I studied the social organization and foraging ecology of eastern coyotes (<i>Canis latrans</i>) in Nova Scotia, from 1992 to 1997. Breeding pairs formed the nucleus of coyote social groups and generally traveled with 1-3 other coyotes during winter. Mean winter traveling group size was similar for packs utilizing white-tailed deer (<i>Odocoileus virginianus</i>) or snowshoe hare (<i>Lepus americanus</i>) as a primary food item. Thus, increased use of large prey was insufficient to explain group formation and cohesion of coyotes. Home-range sizes decreased significantly with deer and hare densities. Coyotes used the same territories during winter and summer, and from year to year. During winter, coyotes used, and killed deer, in areas of low deer density proportionately more than expected, likely owing to the increased vulnerability of deer in these areas. Territoriality prevented coyotes from concentrating in deer wintering areas. Based on the analysis of 2,443 scats, deer and hare were the dominant food items. During winter, coyotes killed 76-86% of the deer they consumed. Most deer killed by coyotes were not malnourished. Deer killing rates were negatively correlated with hare density. Mean urinary urea nitrogen: creatinine ratios were correlated positively with hare density. Overall, high use of deer appeared to have been associated with increased vulnerability due to winter severity or, in the case of young fawns, inability to escape. During mild winters, coyotes are forced to focus their hunting efforts on prey other than deer, regardless of density, due to low vulnerability of deer. When severe winter conditions occur, coyotes switch to feeding mainly on deer. Coyotes exhibited a Type I numerical response to the total biomass of deer and hares. Survival of fawns during summer was positively correlated with hare density. However, the total response of coyotes to changes in deer and hare density indicated that the presence of hare increased predation on deer by supporting higher coyote densities. A model based on the total response of coyotes to changes in deer and hare abundance predicted that food competition rather than predation probably regulated deer populations. Extirpation due to intense predation was a possible outcome for deer at densities <0.6 deer/km2.

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Rooks (Corvus frugilegus) are colonially breeding corvids found in most agricultural landscapes. Colonies in the County Durham area tend to be clustered at distances up to 500 m, but otherwise show little pattern in terms of spacing or size. Colony size was comparable between sites as changes in colony nest counts were allowed to stabilise before the whole area was surveyed. When measuring nest build-up at a sample of colonies in 1996, no further significant increases occurred after 9th April. The spatial size distribution of colonies was maintained between years. The distribution and size of breeding colonies is modelled in relation to the interaction between the spatial distribution of the foraging habitat and potential intraspecific competitors, with the identification of the distance over which this interaction is strongest. The satellite derived habitat data used for the modelling were part of the ITE Land Cover Map of Great Britain. However, their correspondence with ground reference data was found to be severely lacking. Thus, for modelling the availability of nesting habitat, OS woodland data were used as these identified more of the extant rookery sites, whilst the ITE data were retained for quantifying the foraging habitat. Logistic regression showed that the distribution of colony sites was influenced by the availability of woodland blocks large enough to hold a colony, proximity to roads and buildings, and by the amount of pasture within 1 km. Other suitable sites with these characteristics remained unoccupied within the distribution. Partial Correlations showed that interactions between the spatial distribution of the foraging habitat and competitors influenced colony size at distances up to 6 km, suggesting their effect outside of the breeding season. The multiple regression model built with variable values for this distance explained 31% of the variance in colony size. When applied to the potential breeding sites identified using the logistic regression, most sites still remained suitable. This suggests the distribution is not saturated and that limited availability of breeding habitat is not the cause of the nesting aggregations. The broad correlation of Rook abundance to foraging habitat and potential competitors corresponds to an ideal free distribution of individuals across colony sites. This is supported by models of Rook numbers in relation to parish agricultural statistics produced by MAFF. These again show the importance of pasture as a probable foraging resource, and how pasture quality could be important to Rook numbers. The models also supported the ideal free predictions of spatial variation in Rook abundance in relation to habitat, and the response of colony sizes to temporal change in habitat quality.

<I>Rhinolophus hipposideros </I>has declined across its range. This study aimed to investigate aspects of its roosting, reproductive and foraging ecology which may have caused this decline. <I>R. hipposideros </I>is confined to south west Britain. It selects roosts in areas of undulating countryside with hedgerows and tree lines. Roosts were located predominantly in the roof voids of 19^th century buildings with stone walls and slate roofs, close to woodland and connected to it by hedgerows or tree lines. <I>R. hipposideros </I>has a long gestation period (78 days) and proportionately larger neonate (34% mothers mass) compared to other bat species. Post-natal growth was one of the fastest recorded for a bat species. The number of pups produced by colonies averaged 38% of pre-parturition counts of adults. Ambient temperature in May was shown to influence the reproductive phenology of this species. Patterns of roost occupancy and activity were investigated in a maternity, satellite, night and hibernation roost. Numbers of adults in the maternity roost peaked just before parturition. The timing of emergence and return from the maternity roost each night was correlated with ambient light levels. The duration of foraging each night was correlated with date and was reduced on nights with heavy rainfall. The importance of night roosts to heavily pregnant bats was demonstrated. During the winter most feeding took place before the end of December but successful foraging occurred throughout the winter. <I>R. hipposideros </I>foraged in woodlands, hedgerows and tree lines within 2-3 km of the maternity roost. It hunted close to vegetative clutter catching prey by hawking, gleaning and in late pregnancy by fly-catching, using hedgerows and tree lines as commuting routes between foraging areas and roosts. The implications of this study for the conservation of this species are discussed and management recommendations made.

Dopamine has an important role in normal cognition and reward processing, both of which are impaired in disorders involving dopamine dysfunction such as addiction, schizophrenia, and Parkinson's disease. However, our understanding of the interplay between different aspects of the dopamine system and reward-guided behavior in humans is limited. Food is an important type of reward that is critical for survival and impacts the decisions we make every day. Here, we characterize the relationship between two food-reward related phenotypes and dopamine synthesis capacity (related to tonic dopamine) as well as dopamine D1 and D2 receptor availability in healthy humans. First, we examined the link between dopamine synthesis and receptor availability and body mass regulation in 117 individuals with body mass index (BMI) values ranging from normal to obese. We found that current BMI was related to a pattern of increased dopamine synthesis in the hypothalamus, a region important for homeostatic control of appetite, but decreased dopamine D₂ receptor availability in the midbrain, where D₂ autoreceptors regulate dopamine release throughout the brain. This suggests that increased BMI is related to a dopamine imbalance between homeostatic drivers of appetite and reward system regulatory control mechanisms that could result in an overactive, unregulated intake of food. Building on this finding, we studied the link between dopamine synthesis capacity and receptor availability and an important food-reward related behavior, foraging. Fifty-seven healthy volunteers completed a computer-based foraging task where we measured their threshold for leaving one group of rewards to search for another in four different reward environments varying from a low to high rate of reward receipt. We found that two particular patterns of dopamine synthesis and receptor availability in the anterior cingulate cortex and basal ganglia were linked to the amount that individuals changed their threshold based on the reward rate of the environment. Finally, since the prefrontal cortex is known to be important for reward-guided behavior, we implemented two methodological advancements aimed to address limitations that make it difficult to measure cortical dopamine in humans with PET imaging. The first method involves partial volume correction and surface-based smoothing in order to increase the signal to noise in the cortex. The second method is a data-driven PET data parcellation and automated reference region selection algorithm to optimize the voxels included in the reference region. In conclusion, we have characterized the dopaminergic contribution of two different foodreward guided phenotypes and have developed two techniques that will aid future research on the role of cortical dopamine. Understanding the neural mechanisms underlying these rewardguided behaviors helps us to not only understand normal behavior, but also serves as a reference for comparison when studying related pathological states.

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A series of studies was carried out in order to ascertain some of the ecological determinants of the foraging and caching behaviour of heteromyid rodents (kangaroo rats, Dipodomys, and pocket mice, Chaetodipus). The results show that heteromyids are sensitive to cues of predation while they are foraging. They put more effort into foraging under the safety of cover and in the dark of the new moon, when risk of predation from visually hunting predators is low. They also modulate their selectivity in relation to cues of predation risk, requiring a better pay-off(a more valuable food) as risk increases. The kangaroo rats and pocket mice compete for resources, and the pocket mice are at an aggressive disadvantage to the kangaroo rats at primary resource patches. However, the pocket mice compensate at least partially for their loss by engaging in cache pilferage. Finally, a study of the scatter caching decisions made by kangaroo rats demonstrates that they adaptively modulate cache spacing by placing more valuable seeds into caches that are more widely spaGed. This differential spacing leads to decreased probability that pilferers conducting area-localised search after encountering one cache will be able to locate further caches. The results are discussed in relation to current theory and empirical findings. / Thesis / Doctor of Philosophy (PhD)

The current study utilized two experiments to assess Smith's (1981) simple per capita-maximization model, which provides a quantitative framework for predicting optimal group sizes in social foraging contexts. Participants engaged in a social foraging task where they chose to forage for points exchangeable for lottery prizes either alone or in a group that has agreed to pool and share all resources equally. In Experiment 1, groups (“settlements”) of 10 or 12 participants made repeated group membership choices. Settlements were exposed to three conditions in which the optimal group size was either 2, 5, or 2 for the 10 person settlement or 3, 4, or 6 for the 12 person settlement. A linear regression of the data from Experiment 1 revealed a strong relationship between the observed group sizes and group sizes predicted by the simple per capita maximization model. Experiment 2 was a systematic replication of Experiment 1 in which single participants foraged for shared resources with groups of automated players in a computerized simulation. Automated player group choices mirrored group choices of participants in Experiment 1; excluding the data for the best performing participant. Thus, the participant acted essentially in the stead of the best performing participant for each condition. Two logistic regressions provided mixed support for the model, while failing to replicate the results of Experiment 1, providing mixed support for the use of the simple per capita maximization model in predicting group sizes in social foraging contexts.

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