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Contributors
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- By Mitchell Aboulafia, Frederick Adams, Marilyn McCord Adams, Robert M. Adams, Laird Addis, James W. Allard, David Allison, William P. Alston, Karl Ameriks, C. Anthony Anderson, David Leech Anderson, Lanier Anderson, Roger Ariew, David Armstrong, Denis G. Arnold, E. J. Ashworth, Margaret Atherton, Robin Attfield, Bruce Aune, Edward Wilson Averill, Jody Azzouni, Kent Bach, Andrew Bailey, Lynne Rudder Baker, Thomas R. Baldwin, Jon Barwise, George Bealer, William Bechtel, Lawrence C. Becker, Mark A. Bedau, Ernst Behler, José A. Benardete, Ermanno Bencivenga, Jan Berg, Michael Bergmann, Robert L. Bernasconi, Sven Bernecker, Bernard Berofsky, Rod Bertolet, Charles J. Beyer, Christian Beyer, Joseph Bien, Joseph Bien, Peg Birmingham, Ivan Boh, James Bohman, Daniel Bonevac, Laurence BonJour, William J. Bouwsma, Raymond D. Bradley, Myles Brand, Richard B. Brandt, Michael E. Bratman, Stephen E. Braude, Daniel Breazeale, Angela Breitenbach, Jason Bridges, David O. Brink, Gordon G. Brittan, Justin Broackes, Dan W. Brock, Aaron Bronfman, Jeffrey E. Brower, Bartosz Brozek, Anthony Brueckner, Jeffrey Bub, Lara Buchak, Otavio Bueno, Ann E. Bumpus, Robert W. Burch, John Burgess, Arthur W. Burks, Panayot Butchvarov, Robert E. Butts, Marina Bykova, Patrick Byrne, David Carr, Noël Carroll, Edward S. Casey, Victor Caston, Victor Caston, Albert Casullo, Robert L. Causey, Alan K. L. Chan, Ruth Chang, Deen K. Chatterjee, Andrew Chignell, Roderick M. Chisholm, Kelly J. Clark, E. J. Coffman, Robin Collins, Brian P. Copenhaver, John Corcoran, John Cottingham, Roger Crisp, Frederick J. Crosson, Antonio S. Cua, Phillip D. Cummins, Martin Curd, Adam Cureton, Andrew Cutrofello, Stephen Darwall, Paul Sheldon Davies, Wayne A. Davis, Timothy Joseph Day, Claudio de Almeida, Mario De Caro, Mario De Caro, John Deigh, C. F. Delaney, Daniel C. Dennett, Michael R. DePaul, Michael Detlefsen, Daniel Trent Devereux, Philip E. Devine, John M. Dillon, Martin C. Dillon, Robert DiSalle, Mary Domski, Alan Donagan, Paul Draper, Fred Dretske, Mircea Dumitru, Wilhelm Dupré, Gerald Dworkin, John Earman, Ellery Eells, Catherine Z. Elgin, Berent Enç, Ronald P. Endicott, Edward Erwin, John Etchemendy, C. Stephen Evans, Susan L. Feagin, Solomon Feferman, Richard Feldman, Arthur Fine, Maurice A. Finocchiaro, William FitzPatrick, Richard E. Flathman, Gvozden Flego, Richard Foley, Graeme Forbes, Rainer Forst, Malcolm R. Forster, Daniel Fouke, Patrick Francken, Samuel Freeman, Elizabeth Fricker, Miranda Fricker, Michael Friedman, Michael Fuerstein, Richard A. Fumerton, Alan Gabbey, Pieranna Garavaso, Daniel Garber, Jorge L. A. Garcia, Robert K. Garcia, Don Garrett, Philip Gasper, Gerald Gaus, Berys Gaut, Bernard Gert, Roger F. Gibson, Cody Gilmore, Carl Ginet, Alan H. Goldman, Alvin I. Goldman, Alfonso Gömez-Lobo, Lenn E. Goodman, Robert M. Gordon, Stefan Gosepath, Jorge J. E. Gracia, Daniel W. Graham, George A. Graham, Peter J. Graham, Richard E. Grandy, I. Grattan-Guinness, John Greco, Philip T. Grier, Nicholas Griffin, Nicholas Griffin, David A. Griffiths, Paul J. Griffiths, Stephen R. Grimm, Charles L. Griswold, Charles B. Guignon, Pete A. Y. Gunter, Dimitri Gutas, Gary Gutting, Paul Guyer, Kwame Gyekye, Oscar A. Haac, Raul Hakli, Raul Hakli, Michael Hallett, Edward C. Halper, Jean Hampton, R. James Hankinson, K. R. Hanley, Russell Hardin, Robert M. Harnish, William Harper, David Harrah, Kevin Hart, Ali Hasan, William Hasker, John Haugeland, Roger Hausheer, William Heald, Peter Heath, Richard Heck, John F. Heil, Vincent F. Hendricks, Stephen Hetherington, Francis Heylighen, Kathleen Marie Higgins, Risto Hilpinen, Harold T. Hodes, Joshua Hoffman, Alan Holland, Robert L. Holmes, Richard Holton, Brad W. Hooker, Terence E. Horgan, Tamara Horowitz, Paul Horwich, Vittorio Hösle, Paul Hoβfeld, Daniel Howard-Snyder, Frances Howard-Snyder, Anne Hudson, Deal W. Hudson, Carl A. Huffman, David L. Hull, Patricia Huntington, Thomas Hurka, Paul Hurley, Rosalind Hursthouse, Guillermo Hurtado, Ronald E. Hustwit, Sarah Hutton, Jonathan Jenkins Ichikawa, Harry A. Ide, David Ingram, Philip J. Ivanhoe, Alfred L. Ivry, Frank Jackson, Dale Jacquette, Joseph Jedwab, Richard Jeffrey, David Alan Johnson, Edward Johnson, Mark D. Jordan, Richard Joyce, Hwa Yol Jung, Robert Hillary Kane, Tomis Kapitan, Jacquelyn Ann K. Kegley, James A. Keller, Ralph Kennedy, Sergei Khoruzhii, Jaegwon Kim, Yersu Kim, Nathan L. King, Patricia Kitcher, Peter D. Klein, E. D. Klemke, Virginia Klenk, George L. Kline, Christian Klotz, Simo Knuuttila, Joseph J. Kockelmans, Konstantin Kolenda, Sebastian Tomasz Kołodziejczyk, Isaac Kramnick, Richard Kraut, Fred Kroon, Manfred Kuehn, Steven T. Kuhn, Henry E. Kyburg, John Lachs, Jennifer Lackey, Stephen E. Lahey, Andrea Lavazza, Thomas H. Leahey, Joo Heung Lee, Keith Lehrer, Dorothy Leland, Noah M. Lemos, Ernest LePore, Sarah-Jane Leslie, Isaac Levi, Andrew Levine, Alan E. Lewis, Daniel E. Little, Shu-hsien Liu, Shu-hsien Liu, Alan K. L. Chan, Brian Loar, Lawrence B. Lombard, John Longeway, Dominic McIver Lopes, Michael J. Loux, E. J. Lowe, Steven Luper, Eugene C. Luschei, William G. Lycan, David Lyons, David Macarthur, Danielle Macbeth, Scott MacDonald, Jacob L. Mackey, Louis H. Mackey, Penelope Mackie, Edward H. Madden, Penelope Maddy, G. B. Madison, Bernd Magnus, Pekka Mäkelä, Rudolf A. Makkreel, David Manley, William E. Mann (W.E.M.), Vladimir Marchenkov, Peter Markie, Jean-Pierre Marquis, Ausonio Marras, Mike W. Martin, A. P. Martinich, William L. McBride, David McCabe, Storrs McCall, Hugh J. McCann, Robert N. McCauley, John J. McDermott, Sarah McGrath, Ralph McInerny, Daniel J. McKaughan, Thomas McKay, Michael McKinsey, Brian P. McLaughlin, Ernan McMullin, Anthonie Meijers, Jack W. Meiland, William Jason Melanson, Alfred R. Mele, Joseph R. Mendola, Christopher Menzel, Michael J. Meyer, Christian B. Miller, David W. Miller, Peter Millican, Robert N. Minor, Phillip Mitsis, James A. Montmarquet, Michael S. Moore, Tim Moore, Benjamin Morison, Donald R. Morrison, Stephen J. Morse, Paul K. Moser, Alexander P. D. Mourelatos, Ian Mueller, James Bernard Murphy, Mark C. Murphy, Steven Nadler, Jan Narveson, Alan Nelson, Jerome Neu, Samuel Newlands, Kai Nielsen, Ilkka Niiniluoto, Carlos G. Noreña, Calvin G. Normore, David Fate Norton, Nikolaj Nottelmann, Donald Nute, David S. Oderberg, Steve Odin, Michael O’Rourke, Willard G. Oxtoby, Heinz Paetzold, George S. Pappas, Anthony J. Parel, Lydia Patton, R. P. Peerenboom, Francis Jeffry Pelletier, Adriaan T. Peperzak, Derk Pereboom, Jaroslav Peregrin, Glen Pettigrove, Philip Pettit, Edmund L. Pincoffs, Andrew Pinsent, Robert B. Pippin, Alvin Plantinga, Louis P. Pojman, Richard H. Popkin, John F. Post, Carl J. Posy, William J. Prior, Richard Purtill, Michael Quante, Philip L. Quinn, Philip L. Quinn, Elizabeth S. Radcliffe, Diana Raffman, Gerard Raulet, Stephen L. Read, Andrews Reath, Andrew Reisner, Nicholas Rescher, Henry S. Richardson, Robert C. Richardson, Thomas Ricketts, Wayne D. Riggs, Mark Roberts, Robert C. Roberts, Luke Robinson, Alexander Rosenberg, Gary Rosenkranz, Bernice Glatzer Rosenthal, Adina L. Roskies, William L. Rowe, T. M. Rudavsky, Michael Ruse, Bruce Russell, Lilly-Marlene Russow, Dan Ryder, R. M. Sainsbury, Joseph Salerno, Nathan Salmon, Wesley C. Salmon, Constantine Sandis, David H. Sanford, Marco Santambrogio, David Sapire, Ruth A. Saunders, Geoffrey Sayre-McCord, Charles Sayward, James P. Scanlan, Richard Schacht, Tamar Schapiro, Frederick F. Schmitt, Jerome B. Schneewind, Calvin O. Schrag, Alan D. Schrift, George F. Schumm, Jean-Loup Seban, David N. Sedley, Kenneth Seeskin, Krister Segerberg, Charlene Haddock Seigfried, Dennis M. Senchuk, James F. Sennett, William Lad Sessions, Stewart Shapiro, Tommie Shelby, Donald W. Sherburne, Christopher Shields, Roger A. Shiner, Sydney Shoemaker, Robert K. Shope, Kwong-loi Shun, Wilfried Sieg, A. John Simmons, Robert L. Simon, Marcus G. Singer, Georgette Sinkler, Walter Sinnott-Armstrong, Matti T. Sintonen, Lawrence Sklar, Brian Skyrms, Robert C. Sleigh, Michael Anthony Slote, Hans Sluga, Barry Smith, Michael Smith, Robin Smith, Robert Sokolowski, Robert C. Solomon, Marta Soniewicka, Philip Soper, Ernest Sosa, Nicholas Southwood, Paul Vincent Spade, T. L. S. Sprigge, Eric O. Springsted, George J. Stack, Rebecca Stangl, Jason Stanley, Florian Steinberger, Sören Stenlund, Christopher Stephens, James P. Sterba, Josef Stern, Matthias Steup, M. A. Stewart, Leopold Stubenberg, Edith Dudley Sulla, Frederick Suppe, Jere Paul Surber, David George Sussman, Sigrún Svavarsdóttir, Zeno G. Swijtink, Richard Swinburne, Charles C. Taliaferro, Robert B. Talisse, John Tasioulas, Paul Teller, Larry S. Temkin, Mark Textor, H. S. Thayer, Peter Thielke, Alan Thomas, Amie L. Thomasson, Katherine Thomson-Jones, Joshua C. Thurow, Vzalerie Tiberius, Terrence N. Tice, Paul Tidman, Mark C. Timmons, William Tolhurst, James E. Tomberlin, Rosemarie Tong, Lawrence Torcello, Kelly Trogdon, J. D. Trout, Robert E. Tully, Raimo Tuomela, John Turri, Martin M. Tweedale, Thomas Uebel, Jennifer Uleman, James Van Cleve, Harry van der Linden, Peter van Inwagen, Bryan W. Van Norden, René van Woudenberg, Donald Phillip Verene, Samantha Vice, Thomas Vinci, Donald Wayne Viney, Barbara Von Eckardt, Peter B. M. Vranas, Steven J. Wagner, William J. Wainwright, Paul E. Walker, Robert E. Wall, Craig Walton, Douglas Walton, Eric Watkins, Richard A. Watson, Michael V. Wedin, Rudolph H. Weingartner, Paul Weirich, Paul J. Weithman, Carl Wellman, Howard Wettstein, Samuel C. Wheeler, Stephen A. White, Jennifer Whiting, Edward R. Wierenga, Michael Williams, Fred Wilson, W. Kent Wilson, Kenneth P. Winkler, John F. Wippel, Jan Woleński, Allan B. Wolter, Nicholas P. Wolterstorff, Rega Wood, W. Jay Wood, Paul Woodruff, Alison Wylie, Gideon Yaffe, Takashi Yagisawa, Yutaka Yamamoto, Keith E. Yandell, Xiaomei Yang, Dean Zimmerman, Günter Zoller, Catherine Zuckert, Michael Zuckert, Jack A. Zupko (J.A.Z.)
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- The Cambridge Dictionary of Philosophy
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Xylo-oligosaccharides alone or in synbiotic combination with Bifidobacterium animalis subsp. lactis induce bifidogenesis and modulate markers of immune function in healthy adults: a double-blind, placebo-controlled, randomised, factorial cross-over study
- Caroline E. Childs, Henna Röytiö, Esa Alhoniemi, Agnes A. Fekete, Sofia D. Forssten, Natasa Hudjec, Ying Ni Lim, Cara J. Steger, Parveen Yaqoob, Kieran M. Tuohy, Robert A. Rastall, Arthur C. Ouwehand, Glenn R. Gibson
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- British Journal of Nutrition / Volume 111 / Issue 11 / 14 June 2014
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- 24 March 2014, pp. 1945-1956
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- 14 June 2014
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Prebiotics, probiotics and synbiotics are dietary ingredients with the potential to influence health and mucosal and systemic immune function by altering the composition of the gut microbiota. In the present study, a candidate prebiotic (xylo-oligosaccharide, XOS, 8 g/d), probiotic (Bifidobacterium animalis subsp. lactis Bi-07, 109 colony-forming units (CFU)/d) or synbiotic (8 g XOS+109 CFU Bi-07/d) was given to healthy adults (25–65 years) for 21 d. The aim was to identify the effect of the supplements on bowel habits, self-reported mood, composition of the gut microbiota, blood lipid concentrations and immune function. XOS supplementation increased mean bowel movements per d (P= 0·009), but did not alter the symptoms of bloating, abdominal pain or flatulence or the incidence of any reported adverse events compared with maltodextrin supplementation. XOS supplementation significantly increased participant-reported vitality (P= 0·003) and happiness (P= 0·034). Lowest reported use of analgesics was observed during the XOS+Bi-07 supplementation period (P= 0·004). XOS supplementation significantly increased faecal bifidobacterial counts (P= 0·008) and fasting plasma HDL concentrations (P= 0·005). Bi-07 supplementation significantly increased faecal B. lactis content (P= 0·007), lowered lipopolysaccharide-stimulated IL-4 secretion in whole-blood cultures (P= 0·035) and salivary IgA content (P= 0·040) and increased IL-6 secretion (P= 0·009). XOS supplementation resulted in lower expression of CD16/56 on natural killer T cells (P= 0·027) and lower IL-10 secretion (P= 0·049), while XOS and Bi-07 supplementation reduced the expression of CD19 on B cells (XOS × Bi-07, P= 0·009). The present study demonstrates that XOS induce bifidogenesis, improve aspects of the plasma lipid profile and modulate the markers of immune function in healthy adults. The provision of XOS+Bi-07 as a synbiotic may confer further benefits due to the discrete effects of Bi-07 on the gut microbiota and markers of immune function.
Impact of polydextrose on the faecal microbiota: a double-blind, crossover, placebo-controlled feeding study in healthy human subjects
- Adele Costabile, Francesca Fava, Henna Röytiö, Sofia D. Forssten, Kaisa Olli, Judith Klievink, Ian R. Rowland, Arthur C. Ouwehand, Robert A. Rastall, Glenn R. Gibson, Gemma E. Walton
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- British Journal of Nutrition / Volume 108 / Issue 3 / 14 August 2012
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- 21 November 2011, pp. 471-481
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- 14 August 2012
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In this placebo-controlled, double-blind, crossover human feeding study, the effects of polydextrose (PDX; 8 g/d) on the colonic microbial composition, immune parameters, bowel habits and quality of life were investigated. PDX is a complex glucose oligomer used as a sugar replacer. The main goal of the present study was to identify the microbial groups affected by PDX fermentation in the colon. PDX was shown to significantly increase the known butyrate producer Ruminococcus intestinalis and bacteria of the Clostridium clusters I, II and IV. Of the other microbial groups investigated, decreases in the faecal Lactobacillus–Enterococcus group were demonstrated. Denaturing gel gradient electrophoresis analysis showed that bacterial profiles between PDX and placebo treatments were significantly different. PDX was shown to be slowly degraded in the colon, and the fermentation significantly reduced the genotoxicity of the faecal water. PDX also affected bowel habits of the subjects, as less abdominal discomfort was recorded and there was a trend for less hard and more formed stools during PDX consumption. Furthermore, reduced snacking was observed upon PDX consumption. This study demonstrated the impact of PDX on the colonic microbiota and showed some potential for reducing the risk factors that may be associated with colon cancer initiation.
Structural and physiological adaptation to light environments in neotropical Heliconia (Heliconiaceae)
- Philip W. Rundel, M. Rasoul Sharifi, Arthur C. Gibson, Karen J. Esler
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- Journal of Tropical Ecology / Volume 14 / Issue 6 / November 1998
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- 01 November 1998, pp. 789-801
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Influence of habitat on physiological and structural characteristics was investigated for broad-leaved tropical monocotyledons in the genus Heliconia (Heliconiaceae). Seven species were selected from three different light regimes, enabling an analysis of the extent to which this genus has adapted its photosynthetic strategies and morphological characteristics to different daily photon flux densities (PFD). Predictably, light response curves showed a clear gradient with respect to light saturation and rates of maximum net assimilation (Amax). Heliconia latispatha, an open site species, showed saturation at higher PFD (1400 μmol m−2 s−1) and higher Amax (14–16 μmol m−2 s−1) than H. mathiasiae, a forest edge species (PFD 1000 μmol m−2 s−1; Amax 7.5–8.5 μmol m−2 s−1) and H. irrasa of deep-shade forest understorey (PFD 250 μmol m−2 s−1; Amax 3.5 mol m−2 s−1). Leaf blade areas were largest in open sites, and leaf specific mass was also significantly higher, but leaf support efficiency was highest in understorey species. Species in open sites had thicker leaves with more chlorenchyma, whereas deep-shade species had very thin leaves and low stomatal densities. These rapidly growing herbaceous perennials appear to allocate much of their above-ground biomass to leaf tissues and have a relatively low investment in support tissues. This contrasts with understorey palms, in which leaf form and structural investment has been interpreted as a trade-off between economy and protection against tissue loss from falling branches. Presence of below-ground rhizomes in Heliconia may provide the key to this difference.
Contents
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp vii-viii
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Main index
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp 357-369
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Historical prologue on Rock Valley studies
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp xi-xviii
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2 - Physical geography of Rock Valley
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp 21-54
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Preface
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp ix-x
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Summary
The Mojave Desert is an expansive region of arid western North America, primarily in eastern California and southern Nevada. This is a winter rainfall desert, which, like the Negev in Israel, experiences drought conditions during the very hot summer months and occasional rain during the cooler months in late fall and winter. Researchers, especially those from academic institutions with close access to the Mojave Desert, have utilized key research sites to investigate how animals and plants cope with the rigors of desert life. Of the several Mojave Desert research sites, none has been as productive as a creosote bush desert scrub located in Rock Valley on the Nevada Test Site (NTS). The Nevada Test Site, operated by the United States Department of Energy (DOE), occupies 350 000 hectares of arid and semiarid terrains in central-southern Nevada. The location of this large reservation is particularly interesting because NTS straddles the geographic boundary between the Great Basin, which is classified as a cold desert, and the Mojave Desert.
As discussed briefly in our Historical Prologue, the history of ecological research at NTS dates back to 1951, when UCLA researchers were first permitted access, especially to its disturbed lands. Under research contracts with the former Atomic Energy Commission (AEC), NTS eventually was designated as a base for investigating patterns and processes of desert ecosystems, with special emphasis on the communities of the Mojave Desert, found in the southern portions of the reservation.
Research facilities at Rock Valley have existed since the early 1960s, when the AEC agreed to utilize this relatively pristine basin for long-term studies on the effects of low-level gamma radiation exposure to desert populations of plants and animals.
6 - Adaptations of Mojave Desert animals
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp 130-154
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Summary
Desert environments produce extreme conditions for survival of animals, just as for plants (Chapter 3). High temperature and low water availability make thermoregulation an acute problem during the summer, whereas cold temperatures and low food availablility during winter make aboveground activity energetically inefficient for most desert animals. Lack of water presents special problems for animals that produce liquid excreta, and these osmotic difficulties are magnified when diets contain materials that are high in solutes. Nutrient resources, be they plant tissues for herbivores or prey for carnivores, are often low in abundance and poor in quality, and individual food items tend to be available only for short intervals. Moreover, coexisting species must share those limited resources. Consequently, each resident species must have a set of adaptations to cope with stresses during its lifetime, and desert animals, like plants, utilize physiological, morphological, and phenological adaptations to either tolerate or avoid stresses. Unlike plants, however, animals have the ability to alter their environment through movement and thus possess intriguing suites of behavioral adaptive responses.
HEAT BALANCE AND THERMOREGULATION
Problems of heat in deserts
Strategies for maintaining reasonable
Consequently, each resident species must have a set of adaptations to cope with stresses during its lifetime, and desert animals, like plants, utilize physiological, morphological, and phenological adaptations to either tolerate or avoi stresses. Unlike plants, however, animals have the ability to alter their environment through movement and thus possess intriguing suites of behavioral adaptive responses. Strategies for maintaining reasonable thermal balance are of critical importance for ecological success of each animal species in a desert environment, especially the hot, dry conditions of summer months in the Mojave Desert, where midday temperatures commonly exceed 40°C and the ground surface may heat up to 70°C from intense solar radiation.
Frontmatter
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp i-vi
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12 - Nitrogen cycling
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp 274-289
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Summary
Because of the relatively low biomass in most desert scrub communities, the proportion of total system nitrogen held by the biomass is relatively small compared with that of other ecosystems (Skujins 1981). Typically 70–98% of total system nitrogen in deserts is contained within the soil compartment, but the absolute levels of soil nitrogen are still very low. Environmental factors sharply limit nitrogen inputs to desert soils. Precipitation is low and restricts atmospheric inputs of nitrogen as wetfall, and significant amounts of nitrogen fixation only occur in areas where cyanobacterial or lichen crusts are well developed or where nodulated woody legumes comprise a major portion of the vegetation cover. The extensive size of most desert regions acts to limit dryfall of particulate or gaseous nitrogen, as well as animal inputs of nitrogen. When system inputs of nitrogen through the atmosphere (wetfall and dryfall), fixation, and animal activities are low, then it is very difficult to build up large pools of nitrogen. Hence, whereas drought limitations on primary production are very pervasive in desert ecosystems, nitrogen may also be an important limiting factor in years when rainfall is plentiful (Ettershank, Ettershank, Bryant, & Whitford, 1978; Lauenroth, Dodd, & Sims 1978; Romney, Wallace, & Hunter 1978; Sharifi, Meinzer, Nilsen, Rundel, Virginia, Jarrell, & Herman 1988; Fisher, Zak, Cunningham, & Whitford 1988).
The dispersed pattern of perennials produces a mosaic of nitrogen distribution with relatively high concentrations of nitrogen occurring beneath shrubs, and low concentrations in open areas between shrubs (Chapter 2). This characteristic patterning of nitrogen distribution has been termed ‘islands of fertility’ (Muller 1953; Garcia- Moya & McKell 1970).
Ecological Communities and Processes in a Mojave Desert Ecosystem
- Philip W. Rundel, Arthur C. Gibson
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- 19 October 2009
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- 26 January 1996
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Deserts provide a harsh and inhospitable environment for plants and animals, and the ecosystem is correspondingly fragile and prone to disruption by a variety of external factors. The Mojave Desert is a winter-rainfall desert, experiencing drought in the summer months, and occasional rain during the cooler winter months. For many years, it has attracted the attention of ecologists and conservation biologists concerned to maintain the unique status of this region. This book provides a broad overview of plant and animal ecology in the Mojave Desert, presented with a focus on data from Rock Valley, Nevada. The data from many major research projects is synthesized into a description of community structure and dynamics in desert ecosystems.
7 - Mammals
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp 155-173
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In Mojave desert scrub during the hot daytime mammals are infrequently seen, but at night the desert landscape becomes a very active place when they emerge from their sites of safety to forage (Chapter 6). Chief among these are the small fossorial rodents, particularly Heteromyidae, which constitute a community of several different species and size classes busily harvesting dry fruits and seeds to cache within the burrows. Population densities of heteromyids characteristically show marked seasonal and yearly fluctuations at any site as well as between sites, and density changes have been monitored relatively easily because heteromyid rodents can be efficiently captured and released without injury. Therefore, these rodent communities have been heavily used in studies of patterns and processes in community ecology and population biology (Reichman 1991), particularly at long-term sampling sites, such as in Rock Valley.
MAMMALS OF THE NEVADA TEST SITE
The mammal fauna of the Nevada Test Site consists of 47 species (Allred & Beck 1963; Allred, Beck, & Jorgensen 1963; Jorgensen & Hayward 1963, 1965; O'Farrell & Emery 1976), of which half are rodents (Table 7.1). Many rodent species are members of the families Cricetidae (7 spp.) and Heteromyidae (9 spp.); these groups are common aridland species throughout western North America, including other Mojave Desert areas (Miller & Stebbins 1964). Other mammals occurring on NTS are wideranging species: 4 species of insectivorous bats, 3 species of shrews and 3 of lagomorphs, 7 species of carnivores, and 6 species of large grazers, including occasional wild horses (Equus caballus), domestic cattle (Bos taurus), and wild burros (E. asinus).
5 - Mojave Desert annuals
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp 113-129
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Herbaceous plants, displaying several differing growth forms, constitute a characteristic and diverse element of the flora for warm desert regions of North America (Chapter 3), and the Mojave Desert in particular. More than 85% of herbaceous species found on the Nevada Test Site and adjacent parts of central-southern Nevada are annuals, including those that complete their life cycles in the spring or in the summer, and herbaceous perennials and biennials (53%), which also may be either spring or summer active (Beatley 1976a; Mulroy & Rundel 1977). Whereas within a single week the standing biomass of herbaceous plants is generally small in comparison with that of the shrubs, net primary productivity by annuals during a favorable rain-year may approach 50% of the total for shrubs. Desert annuals tend to have relative high protein concentration in their tissues, but generally low levels of complex structural carbohydrates and toxic secondary compounds, so that these plants are important food resources for desert animals. Nitrogen buildup from annual plants may also serve as an important buffer for ecosystem nitrogen pools in these desert regions.
GENERAL ATTRIBUTES OF MOJAVE DESERT ANNUALS
Germination requirements
The physiological controls of germination in desert annuals have important ecological implications for their establishment and reproductive success. Many of the experimental scientific studies of desert annuals have been conducted on species of the Mojave Desert, beginning with early quantitative studies on germination requirements (Went 1948, 1949, 1955; Went & Westergaard 1949; Juhren, Went, & Phillips 1956).
References
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp 318-349
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13 - Human impacts on Mojave Desert ecosystems
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 26 January 1996, pp 290-317
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Summary
Desert ecosystems have in recent times been subjected increasingly to untested contacts with humans and their characteristic activities. Within the past 40 years there has been heavy use of desert scrub communities for recreational purposes, military testing, and construction projects, all of which have modified physical characteristics of soil and altered the composition of desert scrub vegetation and impacted animal populations. Because deserts, by their very definition, receive little annual rainfall, effects from human disturbance can persist for long periods of time, and research has shown that impacts to the ecosystem are extremely long term. Most applied ecological studies in desert regions have been conducted for environmental impact reports, which can access the biological resources at a site relative to undisturbed parcels of desert vegetation, such as at Rock Valley. Such unpublished analyses make recommendations for minimizing impacts of human activities and mitigating what damage is done. There are relatively few articles that describe carefully designed experiments for individual types of human impacts, analyzing short- and long-term effects on desert ecosystems using treatments of differing durations under wet and dry conditions and on various soil types. One goal is to learn which activities forever alter characteristics of natural desert communities versus those that, especially by unaided processes, return a habitat to predisturbance conditions.
SECONDARY PLANT SUCCESSION
Early analyses by desert plant ecologists provided no convincing evidence that plant succession occurred in desert ecosystems (Shreve & Hinckley 1937; Muller 1940; Shreve 1942. Many studies in the Mojave Desert have focused on the topic of secondary plant succession, i.e., recruitment of a new resident plant community following complete removal of shrubs leading to the return of a mature, relatively stable assemblage of of long-lived shrubs (Vasek 1979/80, 1983; Rowlands 1980).
10 - Arthropods
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp 214-255
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Summary
Invertebrates comprise the largest and most diverse segment of faunal biomass in deserts, and in particular, desert arthropods play fundamental roles in ecosystem processes of carbon and nutrient cycling and plant reproductive biology, especially as pollinators. Included also are important herbivores, which limit net primary production by vascular plants, both of fresh shoots and reproductive structures above ground and roots and stems below ground. Many arthropods, for example, microarthropods, ants, and beetles, play important roles in decomposition processes. Still other species are predators, consumers of other arthropods. To complete the food web, one finds that especially the large, palatable forms are preferred, juicy prey items for insectivorous vertebrates, such as lizards, cricetid rodents, and predaceous birds, and most vertebrates consume arthropods whenever water and typical food items become scarce.
TROPHIC SPECIALIZATIONS
At least seven categories of trophic specialization for desert invertebrates have been identified (Crawford 1981). Above ground there are foliage (leaf and stem) herbivores, pollinators, and granivores. Operating to regulate each of these groups are diverse assemblages of carnivorous invertebrates, in addition to the vertebrate predators. Within each trophic guild feeding habits for individual species vary from generalist to highly specialist. Belowground consumers include root herbivores, which feed on living tissues, and coprovores, necrovores, and detritivores, which help to recycle dead organic matter. Root herbivores, particularly cicada, beetle, and lepidopteran larvae, are important members of the soil fauna beneath shrubs. Desert coprovores and detritivores, along with associated carnivores, often live on soil surface among litter. Dung beetles and isopods are perhaps the best known of detritivores and coprovores, but many other invertebrate groups are represented (Crawford 1979).
11 - Soil organisms and seed reserves
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 26 January 1996, pp 256-273
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Summary
The soil environment contains a variety of organisms not treated in previous chapters that yet play major ecological roles in many processes of carbon and nutrient fluxes. These organisms include cryptogamic plants living on the soil surface, such as soil algae and cyanobacteria, lichens, and bryophytes. Although at Rock Valley they do not form a large cover or biomass, such cryptogams provide important nitrogen inputs to many other desert ecosystems. Within the soil matrix occur many types of organisms, including a microflora of bacteria, actinomycetes, and a variety of fungi, and a microfauna that is dominated by such microarthropods as collembolans and mites, nematodes, and protozoa, which have a significant influence on decomposition processes in soil. In addition, soil reserves of vascular plant seeds provide a critically important food resource for granivorous animals (Chapters 7 and 9) as well as a critical pool for future establishment of herbs (Chapter 5) and shrub species (Chapter 4) when favorable rains occur.
CRYPTOGAMIC PLANTS
Cryptogamic plants are generally much less abundant in dry desert ecosystems than in more mesic habitats. Nevertheless, even small biomasses of some of these groups may be ecologically important. This is particularly true for soil crusts and lichens with cyanobacteria (blue-green algae) symbionts, which are able to fix atmospheric nitrogen. General structure and function of soil crusts in the stability of soils from arid and semiarid lands has been reviewed in detail by West (1980).
Shields and Drouet (1962) described the general distribution of terrestrial algae and cyanobacteria of NTS from soil samples taken from 1957 to 1959 in Yucca Flat, Frenchman Flat, and Jackass Flats.
9 - Birds
- Philip W. Rundel, University of California, Los Angeles, Arthur C. Gibson, University of California, Los Angeles
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- Ecological Communities and Processes in a Mojave Desert Ecosystem
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- 19 October 2009
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- 26 January 1996, pp 197-213
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Desert scrub habitats, which have low annual precipitation, simple vegetational structure, and low primary production, support few resident bird populations unless permanent water is available (Serventy 1971). For each continent there is a very short list of species that are truly characteristic of thriving under desert conditions. For example, despite biogeographic dominance of desert and semi-desert environments in Australia, which comprise the central 70% of that continent, Keast (1959) identified only 17 bird species as characteristic of the region, just 3% of total breeding avifauna. Likewise, in North America only 31 species of birds are listed as desert inhabitants (MacMahon 1979). Nevertheless, in spring and fall transient populations of many bird species migrate through dryland habitats on the Desert scrub habitats, which have low annual precipitation, simple vegetational structure, and low primary production, Nevada Test Site, and some bird species are seasonal or year-round residents, having some adaptations for desert life (Dawson & Bartholomew 1968; Dawson 1984).
BIRDS OF THE NEVADA TEST SITE
The avifauna of the Nevada Test Site consists of 220 species (Table 9.1; data as of 1991) of which at least 160 were classified as transients (Allred et al. 1963; Hayward et al. 1963; O' Farrell & Emery 1976; Castetter & Hill 1979; BECAMP 1991b Many transients were sighted during biannual mass bird migrations as part of the western North America flyway, and birds rest and feed at NTS during cool months, especially when precipitation occurs (Chapter 2) and creates temporary standing water. On-site breeding has only been confirmed at NTS for 31 species, largely those living at the higher, cooler, less ari habitats.