K, Na), total free and organically-bound iron content, and lead and zinc concentrations. Morphological and chemical changes within the soil profiles were examined to shed light on the processes and pathways of soil formation, and one-way analysis of variance (ANOVA) was used to compare topsoil characteristics between the different plantations. Morphological and chemical changes within the soil profiles indicated that organic matter accumulation and mor humus formation, acidification, clay translocation (lessivage) and incipient podzolisation were the dominant pedogenic processes. There are very few systematic age-related changes in soil morphological or physical and chemical characteristics, possibly due to a combination of young stand ages, high topsoil variability, soil mixing due to drainage operations and silvicultural practices. There are, however, a number of statistically significant but non-systematic differences in soil properties between the different aged plantation blocks. Possible associations between these differences and age-related litter production and root growth, and silvicultural operations such as understory control, plantation thinning and selective harvesting are explored

Evolution of Norms and Conservation Rules in Two Fisheries

Dr. James M. Acheson and Dr. Ann Acheson will undertake research on the processes by which rules to regulate natural resources come into being and the reasons they are followed or ignored. Most renewable natural resources are in a state of decline, including fisheries, grasslands, and forests. One reason is that rules and laws to conserve natural resources often fail to work well. This team of researchers will seek to understand the underlying reasons by studying two fisheries in the Gulf of Maine: the lobster industry, where effective rules have been developed and catches are at record highs, and the groundfish industry (which includes such fish as cod and haddock) where catches are at historic low levels and management appears to be ineffective. To study how these two management systems evolved, the project has four related components: (1) a study of the current culture and social organization of these two industries; (2) a historical study designed to understand how a conservation ethic arose in the lobster industry, while groundfishermen are just now beginning to try to conserve; (3) controlled laboratory experimental games done with Maine fishermen to explore when people will constrain their own exploitive efforts; (4) an evolutionary game theory model to integrate findings from the other parts of the project. The project will be carried out by an interdisciplinary team of anthropologists with extensive knowledge of Maine fisheries and fisheries policy, and economists with expertise in game theory. This project seeks to answer two important questions. First, how do norms and rules come into being? Second, what are the factors leading people to conserve or overexploit resources? This research has theoretical importance for social scientists seeking to understand the origins and persistence of social rules and institutions. The research findings also will have practical implications for resource managers, legislators, and policy makers

What Does the Future Hold for Maine’s Lobster Industry?

The Maine lobster industry is one of the most successfully managed fisheries in the world. Catches have been at record high levels since the 1990s due to favorable environmental factors, regulations enacted over a period of years, and the conservation ethic of fishermen. The industry faces problems that threaten its future: shell disease, climate change, increased regulations to protect right whales, and economic uncertainty. Several approaches could help protect the lobster industry, including enacting lower trap limits, expanding markets for live and processed lobster, and increasing in-state processing capacity. The latter two are already underway, but prospects for lower trap limits are uncertain

Modeling Disaster: The Failure of Management of the New England Groundfish Industry

Most of the worlds' marine fisheries are overexploited or endangered, including the New England groundfishery, once one of the world’s most prolific. After 35 years of management, stock sizes and catches are lower now than ever. We argue that New England groundfishermen are caught in a prisoner’s dilemma, from which they have failed to escape. We then suggest a set of policies to get these groudnfishermen out of their dilemma.Fishermen's dilemma, fishery management, New England fisheries

Phosphoenolpyruvate Carboxykinase Assayed at Physiological Concentrations of Metal Ions Has a High Affinity for CO2

The effect of Mn2+/Mg2+ concentration on the activity of intact, homogeneous phosphoenolpyruvate carboxykinase (PEPCK) from leaves of the C4 grass, Guinea grass (Panicum maximum), have been investigated. Assay conditions were optimized so that PEPCK activity could be measured at concentrations of Mn2+/Mg2+ similar to those found in the cytosol (low micromolar Mn2+ and millimolar Mg2+). PEPCK activity was totally dependent on Mn2+ and was activated at low micromolar concentrations of Mn2+ by millimolar concentrations of Mg2+. Therefore, at physiological concentrations of Mn2+, PEPCK has a requirement for Mg2+. Assay at physiological concentrations of Mn2+/Mg2+ led to a marked decrease in its affinity for ATP and a 13-fold increase in its affinity for CO2. The Km (CO2) was further decreased by assay at physiological ATP to ADP ratios, reaching values as low as 20 μM CO2, comparable with the Km (CO2) of ribulose 1,5-bisphosphate carboxylase-oxygenase. This means that PEPCK will catalyze a reversible reaction and that it could operate as a carboxylase in vivo, a feature that could be particularly important in algal CO2-concentrating systems

Effects of Phosphorylation on Phosphoenolpyruvate Carboxykinase from the C4 Plant Guinea Grass

In the C4 plant Guinea grass (Panicum maximum), phosphoenolpyruvate carboxykinase (PEPCK) is phosphorylated in darkened leaves and dephosphorylated in illuminated leaves. To determine whether the properties of phosphorylated and non-phosphorylated PEPCK were different, PEPCK was purified to homogeneity from both illuminated and darkened leaves. The final step of the purification procedure, gel filtration chromatography, further separated phosphorylated and non-phosphorylated forms. In the presence of a high ratio of ATP to ADP, the non-phosphorylated enzyme had a higher affinity for its substrates, oxaloacetate and phosphoenolpyruvate. The activity of the non-phosphorylated form was up to 6-fold higher when measured at low substrate concentrations. Comparison of proteoloytically cleaved PEPCK from Guinea grass, which lacked its N-terminal extension, from yeast (Saccharomyces cerevisiae), which does not possess an N-terminal extension, and from the C4 plant Urochloa panicoides, which possesses an N-terminal extension but is not subject to phosphorylation, revealed similar properties to the non-phosphorylated full-length form from Guinea grass. Assay of PEPCK activity in crude extracts of Guinea grass leaves, showed a large difference between illuminated and darkened leaves when measured in a selective assay (a low concentration of phosphoenolpyruvate and a high ratio of ATP to ADP), but there was no difference under assay conditions used to estimate maximum activity. Immunoblots of sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels showed no difference in the abundance of PEPCK protein in illuminated and darkened leaves. There were no light/dark differences in activity detected in maize (Zea mays) leaves, in which PEPCK is not subject to phosphorylation