Savannas comprise over one eighth of the world's land surface with some 50 Mha in North America alone. They are productive systems supporting a high level of both faunal and floral diversity and are of increasing socioeconomic importance. The maintenance and formation of savannas have been attributed to climate, soils, herbivory and fire. However, the reasons for the coexistence of trees and the grass layer have still to be determined. These two contrasting life forms create a complex of intra- and interspecific positive, negative, and neutral interactions, few of which have been quantified. Under lower-than-average rainfall, tree effects on grasses in a Prosopis savanna in northern Texas were largely neutral with few measurable competitive or facultative effects from the tree canopy. However, grasses demonstrated increased productivity where belowground competition with neighboring trees was removed. Similarly, tree growth increased following the removal of grasses under and around individual trees, particularly on shallower soils, but only during a season of significant precipitation. Low intensity burning of grasses enhanced growth of adult trees, but patterns were inconsistent between two different sites. Moderate clipping around individual trees had no apparent effect on tree growth. Intraspecific competition between savanna trees was not evident, but may have been blurred by an extensive, lateral distribution of near-surface roots. Overall, tree intraspecific competition was neutral regardless of soil depth, suggesting lateral tree roots may be only used opportunistically. Although some competitive relationships were verified, the differences in the responses between the two years of study, and at different sites indicated that soil depth and climate may have overriding impacts on tree-grass interactions and savanna dynamics in this system.

Drawing insights from strategic management and international business literature, the present study develops an integrated model to explain the competitive actions between multinational firms in a global context. Accordingly, two research questions are addressed: What key factors explain the competitive actions of multinational firms? What key factors moderate the competitive tensions experienced by different pairs of multinational firms? Using structured content analysis to identify competitive actions, the empirical findings of the present study suggest that subsidiary control, MNE size, national culture, government regulations and multimarket contact are all likely to exert important impact on a multinational firm's motivation and capability to compete and therefore influence its competitive aggressiveness in foreign markets.

Finding an explanation for the rise and persistence of European unemployment has been one of the main research programmes of labour economists during the last decade. In this doctoral thesis, we contribute to this literature by questioning the causes of unemployment persistence in Belgium. To that purpose, we conduct an in-depth econometric analysis of the flows out of unemployment in this country. In Chapters 2 and 3, we study the behaviour of the exit rate out of unemployment over duration and calendar time. In Chapter 3, we investigate whether this behaviour differs according to the place of living and the skill level, as measured by the level of education. Finally, in Chapter 4, we determine to what extent the divergences in the rate of flowing from unemployment between workers with different levels of education can be explained by a skill mismatch phenomenon and/or by a job competition story. By refining the causes of unemployment persistence in Belgium, our doctoral research also contributes to the design of more effective labour market policies.

A “last resort” is argued to be nothing more than a winning, i.e. grammatical form, once it is understood in terms of competition between alternative candidates. It is a theorem of OT that we find last resort effects, since it follows from the nature of competition and constraint interaction.

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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.

In this study I assessed the potentials of selected, established perennial grasses to maintain site occupancy in the foothills ecosystem of the Rogue River Valley of southwest Oregon which is currently dominated by a variety of annual plants. The first evaluation compared growth curves of the perennial grasses and contrasted them to growth patterns of residual annual plants. Periods of growth varied among the perennial grasses studied. Of the perennial grasses, Idaho fescue (Festuca idahoensis), a native, and Berber orchardgrass (Dactylis glomerata var. 'Berber'), introduced, most closely emulated the growth patterns of the majority of the annual plants. Relative to the other perenial grasses tested, they initiated growth earlier, continued some growth through the winter and matured earlier. Once established, they should be able to effectively compete with the resident annuals for resources and maintain their populatiOhs. To assess the potential for competition for available moisture, the second evaluation considered timing and extent of soil moisture extraction by the perennial grasses and the resident annual community through the periods of active growth. This verified growth analysis results. Idaho fescue and Berber orchardgrass extracted moisture earlier than the other perennial grasses. Perennial grass plots and plots dominated by yellow starthistle (Centaurea solstitialis) end of season residual soil moisture levels were similar. Resident annual grasses left considerably more soil moisture. In years with an early summer drought, the earlier growing perennial grasses should be able to satisfy growth requirements and persist. An assessment was also made of the abilities of several selected established perennial grasses to resist reinvasion by resident annual plants. Earlier growing perennial grasses such as Berber orchardgrass and Idaho fescue suppressed the annuals more effectively than the later growing perennial grasses. Of the perennial grasses studied, those emulating the growth patterns of the annuals have been the Most competitive and have maintained the most vigorous stands. / Graduation date: 1990

Technological position is a dimension along which organizations can either differentiate from or mimic the behavior of other organizations in the technological landscape. This paper is aimed at providing empirical evidence of the specific ways in which an organization’s technological position choice is impacted by the tension that arises from technological co-location; the information available to the focal firm; and the focal firm’s usage of such information. In this dissertation I examine the factors influencing technological agglomerations in technological positions in the technological landscape. I further examine how the organization’s experience impacts its strategic positioning choice while facing the tradeoff between the expected derivatives of co-location - opportunities and competition. I argue and find that an organization strategically positions itself in the technological landscape based not only on the information it has gathered on its technological environment but also using its own experience and information. Further, my findings show that the organization’s technological positioning choice reflects the tension between opportunity and competition, which questions the notion of isomorphism.

Reforms that expand school choice have been the focus of considerable policy interest, not least as a possible means of improving public school performance. According to the standard argument, increased choice will intensify competition, forcing public schools to improve quality in order to retain enrolment. Yet in principle, increased choice need not always raise performance, pointing to the need for careful empirical analysis. A key challenge in measuring the effects of greater choice on school performance is that convincing variation in choice is often hard to come by, especially in cross-sectional studies. And while school choice policy experiments have the advantage that choice increases in a clear way, few large-scale school choice policies have been implemented in North America. An important exception is the 2002 Ontario tuition tax credit, which eased access to private schools throughout Canada's most populous province. Analyzing the effects of the tax credit reform provides the focus of this thesis. The thesis begins by presenting the literature and gaps in existing research. The next chapter presents a model to clarify the link between increases in competition and school performance, and to motivate the empirical identification strategy. To set the stage for the main empirical analysis, I also provide some relevant institutional background relating to the Ontario education policy environment and the Ontario tuition tax credit as well as a descriptive analysis on the Ontario private school market. I then present an initial examination of the possible performance effects of the Ontario tuition tax credit using a difference-in-differences setup, before turning to the main empirical analysis, which exploits the differential competitive effects for public schools in districts with relative to those without a significant private school presence. The empirical results indicate that public school performance improved for schools facing the greatest competitive pressures following the introduction of the policy, controlling for a host of other relevant factors. To assess whether the effect is due primarily to increases in productivity, the analysis controls carefully for a series of alternative mechanisms. Overall, the Ontario findings are consistent with increased choice giving rise to productivity improvements in public schools.