Empirical and theoretical investigations of aspects of the ideal free distribution (IFD) are presented, with particular emphasis on interactions between individuals within foraging groups. An overview of the theory is presented, and the implications of the work included in this thesis to ideal free distribution theory are discussed. The effect of group size on the relative competitive ability of individual fish within a foraging group is shown to be dependent upon the difference in body size between two focus individuals in a group, but this difference itself has no direct effect on relative competitive ability. A subsequent empirical test of a novel mathematical tool reveals that there is no simple general rule for describing how relative competitive ability will change with group size, and that very specific knowledge of the system under study is needed in order to produce robust predictions. The relative abilities of individual chiclids to obtain food under scramble competition are shown to be highly repeatable between trials. However, when given a choice between two patches differing only in their temporal variability in input about an identical mean, an individual's rank based on intake in one patch was uncorrelated with either its uptake in the other patch or its intake in either of two different trial types. The basis for, and consequence of, this dependence of relative competitive ability on the context of the foraging situation are discussed. The general case (previously unexposed in the literature) where the effect of interference can vary between patches is examined. Simulations from an individual-based model reveal a decrease in the number of stable equilibrium distributions as the competitive advantage of the dominant phenotype declines in one patch, leading eventually to a single stable equilibrium, in which both phenotypes are found on both patches.

The work reported in this thesis is divided into 3 main sections as follows. Section 1. The external morphology of byssus threads produced by Mytilus edulis and Modiolus modiolus was studied by scanning electron microscopy. Section 2. Several laboratory experiments were performed to determine how sediment with stones at different layers and of different particle size ranges affects byssus thread production. These experiments were: (i) An initial experiment to determine the rate of byssus thread production. (ii) The response of single animals and groups of animals to different particle size ranges of sediment. (iii) The response of single animals and groups of animals to experimental sediments (particle size range < 2.0cm) with stones present or not present at different depths. Section 3. Experiments were performed to determine the effects of single animals and groups of animals on sediment stability. All experiments were performed under controlled conditions in an experimental sea water flume. These experiments were: (i) the effects of single animals on sediment stability in different particle size ranges of sediment. (ii) the effects of groups of animals on sediment stability in different particle size ranges of sediment. (iii) the effects of groups of animals on sediment stability in sediment of particle size < 2.00mm, with stones present or not present at different depths.

No aInitially, the thesis investigated the ecological energetics of N. norvegicus in order to construct an energy budget which could be used to estimate scope for growth. The diet of the Norway lobster Nephrops norvegicus in the Firth of Clyde was found to consist of crustaceans, molluscs, and to a lesser extent polychaetes and echinoderms. The proportion of bivalves was higher in the diet of N. norvegicus from south of Little Cumbrae than in the diet of N. norvegicus from south of Ailsa Craig which contained larger proportions of crustaceans and echinoderms. This appears to reflect the faunal composition of the areas. Despite a number of measures taken to preserve stomach contents, a large proportion of the diet was found to be macerated beyond recognition, particularly in the stomachs of animals from the south of Ailsa Craig stocklet. There were marked interspecific differences in the energy contents and organic contents of prey organisms. The calorific values of the prey items were found to vary according to the proportion of organic matter in the tissue. Organisms with low organic contents such as brittle stars had lower calorific values than organisms with a large organic proportion such as soft-bodied polychaetes. Amounts of food consumption were calculated in 4h intervals over a 24h period. Results suggested that foraging is highest during the night at 2200-0200. A smaller increase in food consumption was also noticed during the morning at 0600-1000 and 1000-1400. The lowest amount of food was consumed between 1400-1800. Two different models were used to estimate the daily amounts of food consumption. The values obtained ranged from 476.5mg day-1 (wet weight) at Ailsa Craig in November to 1206.2 mg day-1 (wet weight) at Little Cumbrae in May.

No description available.

Game theory has been used to investigate a wide range of evolutionary questions, and has been important in explaining apparently selfish patterns in animal behaviour, and behaviours that do not appear to benefit the individual. The modelling chapters in this thesis develop new game theory approaches to modelling animal conflict, investigating the acquisition of territories and the trade-offs that occur between behaviours. Many game theory models of conflicts between individuals make predictions regarding the duration of fights in relation to asymmetries in resource holding potential (RHP). Duration is often interpreted as a result of mutual assessment of RHP, allowing the weaker individual to avoid costly interactions. However, the duration of a contest may also be the result of each individual persisting to a threshold determined by its own RHP, in fiddler crabs, Uca mjoebergi, I show that duration of contests increases with increasing size of the loser, and decreases, but to a lesser extent, with increasing size of the winter, suggesting that neither the mutual assessment or individual threshold hypothesis can explain fight duration in this species. Instead, individual cost thresholds may determine duration, but larger opponents may inflict costs more rapidly, consistent with the cumulative assessment game of animal conflict. In animal contests, the larger opponent is often victorious, but contests are often initiated by individuals that have little chance of winning (generally smaller individuals). A number of hypotheses may explain this behaviour, including a lack of alternative options (the ‘desperado effect’). Recent work has suggested that likely losers attack first due to an error in perception: they mistakenly perceive their chances of winning as being greater than they are. Using a game theoretical model, I show that if smaller individuals can accurately assess their chance of winning, if this chance is relatively high, and if they have few alternative options, they are predicted to be as aggressive as their larger opponents. In addition, when resources are abundant, and small individuals have some change of winning, they may be more aggressive than their larger opponents. Using a game theory model, I show that avoidance of a single fight location can be adaptive if the benefits of access to the area are low compared to the costs of fighting. Low fight costs and high population densities lead to the break down of territoriality and the formation of large, overlapping home ranges.

No description available.

Studies of the phenotypes of animals at different parts of their geographic range often reveal striking variability. It is of considerable fundamental and applied interest to discover the extent to which such variation depends on genetic as opposed to environmental differences. A first step towards disentangling these effects is to use an empirical approach known as the common environment method in which wild-caught juveniles from different regions are reared under common laboratory conditions. I used this approach to determine the population and thermal responses of Atlantic cod, a species with a wide distribution and geographic variation in life history traits. Life history traits were investigated in cod from three areas around the British Isles of differing thermal regimes, namely St Andrews Bay on the Scottish east coast, the Clyde Sea on the Scottish west coast, and from near Lowestoft in the southern North Sea. Concurrently haemoglobin genotype and behaviour were also studied. Spatially significant differences in life history traits and thermal responses were revealed in juvenile and adult growth rate, gonadal investment and behaviour, suggestive of population differentiation. Behavioural differences between cod of differing haemoglobin genotypes were also demonstrated. Results suggested that juvenile growth rates may be modified by competitive interactions. At a group level, growth rate of cod from the Clyde Sea was suppressed in the presence of cod from St Andrews Bay. Pairwise trials demonstrated that cod from the Clyde Sea consumed a higher prey share than those from St Andrews Bay but that those from St Andrews Bay were more aggressive and thus could potentially restrict feeding of cod from the Clyde Sea, resulting in a reduced growth rate. There were no population differences in the distribution of haemoglobin genotype, but haemoglobin genotype did have a strong influence on behaviour in pairwise contests. Cod of the HbI-2*2 genotype displayed a higher level of aggression than other genotypes and this effect was stronger than the population difference. Juvenile cod from the Clyde Sea exhibited a growth rate 24 % higher than those from St Andrews Bay. Cod from the Clyde Sea and from Lowestoft expressed higher growth rates as adults than those from St Andrews Bay. Body size and thus growth appeared to be the main driver of fecundity in the females and body size and liver were the main influences on gonadosomatic index (GSI) in the males. Females from the Clyde Sea invested more into fecundity than those from St Andrews Bay and males from St Andrews Bay had a higher testis investment than those from the Clyde Sea and Lowestoft. Temperature had a large influence on both the juvenile growth and egg development. Growth rate increased linearly and in parallel over the experimental temperatures, within their normal range. Egg development was strongly affected by temperature, resulting in a decrease in hatch time and an increase in embryonic cardiac rate, and a smaller larval size at hatch for a given temperature at higher temperatures. Temperature did not directly influence fecundity or GSI in males but warmer temperatures resulted in higher growth rates and thus a larger body size, which in turn resulted in a greater fecundity or GSI. These differences in life history traits, demonstrated under controlled environment conditions, raises the possibility that there may be a genetic basis to the variation and that cod may be locally adapted to their thermal environments in areas around the British Isles. However, effects of environmental differences prior to capture, including maternal effects, cannot be ruled out. This greater understanding of life history variation in cod will be important in the conservation of phenotypic diversity, vital for the long-term persistence of the species, while the findings of plasticity in response to temperature will enhance predictions of responses to sea temperature rise.

No description available.