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  • 1
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    Ecological meltdown in predator-free forest fragments (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-12-01
    Description: The manner in which terrestrial ecosystems are regulated is controversial. The "top-down" school holds that predators limit herbivores and thereby prevent them from overexploiting vegetation. "Bottom-up" proponents stress the role of plant chemical defenses in limiting plant depredation by herbivores. A set of predator-free islands created by a hydroelectric impoundment in Venezuela allows a test of these competing world views. Limited area restricts the fauna of small (0.25 to 0.9 hectare) islands to predators of invertebrates (birds, lizards, anurans, and spiders), seed predators (rodents), and herbivores (howler monkeys, iguanas, and leaf-cutter ants). Predators of vertebrates are absent, and densities of rodents, howler monkeys, iguanas, and leaf-cutter ants are 10 to 100 times greater than on the nearby mainland, suggesting that predators normally limit their populations. The densities of seedlings and saplings of canopy trees are severely reduced on herbivore-affected islands, providing evidence of a trophic cascade unleashed in the absence of top-down regulation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Terborgh, J -- Lopez, L -- Nunez, P -- Rao, M -- Shahabuddin, G -- Orihuela, G -- Riveros, M -- Ascanio, R -- Adler, G H -- Lambert, T D -- Balbas, L -- New York, N.Y. -- Science. 2001 Nov 30;294(5548):1923-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Center for Tropical Conservation, Duke University, Box 90381, Durham, NC 27708, USA. manu@duke.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11729317" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Ants/physiology ; Anura/physiology ; Birds/physiology ; *Ecosystem ; Female ; *Food Chain ; Fresh Water ; *Geography ; Haplorhini/physiology ; Iguanas/physiology ; Lizards/physiology ; *Models, Biological ; Population Density ; Power Plants ; Reproduction ; Rodentia/physiology ; Spiders/physiology ; Swine/physiology ; Trees/*physiology ; Venezuela
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Modelling heating of liver tumours with heterogeneous magnetic microsphere deposition (2005)
    Institute of Physics
    Details
    Publication Date: 2005-06-01
    Print ISSN: 0031-9155
    Electronic ISSN: 1361-6560
    Topics: Biology , Medicine , Physics
    Published by Institute of Physics
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  • 3
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    The Genomic Diversification of the Whole Acinetobacter Genus: Origins, Mechanisms, and Consequences (2014)
    Oxford University Press
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    Publication Date: 2014-10-31
    Description: Bacterial genomics has greatly expanded our understanding of microdiversification patterns within a species, but analyses at higher taxonomical levels are necessary to understand and predict the independent rise of pathogens in a genus. We have sampled, sequenced, and assessed the diversity of genomes of validly named and tentative species of the Acinetobacter genus, a clade including major nosocomial pathogens and biotechnologically important species. We inferred a robust global phylogeny and delimited several new putative species. The genus is very ancient and extremely diverse: Genomes of highly divergent species share more orthologs than certain strains within a species. We systematically characterized elements and mechanisms driving genome diversification, such as conjugative elements, insertion sequences, and natural transformation. We found many error-prone polymerases that may play a role in resistance to toxins, antibiotics, and in the generation of genetic variation. Surprisingly, temperate phages, poorly studied in Acinetobacter , were found to account for a significant fraction of most genomes. Accordingly, many genomes encode clustered regularly interspaced short palindromic repeats (CRISPR)-Cas systems with some of the largest CRISPR-arrays found so far in bacteria. Integrons are strongly overrepresented in Acinetobacter baumannii , which correlates with its frequent resistance to antibiotics. Our data suggest that A. baumannii arose from an ancient population bottleneck followed by population expansion under strong purifying selection. The outstanding diversification of the species occurred largely by horizontal transfer, including some allelic recombination, at specific hotspots preferentially located close to the replication terminus. Our work sets a quantitative basis to understand the diversification of Acinetobacter into emerging resistant and versatile pathogens.
    Electronic ISSN: 1759-6653
    Topics: Biology
    Published by Oxford University Press
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