THEORETICAL AND EMPIRICAL PROBLEMS IN MODELING OPTIMAL REPLACEMENT OF FARM MACHINES

Farm Management,

AN EVALUATION OF EXPECTED VALUE AND EXPECTED VALUE-VARIANCE CRITERIA IN ACHIEVING RISK EFFICIENCY IN CROP SELECTION

This article evaluates the performance of expected value and expected value-variance criteria in achieving risk efficiency in crop selection. Results indicate that the expected returns criterion achieves risk efficiency in many situations because of constraints. However, in the absence of many constraints the expected returns criterion performs poorly except when highly mean-dominant activities are present. The expected value-variance criterion achieves a high degree of risk efficiency for all situations examined. This result implies that criteria more complex than expected value-variance are not necessary for crop selection analysis, given empirical returns distributions.Crop Production/Industries,

AN ANALYSIS OF THE SOUTHEASTERN FEEDER PIG MARKET

Livestock Production/Industries,

Relationships between environmental conditions, energetic strategies and performance in juvenile Atlantic salmon, Salmo salar

Energy is the fundamental currency of life that drives organismal growth and development. Energy requirements vary greatly between species but also within species due to differences in physiology, behaviour and life history. The consequence of this variation is of great interest to ecologists, as it is potentially a trait upon which natural selection can act. One of the main components of an organism’s energy budget is its baseline level of metabolism, hereafter termed its standard metabolic rate (SMR). It has been shown in several species of salmonid fish that a high standard metabolic rate correlates with dominance, aggression and boldness. This competitive advantage has been shown to result in higher growth over conspecifics in simple lab environments, but the ecological consequences are less clear. This thesis examined the performance of contrasting metabolic strategies across a range of environmental conditions to ascertain the ecological consequences of SMR variation. Experiments also investigated the relationships between SMR, food intake and absorption efficiency to help relate energetic strategies to performance. The effects of environment on the outcome of different energetic strategies were profound. Higher population densities increased intraspecific competition for preferable feeding territories, but fish with a higher SMR tended to be the best competitors and so were most likely to get a preferred territory (Chapter 2). However, for a given quality of feeding territory, whether relatively good or poor, lower SMR individuals grew best due to their lower energy requirements. The benefit to high SMR fish of being able to secure better territories was diminished under less predictable feeding conditions, and disappeared under a structurally complex habitat, resulting in these fish having no performance advantage over fish with a lower SMR (Chapter 3). These high SMR individuals performed poorly in the presence of low densities of a heterospecific competitor, being subject to a disproportionate proportion of the aggression from a more dominant species (brown trout, Chapter 4). At higher densities of trout, intraspecific interactions appeared much more important for both species, resulting in the salmon with the highest SMR exhibiting the fastest growth. These three chapters demonstrate that environmental conditions, both abiotic and biotic, have great consequences for the success of different energetic strategies. The consequences of metabolic strategy on physiology proved just as interesting. High SMR individuals expended more energy when digesting a given size of meal but reduced the duration of this specific dynamic action (SDA, the rise in metabolism associated with processing and digesting a meal) response (Chapter 5). This suggested that their digestion was more rapid than that of low SMR fish, but this did not lead to a higher rate of food consumption (Chapter 5) nor did they sacrifice absorption efficiency (Chapter 6). This thesis demonstrates that the performance of fish with alternative energetic strategies is dependent on the prevailing environmental conditions, which helps explain the persistence of variation in SMR within populations

The interplay between aerobic metabolism and antipredator performance: vigilance is related to recovery rate after exercise

When attacked by a predator, fish respond with a sudden fast-start motion away from the threat. Although this anaerobically-powered swimming necessitates a recovery phase which is fueled aerobically, little is known about links between escape performance and aerobic traits such as aerobic scope (AS) or recovery time after exhaustive exercise. Slower recovery ability or a reduced AS could make some individuals less likely to engage in a fast-start response or display reduced performance. Conversely, increased vigilance in some individuals could permit faster responses to an attack but also increase energy demand and prolong recovery after anaerobic exercise. We examined how AS and the ability to recover from anaerobic exercise relates to differences in fast-start escape performance in juvenile golden gray mullet at different acclimation temperatures. Individuals were acclimated to either 18, 22, or 26°C, then measured for standard and maximal metabolic rates and AS using intermittent flow respirometry. Anaerobic capacity and the time taken to recover after exercise were also assessed. Each fish was also filmed during a simulated attack to determine response latency, maximum speed and acceleration, and turning rate displayed during the escape response. Across temperatures, individuals with shorter response latencies during a simulated attack are those with the longest recovery time after exhaustive anaerobic exercise. Because a short response latency implies high preparedness to escape, these results highlight the trade-off between the increased vigilance and metabolic demand, which leads to longer recovery times in fast reactors. These results improve our understanding of the intrinsic physiological traits that generate inter-individual variability in escape ability, and emphasize that a full appreciation of trade-offs associated with predator avoidance and energy balance must include energetic costs associated with vigilance and recovery from anaerobic exercise

Soybean Production

This publication provides information about the growth of soybeans as well as their sequence in a cropping rotation and use for forage. Recommendations are also included for production practices, weed control, weather conditions, and harvesting

Kinetic studies on the solvolyses of alkyl halides in the presence of added nucleophiles

Not availabl