Coral reefs have high biodiversity among the many marine ecosystems. Many hypotheses explain marine biodiversity, e.g., the Intermediate Disturbance Hypothesis, the Lottery hypothesis and the Resource Allocation Hypothesis, but there is no mention of the possible role of seasonal effects. Here, we propose the Seasonal Recruitment Hypothesis to explain the possible role of seasonal recruitment and succession in a disturbed ecosystem. In this investigation, we tested several prediction of the hypothesis: a. Does recruitment have seasonal variation? b. Does variable recruiting communities diverge in succession? c. Are high biodiversities of coral reefs contributed by different communities originating from patches created in different seasons? In this study, we used plastic plates as proxy of empty space generated after disturbance to survey the seasonal patterns of settling benthos. Recruitment plates were placed and retrieved at two-month intervals for two consecutive years. Then, the composition and densities of settled taxa were estimated. The PRIMER software was used to compare the community similarities. We looked for possible seasonal patterns in each benthic populations but found few not real examples of such. Although there is difference between communities started in different seasons, no cyclic pattern in similarity was found by MDS plots in two years of recruitment communities. There are variations of recruitment community between different year and month, and the community structures converged after succession. These results do not support the prediction of the Seasoanl Recruitment Hypothesis.

Red spruce is a shade-tolerant conifer whose distribution and abundance reflect Quaternary climate history as well as natural and anthropogenic disturbances. This species once extended further south than its present localities, because of natural and anthropogenic disturbances such as logging, windthrow, and fire. Little is known about the disturbance regime of this species, because long term stand dynamics are difficult to obtain. This-long lived species is hypothesized to be suffering a decline in radial growth, density and abundance at the present time. Recent research suggests pollution, biotic stresses, climate change and natural stand dynamics are the driving forces behind these decreases. The purpose of this study is to investigate the influence of fire in a mesic ecosystem, specifically a high-elevation red spruce (Picea rubens Sarg.) forest on Whitetop Mountain in the southern Appalachian Mountains. Six plots were established in a high elevation red spruce stand to characterize the stand composition. Tree ring data were collected to investigate radial growth relations to inter-annual climatic variability and cross-sections were used to investigate fire history. Red spruce continued to establish throughout the 19th century until a severe fire occurred in 1919 and caused a new cohort of yellow birch (Betula alleghaniensis Britt.) to establish within the stand. Logging and fire caused high mortality in the stand, yet many spruce remain that outdate the past disturbances. Red spruce saplings continue to persist in the stand, showing regeneration despite the abundant hardwoods. Moisture was the main contributing factor to red spruce growth in the dendroclimatic analysis. Red spruce radial growth was significantly correlated to high precipitation and low temperatures of the previous growing season, which is similar to recent research results. This study collaborates the current literature on red spruce growth along with the results found here in creating a model to represent the growth characteristics of red spruce when inter-mixed with hardwoods after a severe disturbance.

CEO succession decisions are an important part of boards of directors’ responsibilities to shareholders. I study two aspects of these decisions. First, I examine whether or not forced CEO departure decisions are based on information that the board of directors has, but external investors do not. I find that the proxy for private information in the forced CEO departure decision is positively related to abnormal returns at the forced CEO departure announcement. This is consistent with the hypotheses that prior to the departure announcement, investors underestimate the probability of forced CEO departure, and that private information revealed in forced CEO departure announcements has positive implications for firm value. A second question related to boards of directors’ CEO succession decisions concerns their decisions to participate in the external market for CEO talent. I find evidence suggesting that board decisions to participate in the external market for CEO talent are influenced by the costs and benefits of doing so. Specifically, cross sectional analyses of a proxy for industry homogeneity shows that this variable is positively related to external labor market participation, more standardized search processes, and a higher likelihood that a newly appointed CEO will survive three years or more. These findings are generally consistent with prediction that when industries are more homogenous, external search costs are lower, and higher quality matches may be obtained. I also test hypotheses related to benefits of matching to individuals with industry specific skills versus general management skills. I find that for several alternative proxies for industry specific skill demand, there is a negative relation between demand for industry specific skills and the decision to hire externally outside the industry. This can be interpreted as support for hypotheses that cross sectional variation in benefits associated with industry specific skills leads to fewer CEO appointments outside the industry, while benefits of general management skills are associated with a higher likelihood of inter-industry CEO appointment.

Univ., Diss.--Paris, 2004.

Inaug.-diss.--Göttingen. / Lebenslauf. Half-title (p. [12]): ... Januar bis Juli 1778. "Literatur": p. v-x.

The astounding complexity of microbial communities limits the ability to study the role of genomic diversity in shaping the community composition at the species level. With the advancement and increased affordability of high-throughput sequencing methods, it is increasingly recognized that genomic diversity at the sub-species level plays an important role in selection during microbial community succession. Recent studies using the cpn60 universal target (UT) have shown that it is a high-resolution tool that provides superior resolution in comparison to 16S rRNA based tools and can predict genome relatedness. However, studies to characterize the nature and degree of genome content differences predicted by cpn60 UT sequence relationships have not been conducted. In this work, we focused on the Enterococcus community obtained from feces of healthy pigs. Enterococci are both accessible with selective culture, and interesting since the genus includes members that are significant human pathogens and others that are used as probiotics. Previous work has shown that cpn60 UT sequences can resolve pig fecal Enterococcus faecalis and E. hirae into phylogenetically and phenotypically distinct ecotypes. The utility of cpn60 UT sequences for resolution of Enterococcus species was first established in the year 2000, and this demonstration included 17 Enterococcus species. We have expanded the analysis to include all currently recognized Enterococcus species and confirmed that cpn60 UT sequences provide higher resolution than 16S rRNA sequences for identification of Enterococcus species. In addition, we showed that cpn60 UT sequences could resolve sub-groups in E. faecium consistent with results obtained from comparison of whole genome sequences. GTG rep PCR based clusters for E. faecalis and E. hirae isolates were generally consistent with the cpn60 defined Enterococcus ecotypes observed in our previous study, suggesting that cpn60 UT sequences predict overall genomic relationships. Results from analysis of CRISPR sequences provided insights into the extensive networking and transfer of genetic material that takes place within the intestinal Enterococcus community. We conducted whole genome sequencing of representative isolates to characterize further the genomic diversity in cpn60 defined E. hirae ecotypes to determine the nature and degree of genome content differences predicted by cpn60 UT sequences. Differences in phosphotransferase systems, amino acid metabolism pathways for glutamine, proline and selenocystiene, potassium-transporting ATPases, copper homeostasis systems and putative prophage associated sequences, CRISPRs and antibiotic resistance genes were observed. Results from in vitro growth competition assays showed that isolates from E. hirae-1 and E. hirae-2 were able to out-compete isolates from the E. hirae-3 ecotype, consistent with the relatively low abundance of E. hirae-3 relative to E. hirae-1 and E. hirae-2 previously observed in the pig fecal microbiome, and with observed gene content differences between the ecotypes. Results presented in this thesis provide a genomic basis for the definition of ecotypes within E. hirae and confirm the utility of the cpn60 UT sequence for high resolution profiling of complex microbial communities.

Primary plant succession was examined on the foreland of the retreating Twin Glacier at Alexandra Fjord, Ellesmere Island. The position of the glacial front was monitored directly from 1980 to 1995 (except 1986-1991), and airphotos show the position of the glacier in 1959. Hence, there was an excellent opportunity to study primary succession where there was adequate chronological control. Presently, a well preserved pre-Little Ice Age plant community and organically rich (paleo) soil are being released from the Twin Glacier, in addition to glacio-fluvial sediments, rendering this foreland study unique. A terrain age scheme was developed using direct retreat measurements, airphotos and Salix aging. The relationship between the clump diameters of Luzula confusa and terrain age was determined to provide an alternative to lichenometry. Vegetation cover was assessed in 1994 and 1995 using a stratified random design. TWINSPAN and canonical correspondence analysis (detrended and non-detrended) were used together to examine vegetation patterns in relation to environmental variables. Soil seed bank and seed rain patterns were examined in relation to the above-ground vegetation. The seed bank was sampled in 1994, including samples from paleo-soil and glacio-fluvial sediment. To assess the fall-winter seed rain, seeds were collected between mid-August 1994 and early June 1995, using seed traps (artificial turf). Winter seed rain was sampled by collecting snow-core samples in early June 1995. Terrain age accounted for most of the variation in species composition over the study area. By directional-replacement, the succession followed four main stages of dominance in 44+ years: mosses —> graminoid-forb —> deciduous shrub-moss —> evergreen dwarf-shrubmoss. There was little difference in the successional sequences exhibited by the vegetation growing on the paleo-soil compared to that growing on the glacio-fluvial sediment. The relationship between the Luzula confusa clump diameters and terrain age was logarithmic. Luzula confusa dominated the above-ground vegetation, as well as, the germinable seed bank and seed rain. The average germinable seed bank, fall-winter seed rain and winter seed rain densities were 367 ± 32, 384 ± 47 and 180 ± 53 seeds/m2, respectively. The seed bank was significantly positively correlated with the above-ground vegetation cover for all species combined, Luzula confusa (monocotyledons), dicotyledons and Papaver radicatum. There was a significant positive correlation between the fall-winter seed rain and the above-ground vegetation cover for Luzula confusa. No difference was detected in seed bank density between the paleo-soil and the glacio-fluvial sediment. However, the total vegetation cover was significantly higher on the paleo-soil. The relationship determined between Luzula confusa clump diameters and terrain age appears to be a valuable alternative to lichenometry on the Twin Glacier foreland. Although the results showed that directional-replacement is possible in high arctic environments, this mode of succession is likely atypical of such environments; the Twin Glacier foreland is located in one of the very few polar oases in the Queen Elizabeth Islands. The positive correlation of the above-ground vegetation with the seed bank and fall-winter seed rain suggests that colonization is largely constrained by seed availability. The winter seed rain appears to be relatively important on the Twin Glacier foreland. The higher vegetation cover on the paleosoil versus the glacio-fluvial sediment suggests, at least for some species, that the former provides conditions more favourable for establishment and growth than the latter.

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