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Thresholds and Legacy Effects of Tropical Floodplain Fish Assemblages in Response to Flood Attributes

Description: Natural flow regimes are critical for sustaining biodiversity and river integrity. Floods and droughts form an important component of river systems and control population sizes and species diversity across space and time. Modification of flow regimes, including disruption of the timing, magnitude and duration of flooding, is a global problem, and many new impoundments are planned for large river-floodplain ecosystems in the tropics. Flow modifications may cause dramatic non-linear responses in population sizes and have lasting effects through time, but such topics are poorly investigated over multi-year scales, especially in highly diverse tropical ecosystems. Using a long-term dataset from the Upper Paraná River floodplain, Brazil, I tested for threshold and legacy effects of fish assemblages to flood attributes, such as timing, magnitude, duration, rate of change and variation. Specifically, I hypothesized that long duration, high magnitude floods would elicit threshold responses in long-distance migratory fish species and these responses result in significant legacy effects detectable over multiple years. Consistent positive threshold responses to increasing flood duration and magnitude were detected for many species and not significantly correlated with reproductive guilds. Legacy effects were prevalent (i.e. identified for more than 90% of species) and including flood attributes from previous years increased variance explained in species abundances by 15-20% compared to contemporary flood attributes alone. Contrary to my hypotheses, flood duration did not elicit strong legacy effects and species from the same reproductive guild did not have similar legacy effects models. The prevalence of legacy effects across almost all species in this diverse study system highlights the need to consider such dynamics in other systems. My results provide targets for management and conservation actions, such as environmental flow releases from upstream reservoirs. Environmental flows releases may play a significant role in sustainability of the floodplain and other tropical floodplain ecosystems affected by ...
Date: December 2015
Creator: Hoeinghaus, Ana Paula Ferrari
Partner: UNT Libraries

Effects of Macrophyte Functional Diversity on Taxonomic and Functional Diversity and Stability of Tropical Floodplain Fish Assemblages

Description: Multiple dimensions of biodiversity within and across producer and consumer guilds in the food web affect an ecosystem’s functionality and stability. Tropical and subtropical aquatic ecosystems, which are extremely diverse, have received much less attention than terrestrial ecosystems in regards to the effects of biodiversity on ecosystem functioning. We conducted a field experiment that tested for effects of macrophyte functional diversity on diversity and stability of associated fish assemblages in floodplain lakes of the Upper Paraná River floodplain, Brazil. Three levels of macrophyte functional diversity were maintained through time in five floodplain lakes and response variables included various components of fish taxonomic and functional diversity and stability. Components of functional diversity of fish assemblages were quantified using a suite of ecomorphological traits that relate to foraging and habitat use. Response variables primarily distinguished macrophyte treatments from the control. Macrophyte treatments had, on average, double the number of species and total abundance than the control treatment, but only limited effects on stability. The high diversity treatment was essentially nested within the low diversity for assemblage structure and had similar or even slightly lower levels of species richness and abundance in most cases. Gymnotiformes and young-of-year were diverse and relatively abundant in macrophyte treatments contributing to the large differences in diversity between macrophyte and control treatments. Higher fish diversity in structured habitats compared to more homogenous habitats is likely associated with increased ecomorphological diversity to exploit heterogeneous microhabitats and resources provided by the macrophytes.
Date: August 2015
Creator: Treviño, Jessica Marie
Partner: UNT Libraries

Elizabeth Bishop in Brasil: An Ongoing Acculturation

Description: Elizabeth Bishop (1911–1979), one of the foremost modern American poets, lived in Brasil during seventeen-odd years beginning in 1951. During this time she composed the poetry collection Questions of Travel, stand-alone poems, and fragments as well as prose pieces and translations. This study builds on the work of critics such as Brett Millier and Lorrie Goldensohn who have covered Bishop’s poetry during her Brasil years. However, most American critics have lacked expertise in both Brasilian culture and the Portuguese language that influenced Bishop’s poetry. Since 2000, in contrast, Brasilian critic Paulo Henriques Britto has explored issues of translating Bishop’s poetry into Portuguese, while Maria Lúcia Martins and Regina Przybycien have examined Bishop’s Brasil poems from a Brasilian perspective. However, American and Brasilian scholars have yet to recognize Bishop’s journey of acculturation as displayed through her poetry chronologically or the importance of her belated reception by Brasilian literary and popular culture. This study argues that Bishop’s Brasil poetry reveals her gradual transformation from a tourist outsider to a cultural insider through her encounters with Brasilian history, culture, language, and politics. It encompasses Bishop’s published and unpublished Brasil poetry, including drafts from the Elizabeth Bishop Papers at Vassar College. On a secondary level, this study examines a reverse acculturation in how Brasilian popular and literary communities have increasingly focused on Bishop since her death, culminating in the 2013 film, Flores Raras (Reaching for the Moon in English). Understanding this extremely rare and sustained intercultural junction of Bishop in Brasil, a junction that no American poet has made since, adds a crucial angle to twentieth-first century transnational literary perspectives.
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Date: August 2014
Creator: Neely, Elizabeth
Partner: UNT Libraries

Stock Returns and the Brazilian Default an Analysis of the Efficient Market and Contagion Effect Hypotheses

Description: This thesis attempts to analyze the market response of stock prices of major U.S. banks to the February, 1987 Brazilian loan default announcement. The study's general hypothesis is that the market revalued stock prices according to each bank's amount of Brazilian loan exposure. The first chapter examines the significance of the default announcement. A survey of related literature is presented in the second chapter. Chapter III specifies the methodological techniques involved in analysis of the data. Chapter IV reports the findings of the study. Conclusions about the results are drawn in Chapter V. The results indicate the market is efficient. They also suggest that individual exposure was the major determinant of bank stock price decline.
Date: August 1988
Creator: Mynatt, Joseph Ross
Partner: UNT Libraries