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Frequency Dependence of Radar Meteor Echo Rates
- R. M . Thomas, P. S. Whitham, W. G. Elford
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- Journal:
- Publications of the Astronomical Society of Australia / Volume 6 / Issue 3 / 1986
- Published online by Cambridge University Press:
- 25 April 2016, pp. 303-306
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Meteor rates have been measured with a large HF Radar at a number of frequencies. At the top end of the HF band our results match those of Greenhow (1963). However at lower frequencies we find high echo rates which indicate that past observations measured only a few percent of the total meteor flux incident on the Earth’s atmosphere. This explains the ‘missing mass’ discrepancy observed when radar results are compared with satellite or visual data. Accounting for’this missing mass results in a four-fold increase in the calculated total meteoroid mass influx to the surface of the Earth from 4000 to 16,000 tonnes per year. Our results also imply that the majority of echoes originate from altitudes above 100 km.
Chapter Sixteen - Perspective
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- By Gerard J. Allan, Department of Biological Sciences, Northern Arizona University, Stephen M. Shuster, Department of Biological Sciences, Northern Arizona University, Scott Woolbright, The Institute for Genomic Biology, University of Illinois, Faith Walker, Department of Biological Sciences, Northern Arizona University, Nashelly Meneses, Department of Biological Sciences, Northern Arizona University, Arthur Keith, Department of Biological Sciences, Northern Arizona University, Joseph K. Bailey, Department of Ecology and Evolutionary Biology, University of Tennessee, Thomas G. Whitham, Department of Biological Sciences, Northern Arizona University
- Edited by Takayuki Ohgushi, Kyoto University, Japan, Oswald Schmitz, Yale University, Connecticut, Robert D. Holt, University of Florida
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- Book:
- Trait-Mediated Indirect Interactions
- Published online:
- 05 February 2013
- Print publication:
- 06 December 2012, pp 295-323
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Summary
Introduction
Trait-mediated indirect interactions (TMIIs) are important mediators of community diversity and structure and associated ecosystem processes. Elucidating the genetic basis of ecologically important phenotypic traits is the first step toward understanding the complex interactions that occur among community members. Molecular markers routinely used in quantitative trait loci (QTL) analyses (e.g., amplified fragment length polymorphisms (AFLPs), simple sequence repeats (SSRs)) have provided researchers with a toolbox for investigating the genetic basis of heritable traits. A goal of this research is to link genetically based traits to community interactions and ecosystem function. Ultimately, this insight can open a window onto the evolutionary dynamics that shape community structure and associated ecosystem processes (e.g., nutrient cycling). Such an approach is important as it bears on the continued development of the field of community genetics, which seeks to understand the genetic interactions that occur between species and their abiotic environment in complex communities (e.g., Whitham et al. 2003, 2006; Johnson and Agrawal 2005; LeRoy et al. 2006; Bangert et al. 2006a, b; Schweitzer et al. 2008; Crutsinger et al. 2009; Bailey et al. 2009).
Chapter Nineteen - Functional and heritable consequences of plant genotype on community composition and ecosystem processes
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- By Jennifer A. Schweitzer, Department of Ecology and Evolutionary Biology, University of Tennessee, Joseph K. Bailey, Department of Ecology and Evolutionary Biology, University of Tennessee, Dylan G. Fischer, Environmental Studies Program, The Evergreen State College, Carri J. LeRoy, Environmental Studies Program, The Evergreen State College, Thomas G. Whitham, Department of Biological Sciences, Northern Arizona University, Stephen C. Hart, School of Natural Sciences and Sierra Nevada Research Institute, University of California – Merced
- Edited by Takayuki Ohgushi, Kyoto University, Japan, Oswald Schmitz, Yale University, Connecticut, Robert D. Holt, University of Florida
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- Book:
- Trait-Mediated Indirect Interactions
- Published online:
- 05 February 2013
- Print publication:
- 06 December 2012, pp 371-390
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Summary
Introduction
Foundation species represent excellent model systems for understanding the broad consequences of variation on community and ecosystem processes as they provide a focal resource upon which associated interacting species depend. As foundation species (Dayton 1972; Ellison et al. 2005), trees and other dominant plants often create stable conditions via plant traits that allow dependent communities to assemble regularly and influence ecosystem processes such as net primary productivity (NPP) and soil fertility (i.e., nutrient cycling, via accumulations of leaf or root organic matter or root exudates; Zinke 1962; Zak et al. 1986; Binkley and Giardina 1998; Bartelt-Ryser et al. 2005; Wardle 2006). Recent studies in both terrestrial and aquatic habitats have shown that intraspecific genetic variation (defined at multiple genetic scales, including introgression [movement of genes from one species to another], genotypic diversity [studies manipulating the number of genotypes in a population] and genotypic variation [variation among genotypes]) in foundation plants can have community-wide consequences. Intraspecific variation affects associated vertebrate, arthropod and microbial community composition or activity and ecosystem level processes (recently reviewed in Johnson and Stinchcombe 2007; Hughes et al. 2008; Whitham et al. 2008; Bailey et al. 2009). For example, genetic variation resulting from the introgression of genes from one species to another through the process of hybridization has been shown to have important consequences for associated species, communities and ecosystem processes in multiple hybridizing plant species, including Salix spp., Eucalyptus spp., Quercus spp. and Populus spp. (Fritz et al. 1994; Dungey et al. 2000; Hochwender and Fritz 2004; Ito and Ozaki 2005; Wimp et al. 2005; Tovar-Sanchez and Oyama 2006; Bangert et al. 2008). In the Populus system specifically, recent field and common garden studies have shown that genetic variation across a hybridizing system (P. fremontii, P. angustifolia and their natural F1 and backcross hybrids) results in shifts in plant traits, including secondary chemistry, plant water use and above- and belowground productivity (Fischer et al. 2004; Rehill et al. 2006; Schweitzer et al. 2008a; Lojewski et al. 2009). Whether due directly or indirectly to these plant traits, rates of leaf litter decomposition, total belowground carbon (C) allocation and pools of soil nitrogen (N) and rates of net N mineralization also shift along this genetic gradient (Schweitzer et al. 2004, 2008, b; LeRoy et al. 2006; Whitham et al. 2006; Lojewski et al. 2009; Fischer et al. 2007, 2010).
Chapter Fourteen - From genes to ecosystems
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- By Joseph K. Bailey, Department of Ecology and Evolutionary Biology, University of Tennessee, Jennifer A. Schweitzer, Department of Ecology and Evolutionary Biology, University of Tennessee, Francisco Úbeda, Department of Ecology and Evolutionary Biology, University of Tennessee, Benjamin M. Fitzpatrick, Department of Ecology and Evolutionary Biology, University of Tennessee, Mark A. Genung, Department of Ecology and Evolutionary Biology, University of Tennessee, Clara C. Pregitzer, Department of Ecology and Evolutionary Biology, University of Tennessee, Matthew Zinkgraf, Department of Biological Sciences, Northern Arizona University, Thomas G. Whitham, Department of Biological Sciences, Northern Arizona University, Arthur Keith, Department of Biological Sciences, Northern Arizona University, Julianne M. O’Reilly-Wapstra, Bradley M. Potts, School of Plant Science, University of Tasmania, Brian J. Rehill, Department of Chemistry, US Naval Academy, Carri J. LeRoy, Environmental Studies Program, The Evergreen State College, Dylan G. Fischer, Environmental Studies Program, The Evergreen State College
- Edited by Glenn R. Iason, Marcel Dicke, Wageningen Universiteit, The Netherlands, Susan E. Hartley, University of York
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- Book:
- The Ecology of Plant Secondary Metabolites
- Published online:
- 05 August 2012
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- 19 April 2012, pp 269-286
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Summary
Introduction
Relatively little is understood about the extent to which evolution in one species can result in changes to associated communities and ecosystems, the potential mechanisms responsible for those changes (genetic drift, gene flow or natural selection), the phenotypes or candidate genes that may link ecological and evolutionary dynamics, or the role of rapid evolution and feedbacks. However, linking genes and ecosystems in this manner is fundamental to placing community structure and ecosystem function in an evolutionary framework. This is not an easy endeavour as the field of community genetics is multi-disciplinary (Whitham et al., 2006), and ecological and evolutionary dynamics occur at different spatial and temporal scales. Recent reviews show that plant genetic variation can have extended consequences at the community and ecosystem level (extended phenotype; Whitham et al., 2003) affecting arthropod diversity, soil microbial communities, trophic interactions, carbon dynamics and soil nitrogen availability (Whitham et al., 2006; Johnson & Stinchcombe, 2007; Hughes et al., 2008; Bailey et al., 2009a). Its effects are not limited to single systems or even foundation species, but are common across broadly distributed plant and animal systems, and can have effects at the community and ecosystem level of similar magnitude to traditional ecological factors, such as differences among species (Bailey et al., 2009a, b).
Theory in the fields of community genetics (Shuster et al., 2006; Whitham et al., 2006) and co-evolution (Thompson, 2005) also supports the connection between evolutionary and ecological dynamics (Johnson et al., 2009). Multiple investigators argue that community and ecosystem phenotypes represent complex traits related to variation in the fitness consequences of inter-specific indirect genetic effects (IIGEs) (Thompson, 2005; Shuster et al., 2006; Whitham et al., 2006; Tetard-Jones et al., 2007). In their most basic form, IIGEs occur when the genotype of one individual affects the phenotype and fitness of an associated individual of a different species (Moore et al.,1997; Agrawal et al., 2001; Shuster et al., 2006; Wade, 2007). Such interactions are important in the geographic mosaic theory of co-evolution (Thompson, 2005), the development of community heritability (Shuster et al., 2006) and non-additive responses of community structure, biodiversity and ecosystem function (Bailey et al., 2009a). Empirical evidence for the effects of plant genetic variation on communities and ecosystems, paired with growing theoretical models explaining evolutionary mechanisms for these results, provides a solid foundation for understanding how evolutionary processes, such as drift and selection, may affect community structure and ecosystem function.
3 - A community and ecosystem genetics approach to conservation biology and management
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- By Thomas G. Whitham, Northern Arizona University, Catherine A. Gehring, Northern Arizona University, Luke M. Evans, Northern Arizona University, Carri J. LeRoy, The Evergreen State College, Randy K. Bangert, Idaho State University, Jennifer A. Schweitzer, University of Tennessee, Gerard J. Allan, Northern Arizona University, Robert C. Barbour, University of Tasmania, Dylan G. Fischer, The Evergreen State College, Bradley M. Potts, University of Tasmania, Joseph K. Bailey, Northern Arizona University
- Edited by J. Andrew DeWoody, Purdue University, Indiana, John W. Bickham, Purdue University, Indiana, Charles H. Michler, Purdue University, Indiana, Krista M. Nichols, Purdue University, Indiana, Gene E. Rhodes, Purdue University, Indiana, Keith E. Woeste, Purdue University, Indiana
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- Book:
- Molecular Approaches in Natural Resource Conservation and Management
- Published online:
- 05 July 2014
- Print publication:
- 14 June 2010, pp 50-73
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Summary
INTRODUCTION
The emerging field of community and ecosystem genetics has so far focused on how the genetic variation in one species can influence the composition of associated communities and ecosystem processes such as decomposition (see definitions in Table 3–1; reviews by Whitham et al. 2003, 2006; Johnson & Stinchcombe 2007; Hughes et al. 2008). A key component of this approach has been an emphasis on understanding how the genetics of foundation plant species influence a much larger community. It is reasoned that because foundation species structure their ecosystems by creating locally stable conditions and provide specific resources for diverse organisms (Dayton 1972; Ellison et al. 2005), the genetics of these species as “community drivers” are most important to understand and most likely to have cascading ecological and evolutionary effects throughout an ecosystem (Whitham et al. 2006). For example, when a foundation species’ genotype influences the relative fitness of other species, it constitutes an indirect genetic interaction (Shuster et al. 2006), and when these interactions change species composition and abundance among individual tree genotypes, they result in individual genotypes having distinct community and ecosystem phenotypes. Thus, in addition to an individual genotype having the “traditional” phenotype that population geneticists typically consider as the expression of a trait at the individual and population level, community geneticists must also consider higher-level phenotypes at the community and ecosystem level. The predictability of phenotypes at levels higher than the population can be quantified as community heritability (i.e., the tendency for related individuals to support similar communities of organisms and ecosystem processes; Whitham et al. 2003, 2006; Shuster et al. 2006).
13 - Biodiversity is related to indirect interactions among species of large effect
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- By Joseph K. Bailey, Northern Arizona University, Thomas G. Whitham, Northern Arizona University
- Edited by Takayuki Ohgushi, Kyoto University, Japan, Timothy P. Craig, University of Minnesota, Duluth, Peter W. Price, Northern Arizona University
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- Book:
- Ecological Communities
- Published online:
- 12 August 2009
- Print publication:
- 04 January 2007, pp 306-328
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Summary
Introduction
Because communities are structured by the interactions among species, indirect interactions (i.e., effects of one species on another mediated by a third) are likely to play a major role in determining community composition. Through indirect interactions with plants, herbivores can have large effects on community composition by creating habitats and conditions to which other species respond. For example, beaver herbivory of cottonwoods increases phytochemical defensive compounds in resprout cottonwoods that positively affect the abundance of a leaf-chewing chrysomelid beetle (Martinsen et al. 1998). Herbivores can create these habitats or conditions by modifying plant architecture (Nakamura and Ohgushi 2003), secondary chemistry (Karban and Baldwin 1997), plant species composition (Johnston and Naiman 1990, Chadde and Kay 1991), building of structures (Cappuccino 1993, Jones et al. 1994, Dickson and Whitham 1996, Martinsen et al. 2000, Bailey and Whitham 2003), changes to the spatial distribution of habitat (Chadde and Kay 1991), or some combination of these effects, any of which can influence community composition. When herbivores are dominant species, keystone species (Hunter 1992) and/or ecosystem engineers, they can have strong positive or negative effects on associated species (Jones et al. 1997, Wimp and Whitham 2001, Bailey and Whitham 2002). Hereafter, we refer to such organisms as species of large effect, i.e., species which create ecological conditions to which other species respond resulting in a change in community composition.
12 - Host plants mediate aphid–ant mutualisms and their effects on community structure and diversity
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- By Gina M. Wimp, University of Maryland, Thomas G. Whitham, Northern Arizona University
- Edited by Takayuki Ohgushi, Kyoto University, Japan, Timothy P. Craig, University of Minnesota, Duluth, Peter W. Price, Northern Arizona University
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- Book:
- Ecological Communities
- Published online:
- 12 August 2009
- Print publication:
- 04 January 2007, pp 275-305
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Introduction
Much of the emphasis in studying mutualisms has been placed on defining the strength of these associations and the conditions that cause their collapse (Bronstein 1994, 1998). Yet, very few studies of aphid–ant mutualisms have linked the importance of host plant traits with the establishment and persistence of these mutualisms. Aphid performance, as well as the quality and quantity of their honeydew, may be affected by differences in host plant genetics or through environmentally induced effects on host plant quality. Differences among host plants that influence the attractiveness of aphids to tending ants can therefore alter the nature and strength of this association. The importance of host plants in determining the establishment and persistence of aphid–ant mutualisms could have consequences for biodiversity if these aphid–ant mutualisms play an important role in the structure and diversity of ecological communities.
The idea that mutualisms are important components of ecological communities arose 130 years ago (van Beneden 1875, French paper cited in Boucher 1985). However, much of the theoretical and empirical work in ecology for the past 70 years has supported the view that antagonistic interactions among species are more important than positive interactions in determining community organization. Yet, empirical data on an array of different mutualisms has shown that they can be important to community structure and diversity.
Temporal variation in temperature and rainfall differentially affects ectomycorrhizal colonization at two contrasting sites
- RANDY L. SWATY, CATHERINE A. GEHRING, MATT VAN ERT, TAD C. THEIMER, PAUL KEIM, THOMAS G. WHITHAM
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- Journal:
- The New Phytologist / Volume 139 / Issue 4 / August 1998
- Published online by Cambridge University Press:
- 01 August 1998, pp. 733-739
- Print publication:
- August 1998
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We examined the roles that seasonal shifts in precipitation and temperature played in the ectomycorrhizal (ECM) colonization of pinyon pine (Pinus edulis Engelm.) at two contrasting sites in northern Arizona. Pinyons growing in ash and cinder soils experienced much greater water and nutrient stress than pinyons growing nearby in sandy-loam soils. Over a one year period, we obtained monthly measurements of ECM colonization, root zone soil moisture and temperature, and air temperature and precipitation. Four major patterns emerged. Firstly, although climate as measured by ambient temperature and precipitation did not vary between the two sites, soil temperature was significantly higher and soil moisture significantly lower at the cinder site than at the sandy-loam site. Secondly, ECM colonization was significantly higher at the cinder site for 5 of 12 months. Thirdly, although nearly 70% of the variation in ECM colonization of pinyons growing in cinder soil was predicted by a combination of soil moisture and soil temperature, these same variables had little predictive power for pinyons growing in sandy-loam soils. Air temperature and precipitation were also significantly correlated with ECM colonization at the cinder site but not the sandy-loam site. Fourthly, a watering experiment showed that ECM colonization significantly increased with supplemental water at the cinder site, but not at the sandy-loam site. Thus, in two sites that did not differ in plant community or climate, ectomycorrhizas in cinder soils were far more sensitive to changes in moisture and temperature than ectomycorrhizas in sandy-loam soils.