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Biodiversity  [cached]
Editorial Office
Koers : Bulletin for Christian Scholarship , 2006, DOI: 10.4102/koers.v71i2-4.252
Abstract: The origin of life and the development of biodiversity
Multitrophic functional diversity predicts ecosystem functioning in experimental assemblages of estuarine consumers  [PDF]
Jonathan S Lefcheck,J. Emmett Duffy
PeerJ , 2015, DOI: 10.7287/peerj.preprints.540v1
Abstract: The use of functional traits to explain biodiversity effects on ecosystem functioning has attracted intense recent interest, yet very few a priori manipulations of functional diversity have been attempted to date, especially from a food web perspective. Here, we simultaneously manipulated multiple functional traits of estuarine grazers and predators within multiple levels of species richness to test whether species richness or functional diversity is a better predictor of ecosystem functioning in multitrophic estuarine food webs. Community functional diversity better predicted the majority of ecosystem responses based on results from generalized linear mixed effects models. Structural equation modeling revealed that this outcome was independently attributable to functional diversity of both trophic levels, with stronger effects observed for predators. Functional complementarity was also important, as species with different combinations of traits influenced different ecosystem functions. Our study is the first to extend experimental investigations of functional diversity to a multilevel food web, and demonstrates that functional diversity is more effective than species richness in predicting ecosystem functioning in a food web context.
Cyanogenic Pseudomonads Influence Multitrophic Interactions in the Rhizosphere  [PDF]
Thimmaraju Rudrappa, Robert E. Splaine, Meredith L. Biedrzycki, Harsh P. Bais
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0002073
Abstract: In the rhizosphere, plant roots cope with both pathogenic and beneficial bacterial interactions. The exometabolite production in certain bacterial species may regulate root growth and other root-microbe interactions in the rhizosphere. Here, we elucidated the role of cyanide production in pseudomonad virulence affecting plant root growth and other rhizospheric processes. Exposure of Arabidopsis thaliana Col-0 seedlings to both direct (with KCN) and indirect forms of cyanide from different pseudomonad strains caused significant inhibition of primary root growth. Further, we report that this growth inhibition was caused by the suppression of an auxin responsive gene, specifically at the root tip region by pseudomonad cyanogenesis. Additionally, pseudomonad cyanogenesis also affected other beneficial rhizospheric processes such as Bacillus subtilis colonization by biofilm formation on A. thaliana Col-0 roots. The effect of cyanogenesis on B. subtilis biofilm formation was further established by the down regulation of important B. subtilis biofilm operons epsA and yqxM. Our results show, the functional significance of pseudomonad cyanogenesis in regulating multitrophic rhizospheric interactions.
Insect-plant interactions: new pathways to a better comprehension of ecological communities in Neotropical savannas
Del-Claro, Kleber;Torezan-Silingardi, Helena M;
Neotropical Entomology , 2009, DOI: 10.1590/S1519-566X2009000200001
Abstract: the causal mechanisms shaping and structuring ecological communities are among the most important themes in ecology. the study of insect-plant interactions in trophic nets is pointed out as basic to improve our knowledge on this issue. the cerrado tropical savanna, although extremely diverse, distributed in more than 20% of the brazilian territory and filled up with rich examples of multitrophic interactions, is underexplored in terms of biodiversity interaction. here, this ecosystem is suggested as valuable to the study of insect-plant interactions whose understanding can throw a new light at the ecological communities' theory. three distinct systems: extrafloral nectary plants or trophobiont herbivores and the associated ant fauna; floral herbivores-predators-pollinators; and plants-forest engineers and associated fauna, will serve as examples to illustrate promising new pathways in cerrado. the aim of this brief text is to instigate young researchers, mainly entomologists, to initiate more elaborated field work, including experimental manipulations in multitrophic systems, to explore in an interactive way the structure that maintain preserved viable communities in the neotropical savanna.
Modeling the Building Blocks of Biodiversity  [PDF]
Lucas N. Joppa, Rich Williams
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0056277
Abstract: Background Networks of single interaction types, such as plant-pollinator mutualisms, are biodiversity’s “building blocks”. Yet, the structure of mutualistic and antagonistic networks differs, leaving no unified modeling framework across biodiversity’s component pieces. Methods/Principal Findings We use a one-dimensional “niche model” to predict antagonistic and mutualistic species interactions, finding that accuracy decreases with the size of the network. We show that properties of the modeled network structure closely approximate empirical properties even where individual interactions are poorly predicted. Further, some aspects of the structure of the niche space were consistently different between network classes. Conclusions/Significance These novel results reveal fundamental differences between the ability to predict ecologically important features of the overall structure of a network and the ability to predict pair-wise species interactions.
Numerical responses in resource-based mutualisms: a time scale approach  [PDF]
Tomás A. Revilla
Quantitative Biology , 2013,
Abstract: In mutualisms where there is exchange of resources for resources, or resources for services, the resources are typically short lived compared with the lives of the organisms that produce and make use of them. This fact allows a separation of time scales, by which the numerical response of one species with respect to the abundance of another can be derived mechanistically. These responses can account for intra-specific competition, due to the partition of the resources provided by mutualists, in this way connecting competition theory and mutualism at a microscopic level. It is also possible to derive saturating responses in the case of species that provide resources but expect a service in return (e.g. pollination, seed dispersal) instead of food or nutrients. In both situations, competition and saturation have the same underlying cause, which is that the generation of resources occur at a finite velocity per individual of the providing species, but their depletion happens much faster due to the acceleration in growth rates that characterizes mutualism. The resulting models can display all the basic features seen in many models of facultative and obligate mutualisms, and they can be generalized from species pairs to larger communities. The parameters of the numerical responses can be related with quantities that can be in principle measured, and that can be related by trade-offs, which can be useful for studying the evolution of mutualisms. Abstract Keywords: mutualism, resources, services, steady-state, functional and numerical response
Mutualism Disruption Threatens Global Plant Biodiversity: A Systematic Review  [PDF]
Clare E. Aslan, Erika S. Zavaleta, Bernie Tershy, Donald Croll
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0066993
Abstract: Background As global environmental change accelerates, biodiversity losses can disrupt interspecific interactions. Extinctions of mutualist partners can create “widow” species, which may face reduced ecological fitness. Hypothetically, such mutualism disruptions could have cascading effects on biodiversity by causing additional species coextinctions. However, the scope of this problem – the magnitude of biodiversity that may lose mutualist partners and the consequences of these losses – remains unknown. Methodology/Principal Findings We conducted a systematic review and synthesis of data from a broad range of sources to estimate the threat posed by vertebrate extinctions to the global biodiversity of vertebrate-dispersed and -pollinated plants. Though enormous research gaps persist, our analysis identified Africa, Asia, the Caribbean, and global oceanic islands as geographic regions at particular risk of disruption of these mutualisms; within these regions, percentages of plant species likely affected range from 2.1–4.5%. Widowed plants are likely to experience reproductive declines of 40–58%, potentially threatening their persistence in the context of other global change stresses. Conclusions Our systematic approach demonstrates that thousands of species may be impacted by disruption in one class of mutualisms, but extinctions will likely disrupt other mutualisms, as well. Although uncertainty is high, there is evidence that mutualism disruption directly threatens significant biodiversity in some geographic regions. Conservation measures with explicit focus on mutualistic functions could be necessary to bolster populations of widowed species and maintain ecosystem functions.
Housekeeping Mutualisms: Do More Symbionts Facilitate Host Performance?  [PDF]
Adrian C. Stier, Michael A. Gil, C. Seabird McKeon, Sarah Lemer, Matthieu Leray, Suzanne C. Mills, Craig W. Osenberg
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0032079
Abstract: Mutualisms often involve one host supporting multiple symbionts, whose identity, density and intraguild interactions can influence the nature of the mutualism and performance of the host. However, the implications of multiple co-occurring symbionts on services to a host have rarely been quantified. In this study, we quantified effects of decapod symbionts on removal of sediment from their coral host. Our field survey showed that all common symbionts typically occur as pairs and never at greater abundances. Two species, the crab Trapezia serenei and the shrimp Alpheus lottini, were most common and co-occurred more often than expected by chance. We conducted a mesocosm experiment to test for effects of decapod identity and density on sediment removal. Alone, corals removed 10% of sediment, but removal increased to 30% and 48% with the presence of two and four symbionts, respectively. Per-capita effects of symbionts were independent of density and identity. Our results suggest that symbiont density is restricted by intraspecific competition. Thus, increased sediment removal from a coral host can only be achieved by increasing the number of species of symbionts on that coral, even though these species are functionally equivalent. Symbiont diversity plays a key role, not through added functionality but by overcoming density limitation likely imposed by intraspecific mating systems.
Plant chemical defence: a partner control mechanism stabilising plant - seed-eating pollinator mutualisms
Sébastien Ibanez, Christiane Gallet, Fanny Dommanget, Laurence Després
BMC Evolutionary Biology , 2009, DOI: 10.1186/1471-2148-9-261
Abstract: This study shows that plant chemical defence against developing larvae constitutes another partner sanction mechanism in nursery mutualisms. It documents the chemical defence used by globeflower Trollius europaeus L. (Ranunculaceae) against the seed-eating larvae of six pollinating species of the genus Chiastocheta Pokorny (Anthomyiidae). The correlative field study carried out shows that the severity of damage caused by Chiastocheta larvae to globeflower fruits is linked to the accumulation in the carpel walls of a C-glycosyl-flavone (adonivernith), which reduces the larval seed predation ability per damaged carpel. The different Chiastocheta species do not exploit the fruit in the same way and their interaction with the plant chemical defence is variable, both in terms of induction intensity and larval sensitivity to adonivernith.Adonivernith accumulation and larval predation intensity appear to be both the reciprocal cause and effect. Adonivernith not only constitutes an effective chemical means of partner control, but may also play a key role in the sympatric diversification of the Chiastocheta genus.Conflicts of interest are frequent in interspecific mutualisms [1,2]. Plant/seed-eating pollinator mutualisms involve a plant pollinated by an insect whose larvae develop upon the plant's seeds. In these nursery pollination mutualisms, the conflict lies in the number of seeds eaten by the pollinator's larvae that therefore will not contribute to the plant's fitness [3-6]. As a consequence, evolutionary theory predicts that plants evolve traits that limit the costs imposed by the insect partners. Despite this broad prediction, attempts to identify mechanisms of partner control in nursery mutualisms have so far fell short in pinpointing a general mechanism. Pellmyr & Huth [7] showed that the selective abortion of fruits in the Yucca - Yucca moth interaction was an effective defence against the developing larvae, but this mechanism was found in only one of the three Yu
Conditional indifference and conditional preservation  [PDF]
Gabriele Kern-Isberner
Computer Science , 2000,
Abstract: The idea of preserving conditional beliefs emerged recently as a new paradigm apt to guide the revision of epistemic states. Conditionals are substantially different from propositional beliefs and need specific treatment. In this paper, we present a new approach to conditionals, capturing particularly well their dynamic part as revision policies. We thoroughly axiomatize a principle of conditional preservation as an indifference property with respect to conditional structures of worlds. This principle is developed in a semi-quantitative setting, so as to reveal its fundamental meaning for belief revision in quantitative as well as in qualitative frameworks. In fact, it is shown to cover other proposed approaches to conditional preservation.
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