Institution
University of Georgia
Education•Athens, Georgia, United States•
About: University of Georgia is a education organization based out in Athens, Georgia, United States. It is known for research contribution in the topics: Population & Gene. The organization has 41934 authors who have published 93622 publications receiving 3713212 citations. The organization is also known as: UGA & Franklin College.
Topics: Population, Gene, Poison control, Context (language use), Genome
Papers published on a yearly basis
Papers
More filters
••
Michigan State University1, University of California, Davis2, University of California, Santa Barbara3, Grinnell College4, Florida Institute of Technology5, University of California, San Diego6, Smithsonian Institution7, Cornell University8, Academy of Natural Sciences of Drexel University9, Dartmouth College10, Yale University11, University of Chicago12, University of Missouri13, University of Georgia14, University of British Columbia15
TL;DR: Two major hypotheses for the origin of the latitudinal diversity gradient are reviewed, including the time and area hypothesis and the diversification rate hypothesis, which hold that tropical regions diversify faster due to higher rates of speciation, or due to lower extinction rates.
Abstract: A latitudinal gradient in biodiversity has existed since before the time of the dinosaurs, yet how and why this gradient arose remains unresolved. Here we review two major hypotheses for the origin of the latitudinal diversity gradient. The time and area hypothesis holds that tropical climates are older and historically larger, allowing more opportunity for diversification. This hypothesis is supported by observations that temperate taxa are often younger than, and nested within, tropical taxa, and that diversity is positively correlated with the age and area of geographical regions. The diversification rate hypothesis holds that tropical regions diversify faster due to higher rates of speciation (caused by increased opportunities for the evolution of reproductive isolation, or faster molecular evolution, or the increased importance of biotic interactions), or due to lower extinction rates. There is phylogenetic evidence for higher rates of diversification in tropical clades, and palaeontological data demonstrate higher rates of origination for tropical taxa, but mixed evidence for latitudinal differences in extinction rates. Studies of latitudinal variation in incipient speciation also suggest faster speciation in the tropics. Distinguishing the roles of history, speciation and extinction in the origin of the latitudinal gradient represents a major challenge to future research.
1,435 citations
••
01 Jan 1996TL;DR: The origin of cation exchange capacity (CEC) lies in the negative charges carried by soil particles, usually clay, organic matter and sesquioxides as discussed by the authors, which fall into two distinct categories, being either permanent or variable.
Abstract: The origin of cation exchange capacity (CEC) lies in the negative charges carried by soil particles, usually clay, organic matter and sesquioxides. A full discussion of the origin and nature of these charges is presented in Chapter 41 (Zelazny et aI., 1996). Basically these charges fall into two distinct categories, being either permanent or variable (i.e., pH dependent) depending on whether or not ambient conditions (pH or salts) in the soil solution affect their magnitude. Much confusion in the literature concerning the measurement and interpretation of CEC has stemmed from the lack of recognition that these charges fall into two distinct categories exhibiting different behavior. These problems will be addressed in the discussion of the methods for the determination of CEC.
1,430 citations
••
TL;DR: Soil pH was the best predictor of bacterial community composition across this landscape while fungal community composition was most closely associated with changes in soil nutrient status, suggesting specific changes in edaphic properties, not necessarily land-use type itself, may best predict shifts in microbialcommunity composition across a given landscape.
Abstract: Land-use change can have significant impacts on soil conditions and microbial communities are likely to respond to these changes. However, such responses are poorly characterized as few studies have examined how specific changes in edaphic characteristics do, or do not, influence the composition of soil bacterial and fungal communities across land-use types. Soil samples were collected from four replicated ( n = 3) land-use types (hardwood and pine forests, cultivated and livestock pasture lands) in the southeastern US to assess the effects of land-use change on microbial community structure and distribution. We used quantitative PCR to estimate bacterial–fungal ratios and clone libraries targeting small-subunit rRNA genes to independently characterize the bacterial and fungal communities. Although some soil properties (soil texture and nutrient status) did significantly differ across land-use types, other edaphic factors (e.g., pH) did not vary consistently with land-use. Bacterial–fungal ratios were not significantly different across the land-uses and distinct land-use types did not necessarily harbor distinct soil fungal or bacterial communities. Rather, the composition of bacterial and fungal communities was most strongly correlated with specific soil properties. Soil pH was the best predictor of bacterial community composition across this landscape while fungal community composition was most closely associated with changes in soil nutrient status. Together these results suggest that specific changes in edaphic properties, not necessarily land-use type itself, may best predict shifts in microbial community composition across a given landscape. In addition, our results demonstrate the utility of using sequence-based approaches to concurrently analyze bacterial and fungal communities as such analyses provide detailed phylogenetic information on individual communities and permit the robust assessment of the biogeographical patterns exhibited by soil microbial communities.
1,420 citations
••
TL;DR: Using a comprehensive sample of nearly 7,000 firms from 1990 to 2004, this paper examined corporate board structure, its trends, and its determinants, finding that firms structure their boards in response to the costs and benefits of the board's monitoring and advising roles.
Abstract: Using a comprehensive sample of nearly 7,000 firms from 1990 to 2004, this paper examines corporate board structure, its trends, and its determinants We study how board structure has evolved over time and, more importantly, we compare board structure across small and large firms in ways suggested by recent theoretical work Overall, our evidence suggests that firms structure their boards in response to the costs and benefits of the board's monitoring and advising roles Our models explain as much as 45% of the observed variation in board structure Further, small and large firms have dramatically different board structures For example, board size was falling in the 1990s for large firms, a trend that reversed at the time of mandated reforms, while board size was relatively flat over the 1990s for small and medium-sized firms
1,415 citations
••
TL;DR: The decomposition method can be an effective procedure for analytical solution of a wide class of dynamical systems without linearization or weak nonlinearity assumptions, closure approximations, perturbation theory, or restrictive assumptions on stochasticitiy as mentioned in this paper.
1,409 citations
Authors
Showing all 42268 results
Name | H-index | Papers | Citations |
---|---|---|---|
Rob Knight | 201 | 1061 | 253207 |
Feng Zhang | 172 | 1278 | 181865 |
Zhenan Bao | 169 | 865 | 106571 |
Carl W. Cotman | 165 | 809 | 105323 |
Yoshio Bando | 147 | 1234 | 80883 |
Mark Raymond Adams | 147 | 1187 | 135038 |
Han Zhang | 130 | 970 | 58863 |
Dmitri Golberg | 129 | 1024 | 61788 |
Godfrey D. Pearlson | 128 | 740 | 58845 |
Douglas E. Soltis | 127 | 612 | 67161 |
Richard A. Dixon | 126 | 603 | 71424 |
Ajit Varki | 124 | 542 | 58772 |
Keith A. Johnson | 120 | 798 | 51034 |
Gustavo E. Scuseria | 120 | 658 | 95195 |
Julian I. Schroeder | 120 | 315 | 50323 |