The successional dynamics of lightning-initiated canopy gaps in the mangrove forests of Shark River, Everglades National Park, USA

Gap succession is a significant determinant of structure and development in most forest communities. Lightning strikes are an important source of canopy gaps in the mangrove forest of Everglades National Park. I investigated the successional dynamics of lightning-initiated canopy gaps to determine their influence on forest stand structure of the mixed mangrove forests ( Rhizophora mangle, Laguncularia racemosa, and Avicennia germinans ) of the Shark River. I measured gap size, gap shape, light environment, soil characteristics, woody debris, and fiddler crab abundance. I additionally measured the vegetative composition in a chronosequences of gap successional stages (new, recruiting, and growing gaps). I recorded survivorship, recruitment, growth and soil elevation dynamics within a subset of new and growing gaps. I determined the relationship between intact forest soil elevation and site hydrology in order to interpret the effects of lightning disturbance on soil elevation dynamics. ^ Gap size averaged 289 ± 20 m2 (± 1SE) and light transmittance decreased exponentially as gaps filled with saplings. Fine woody debris was highest in recruiting gaps. Soil strength was lower in the gaps than in the forest. The abundance of large and medium fiddler crab burrows increased linearly with total seedling abundance. Soil surface elevation declined in newly formed lightning gaps; this loss was due to a combination of superficial erosion (8.5 mm) and subsidence (60.9 mm). A distinct two-cohort recruitment pattern was evident in the seedling/sapling surveys, suggesting a partitioning of the succession between individuals present before and after lightning strike. In new gaps, the seedling recruitment rate was twice as high as in forest and the sapling population increased. At the growing gap stage, R. mangle seedling mortality was 10 times greater and sapling mortality was 13 times greater than recruitment. Growing gaps had reduced seedling stem elongation, sapling growth and adult growth. However, a few individuals (R. mangle saplings) were able to recruit into the adult life stage. In conclusion, the high density of R. mangle seedlings and saplings imply that lightning strike disturbances in these mangrove forests favor their recruitment over that of A. germinans and L. racemosa. ^

Three essays on entrepreneurial entry, serial entrepreneurship, and labor turnover

This study explores two important aspects of entrepreneurship — liquidity constraints and serial entrepreneurs, with an additional analysis of occupational choice among wage workers. In the first essay, I revisit the question of whether entrepreneurs face liquidity constraints in business formation. The principle challenge is that wealth is correlated with unobserved ability, and adequate instruments are often difficult to identify. This paper uses the son's birth order as an instrument for household wealth. I exploit the data available in the Korean Labor and Income Panel Study, and find evidence of liquidity constraints associated with self-employment in South Korea. The second essay develops and tests a model that explains entry into serial entrepreneurship and the performance of serial entrepreneurs as the result of selection on innate ability. The model supposes that agents establish businesses with imperfect information about their entrepreneurial ability and the profitability of business ideas. Agents continually observe signals with which they update their beliefs, and this process eventually determines their next business choice. Selection on ability induces a positive correlation between entrepreneurial experience (measured by previous business earnings and founding experience) and serial business formation, as well as its subsequent performance. The predictions in the model are tested using panel data from the NLSY79. The analysis permits a distinction to be made between selection on innate ability and learning by doing. Motivated by previous empirical findings that white-collar workers had higher turnover rates than blue-collar workers during firm expansion, the third essay further examines job turnover among workers with or without specific skills. I present a search-matching model, which predicts that when firm growth is driven by technological advance, workers whose skills are specific to the obsolete technology show a higher tendency to separate from their jobs. This hypothesis is tested with data from the PSID. I find supportive evidence that in the context of technological change, having an occupation requiring specific skills, such as computer specialists or engineers, increases the odds of job separation by nearly eight percent. ^

Three essays on self-employment transitions, organizational capital, and firm formation

This dissertation explores how economic, organizational, and personal factors affect self-employment transitions, occupational decisions, and firm formation activities of individuals at different positions in the skill distribution. The first essay of my dissertation studies how local unemployment rates differentially affect entry into self-employment by individuals at different places in the skill distribution. The empirical results show a positive correlation between local unemployment rates and entry into self-employment for low-ability workers, but not for high-ability workers. Including employer size to eliminate possible distortions showed that the positive association between unemployment and self-employment among low-ability workers is in fact driven by the small firm effect. Controlling for firm size yields a negative association between unemployment and self-employment among high-ability workers. Effects of organizational capital, human capital and physical capital, on the firm formation activities of people at distinct skill levels depend on the type of the industry which is chosen for the new firm. Two types of industries, capital-intensive and ability-intensive, are utilized to explore this hypothesis in the second essay. A capital-intensive industry requires more physical investment, and consequently more funds, whereas, an ability-intensive industry requires more human capital. It is shown that high human capital requirements are associated with higher earnings among the most able individuals, and therefore makes them more likely to found firms in an ability-intensive industry. Wealthy people are more likely to establish both capital-intensive and ability-intensive firms, even though the amount of funds necessary for two industry types differs. Moreover, entry into both industries is predicted to happen later in life due to the removal of entry barriers constituted by required investment spending using savings when old. Empirical mixed results are observed. The third essay investigates earning differentials between future entrepreneurs and their non-entrepreneurial colleagues. Results show that high-ability firm-owners in an ability-intensive industry were earning more than those that remained in wage-work, whereas, low-ability firm-owners in a capital-intensive industry were earning less than those remaining in paid-work.

This was uncalled for : Dave Eggers' A heartbreaking work of staggering genius subverts the genre of traditional autobiography as an attempt at rendering his life

The purpose of this thesis was to explore why and how the author Dave Eggers subverts the genre of traditional autobiography in his memoir A Heartbreaking Work of Staggering Genius. I compared Eggers' work to Gertrude Stein's The Autobiography of Alice B. Toklas and William S. Burroughs' Junky. I found that like Stein and Burroughs, Eggers utilized various rhetorical devices outside of traditional autobiography because he could not find the means to express himself within the genre. Eggers employed various rhetorical methods reserved for fictional texts, such as stream of consciousness, characterization, and irony, in order to reconcile his feelings towards his parents' deaths and render those feelings in his memoir. I established that Eggers concluded his memoir with impossibility of arriving at one Meaning that could summate his tragic experience. Thus, I proved that Eggers gave the reader the only authentic interpretation he could: the memoir as a small, incomplete glimpse into his life.