1,720,962 research outputs found
The Ecology of West Nile Virus in Atlanta, Georgia
Get PDFWest Nile virus (WNV) is a vector-borne virus that has caused hundreds of human deaths
and has cost the United States millions of dollars each year since its first emergence in 1999. To
understand the ecology of West Nile virus prevalence and the influence of the dilution effect, I
will build on preliminary results to test several hypotheses related to the population and habitat
of mosquito and birds in Atlanta, Georgia. The dilution effect, which states that disease
prevalence can be reduced by biodiversity, has yet to be tested in the southeast United States in
relation to both tree and avian diversity. To address these questions, I established a series of sites
in Atlanta that span from different forest patch sizes, pine and hardwood composition, and socio
economic scenarios. The data indicate that the number of adult and gravid mosquitoes are
positively related to older homes, surrounded by primarily hardwood trees. The vector index (VI)
was also positively related to older homes and hardwood habitat. However, the VI was not
correlated to either avian or tree diversity. This study demonstrated that avian diversity and
evenness were associated with smaller trees with less species diversity. Additionally, avian
species diversity was higher in newer neighborhoods that were built after the 1960s. Avian
diversity was also highly correlated to the number of corvids, which rejected the hypothesis that
predicted corvids having a negative impact on avian diversity indices. Sites with a large number
of avian individuals were associated with higher amounts of both blue jays and American robins.
Corvids were not abundant in sites that were more urban and consisted mostly of pine trees.
Finally, this study detected no correlation between the vector for WNV and any of the
parameters involving avian diversity or specific species abundance
Nutrient Dynamics in an Old-Growth Bottomland Forest: Congaree National Park, South Carolina
Get PDFFloodplains are important landscapes that act as boundaries between terrestrial and aquatic ecosystems. Past research efforts have illustrated that floodplains perform many beneficial functions, such as sediment retention and nutrient transformations, but little is known about old-growth riparian forests due to historical wetland losses in the United States. Thus, the goal of this study was to examine the effect of floodplain landscape variability on nutrient storage and transformations within an old-growth floodplain forest at Congaree National Park (CONG), South Carolina. Our specific objectives were to quantify: (i) soil organic carbon (SOC) storage, (ii) key biogeochemical indices such as microbial biomass, net nitrogen (N) mineralization, and soil phosphorus (P) saturation, and (iii) woody debris decomposition rates and nutrient dynamics. We measured SOC pools in four distinct floodplain landscapes (natural levee, flats, hydric mineral soil wetlands, hydric organic soil wetlands) within CONG. Mean SOC stocks (0-200 cm) were significantly greater in hydric mineral and organic soils when compared to non-wetland soil landscapes because of deep carbon (C) stocks associated with buried surfaces. We also measured biogeochemical indices and woody debris decomposition over a 2 year period on a soil toposequence ranging from the well drained river levee to a poorly drained backswamp. Soil microbial biomass was relatively consistent throughout the study, unlike net N mineralization, which showed significant seasonal variations. Nitrate (NO3-N) was the predominant product of net N mineralization and soil P saturation was low across all toposequence positions. Prolonged drought conditions during the study allowed red imported fire ants to infest and damage the outer bark of downed woody debris. Invertebrate activity and microbial mineralization contributed to extremely fast wood decay rates in all landscapes. Woody debris C content decreased throughout the study, while N and P displayed periods of net immobilization. Results from this research indicate that the soils in the old-growth floodplain forests of CONG function as a sink for C, N, and P. However, rapid woody debris turnover rates and net NO3-N production suggest that the Park may mineralize nutrients quickly from forest litter and be relatively leaky with regard to ecosystem N retention
Influence of microtopography and nutrient limitation on belowground productivity in an old-growth floodplain forest at Congaree National Park, SC, USA
No full textThis study was designed to improve our understanding of nutrient cycling, C storage and belowground net primary productivity (BNPP) in an old-growth floodplain forest. Four microsites were established parallel to the Congaree River on a floodplain in Congaree National Park, SC, decreasing in elevation from the river (natural levee > flat > transitional > backswamp). Response variables for each microsite included: BNPP (June 2011-March 2013) and results from two fertilized root in-growth core studies (summer 2012, fall 2012). BNPP decreased significantly in the following order: natural levee, flat, transitional, and backswamp. Combined N+P fertilization treatments significantly increased fine root productivity relative to the control, suggesting that N and P co-limit fine root productivity in this floodplain forest. Results indicate that significant differences in root growth patterns and nutrient dynamics occur along an elevational gradient, and water availability has a greater effect on fine root productivity than does a single nutrient
The Effects of Fertilization and Four Years of Throughfall Reduction on Leaf Physiology of Loblolly Pine (Pinus taeda L.)
Get PDFLoblolly pine (Pinus taeda L.) is the most widely planted pine species in the southeastern United States. Increased frequency of drought associated with projected climate change may negatively impact loblolly pine productivity. The objective of this study was to evaluate the main and interactive effects of reduced water availability, achieved by throughfall reduction, and one-time fertilization on factors that affect loblolly pine productivity. Leaf-level physiology, and growth were monitored over the third and fourth year of treatment. After four years of throughfall reduction treatment, no interactive treatment effects on light-saturated net photosynthesis (Pnet), stomatal conductance (gs), or growth were observed. Neither fertilization nor throughfall reduction treatment effected growth efficiency, midday leaf water potential (ΨL), ΔΨL, or leaf-specific hydraulic conductance. Fertilization, regardless of throughfall reduction treatment, increased all growth variables except for height, increased radiation use efficiency of stemwood production (εstem), increased intercepted photosynthetically active radiation, and increased leaf area index. However, fertilization decreased Pnet and gs likely due to increased leaf evaporative demand associated with higher LAI. Throughfall reduction decreased LAI and, in 2014, throughfall reduction reduced the leaf area to sapwood area ratio (AL:AS) thereby increasing water supply per unit foliage resulting in no effect of throughfall reduction on leaf-level gas exchange. Conversely, both treatments decreased Δ13C discrimination indicating higher water use efficiency (WUE) and reduced gs in response to throughfall reduction treatment not detected by instantaneous leaf-level gas exchange measurements. The results of this study indicate that while fertilization can increase growth regardless of throughfall reduction, higher LAI with fertilization may increase water use and increase short-term leaf-level drought susceptibility. In a more drought prone future climate, management strategies that utilize fertilization to increase growth may result in diminished fertilization responses due to the impact of fertilization on leaf-level drought susceptibility. In order to maintain future productivity, management strategies such as density management may be required to reduce fertilization’s impact on water use
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The Effects of 40% Throughfall Reduction on Soil Respiration in a Longleaf Pine Plantation
Get PDFLongleaf pine (Pinus palustris) forests can serve as disturbance-resistant, long-term carbon sinks, but net ecosystem productivity of longleaf pine forests has been shown to be sensitive to drought. Soil respiration (Rs) is often the largest component of ecosystem respiration and can be sensitive to drought. The primary objective of this study is to explore the influence of drought, imposed by a 40% reduction in throughfall (TR40), relative to ambient throughfall treatment (TR0) on soil respiration (Rs), heterotrophic respiration (Rh) and fine root biomass. The study was conducted in a longleaf pine plantation located in the Chattahoochee Fall Line Region in Georgia. During a naturally occurring severe drought in 2016, soil moisture and Rs declined to near zero in both treatments, and TR treatment had no effect on Rs, soil moisture, or soil temperature. In 2017, TR40 reduced Rs from 13.8% to 21.6% on six of the 12 measurement dates. Annual Rs ranged from 9.96 Mg C ha-1 yr-1 in the TR0 treatment to 8.70 Mg C ha-1 yr-1 in the TR40 treatment, and Q10 was reduced from 1.92 to 1.67 by TR40. Soil temperature and soil moisture explained the majority of the variation in Rs in 2016 (68% in TR0 and 68% in TR40) and 2017 (54% in TR0 and 42% in TR40). Surrounding tree basal area and distance to nearest tree each accounted for up to 6% of the variation in Rs. Throughfall reduction treatment did not significantly reduce fine root biomass or shift the spatial distribution of fine root biomass in response to TR trays. Heterotrophic respiration accounted for the majority of soil respiration (72.4-89.4%). Throughfall reduction altered the contribution of Rh to Rs in August 2017, suggesting that autotrophic respiration (Ra) was decreased. Results suggest that Ra may be more sensitive to moderate drought in longleaf pine forests but both Ra and Rh are sensitive to soil moisture below the wilting point
Coral Reefs and Climate Change: Examining Two Institutional Approaches to Managing a Novel Marine Ecosystem
Get PDFMuch of Florida’s economy is tied to the third-largest barrier reef in the world, the
Florida Reef Tract. However, because of anthropogenic threats, it is not the thriving ecosystem it
once was, and its persistence requires different management strategies than what may have been
conventionally considered. Two entities have emerged to address this problem: the Florida Keys
National Marine Sanctuary and the Southeast Florida Coral Reef Initiative. I therefore ask: How
does coral reef management vary over the different spatial extents and structures of these
organizations? And, how do these organizations vary in incorporating important aspects of novel
ecosystem management? Using 1122 statements from news documents, public meeting
transcripts, and stakeholder interviews, I compare the institutional elements of each organization
and determine the importance they place on five management considerations, which improve
novel ecosystem management. My results indicate significant institutional differences between
the two, one marked by a focus on regulations and authority and the other by a focus on data
collection, and preparednes
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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