Spatial competition, in the context of industry-wide changes in retailing formats and strategies, is addressed in this dissertation from a theoretical modelling perspective. Chapter2 develops a normative individual choice model to explore how "power retailers" affect grocery shopping behaviour, and, consequently, market share. Power retailers are very large retail outlets that compete primarily on price, and are known variously as warehouse clubs, category killers, and superstores. The model shows that consideration of consumer stockpiling can lead to an "increasing returns" nonlinear response of market share to price reductions, and that the effect is not noticeable when competitors have small price differences. The model also differentiates between perishable and nonperishable goods, and shows that this may drive planned multistore shopping. Chapter 3 starts with the observation that competent management in many sectors of retailing, including grocery retailing, requires an ability to respond quickly and effectively to unexpected adversity. This dynamic is included in an oligopolistic spatial interaction model, and the system is shown to evolve to a novel and robust stochastic steady state known as self-organized criticality (SOC). One characteristic of the SOC state is that it allows small exogenous shocks to produce large responses at a rate greater than would be expected if the law of large numbers applied. This work represents the first known investigation of SOC in a marketing setting.

The dynamics of airline deregulation have resulted in significant changes in airline competition and network structure. This dissertation examines airline competition and network structures in the presence of low-cost entry in a deregulated environment. / The first chapter investigates the effect of low-cost entry on the equilibrium network choice of a monopolistic air carrier. This essay differs from previous analyses in that it incorporates asymmetric city sizes, and distances as a determinant of costs into the model. Numerical exercises illustrate that the threat of entry may result in an entry accommodating, an entry deterring or even an interlining equilibrium, depending on demand and cost conditions and on the level of fixed costs of connecting city pairs. In particular, when the demand in city-pair markets are identical and cities are equal distance apart, the monopolist restructures its network in an attempt to minimize the competitive effect of entry. If demands vary across city pairs and distance is a factor of cost, then the restructuring of the network may be an entry deterring strategy. The incorporation of distance not only influences the number of direct connections between city pairs but may also affect how city pairs are connected within the network. / In Essay Two the model is extended to a duopolistic airline market in which network structures are endogenously determined by the competition between two incumbent airlines; numerical exercises are then used to demonstrate how the threat of entry by a low-cost airline affects the network choices of these incumbent carriers. The main result of the essay is that, in many situations, incumbent carriers restructure their networks in order to compete with potential entrants. The results indicate that incumbents' response to the threat of entry depends on the potential entrant's cost advantage and on the fixed costs of connecting city pairs. In particular, if the fixed costs of connecting city pairs are low and the cost advantage of the entrant is significant then entry may not affect the network structure of incumbent carriers. However, at higher fixed costs at least one incumbent will adjust its network in an attempt to soften the competitive effect of entry. Furthermore, the numerical exercises show that the threat of entry not only affects the equilibrium network structure but may also result in one incumbent leaving the industry and the potential entrant actually entering. / Essay Three studies network competition and welfare implications in partially and fully liberalized transatlantic markets using the model developed in Essay Two. This essay illustrates some conditions under which the price and welfare effects of an open-skies agreement depend on the equilibrium network choice of the competing airlines. In particular, network choices of airlines may result in higher prices on some transatlantic routes and if pre-liberalized domestic markets are competitive price reductions on domestic routes could be negligible. Another finding is that the opening of transatlantic markets mainly redistribute airlines' market shares and as a result the expected increase in passenger traffic may not be realized.

In this thesis, I describe three experimental studies that investigate the hotly debated role of competition in structuring communities in unproductive habitats. The studies were done in a boreal forest understory plant community in the southwestern Yukon. The first study was a traditional neighbour removal experiment. Ten of the most common species were transplanted as seedlings into transects with and without neighbours in a factorial design with two levels of water addition and two levels of fertilizer addition. The presence of neighbours increased survival and biomass of 6 species indicating a facilitative effect of neighbouring plants. The second study used the Community Density Series (CDS) methodology. The first of these was a 10-speciesexperimental community established from seed and grown in sandboxes at 6 densities with 2 watering levels and 2 fertilizer levels in a factorial design. At the community level, density dependence was observed at all life stages, but was not consistently competitive or facilitative - both emergence and final per plant shoot mass were density dependent, while survival to the end of the season was inversely density dependent. The effect of water was positive at seed emergence whereas fertilizer negatively affected survival. Species specific responses were also dependent on life stage. The final study was a 4-year CDS in the field using 9 common understory species at 6 densities and 3 fertilizer levels. Density negatively affected the community every year except for the first with competition being important at all densities above x1/8th the average community density. Constant final yield was reached in plots above the naturalx1 density for the last two years of the study. Responses to density were species-specific and 7 species declined with increasing density. No facilitative effects were observed. These studies demonstrate that density dependence is important in structuring this unproductive boreal understory habitat. The CDS approach allows us to quantify both the intensity and importance of plant competition at the community and species levels and to determine whether the importance of these biotic interactions depend on abiotic factors. The results clearly show that species-specific responses to biotic interactions are not necessarily the same as community level responses and if we are to understand community structure, it is necessary to use appropriate methodologies.

Šis darbas skirtas išnagrinėti esminiams vertikaliųjų susitarimų nekonkuruoti reguliavimo bei vertinimo aspektams pagal EB konkurencijos teisę. Siekiant, kad tai būtų padaryta išsamiai, pirmoje darbo dalyje pateikiama vertikalaus susitarimo samprata. Antrojoje dalyje išanalizuota vertikalaus susitarimo nekonkuruoti samprata bei ekonominis poveikis, o trečiojoje ištirti EB Steigimo sutarties 81 straipsnio taikymo jiems ypatumai. / The purpose of this work is to examine the main aspects of regulation and legal assessment of vertical non-compete obligations under EC competition law. For this reason in the first part of the work the legal concept of vertical agreement is analysed. In the second part the definition and economic effects of non-competition agreements are examined and in the third part – the legal aspects of the application of article 81 of the EC Treaty to non-compete obligations.

The North Mountain of the Annapolis Valley, NS, in eastern Canada, is a ~200 km basalt ridge drained by many small first or second order streams in independent catchments. The area is fairly uniform geologically, presenting an opportunity to compare streams of similar chemistry, slope and aspect, that vary in other respects, such as invertebrate community structure. In this thesis, I examine two macroinvertebrate functional groups to determine key factors influencing their abundance, composition and diversity across catchments. Chapters 2 and 3 are concerned with the predatory invertebrate guild in eight of the streams, in two groups separated by ~65 km. In Chapter 2, I assessed factors influencing composition of the predator guild using similarity matrices. Similarity in predator composition declined with distance, and streams that were more similar in disturbance (spates) were more similar in predator composition. Similarity within one family, Rhyacophilidae, was related to similarity in fish population. Chapter 3 reports the results of laboratory experiments involving two widespread species. Field data suggested an asymmetric interaction between Sweltsa onkos (Plecoptera: Chloroperlidae) and Rhyacophila vibox (Trichoptera: Rhyacophilidae); behavioural observations in artificial streams supported this. In the presence of R. vibox, S. onkos had higher mortality and injury rates, and grew less. The results of these chapters suggest that, although disturbance is important in shaping community structure, the results of interspecific interactions can be detected at large scales. S. onkos can only attain high numbers in streams where fish predation reduces the abundance of R. vibox. Chapter 4 examines biodiversity patterns in the macroinvertebrate detritivore guild in 25 streams encompassing ~80 km of the ridge. Using density and richness of the detritivore community, detrital resource quantity, and top predator abundance, I looked for evidence in support of several mechanisms that can lead to positive species-energy relationships. Patterns conformed to expectations of the ‘More Individuals Hypothesis’. It appears that taxonomic richness of the detritivore guild increases with detrital resource availability because more taxa can attain their minimum viable population size where more resources are available.

The mechanisms that allow invasive species to flourish in novel habitats are poorly understood. A. petiolata (Alliaria petiolata) is an invader of North American forest edge and understory communities. A. petiolata’s success may result from high competitive ability due to its suppression of mycorrhizal fungi used by other species. In a greenhouse experiment, I grew 27 target species in the presence and absence of A.petiolata in soil with and without a history of A. petiolata. I found that soil with a history of A. petiolata had depleted plant available nitrogen and reduced mycorrhizal fungal colonization of target species. A. petiolata competition suppressed the growth of target species less in soils with than without A. petiolata history. Furthermore, I found that tall plants with finer roots more effectively suppressed the growth of A. petiolata. My results suggest that soil feedback effects do not improve A. petiolata’s competitive ability and are unlikely to contribute to A. petiolata invasion.

We use metapopulation models based on a classic competition-colonization trade-off in order to (1) study community responses to spatially structured habitat loss on dynamic landscapes when species are assembled by ecological (biogeographic) processes; and (2) to study how species are assembled into communities by evolutionary mechanisms. In the first part of our study we show how the response of species richness to habitat destruction in dynamic landscapes can be driven by the existence of either the spatial structure of habitat dynamics or by life-history trade-offs among species. In the second part of our study we confirm that competitive trade-off models predict runaway evolution towards stochastic extinction, making it impossible for stable multispecies assemblages to evolve. We demonstrate that by relaxing the strict deterministic nature of competitive exclusion in such models species can avoid selection towards extinction, allowing for the possibility of species co-evolution resulting in stable multispecies assemblages.

The current study explored gender differences in groups of boys and girls in a limited resource context. Forty same-sex groups of four children from kindergarten and grade four were observed during sessions in which groups played first with two different toys and then two different games. The toy and game sessions were constructed so children had to negotiate for a scarce resource (attractive toy and game winner's certificate). In the case of one of the toys the end of a player's turn was obvious to group members (explicit turn-taking toy), in the case of the other toy the end of a turn was not obvious to group members (nonexplicit turn-taking toy). Resource use (time with toy), group variability in resource use, positive affect and self-report measures were collected. Results of the toy sessions revealed both genders were very similar on all the measures; however, girls were significantly more likely to have greater group variance in distributing the nonexplicit turn-taking toy. The two games, one competitive and one noncompetitive, involved players trying to reach a finish line. For the competitive game, only one player could win, but for the noncompetitive game all players could win. During both games, a player could potentially interfere with another player's goal to win. Resource use (interfering), group variability in resource use, positive affect and self-report measures were collected. Results of the game sessions revealed both genders were very similar on all measures, however, during the competitive game, girls were more likely to have greater group variance in interfering. The results are discussed in terms of considering aspects of the context when investigating gender differences in competition.

I've worked in the electrical industry throughout my career, from accounts to the stores, serving as an artisan to sales and finally management, having experienced the dramatic changes industry has undergone in the past few years. The topic has inspired me to investigate the future changes as South African companies are striving for international competitive trading and recognition, couple with an volatile economy. / Thesis (MBA)-University of Natal, Durban, 2003.

Kochia and biennial wormwood are two weeds sometimes found growing in sunflower fields that may be difficult to control. Weed management in sunflowers is usually conducted using a combination of herbicides and mechanical weed control methods. Some farmers are growing sunflowers in reduced tillage systems, which may rely solely on herbicides to manage weeds; however, the spectrum of broadleaf weeds that can be controlled with herbicides is limited. Field experiments were conducted across southern Manitoba to determine the effect of kochia and biennial wormwood density and relative time of weed seedling recruitment on sunflower growth and development, yield and seed quality and to determine action thresholds for each weed. Early emerging kochia (plants that emerged at about the same time as the sunflowers) reduced sunflower yield by as much as 82%, which was greater than early emerging biennial wormwood plants, which reduced yield by as much as 27%. At low weed densities, each kochia plant reduced sunflower yield by 0.52% and each biennial wormwood plant reduced sunflower yield by 0.17%. As the density of early emerging kochia plants increased, sunflower height, stem diameter, leaf counts and head diameter were reduced in some of the experiments. Increasing densities of early emerging biennial wormwood plants had minimal effect on sunflower growth and development. Early emerging kochia and biennial wormwood plants both had the potential to reduce sunflower seed size and seed weight, while late emerging kochia and biennial wormwood (plants that emerged after the 4-leaf stage of the sunflowers) did not affect sunflower seed quality. The action threshold (5% sunflower yield loss) for early emerging kochia was 10 plants per metre square and the action threshold for early emerging biennial wormwood was 36 plants per square metre in the combined site-year analysis. Kochia or biennial wormwood plants that recruited after the 4-leaf stage of the sunflower crop did not affect sunflower yield, or seed quality.