Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99


Any time

2020 ( 44 )

2019 ( 204 )

2018 ( 253 )

2017 ( 250 )

Custom range...

Search Results: 1 - 10 of 192747 matches for " Rhett D. Harrison "
All listed articles are free for downloading (OA Articles)
Page 1 /192747
Display every page Item
Wild Pigs (Sus scrofa) Mediate Large-Scale Edge Effects in a Lowland Tropical Rainforest in Peninsular Malaysia
Junichi Fujinuma, Rhett D. Harrison
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0037321
Abstract: Edge-effects greatly extend the area of tropical forests degraded through human activities. At Pasoh, Peninsular Malaysia, it has been suggested that soil disturbance by highly abundant wild pigs (Sus scrofa), which feed in adjacent Oil Palm plantations, may have mediated the invasion of Clidemia hirta (Melastomataceae) into the diverse tropical lowland rain forest. To investigate this hypothesis, we established three 1 km transects from the forest/Oil Palm plantation boundary into the forest interior. We recorded the distribution of soil disturbance by wild pigs, C. hirta abundance, and environmental variables. These data were analyzed using a hierarchical Bayesian model that incorporated spatial auto-correlation in the environmental variables. As predicted, soil disturbance by wild pigs declined with distance from forest edge and C. hirta abundance was correlated with the level of soil disturbance. Importantly there was no effect of distance on C. hirta abundance, after controlling for the effect of soil disturbance. Clidemia hirta abundance was also correlated with the presence of canopy openings, but there was no significant association between the occurrence of canopy openings and distance from the edge. Increased levels of soil disturbance and C. hirta abundance were still detectable approximately 1 km from the edge, demonstrating the potential for exceptionally large-scale animal mediated edge effects.
Enhanced Structural Complexity Index: An Improved Index for Describing Forest Structural Complexity  [PDF]
Philip Becksch?fer, Philip Mundhenk, Christoph Kleinn, Yinqiu Ji, Douglas W. Yu, Rhett D. Harrison
Open Journal of Forestry (OJF) , 2013, DOI: 10.4236/ojf.2013.31005

The horizontal distribution of stems, stand density and the differentiation of tree dimensions are among the most important aspects of stand structure. An increasing complexity of stand structure is often linked to a higher number of species and to greater ecological stability. For quantification, the Structural Complexity Index (SCI) describes structural complexity by means of an area ratio of the surface that is generated by connecting the tree tops of neighbouring trees to form triangles to the surface that is covered by all triangles if projected on a flat plane. Here, we propose two ecologically relevant modifications of the SCI: The degree of mingling of tree attributes, quantified by a vector ruggedness measure, and a stem density term. We investigate how these two modifications influence index values. Data come from forest inventory field plots sampled along a disturbance gradient from heavily disturbed shrub land, through secondary regrowth to mature montane rainforest stands in Mengsong, Xishuangbanna,Yunnan,China. An application is described linking structural complexity, as described by the SCI and its modified versions, to changes in species composition of insect communities. The results of this study show that the Enhanced Structural Complexity Index (ESCI) can serve as a valuable tool for forest managers and ecologists for describing the structural complexity of forest stands and is particularly valuable for natural forests with a high degree of structural

Evolution of Fruit Traits in Ficus Subgenus Sycomorus (Moraceae): To What Extent Do Frugivores Determine Seed Dispersal Mode?
Rhett D. Harrison, Nina R?nsted, Lei Xu, Jean-Yves Rasplus, Astrid Cruaud
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0038432
Abstract: Fig trees are a ubiquitous component of tropical rain forests and exhibit an enormous diversity of ecologies. Focusing on Ficus subgenus Sycomorus, a phenotypically diverse and ecologically important Old World lineage, we examined the evolution of fruit traits using a molecular phylogeny constructed using 5 kilobases of DNA sequence data from 63 species (50% of global diversity). In particular, we ask whether patterns of trait correlations are consistent with dispersal agents as the primary selective force shaping morphological diversity or if other ecological factors may provide a better explanation? Fig colour, size and placement (axial, cauliflorous, or geocarpic) were all highly evolutionarily liable, and the same fruit traits have evolved in different biogeographic regions with substantially different dispersal agents. After controlling for phylogenetic autocorrelation, we found that fig colour and size were significantly associated with fig placement and plant-life history traits (maximum plant height and leaf area, respectively). However, contrary to prevailing assumptions, fig placement correlated poorly with known dispersal agents and appears more likely determined by other factors, such as flowering phenology, nutrient economy, and habitat preference. Thus, plant life-history, both directly and through its influence on fig placement, appears to have played a prominent role in determining fruit traits in these figs.
Do Epigeal Termite Mounds Increase the Diversity of Plant Habitats in a Tropical Rain Forest in Peninsular Malaysia?
Lydia Beaudrot,Yanjun Du,Abdul Rahman Kassim,Marcel Rejmánek,Rhett D. Harrison
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0019777
Abstract: The extent to which environmental heterogeneity can account for tree species coexistence in diverse ecosystems, such as tropical rainforests, is hotly debated, although the importance of spatial variability in contributing to species co-existence is well recognized. Termites contribute to the micro-topographical and nutrient spatial heterogeneity of tropical forests. We therefore investigated whether epigeal termite mounds could contribute to the coexistence of plant species within a 50 ha plot at Pasoh Forest Reserve, Malaysia. Overall, stem density was significantly higher on mounds than in their immediate surroundings, but tree species diversity was significantly lower. Canonical correspondence analysis showed that location on or off mounds significantly influenced species distribution when stems were characterized by basal area. Like studies of termite mounds in other ecosystems, our results suggest that epigeal termite mounds provide a specific microhabitat for the enhanced growth and survival of certain species in these species-rich tropical forests. However, the extent to which epigeal termite mounds facilitate species coexistence warrants further investigation.
Shifting Baselines on a Tropical Forest Frontier: Extirpations Drive Declines in Local Ecological Knowledge
Zhang Kai, Teoh Shu Woan, Li Jie, Eben Goodale, Kaoru Kitajima, Robert Bagchi, Rhett D. Harrison
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0086598
Abstract: The value of local ecological knowledge (LEK) to conservation is increasingly recognised, but LEK is being rapidly lost as indigenous livelihoods change. Biodiversity loss is also a driver of the loss of LEK, but quantitative study is lacking. In our study landscape in SW China, a large proportion of species have been extirpated. Hence, we were interested to understand whether species extirpation might have led to an erosion of LEK and the implications this might have for conservation. So we investigated peoples' ability to name a selection of birds and mammals in their local language from pictures. Age was correlated to frequency of forest visits as a teenager and is likely to be closely correlated to other known drivers of the loss of LEK, such as declining forest dependence. We found men were better at identifying birds overall and that older people were better able to identify birds to the species as compared to group levels (approximately equivalent to genus). The effect of age was also stronger among women. However, after controlling for these factors, species abundance was by far the most important parameter in determining peoples' ability to name birds. People were unable to name any locally extirpated birds at the species level. However, contrary to expectations, people were better able to identify extirpated mammals at the species level than extant ones. However, extirpated mammals tend to be more charismatic species and several respondents indicated they were only familiar with them through TV documentaries. Younger people today cannot experience the sights and sounds of forest animals that their parents grew up with and, consequently, knowledge of these species is passing from cultural memory. We suggest that engaging older members of the community and linking the preservation of LEK to biodiversity conservation may help generate support for conservation.
Factors Determining Forest Diversity and Biomass on a Tropical Volcano, Mt. Rinjani, Lombok, Indonesia
Gbadamassi G. O. Dossa, Ekananda Paudel, Junichi Fujinuma, Haiying Yu, Wanlop Chutipong, Yuan Zhang, Sherryl Paz, Rhett D. Harrison
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0067720
Abstract: Tropical volcanoes are an important but understudied ecosystem, and the relationships between plant species diversity and compositional change and elevation may differ from mountains created by uplift, because of their younger and more homogeneous soils. We sampled vegetation over an altitudinal gradient on Mt. Rinjani, Lombok, Indonesia. We modeled alpha- (plot) and beta- (among plot) diversity (Fisher's alpha), compositional change, and biomass against elevation and selected covariates. We also examined community phylogenetic structure across the elevational gradient. We recorded 902 trees and shrubs among 92 species, and 67 species of ground-cover plants. For understorey, subcanopy and canopy plants, an increase in elevation was associated with a decline in alpha-diversity, whereas data for ground-cover plants suggested a hump-shaped pattern. Elevation was consistently the most important factor in determining alpha-diversity for all components. The alpha-diversity of ground-cover vegetation was also negatively correlated with leaf area index, which suggests low light conditions in the understorey may limit diversity at lower elevations. Beta-diversity increased with elevation for ground-cover plants and declined at higher elevations for other components of the vegetation. However, statistical power was low and we could not resolve the relative importance to beta-diversity of different factors. Multivariate GLMs of variation in community composition among plots explained 67.05%, 27.63%, 18.24%, and 19.80% of the variation (deviance) for ground-cover, understorey, subcanopy and canopy plants, respectively, and demonstrated that elevation was a consistently important factor in determining community composition. Above-ground biomass showed no significant pattern with elevation and was also not significantly associated with alpha-diversity. At lower elevations communities had a random phylogenetic structure, but from 1600 m communities were phylogenetically clustered. This suggests a greater role of environmental filtering at higher elevations, and thus provides a possible explanation for the observed decline in diversity with elevation.
Befriending Wisdom
Rhett Gayle
Analytic Teaching and Philosophical Praxis , 2011,
Abstract: We live amidst the biggest explosion in knowledge in human history. More and more facts emerge, faster and faster, from the activities of researchers. More and more applications of those facts are then transformed into technologies which in turn allow the further emergence of yet more facts. This process is driven by methodological innovation in the production of knowledge that began crystallizing during the Renaissance and hit its stride during the Enlightenment. Set adrift from its traditional focus on wisdom by Descartes’ accommodation of the new science and cemented into the new paradigm by Kant’s critical move to make philosophy a kind of knowledge, philosophers have been active and full participants in the new approach. There have been suspicions, however, given the ways that certain aspects of modern life seem to have gone astray, that leaving wisdom behind was perhaps, well, unwise. Motivated by this thought, some philosophers want to return to our roots as a discipline focused on wisdom. Philosophers are by strong inclination interested in educating the young, so it is natural for us to want to include our students in this revival. Teaching wisdom in the modern academy, on the other hand, seems a rather difficult task. The notion of the transfer of knowledge, conceived of as collections of facts and their relationships, as the central task of education inclines against teaching wisdom. The methods and attitudes that philosophy has developed while adapting to a world dominated by abundant, scientifically created knowledge, are also impediments. In this paper I will be looking at some of the barriers to teaching wisdom facing a philosopher in modern academia. Broadly, the barriers can be divided into two categories: confusions based on the notion that knowledge is wisdom or at least serves the role that wisdom had previously served, and those arising from the belief that wisdom is a kind of knowledge not too different from the propositional knowledge that other disciplines teach. I will then offer an alternative framework for thinking about the teaching task that focuses on the notion that the goal is not a transfer of knowledge but the beginning of a friendship, a friendship between the student and wisdom.
A method for calculating the imaginary part of the Hadamard Elementary function $G^{(1)}$ in static, spherically symmetric spacetimes
Rhett Herman
Physics , 1998, DOI: 10.1103/PhysRevD.58.084028
Abstract: Whenever real particle production occurs in quantum field theory, the imaginary part of the Hadamard Elementary function $G^{(1)}$ is non-vanishing. A method is presented whereby the imaginary part of $G^{(1)}$ may be calculated for a charged scalar field in a static spherically symmetric spacetime with arbitrary curvature coupling and a classical electromagnetic field $A^{\mu}$. The calculations are performed in Euclidean space where the Hadamard Elementary function and the Euclidean Green function are related by $(1/2)G^{(1)}=G_{E}$. This method uses a $4^{th}$ order WKB approximation for the Euclideanized mode functions for the quantum field. The mode sums and integrals that appear in the vacuum expectation values may be evaluated analytically by taking the large mass limit of the quantum field. This results in an asymptotic expansion for $G^{(1)}$ in inverse powers of the mass $m$ of the quantum field. Renormalization is achieved by subtracting off the terms in the expansion proportional to nonnegative powers of $m$, leaving a finite remainder known as the ``DeWitt-Schwinger approximation.'' The DeWitt-Schwinger approximation for $G^{(1)}$ presented here has terms proportional to both $m^{-1}$ and $m^{-2}$. The term proportional to $m^{-2}$ will be shown to be identical to the expression obtained from the $m^{-2}$ term in the generalized DeWitt-Schwinger point-splitting expansion for $G^{(1)}$. The new information obtained with the present method is the DeWitt-Schwinger approximation for the imaginary part of $G^{(1)}$, which is proportional to $m^{-1}$ in the DeWitt-Schwinger approximation for $G^{(1)}$ derived in this paper.
Prevalence and Infection Load Dynamics of Rickettsia felis in Actively Feeding Cat Fleas
Kathryn E. Reif, Rhett W. Stout, Gretchen C. Henry, Lane D. Foil, Kevin R. Macaluso
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0002805
Abstract: Background Rickettsia felis is a flea-associated rickettsial pathogen recurrently identified in both colonized and wild-caught cat fleas, Ctenocephalides felis. We hypothesized that within colonized fleas, the intimate relationship between R. felis and C. felis allows for the coordination of rickettsial replication and metabolically active periods during flea bloodmeal acquisition and oogenesis. Methodology/Principal Findings A quantitative real-time PCR assay was developed to quantify R. felis in actively feeding R. felis-infected fleas. In three separate trials, fleas were allowed to feed on cats, and a mean of 3.9×106 R. felis 17-kDa gene copies was detected for each flea. A distinct R. felis infection pattern was not observed in fleas during nine consecutive days of bloodfeeding. However, an inverse correlation between the prevalence of R. felis-infection, which ranged from 96% in Trial 1 to 35% in Trial 3, and the R. felis-infection load in individual fleas was identified. Expression of R. felis-infection load as a ratio of R. felis/C. felis genes confirmed that fleas in Trial 3 had significantly greater rickettsial loads than those in Trial 1. Conclusion/Significance Examining rickettsial infection dynamics in the flea vector will further elucidate the intimate relationship between R. felis and C. felis, and facilitate a more accurate understanding of the ecology and epidemiology of R. felis transmission in nature.
The Use of Percutaneous Lumbar Fixation Screws for Bilateral Pedicle Fractures with an Associated Dislocation of a Lumbar Disc Prosthesis
William D. Harrison,David J. Harrison
Case Reports in Orthopedics , 2013, DOI: 10.1155/2013/676017
Abstract: Study Design. Case report. Objective. To identify a safe technique for salvage surgery following complications of total disc replacement. Summary of Background Data. Lumbar total disc replacement (TDR) is considered by some as the gold standard for discogenic back pain. Revision techniques for TDR and their complications are in their infancy. This case describes a successful method of fixation for this complex presentation. Methods and Results. A 48-year-old male with lumbar degenerative disc disease and no comorbidities. Approximately two weeks postoperatively for a TDR, the patient represented with acute severe back pain and the TDR polyethylene inlay was identified as dislocated anteriorly. Subsequent revision surgery failed immediately as the polyethylene inlay redislocated intraoperatively. Further radiology identified bilateral pedicle fractures, previously unseen on the plain films. The salvage fusion of L5/S1 reutilized the anterior approach with an interbody fusion cage and bone graft. The patient was then turned intraoperatively and redraped. The percutaneous pedicle screws were used to fix L5 to the sacral body via the paracoccygeal corridor. Conclusion. The robust locking screw in the percutaneous screw allowed a complete fixation of the pedicle fractures. At 3-year followup, the patient has an excellent result and has returned to playing golf. 1. Introduction Lumbar disc replacement is becoming a popular surgical choice in the management of discogenic back pain. At present, there are good short- and medium-term outcomes in patients receiving lumbar disc prostheses as opposed to the more traditional interbody vertebral fusion. Long-term outcomes are currently under the spotlight as the practice of modern disc replacement enters the third decade of usage. The indications for total disc replacement (TDR) remain specific and the procedure should only be done in valid cases of discogenic back pain in selected patients. Charité III (LINK SB, DePuy, Warsaw, IN, USA) was the TDR of choice in much of America and Europe during the late 90s and onwards. The design is modular, comprising two metal endplate components fashioned with convex articulating surfaces which oppose a central polymer inlay component. Much of the long-term data for TDR has been generated from the largely successful Charité III design. Complications following TDR are poorly understood and remedies to salvage function following complications are in their infancy. Short-term complications of TDR include disruption to vascular and neurological structures during the approach,
Page 1 /192747
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.