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Reidinger, Stefan. "Multitrophic interactions between insect herbivores and soil microbial communities." Thesis, Royal Holloway, University of London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487317.
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Over the last two decades strong evidence has emerged that. interactions between .soil microbes, plants and higher trophic levels can translate into functional changes which affect ecosystem functioning and productivity. One of the most intensively studied soil microbial groups are the arbuscular mycorrhizal fungi that have been demonstrated not only to affect the performance of plants, but also to interact with insect herbivores via the common host. Howeyer, the ecological significance of such interactions on above- and belowground processes often remain~ obscure, since most previous studies were conducted under the . exclusion ofnon-mycorrhizal soil organisms. In order to study mycorrhiza-insect herbivore interactions under ecologically more realistic conditions, the large majority of experiments presented in this thesis were carried out with naturally co-occurring soil microbial communities. Chapter three of this thesis describes experiments in which I examined the effects of insect shoot herbivory on mycorrhizal colonisation and on the community structure of mycorrhizal fungi. Chapter four describes experiments in which I studied the combined effects of insect root herbivory and mycorrhizal fungi on aboveground insect attack. In chapter five I investigated, whether plant-soil feedbacks affect mycorrhizal colonisation, plant chemistry and aboveground insect attack. Furthermore, I tested whether insect herbivore-induced changes. in soil microbial communities affect the performance of a new generation of plants and insect herbivores. The results from these experiments suggest (1) that insect shoot herbivores have less impact on arbuscular mycorrhizal fungi than insect root herbivores, (2) that the outcome of mycorrhiza-insect interactions largely depends on the plant species identity involved, (3) that insect-indu~d changes in non-mycorrhizal soil microbial communities might be an important mechanism eA'Plaining the productivity and composition of plant communities as well as the abundance of insect herbivores and (4) that interactions between mycorrhizal fungi and insect herbivores might sometimes be of low ecological relevance.
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Vicari, Mark. "Interactions between grasses, their fungal invaders, and herbivores." Thesis, Lancaster University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264680.
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Bennett, Alison. "Mechanisms underlying complex interactions between plants, herbivores, and arbuscular mycorrhizal fungi." [Bloomington, Ind.] : Indiana University, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3204279.
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Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2006.Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0048. Adviser: James D. Bever. "Title from dissertation home page (viewed Feb. 9, 2007)."
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Barber, Nicholas A. "Tritrophic interactions in forests direct and indirect interactions between birds, insect herbivores, and oaks /." Diss., St. Louis, Mo. : University of Missouri--St. Louis, 2009. http://etd.umsl.edu/r3561.
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Liess, Antonia. "Nutrient Stoichiometry in Benthic Food Webs – Interactions Between Algae, Herbivores and Fish." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Universitetsbiblioteket [distributör], 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6933.
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Parker, John. "Plant-herbivore interactions consequences for the structure of freshwater communities and exotic plant invasions /." Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-11182005-131013/.
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Thesis (Ph. D.)--Biology, Georgia Institute of Technology, 2006.Mark E. Hay, Committee Chair ; Julia Kubanek, Committee Member ; Joseph Montoya, Committee Member ; J. Todd Streelman, Committee Member ; David M. Lodge, Committee Member. Includes bibliographical references.
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Sieg, Robert Drew. "Chemically-mediated interactions in salt marshes: mechanisms that plant communities use to deter closely associated herbivores and pathogens." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47590.
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Herbivores and pathogens pose a consistent threat to plant productivity. In response, plants invest in structural and/or chemical defenses that minimize damage caused by these biotic stressors. In salt marshes along the Atlantic coast of the United States, a facultative mutualism between snails (Littoraria irrorata) and multiple species of fungi exert intense top-down control of the foundation grass species Spartina alterniflora. Since exposure to herbivores and pathogens are tightly coupled in this system, I investigated whether S. alterniflora utilizes chemical and/or structural defenses to deter both snails and fungi, and examined how plant defenses varied among S. alterniflora individuals and populations. I also assessed how other marsh plants prevent snails from establishing farms, and considered whether interspecific variation in plant chemical defenses influences marsh community structure. Initial experiments revealed that S. alterniflora chemical defenses inhibited L. irrorata and two fungi that snails commonly farm. A caging experiment determined that production of chemical defenses could not be induced in the presence of snails and fungi, nor relaxed in their absence. Through separations chemistry guided by ecological assays, I isolated two distinct classes of chemical defenses from short form S. alterniflora, one of which inhibited fungal growth and the other decreased plant palatability. In a community context, the chemical defenses produced by S. alterniflora were relatively weak compared to those of four other salt marsh plant species, which produced compounds that completely inhibited L. irrorata grazing and strongly hindered fungal growth in lab assays. Nutritional and structural differences among marsh plants did not influence feeding preferences, suggesting that plant secondary chemistry was the primary driver for food selection by snails. It appears that S. alterniflora produces weak chemical defenses that slow down or limit fungal growth and snail herbivory, and may compensate for tissue losses by producing new growth. In contrast, less abundant marsh plants express chemical defenses that completely inhibit fungal farming and deter snail grazing, but doing so may come at a cost to growth or competitive ability. As marsh dieback continues with rising herbivore densities and compounding abiotic stressors, the ecosystem services that salt marshes provide may be lost. Therefore, understanding how and under what conditions salt marsh plants resist losses to herbivores and pathogens will help predict which marsh communities are most likely to be threatened in the future. Initial experiments revealed that S. alterniflora chemical defenses inhibited L. irrorata and two fungi that snails commonly farm. A caging experiment determined that production of chemical defenses could not be induced in the presence of snails and fungi, nor relaxed in their absence. Through separations chemistry guided by ecological assays, I isolated two distinct classes of chemical defenses from short form S. alterniflora, one of which inhibited fungal growth and the other decreased plant palatability. In a community context, the chemical defenses produced by S. alterniflora were relatively weak compared to those of four other salt marsh plant species, which produced compounds that completely inhibited L. irrorata grazing and strongly hindered fungal growth in lab assays. Nutritional and structural differences among marsh plants did not influence feeding preferences, suggesting that differences in plant chemistry were the primary driver for food selection by snails. It appears that S. alterniflora produces weak chemical defenses that slow down or limit fungal growth and snail herbivory, and may compensate for tissue losses by producing new growth. In contrast, less abundant marsh plants express chemical defenses that completely inhibit fungal farming and deter snail grazing, but doing so may come at a cost to growth or competitive ability against S. alterniflora. As marsh dieback continues with rising herbivore densities and compounding abiotic stressors, the ecosystem services that salt marshes provide may be lost. Therefore, understanding how and under what conditions salt marsh plants resist losses to herbivores and pathogens will help predict which marsh communities are most likely to be threatened in the future.
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Parker, John D. "Plant-herbivore interactions : consequences for the structure of freshwater communities and exotic plant invasions." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/9460.
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Invasive exotic species threaten native biodiversity, alter ecosystem structure and function, and annually cost over $100 billion in the US alone. Determining the ecological traits and interactions that affect invasion success are thus critical for predicting, preventing, and mitigating the negative effects of biological invasions. Native herbivores are widely assumed to facilitate exotic plant invasions by preferentially consuming native plants and avoiding exotic plants. Here, I use freshwater plant communities scattered broadly across the Southeastern U.S. to show that herbivory is an important force driving the ecology and evolution of freshwater systems. However, native consumers often preferentially consume rather than avoid exotic over native plants. Analyses of 3 terrestrial datasets showed similar patterns, with native herbivores generally preferring exotic plants. Thus, exotic plants appear defensively nave against these evolutionarily novel consumers, and exotic plants may escape their coevolved, specialist herbivores only to be preferentially consumed by the native generalist herbivores in their new ranges. In further support of this hypothesis, a meta-analysis of 71 manipulative field studies including over 100 exotic plant species and 400 native plant species from terrestrial, aquatic, and marine systems revealed that native herbivores strongly suppressed exotic plants, while exotic herbivores enhanced the abundance and species richness of exotic plants by suppressing native plants. Both outcomes are consistent with the hypothesis that prey are susceptible to evolutionarily novel consumers. Thus, native herbivores provide biotic resistance to plant invasions, but the widespread replacement of native with exotic herbivores eliminates this ecosystem service, facilitates plant invasions, and triggers an invasional meltdown. Consequently, rather than thriving because they escape their co-evolved specialist herbivores, exotic plants may thrive because their co-evolved generalist herbivores have stronger negative effects on evolutionarily nave, native plants.
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Shewhart, Lauren Elizabeth. "How specialist and generalist herbivores are responding to invasive plant threats." Wright State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=wright1462797971.
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Humphrey, Parris Taylor. "The Ecology Of Co-Infection In The Phyllosphere: Unraveling The Interactions Between Microbes, Insect Herbivores, And The Host Plants They Share." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/565900.
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Infection by multiple parasites is a part of everyday life for many organisms. The host immune system may be a central mediator of the many ways parasites might influence one another (and their hosts). Immunity provides a means for the colonized to reduce the success of current and future colonizers and has evolved across the tree of life several times independently. Along the way, the immune systems of plants as well as many groups of animals has evolved perhaps an accidental vulnerability wherein defense against one parasite can increase susceptibility to others. This so-called immune 'cross-talk' is a conundrum worth investigating not only to understand the impact of parasites on focal organisms, but also to better predict how immunity itself influences the evolution and epidemiology of parasites whose spread we might like to curtail. For plants, co-infection often comes from insect herbivores and various bacteria that colonize the leaf interior. Both colonizers can reduce plant fitness directly or indirectly by potentiating future enemies via cross-talk in plant immunity. This phenomenon has largely been studied in laboratory model plants, leaving a substantial gap in our knowledge from native species that interact in the wild. This dissertation helps close this gap by investigating the ecology of co-infection of a native plant by its major insect herbivore and diverse leaf-colonizing bacteria. I revealed that leaf co-infection in the field by leaf-mining herbivores and leaf-colonizing ("phyllosphere") bacteria is substantially more common than single infection by either group and that bacterial infection can cause increased feeding by herbivores in the laboratory. Immune cross-talk can also shape the field-scale patterns of herbivory across a native plant population. Studying the main herbivore of this native plant in detail revealed that, in contrast to many specialist herbivores, our focal species avoids plant defenses likely because it does not possess a specialized means of avoiding their toxicity. Nonetheless, this species may depend on the very same defenses it avoids by being initially attracted to plants that produce them. This foraging strategy is unique among known specialists. Lastly, I moved beyond immune cross-talk to explore how co-occurring phyllosphere bacteria might directly impact one another through competition. In the lab, I found that different growth strategies underlie competitive ability for two major clades of bacteria within the genus Pseudomonas, and that toxin production and resistance may be important mediators of competition within the phyllosphere. However, competitively superior bacteria that produce toxins may indirectly facilitate the survival of inferior competitors through their being toxin resistant, which likely enhances co-existence of diverse bacteria in the phyllosphere. Together, this dissertation has revealed a variety of means by which co-infecting bacteria and insects might influence one another through plant defense cross-talk, as well as how the complex interplay of colonization and competition might affect the structure of leaf microbial communities in nature.
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Gillett, David James. "Effects of habitat quality on secondary production in shallow estuarine waters and the consequences for the benthic-pelagic food web." W&M ScholarWorks, 2010. http://www.vims.edu/library/Theses/Gillett10.pdf.
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Barthelemy, Hélène. "Herbivores influence nutrient cycling and plant nutrient uptake : insights from tundra ecosystems." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-120191.
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Reindeer appear to have strong positive effects on plant productivity and nutrient cycling in strongly nutrient-limited ecosystems. While the direct effects of grazing on vegetation composition have been intensively studied, much less is known about the indirect effect of grazing on plant-soil interactions. This thesis investigated the indirect effects of ungulate grazing on arctic plant communities via soil nutrient availability and plant nutrient uptake. At high density, the deposition of dung alone increased plant productivity both in nutrient rich and nutrient poor tundra habitats without causing major changes in soil possesses. Plant community responses to dung addition was slow, with a delay of at least some years. By contrast, a 15N-urea tracer study revealed that nutrients from reindeer urine could be rapidly incorporated into arctic plant tissues. Soil and microbial N pools only sequestered small proportions of the tracer. This thesis therefore suggests a strong effect of dung and urine on plant productivity by directly providing nutrient-rich resources, rather than by stimulating soil microbial activities, N mineralization and ultimately increasing soil nutrient availability. Further, defoliation alone did not induce compensatory growth, but resulted in plants with higher nutrient contents. This grazing-induced increase in plant quality could drive the high N cycling in arctic secondary grasslands by providing litter of a better quality to the belowground system and thus increase organic matter decomposition and enhance soil nutrient availability. Finally, a 15N natural abundance study revealed that intense reindeer grazing influences how plants are taking up their nutrients and thus decreased plant N partitioning among coexisting plant species. Taken together these results demonstrate the central role of dung and urine and grazing-induced changes in plant quality for plant productivity. Soil nutrient concentrations alone do not reveal nutrient availability for plants since reindeer have a strong influence on how plants are taking up their nutrients. This thesis highlights that both direct and indirect effects of reindeer grazing are strong determinants of tundra ecosystem functioning. Therefore, their complex influence on the aboveground and belowground linkages should be integrated in future work on tundra ecosystem N dynamic.
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Kenworthy, Nigel. "The influence of bottom-up effects on trophic cascades : a case study of Orchestia (Amphipoda) affecting redshank (Tringa totanus) predation risk in a saltmarsh ecosystem." Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/12775.
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Previous research into bottom-up processes on saltmarshes has mainly focused on the influence of plant succession on herbivores. This study will present original research exploring the influence of bottom-up processes in a saltmarsh ecosystem between three trophic levels: Orchestia, redshanks, and sparrowhawks. Density dependence, may be the dominant top-down effect when higher numbers of sparrowhawks and redshanks are present, and may mask top-down and bottom-up trait effects which are constant. Bottom-up effects begin to emerge when cold conditions force redshanks from muddy creeks onto the saltmarsh to forage for Orchestia, because their primary prey, Corophium become less available. Larger flocks form and feeding on Orchestia requires them to balance a need to profit from the best available feeding patches and to be vigilant to sparrowhawk attack. Redshank vulnerability is compounded, because Orchestia hide in cold temperatures, so probing in the soil with their heads down makes them more vulnerable to sparrowhawk attack. Larger flocks may be able to exploit areas closer to sparrowhawk-concealing cover at the terrestrial boundary because they feel safer in greater numbers. Warmer temperatures make Orchestia more active which attracts redshanks, which can simultaneously feed and be vigilant because they peck and catch crawling and jumping Orchestia with their heads up. Consequently, increased flock size may temporarily depress Orchestia abundance, so that redshanks become spaced, leaving isolated individuals more vulnerable to attack. Therefore, it is a temperature-dependent bottom-up process which impacts upon both Orchestia and redshank behaviour, which then may influence the hunting success of sparrowhawks. Whether the characteristics of this saltmarsh ecosystem and the trophic dynamics can be compared to other examples is questionable. Saltmarshes probably differ in their topography and the way in which environmental conditions affect them that then defines which species are present and how these species interact.
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Kay, M. K. (Nod). "An experimental evaluation of resource allocation in island plants with respect to their invertebrate herbivores." Lincoln University, 2008. http://hdl.handle.net/10182/1442.
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New Zealand’s isolation and periods of marine transgression have limited its biota to an extent which can be considered depauperate, even by island standards. Endemic vertebrates are rare and prominent invertebrate families, such as the renowned forest defoliators of the Lymantriidae, are absent. The proven vulnerability of the flora to introduced vertebrates reaffirms a belief in the invasiveness of islands and fuels the contingency plans aimed at averting similar devastation from further alien invertebrate defoliators. Nothofagus is a dominant element of the climax forests of New Zealand and the larger landmasses bordering the South Pacific Ocean. Assessments of the resistance to defoliation of continental and New Zealand species of Nothofagus, and a range of other forest genera endemic to New Zealand, was undertaken using bioassays of naïve polyphagous defoliators. The bioassays were undertaken in Europe, utilising gypsy moth, Lymantria dispar (Lepidoptera: Lymantriidae) and the fall webworm, Hyphantria cunea (Lepidoptera: Arctiidae) as defoliators, fed foliage plants growing in European arboreta. In New Zealand, bioassays utilised Australian painted apple moth, Teia anartoides (Lepidoptera: Lymantriidae) and tree species from local arboreta, gardens and natural populations. Larval growth rate was the primary parameter recorded to assess plant resistance. The relevance of growth rate was investigated by comparison with other recorded parameters and resistance to a surrogate pathogen, in the form of commercially available bio-insecticide. Larval growth rate was positively correlated with survivorship, potential fecundity, mating success and resistance to disease. The growth rate of larvae fed Nothofagus was positively correlated to the species-specific leaf nitrogen content. The results of the bioassays showed that despite the accepted paradigms, New Zealand’s flora was largely resistant to exotic defoliators. As an explanation of this apparent anomaly, the Island Resource Allocation (IRA) hypothesis was developed and posits that ‘the palatability iv of a plant to invertebrate herbivores is proportional to the geographic range of the plant’. The basis for the IRA hypothesis proposes a redefinition of the fundamental ecological principle of the species: area relationship. Islands, or similarly geographically constrained ecosystems, which support lower biodiversity, have impoverished trophic levels and consequently have weaker top-down regulation of herbivores by natural enemies. The IRA hypothesis argues that island ecosystem stability is achieved through the bottom-up process of plant defence. The IRA hypothesis was tested intra-specifically using bioassays using painted apple moth in which larvae were offered foliage of specimens from naturally discontinuous populations of Nothofagus truncata. The results supported the hypothesis in that the smallest populations of N. truncata exhibited the greatest resistance to the defoliator. The IRA hypothesis and a demonstrated mechanism for a differential resistance in Nothofagus species could resolve a number of enduring debates in ecology. Habitat area appears to explain the relative strengths of top-down and bottom-up regulation of herbivores. It also predicts the strengths of reciprocal evolution within the geographic mosaic of co-evolution and highlights the influence of biodiversity in invasive ecology. It may also help to resolve the contentious and extremely relevant debate of the role of biodiversity in ecosystem function.
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Iitembu, Johannes Angala. "Trophic relationships of hake (Merluccius capensis Castelnau, 1851 and M. paradoxus Franca 1960) from the Northern Benguela current ecosystem (Namibia) : inferences from stable isotopes and fatty acids." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1020296.
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Two species of hake (Merluccius capensis and Merluccius paradoxus) account for most of Namibia’s fisheries catch, and they are important secondary consumers in the Benguela Current ecosystem. Inferences on their trophic relationships have been based mainly on stomach content analyses. However, such data are limited temporally because they represent only snapshots of recent feeding, and are quantitatively biased because of variation in the digestion rates of different prey. The principal aim of the thesis was to understand the trophic relationships of two hake species relative to each other, their known prey and top predators (demersal sharks) in the northern Benguela Current ecosystem (Namibia), using time-integrating trophic biomarkers. By using stable isotope (carbon and nitrogen) and fatty acid signatures of their muscle tissues, my overall objectives were to produce new knowledge about 1) hake ontogenic trophic relationships, 2) the contributions of different prey to hake diets, 3) hake dietary differences, and 4) some aspects of hake’s trophic relationships with demersal sharks. Tissues of hake (n=358), their potential prey (n=455), and demersal sharks (n=42) were collected between 2008 and 2012 during demersal bottom trawl surveys off Namibia, for stable isotope and fatty acid analyses. And more...
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Hazelwood, Kirsten. "The role of trophic interactions in shaping tropical tree communities." Thesis, University of Stirling, 2018. http://hdl.handle.net/1893/28637.
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Tropical rainforests contain exceptionally high biodiversity and account for >30% of the world's carbon fixed by photosynthesis. Consequently, there are compelling reasons to deepen our understanding of the mechanisms that maintain these highly diverse forests and of the potential long-term threats to their preservation. An important process shaping tropical plant communities is negative density dependence (NDD). NDD occurs when plant performance is negatively impacted by increased neighbourhood density. Reduced performance at high neighbourhood density is thought to arise through ecological interactions between plants and their natural enemies. Thus in a healthy ecosystem, trophic interactions play vital roles as mechanisms driving NDD and are important as dispersers facilitating escape from NDD mortality. However, interruption to ecological processes caused by human activities, such as hunting, can perturb NDD interactions and cause cascading effects throughout an ecosystem. In my thesis I investigate the role of dispersal and mortality in NDD dynamics of tropical tree communities, as well as investigating local and global impacts of removing ecological interactions in tropical rainforests. In my thesis, I begin by addressing the presence and variation in strength of NDD among tree species and ontogenetic stages, the mechanisms driving NDD, and the role of trophic interactions in this process. The Janzen-Connell hypothesis predicts that host-specific natural enemies drive NDD by selectively reducing conspecific density, and increase diversity by suppressing competitive exclusion, thus allowing heterospecifics to persist. In chapters 2 and 3 of this thesis, I show that mortality driven by conspecific NDD is prevalent at the early life stages, and this effect is considerably stronger during the year after germination. Furthermore, this process is driven exclusively by host-specific fungal pathogens, which cause mortality selectively among conspecifics and drive diversity. As seedlings age beyond their first year, NDD interactions become less impacted by conspecifics but are impacted by closely related neighbours or by general neighbourhood density, representing changes in the mechanism driving NDD as seedlings age, and a decline in host-specificity of natural enemies. Equally, relative growth rates (RGR) are reduced under high neighbourhood density irrespective of species identity. Results suggest insect herbivores are the strongest driver of reduced RGR but not mortality under increased neighbourhood density. As a consequence of stronger inter than intra-specific NDD effects on RGR, insects had no impact on seedling diversity in the short term. This study supports assertions that regionally rare species experience stronger NDD than common species, accounting for the high variability in species relative abundance in the tropics. In the second part of my thesis, I address the role of large vertebrate dispersers in shaping tropical tree communities and the consequences of defaunation for tree assemblage and carbon storage. Dispersal allows seeds to escape NDD and persist to reproductive maturity and is therefore vital for the maintenance of diversity. Vertebrates disperse the seeds of more than 70% of neo-tropical tree species. However, many large vertebrates are becoming scarce due to widespread hunting. The decline of large vertebrates and their role as dispersers is predicted to alter tree community composition. Additionally, large vertebrates are responsible for the dispersal of large-seeded species, which are linked to species with high wood density. With wood density positively associated with carbon storage, there is a potential cascading influence of defaunation on global carbon storage. We investigate the consequences of declining large vertebrate mortality agents in chapter 3, and the consequences of declining large vertebrate dispersers in chapters 4 and 5. Although community composition is altered in a defaunated forest, species dispersed by extirpated fauna do not appear to drive this. In fact we find that many species thought to be heavily reliant on extirpated fauna manage to persist. Although it is thought that the simultaneous loss of seed predation from large terrestrial vertebrates may create compensatory effects, we found little support for this, with an absence of large terrestrial vertebrates driving only temporary changes to species diversity. Neither a loss of large frugivores or large-seeded species lead to declines in species with high wood density, but we detect a worrying decline in large stemmed species, which has negative implications for carbon storage. Overall, my thesis highlights the importance of NDD and trophic interactions, particularly fungal pathogens, at the early life stages in shaping tropical tree communities and in maintaining diversity. I provide evidence that the removal of trophic interactions among larger natural enemies and dispersers does not impact community assemblage in the directional manner found in previous studies. I provide evidence for the variability in response to trophic interactions among species and ontogenetic stages. I show disproportionate relative importance among natural enemies and dispersers in the maintenance of tropical tree assemblage, with implications for conservation and for assessing the consequences for tree diversity under the influence of degradation.
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Løe, Geir. "Ecology and Evolution of Resistance to Herbivory : Trichome Production in Arabidopsis lyrata." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6359.
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Vidal, Mayra Cadorin 1989. "A predação de formigas por Rhinoleucophenga sp. nov. (Diptera, Drosophilidae) e seus efeitos no mutualismo entre formigas e Qualea grandiflora (Vochysiaceae)." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/316186.
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Orientadores: Paulo Sergio Moreira Carvalho de Oliveira, Sebastian Felipe Sendoya EcheverryDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia
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Resumo: Exploradores do mutualismo - indivíduos que utilizam recursos/serviços produzidos pelos mutualistas sem recompensá-lo - podem trazer sérios danos aos mutualistas explorados, principalmente quando acaba matando um dos parceiros mutualistas. Plantas portadoras de NEFs podem manter mutualismos com formigas visitantes, que defendem a planta contra insetos herbívoros. No cerrado de Itirapina (SP), encontramos larvas de uma nova espécie de díptero do gênero Rhinoleucophenga (Drosophilidae) que constroem abrigos de consistência pegajosa em cima dos NEFs de Q. grandiflora. Assim, larvas de Rhinoleucophenga podem interferir no mutualismo formiga-planta, agindo potencialmente como exploradora dessa interação. O presente estudo teve como objetivos principais investigar a história natural dessas larvas, principalmente aspectos do comportamento e interação com Qualea e formigas, e analisar seu possível efeito sobre o mutualismo formiga-Q.grandiflora. Durante observações de campo comprovamos que formigas e outros insetos visitantes dos NEFs podem ficar presos ao abrigo larval e servir de alimento para o díptero. Larvas de Rhinoleucophenga sp. nov. ocorrem em 85% dos indivíduos de Q. grandiflora, principalmente na época chuvosa ocupando preferencialmente nectários ativos, perto do ápice e na face abaxial dos ramos. No levantamento da mirmecofauna visitante de Q. grandiflora encontramos 27 morfoespécies de formigas, sendo as duas mais frequentes Camponotus crassus, e uma espécie do gênero Brachymyrmex, as mesmas que foram mais comumente encontradas presas aos abrigos das larvas mirmecófagas. Vimos que as larvas expõem uma substância líquida na abertura de seu abrigo, que comprovamos possuir composição química muito similar a do néctar extrafloral de Q. grandiflora, o que sugere que as larvas utilizam o néctar da própria planta para atrair suas presas. Na presença de larvas de Rhinoleucophenga, menos formigas visitam as plantas e também por menos tempo. Esse forrageamento diferenciado resultou em menor ataque de formigas a cupins vivos (herbívoros simulados). Além disso, na presença das larvas mirmecófagas houve maior abundância de herbívoros mastigadores e maior área foliar removida por herbívoros. Podemos afirmar que as larvas de Rhinoleucophenga sp. nov. utilizam o recurso da planta sem beneficiá-la. Além disso, as larvas do díptero também prejudicam a planta e suas formigas mutualísticas, uma vez que alimentando-se delas, aumentam a incidência de herbívoros e a herbivoria foliar na planta. Dessa forma, as larvas de Rhinoleucophenga sp. nov. estão agindo como exploradoras e do mutualismo formiga-Qualea grandiflora e predadoras de topo, causando efeito cascata nesse sistema
Abstract: Exploiters of mutualism - individuals that use resources/services offered by mutualists giving nothing in return - can cause serious damages to mutualists, especially when it involves the death of one of the partners. Plants bearing EFNs usually maintain mutualism with aggressive ants, which defend the plant against herbivores. In a cerrado area at Itirapina (SP), we found a new dipteran species of the genus Rhinoleucophenga (Drosophilidae) whose larvae construct sticky shelters on top of active EFNs of Q. grandiflora. Field observations revealed those ants and others insects that visit the EFNs can get trapped at the sticky larval shelters, and are consumed by the larvae. We hypothesized that Rhinoleucophenga larvae could be interfering with the ant-Qualea mutualism, and thus be acting as an exploiter of this interaction. Here, we investigate the natural history of Rhinoleucophenga larvae, mainly its behavior and association with ants and Qualea, and their possible effect on the ant-Qualea mutualism. Larvae of Rhinoleucophenga sp. nov. occur in 85% of the individuals of Qualea grandiflora inspected at Itirapina. Rhinoleucophenga larvae occur mostly during the rainy season, mainly at the apex and abaxial surface of the branches. We found 27 ant species visiting Qualea. The two most frequent visiting species, Brachymyrmex sp. 1 and Camponotus crassus, were most common insects trapped at larval shelters. Chemical analyses revealed that Rhinoleucophenga larvae use Qualea's extrafloral nectar to attract insect prey to their shelters. Qualea branches infested by ant-preying Rhinoleucophenga larvae had ant visitors for less time and in lower numbers than dipteran-free branches. This negative effect on ant foraging activity resulted in decreased levels of ant aggression to live termite-baits (i.e., simulated herbivores) on leaves of dipteran-infested compared to dipteran-free branches. Controlled field experiments demonstrated that branches hosting Rhinoleucophenga larvae had higher numbers of chewing herbivores and higher levels of foliar herbivory than dipteran-free branches. By using Qualea's EFNs as larval shelters and as attractants to ant prey, larvae of Rhinoleucophenga sp. nov. negatively affect both the plant and ant visitors, with cascading effects ultimately resulting in increased herbivore damage to leaves. Thus we can conclude that ant-eating Rhinoleucophenga larvae are acting as exploiters of the mutualism between ants and Q. grandiflora and also as top predator, causing cascade effect on this system
Mestrado
Ecologia
Mestra em Ecologia
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Rossignol, Nicolas. "Hétérogénéité de la végétation et du pâturage : conséquences fonctionnelles en praireis naturelle." Phd thesis, Université Rennes 1, 2006. http://tel.archives-ouvertes.fr/tel-00520859.
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Le pâturage influence la production primaire et la qualité de la végétation et peut, ainsi, avoir un impact sur les flux d'éléments et les cycles biogéochimiques. La conséquence de cette interaction entre herbivores, plantes et sol sur le fonctionnement d'un écosystème peut être variée car l'impact du pâturage sur les fonctions de la végétation dépend des communautés végétales ainsi que de l'intensité du pâturage. L'objectif de cette thèse est d'analyser l'impact d'un gradient d'intensité de pâturage sur le fonctionnement d'une prairie humide. Le modèle biologique de cette étude est une prairie du Marais Poitevin, pâturée depuis le Xe siècle. Trois communautés végétales coexistent au sein de cette prairie, et les variations spatiales de l'intensité du pâturage ont conduit à la création d'une mosaïque de patchs de végétation au sein de chacune de ces communautés. Le gradient spatial d'intensité de pâturage conduit, au sein de chaque communauté, à une hétérogénéité spatiale des processus fonctionnels de la prairie en lien avec l'hétérogénéité de la végétation. De façon générale, on observe le long du gradient croissant d'intensité de pâturage, une diminution de la production primaire, une augmentation de la qualité de végétation ainsi qu'une augmentation du taux de minéralisation nette de l'azote du sol. Au sein de chaque communauté végétale, l'amplitude des variations spatiales du cycle de l'azote apparaît liée à l'amplitude des variations des fonctions de la végétation. L'impact de l'intensité du pâturage sur les fonctions de la végétation découle de deux mécanismes principaux. L'effet à long terme du pâturage influence la composition floristique de la végétation et se répercute sur les fonctions de la végétation. Le gradient croissant d'intensité de pâturage conduit à une modification importante de la composition floristique des communautés végétales. L'impact de ce gradient sur les fonctions de la végétation est plus important lorsque les types fonctionnels dominants en situation non pâturés, des graminoïdes pérennes, sont remplacés par d'autres types fonctionnels, des annuelles et des dicotylédones. En situation pâturée, les fonctions de la végétation sont modulées par une réponse de la végétation à la coupe. La défoliation stimule le taux de croissance de la végétation des patchs. L'intensité de cette stimulation est maximale pour une fréquence de coupe faible et permet une compensation plus ou moins forte de l'impact négatif de la coupe sur la production primaire. Cette réponse est caractéristique de chaque composition floristique. L'interaction entre les effets de la fréquence de défoliation et de la composition floristique conduit à observer, le long du gradient de pâturage, une diminution de production primaire beaucoup plus importante au sein de la communauté méso-hygrophile qu'au sein de la communauté mésophile. L'impact du gradient de pâturage sur les fonctions de la végétation détermine la qualité et la quantité des entrées de matière organique vers le sol et conduit à un impact sur le processus de minéralisation nette de l'azote. En particulier, la quantité de carbone en provenance de la litière végétale apparaît soutenir la croissance microbienne et stimuler le taux d'immobilisation de l'azote par les microorganismes ce qui diminue la quantité d'azote minéral disponible pour la végétation. En conséquence, la réduction des entrées de litières le long du gradient de pâturage conduit à une stimulation du taux de minéralisation nette de l'azote du sol. La stabilité ou la modifications des fonctions de production primaire et de qualité de végétation le long du gradient de pâturage conditionne donc l'impact du pâturage sur les cycles biogéochimiques.
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Lawrence, Janet L. "Conservation of insect natural enemies in heterogeneous vegetable landscapes." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1092761676.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xvi, 166 p.; also includes graphics (some col.). Includes bibliographical references. Available online via OhioLINK's ETD Center.
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Wemheuer, Franziska. "Influence of Grassland Management and Herbivory on Diversity and Ecology of plant-associated Bacterial Communities." Doctoral thesis, 2013. http://hdl.handle.net/11858/00-1735-0000-0022-5FFE-F.
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In den vergangenen Jahren rückten Pflanzen-assoziierte Bakterien auf Grund ihrer Bedeutung für die Pflanzengesundheit und das ökologische Gleichgewicht zunehmend in den Fokus aktueller Forschungen. Trotz der stetig steigenden Zahl wissenschaftlicher Studien ist der Einfluss von Bewirtschaftungsmaßnahmen auf die Diversität dieser Bakteriengemeinschaften in Grünlandökosystemen ver-gleichsweise wenig untersucht. In dieser Studie haben wir neue und interessante Erkenntnisse über die Diversität von Pflanzen-assoziierten Bakterien in Grünlandökosystemen gewonnen.
Sämtliche Untersuchungen dieser Arbeit wurden auf der GrassMan-Fläche in den Mittelgebirgslagen des Solling in Deutschland durchgeführt. Das GrassMan-Experiment wurde 2008 in einer Matrix von Wiesenplots schachbrett-artig auf historisch altem Grünland errichtet. Die Bewirtschaftungsintensität unterschied sich bezüglich der Häufigkeiten (einmal jährlich im Juli oder dreimal jährlich im Mai, Juli und September) und der Düngung (keine Düngung bzw. Düngung mit NPK). Außerdem wurde durch gezielten Herbizid-Einsatz gegen Monokotylen oder gegen Dikotylen ein Gradient in der Anzahl der Pflanzenarten erzeugt.
Die Arbeit umfasst drei Hauptthemen. Erstens wurde der Einfluss verschiedener Bewirtschaftungsmaßnahmen auf die bakterielle Endophyten-gemeinschaft in den drei Grasarten Festuca rubra, Lolium perenne und Dactylis glomerata untersucht. Hierfür wurden im September 2010 und im April, Juli und September 2011 Pflanzenproben auf den Dikotylen-reduzierten Plots gesammelt. Die Umwelt-DNS wurde aus den Proben extrahiert und als Template für 16S PCRs eingesetzt. Die Struktur der bakteriellen Endophyten-Gemeinschaft wurde mittels DGGE-Analyse der erhaltenen PCR-Produkte untersucht.
Wir konnten Unterschiede der Endophyten-Gemeinschaftsstrukturen hinsichtlich der verschiedenen Bewirtschaftungsintensitäten feststellen. Während die Düngung einen starken Effekt auf die bakterielle endophytische Diversität sowohl in F. rubra als auch in L. perenne hatte, wurden die bakteriellen Endo-phyten in D. glomerata nicht dadurch beeinflusst. Die Proben von L. perenne, die von den ungedüngten Plots stammten, bildeten zudem eindeutige Gruppen bei der Analyse der DGGE-Banden bezüglich der zwei Schnitthäufigkeiten. Somit beeinflusste auch die Mahd die bakterielle Endophyten-Gemeinschaft in den Pflanzen. Weiterhin konnten wir einen starken saisonalen Effekt auf die Struktur der endophytischen Gemeinschaft nachweisen. Da saisonale Veränderungen und die Pflanzenart die Zusammensetzung der endophytischen Bakteriengemeinschaft beeinflussten, können sich die Auswirkungen unterschiedlicher Bewirtschaf-tungsintensitäten mit der Zeit und der untersuchten Pflanzenart verändern. Dieses Ergebnis sollte bei zukünftigen Studien berücksichtigt werden.
Das zweite Ziel dieser Arbeit war die Beantwortung der Frage, wie sich oberirdische Herbivorie auf die Bakteriengemeinschaft in der Rhizosphäre auswirkt. Hierfür wurde im Herbst 2010 ein Lysimeter-Experiment auf der GrassMan-Fläche errichtet. Nach einer zweiwöchigen Herbivorie durch Grashüpfer und Schnecken im Sommer 2011 wurden Bodenproben von jedem Lysimeter genommen. Um Einblicke in die Zusammensetzung der bakteriellen Gemeinschaft in der Rhizosphäre zu erhalten, wurde die Gesamt-DNS aus den Bodenproben extrahiert und als Template in 16S rDNS PCRs eingesetzt. Die Gemeinschaftsstruktur wurde mittels DGGE-Analyse bzw. Pyrosequenzierung der erhaltenen PCR Produkte untersucht. Die Herbivorie hatte keinen Einfluss auf die Anzahl der Bakterien (richness), während leichte Änderungen in der relativen Abundanz von einigen Bakteriengruppen festgestellt wurden. So war zum Beispiel die relative Abundanz einer unkultivierten Acidobacterium-Art in den Herbivorie-Lysimetern erhöht.
Bestandteil des Lysimeter-Experiments war zudem die Untersuchung des Einflusses der Pflanzenartenanzahl und der verschiedenen Bewirtschaftungs-maßnahmen auf die bakterielle Gemeinschaft in der Rhizosphäre. Der Einsatz von Herbiziden und eine niedrigere Schnittfrequenz reduzierten die Artenanzahl (richness) der Bakterien in der Rhizosphäre. Die Düngung hatte keinen Einfluss auf die Anzahl der Arten. Weitere Analysen zeigten, dass eine Vielzahl von verschiedenen bakteriellen Taxa in der Rhizosphäre durch die untersuchten Maßnahmen beeinflusst wurde. So war die Abundanz der Acidobacteria in den gedüngten Plots signifikant geringer. Das Gegenteil trat bei den Actinobacteria auf.
Abschließend lässt sich sagen, dass Pflanzen-assoziierte Bakterien sowohl in der Endosphäre und Rhizosphäre durch Bewirtschaftungsmaßnahmen beeinflusst werden. Die Untersuchung der Wirkung von verschiedenen Bewirtschaftungsintensitäten im Grünland und von oberirdischer Herbivorie auf Pflanzen-assoziierte Bakterien kann zu einem besseren Verständnis der multitrophischen Interaktionen zwischen Pflanzenart, Bakteriengemeinschaft und oberirdischen Herbivoren führen. Außerdem können uns die Ergebnisse dieser Arbeit helfen, die Effekte unterschiedlicher Bewirtschaftungsmaßnahmen auf Pflanzen-assoziierte Bakteriengemeinschaften und damit zusammenhängende Effekte auf das Bodenökosystem vorherzusagen.
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Sentis, Arnaud. "Effet de la température sur les interactions trophiques et intraguildes au sein d’un système plante-herbivore-ennemis naturels : modélisation et approches expérimentales." Thèse, 2012. http://hdl.handle.net/1866/8487.
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Il est maintenant reconnu que les changements climatiques ont des impacts importants sur l’ensemble des organismes vivants. Parmi les facteurs de ces changements, la température occupe une place prépondérante pour les organismes ectothermes car elle régule leur métabolisme. Toutefois, bien que les effets de la température sur les individus d’une espèce soient largement connus, les connaissances demeurent limitées quant aux conséquences sur les interactions trophiques. Dans ce contexte, notre étude s’intéresse aux effets de la température sur un système biologique composé d’une plante, le poivron Capsicum annuum L., d’un herbivore, le puceron Myzus persicae Sulzer (proie extraguilde), ainsi que de deux de ses ennemis naturels : la coccinelle maculée Coleomegilla maculata lengi Timberlake (prédateur intraguilde) et la cécidomyie prédatrice Aphidoletes aphidimyza Rondani (proie intraguilde). Dans ce but, nous avons opté pour une approche multiple comprenant : (1) la modélisation des interactions prédateur-proie et intraguilde (prédation entre deux compétiteurs d’espèces différentes qui exploitent une même ressource), (2) la réalisation d’expériences empiriques en laboratoire permettant de tester les prédictions des modèles et de caractériser l’effet de la température et de ses variations sur les composantes du système biologique étudié. Conformément aux prédictions d’un premier modèle, nous mettons en évidence que, lorsque la température augmente, C. maculata est plus efficace pour trouver et manipuler ses proies, ce qui augmente le taux de prédation. En revanche, à haute température son efficacité de recherche décroît, ce qui entraîne une diminution du taux de prédation. L’activité de prédation se limite donc à une fenêtre thermique en dehors de laquelle elle est réduite ou nulle. Par la suite, nous comparons un modèle linéaire et un modèle non-linéaire (saturant à haute densité de proies) afin de déterminer lequel de ces deux modèles décrit le mieux la réponse fonctionnelle d’un prédateur intraguilde, c’est-à-dire la relation entre le nombre de proies consommées et la densité de proies. Nos résultats expérimentaux démontrent que les prédictions du modèle non-linéaire correspondent bien aux observations empiriques, tandis que le modèle linéaire surestime largement le nombre de proies consommées et la fréquence des interactions intraguildes. Par la suite, nous dérivons le modèle non-linéaire afin d’y inclure l’effet de la température. Comme prédit par ce dernier modèle, la prédation intraguilde devient plus fréquente lorsque la température augmente mais diminue lorsqu’il y a davantage de proies extraguildes. Dans une dernière étude, nous soumettons le système biologique à des pics de température. Nos résultats démontrent que ces pics diminuent la fécondité des pucerons, l’accroissement de leurs populations, le poids des larves de coccinelles et le contrôle des pucerons par les coccinelles mais n’ont pas d’effets sur la plante et les relations plante-insecte. Le système biologique s’avère également plus résistant aux pics de température en présence de coccinelles qu’en leur absence. En conclusion, notre étude souligne l’importance de considérer la température dans les interactions trophiques puisqu’elle influence le comportement des organismes et la fréquence de leur interaction, ce qui se répercute au niveau des populations et des communautés.There are several pieces of evidence that climate change significantly impact plants, herbivores, and predators. For ectotherms, temperature is the most important factor associated with these changes as it regulates their metabolism. Although the effects of temperature on individual organisms or populations have been well documented, our understanding about their consequences on trophic and guild interactions remains limited. In this context, we investigated the effects of temperature on complex interactions between a plant, the pepper Capsicum annuum L.; an herbivore, the aphid Myzus persicae Sulzer (extraguild prey); and two of its natural enemies, the ladybeetle Coleomegilla maculata lengi Timberlake (intraguild predator) and the predatory midge Aphidoletes aphidimyza Rondani (intraguild prey). We combined two approaches: (1) modeling predator–prey and intraguild (predation between two species that compete for the same resource) interactions, and (2) testing model predictions and characterizing the effects of temperature on components of our biological system through laboratory experiments. As predicted by the first model, we found that when temperature rises, C. maculata is more efficient at finding and handling prey, which increases predation rate. However, search rate decreases at high temperatures, leading to a reduction in predation. The predatory activity is therefore limited to a temperature window outside of which predation is reduced or absent. The next objective was to compare two models, one linear and one nonlinear, to determine which one best describes the functional response (the relationship between the number of prey consumed and prey density) of an intraguild predator. Results indicated that predictions of the nonlinear model (i.e., saturating at high prey densities) fit empirical observations well while the linear model greatly overestimates the number of prey consumed and the incidence of intraguild predation. Subsequently, we derived the nonlinear model to include the effect of temperature. As predicted by this model, we found that the incidence of intraguild predation increases with temperature but decreases when extraguild prey are more abundant. In a last experiment, we investigated the effects of temperature peaks on each component of our biological system. Results showed that temperature peaks reduce aphid fecundity and thereby population growth, decrease the weight of ladybeetle larvae, and decrease aphid control by ladybeetles, but have no effect on plants or plant–insect relationships. We also observed that the food chain is more resistant to temperature peaks when ladybeetles are included in the system than when they are absent. This suggests that ecosystems with predators exerting strong biotic control on prey population should be more resistant to climate change than ecosystem lacking them. In conclusion, our study highlights the importance of considering temperature in trophic and guild interactions since it influences the behavior of organisms as well as the frequency of interactions that affect population and community dynamics.
Doctorat réalisé en cotutelle entre l'Université de Montréal et l'Université Paul Sabatier-Toulouse III
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Krumins, Jennifer Adams. "The causes and consequences of biodiversity in multitrophic communities." 2007. http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.16526.
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Schlinkert, Hella. "Multitrophic interactions along a plant size gradient in Brassicaceae." Doctoral thesis, 2014. http://hdl.handle.net/11858/00-1735-0000-0022-5DC4-E.
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Das Wissen über Mechanismen, die einen Einfluss auf Muster der Artenvielfalt und biotische Interaktionen haben, ist grundlegend für den Schutz von Biodiversität. Darüber hinaus kann es von direktem ökonomischem Nutzen sein, zum Beispiel im biologischen Pflanzenschutz oder bei Bestäubungsdienstleistungen. Die Größe eines Organismus kann ein solcher Faktor sein, der die Artenzahl und Interaktionen der assoziierten Organismen beeinflusst, denn große Organismen sind auffälliger als kleine und ihr Angebot an Ressourcen und Nischen für mit ihnen assoziierte Organismen ist oft reicher. Bezogen auf Pflanzen könnte daher die Größe einer Pflanze einen erheblichen Einfluss auf die Artenzahl der mit ihr assoziierten Arthropoden und ihre biotischen Interaktionen wie Herbivorie oder Bestäubung haben. Trotzdem ist der Einfluss der Pflanzengröße auf mutualistische und antagonistische Interaktionspartner der Pflanze und der sich daraus ergebende Einfluss auf die reproduktive Fitness der Pflanze bisher nicht umfassend und unter standardisierten Bedingungen untersucht worden.
In der vorliegenden Studie wurden die Auswirkungen der Pflanzengröße auf die Artenzahl von Herbivoren, deren Gegenspielern und Bestäubern untersucht, sowie die Auswirkungen dieser Interaktionspartner auf die Pflanzenfitness. Dabei wurde zusätzlich zwischen endophagen und ektophagen Herbivoren und deren Gegenspielern unterschieden. Außerdem wurden die Herbivoren einzelner Pflanzenkompartimente und deren Gegenspieler separat analysiert. Des Weiteren wurde der Einfluss der Pflanzengröße auf den Herbivorieschaden an den verschiedenen Pflanzenkompartimenten und deren Einfluss auf die reproduktive Fitness der Pflanze, d.h. auf ihre Samenzahl, Tausendkorngewicht und Samengesamtgewicht, untersucht. Zuletzt wurde besonderes Augenmerk auf den Einfluss der Pflanzengröße auf mutualistische und antagonistische Blütenbesucher und deren Einfluss auf die reproduktive Fitness gelegt und untersucht, ob und inwiefern die reproduktive Fitness letztendlich von der Pflanzengröße abhängig ist.
Zur Untersuchung dieser Fragen wurde ein „Common Garden“-Experiment angelegt. Um einen interspezifischen Pflanzengrößengradienten zu erzeugen, wurden 21 annuelle Pflanzenarten aus der Familie der Kreuzblütler (Brassicaceae) ausgewählt, deren Größe von 10 bis 130 cm reichte (gemessen als Pflanzenhöhe vom Boden bis zur Spitze). So konnten die Einflüsse des Habitats und der umgebenden Landschaft für alle Pflanzenarten standardisiert und trotzdem ein breiter Gradient realisiert werden. Dadurch hebt sich diese Studie von den bisherigen ab, die den Effekt von meist intraspezifischer Pflanzengröße auf die assoziierten Tiere anhand wild wachsender Pflanzen untersucht haben. Pflanzengröße sowie Zahl, Biomasse und Größe der unterschiedlichen überirdischen Pflanzenkompartimente (Blüten, Schoten, Blätter, Stängel) sowie Blütendeckung und -farbe wurden aufgenommen. Der Herbivorieschaden an diesen Pflanzenkompartimenten und die reproduktive Fitness (Samenzahl, Tausendkorngewicht und Gesamtsamengewicht) wurden gemessen. An und in Blüten, Schoten, Blättern und Stängeln wurden herbivore, räuberische, parasitäre und bestäubende Arthropoden gezählt.
Die Pflanzengröße hatte einen positiven Einfluss auf die Artenzahl von Herbivoren, deren Gegenspielern und Bestäubern. Das traf ebenso auf endophage und ektophage sowie auf mit Blättern und Schoten assoziierte Herbivore und deren Gegenspieler zu. Des Weiteren konnte ein Anstieg des Herbivorieschadens an Blüten und Schoten mit zunehmender Pflanzengröße festgestellt werden, wohingegen der Schaden an Blättern und Stängeln von der Biomasse des entsprechenden Kompartiments positiv beeinflusst wurde. Der Schaden an Blüten hatte den stärksten Einfluss auf die reproduktive Fitness und reduzierte neben der Samenzahl auch das Tausendkorngewicht und das Gesamtsamengewicht der Pflanze. Die genaue Analyse der blütenbesuchenden Insekten ergab einen positiven Einfluss der Pflanzengröße auf die Abundanz und Artenzahl von Bestäubern (allerdings nicht bei extrem großem Blütenangebot), wie auch auf die Abundanz der adulten und juvenilen Rapsglanzkäfer und deren Parasitierungsrate. Steigende Rapsglanzkäferzahlen verringerten die Samenzahl sowie das Tausendkorngewicht, während die Bestäuber sich lediglich auf die Samenzahl positiv auswirkten. Insgesamt führte ein Anstieg der Pflanzenhöhe zu einer Abnahme des Tausendkorngewichts, aber nicht zu einer Veränderung der Samenzahl oder des Gesamtsamengewichts, was auf einen Ausgleich der Effekte von zunehmender Antagonistenzahl und zunehmender Mutualistenzahl hindeutet.
Großen Pflanzen entstehen also durch ihre Auffälligkeit und Attraktivität für Herbivore hohe Fitnesskosten, wobei insbesondere der Blütenschaden durch Rapsglanzkäfer einen starken negativen Einfluss auf Samenzahl, Tausendkorngewicht und Gesamtsamengewicht hat. Diesen Fitnesskosten großer Pflanzen wirkt der Nutzen durch ihre Auffälligkeit und Attraktivität für Bestäuber entgegen, die die Samenzahl positiv beeinflussen. Hinsichtlich der Samenzahl sollten also große Pflanzen gegenüber kleineren im Vorteil sein, wenn die Insektengemeinschaft des Habitats von Bestäubern dominiert wird. Wird sie aber von herbivoren Blütenbesuchern dominiert, sollten kleine Pflanzen gegenüber großen einen Vorteil haben. Im Gegensatz dazu sollten große Pflanzen immer einen Nachteil bezüglich des Tausendkorngewichts haben, das von Antagonisten, nicht aber von Mutualisten beeinflusst wurde. Der Einfluss der Pflanzengröße auf biotische Interaktionen wurde bisher oft unterschätzt, obwohl er sich auf komplexe Weise über die mutualistischen und antagonistischen Insekten auf die reproduktive Fitness der Pflanze auswirkt.
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Dean, Jennifer M. "Chemical ecology of plant-microbe interactions and effects on insect herbivores." 2008. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-2563/index.html.
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"Algal-herbivore interactions in coastal communities in Tung Ping Chau, Hong Kong." 2005. http://library.cuhk.edu.hk/record=b5892538.
Full textAbstract:
So Ka Yi Erica.Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.
Includes bibliographical references (leaves 243-255).
Abstracts in English and Chinese.
Acknowledgements --- p.i
Abstract --- p.iii
Contents --- p.ix
List of Tables --- p.xii
List of Figures --- p.xix
Chapter Chapter 1 --- General Introduction
Chapter 1.1 --- Introduction --- p.1
Chapter 1.2 --- General Objectives --- p.11
Chapter 1.3 --- Study Site --- p.12
Chapter 1.4 --- Organization of the Thesis --- p.13
Chapter Chapter 2 --- "General Surveys on the Abundance of Algae and Herbivores in A Ma Wan, A Ye Wan and Lung Lok Shui, Tung Ping Chau, Hong Kong"
Chapter 2.1 --- Introduction --- p.16
Chapter 2.2 --- Materials and Methods --- p.20
Chapter 2.2.1 --- Study site --- p.20
Chapter 2.2.2 --- Measurement of water temperature --- p.21
Chapter 2.2.3 --- Measurement of algal percentage cover --- p.22
Chapter 2.2.4 --- Measurement of herbivore density --- p.22
Chapter 2.2.5 --- Investigation on the species richness and diversity of algae and herbivores --- p.23
Chapter 2.2.6 --- Statistical analysis --- p.24
Chapter 2.3 --- Results --- p.27
Chapter 2.3.1 --- Measurement of algal abundance and diversity --- p.27
Chapter 2.3.1.1 --- Percentage cover and morphology --- p.28
Chapter 2.3.1.2 --- Species richness --- p.29
Chapter 2.3.1.3 --- Species diversity --- p.29
Chapter 2.3.1.4 --- Dominance and composition --- p.30
Chapter 2.3.2 --- Measurement of herbivore abundance and diversity --- p.32
Chapter 2.3.2.1 --- Density of herbivores --- p.32
Chapter 2.3.2.2 --- Species richness --- p.33
Chapter 2.3.2.3 --- Species diversity --- p.34
Chapter 2.3.2.4 --- Dominance and composition --- p.34
Chapter 2.3.3 --- Relationships between algae and herbivores --- p.37
Chapter 2.3.3.1 --- Pairwise Pearson Correlation between algae and herbivores in different sites --- p.37
Chapter 2.3.3.2 --- Canonical correlations between algal and herbivorous species --- p.38
Chapter 2.3.4 --- "Water temperature and its relationships with the abundance, richness and diversity of algae and herbivores" --- p.39
Chapter 2.4 --- Discussion --- p.40
Chapter 2.4.1 --- Spatial distribution of algae and herbivores --- p.40
Chapter 2.4.2 --- Seasonal distributions of algae and herbivores --- p.46
Chapter 2.4.3 --- Interactions between algae and herbivores --- p.50
Chapter Chapter 3 --- Growth of Algae in Herbivore-exclusion Manipulative Experiment
Chapter 3.1 --- Introduction --- p.106
Chapter 3.2 --- Materials and Methods --- p.111
Chapter 3.2.1 --- Study site --- p.111
Chapter 3.2.2 --- Manipulative experiment --- p.111
Chapter 3.2.3 --- Investigation on the manipulative experiment --- p.112
Chapter 3.2.3.1 --- Species composition of algae and herbivores --- p.113
Chapter 3.2.3.2 --- Percentage cover of algae and density of herbivores --- p.113
Chapter 3.2.3.3 --- Sizes of herbivores --- p.113
Chapter 3.2.4 --- Detecting the cage effect --- p.114
Chapter 3.2.5 --- Statistical analyses --- p.114
Chapter 3.3 --- Results --- p.117
Chapter 3.3.1 --- Algae --- p.117
Chapter 3.3.1.1 --- Percentage cover --- p.117
Chapter 3.3.1.2 --- Species richness --- p.120
Chapter 3.3.1.3 --- Composition between treatments --- p.121
Chapter 3.3.1.4 --- Compositions between set-ups --- p.121
Chapter 3.3.1.5 --- Effects from caging and clearing --- p.122
Chapter 3.3.2 --- Herbivores --- p.123
Chapter 3.3.2.1 --- Density --- p.123
Chapter 3.3.2.2 --- Species richness --- p.124
Chapter 3.3.2.3 --- Compositions between treatments --- p.124
Chapter 3.3.2.4 --- Compositions between set-ups --- p.125
Chapter 3.3.3 --- Relationships between algae and herbivores --- p.125
Chapter 3.3.3.1 --- Abundance --- p.125
Chapter 3.3.3.2 --- Composition --- p.126
Chapter 3.3.4 --- Sizes of herbivores --- p.128
Chapter 3.3.5 --- Irradiance between treatments --- p.128
Chapter 3.4 --- Discussion --- p.129
Chapter 3.4.1 --- Effects of clearing on algal and herbivore dynamics --- p.130
Chapter 3.4.2 --- Effects of caging on algal and herbivore dynamics --- p.135
Chapter 3.4.3 --- Effects of seasonality of clearing on algal and herbivore dynamics --- p.139
Chapter 3.4.4 --- Interactions of algae and herbivores --- p.142
Chapter Chapter 4 --- Feeding Behavior of Common Herbivores in the Artificial Food Experiment
Chapter 4.1 --- Introduction --- p.216
Chapter 4.2 --- Materials and Methods --- p.218
Chapter 4.2.1 --- Sample collections --- p.218
Chapter 4.2.2 --- Production of artificial foods --- p.219
Chapter 4.2.3 --- Feeding experiments --- p.219
Chapter 4.2.4 --- Statistical analysis --- p.220
Chapter 4.3 --- Results --- p.221
Chapter 4.4 --- Discussion --- p.222
Chapter Chapter 5 --- Summary and Conclusion --- p.233
References --- p.243
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Ranganathan, Yuvaraj. "Ants, Figs, Fig Wasps : The Chemical Ecology Of A Multitrophic System." Thesis, 2011. http://etd.iisc.ernet.in/handle/2005/1959.
Full textAbstract:
Plant–animal interaction systems are complex food webs where the members—plants, pollinators, herbivores, parasites and predators of the pollinators/herbivores—interact with each other in ways which maximize their own fitness. Based on the net outcome, such interactions could be mutually beneficial to the interacting members (mutualism) or beneficial to only one of the interacting members at the cost of the other interacting members (herbivory, predation, parasitism). It is possible that such outcomes are actually a continuum and could swing in either direction from beneficial to detrimental and vice versa. Such transitions happen not only over long time scales, but could also happen within shorter time scales based on conditionalities. Conditional outcomes are those in which the outcome of an interaction between two partners is conditional on the involvement of a third partner. Thus, studying such outcomes necessitates taking into account systems beyond the classical two-partner interactions.
In such complex multitrophic plant–animal interaction systems in which there are direct and indirect interactions between species, comprehending the dynamics of these multiple partners is very important for an understanding of how the system is structured. In Chapter 2 we investigate Ficus racemosa and its community of obligatory mutualistic and parasitic fig wasps that develop within the fig inflorescence or syconium, as well as their interaction with opportunistic ants. We focus on temporal resource partitioning among members of the fig wasp community over the development cycle of the fig syconia during which wasp oviposition and development occur and we study the activity rhythm of the ants associated with this community. We found that the members of the wasp community partitioned their oviposition across fig syconium development phenology and showed interspecific variation in activity across the diel cycle. The wasps presented a distinct sequence in their arrival at fig syconia for oviposition. We documented night oviposition in several fig wasp species for the first time. Ant activity on the fig syconia was correlated with wasp activity and was dependent on whether the ants were predatory or trophobiont-tending species; only numbers of predatory ants increased during peak arrivals of the wasps.
In Chapter 3, we found that predatory ants (Oecophylla smaragdina) patrolling F. racemosa trees were attracted to the odour from fig syconia at different developmental phases, as well as to the odours of fig wasps, whereas other predatory ants (Technomyrmex albipes) responded only to odours of syconia from which fig wasps were dispersing and to fig wasp odour. However, trophobiont-tending ants (Myrmicaria brunnea) patrolling the same trees and exposed to the same volatiles were unresponsive to fig or fig wasp odours. The predatory ants demonstrated a concentration-dependent response towards volatiles from figs receptive to pollinators and those from which wasps were dispersing while the trophobiont-tending ants were unresponsive to such odours at all concentrations. Naıve predatory ants failed to respond to the volatiles to which the experienced predatory ants responded, indicating that the response to fig-related odours is learned.
In Chapter 4 we characterise the dynamics of the volatile bouquet of the fig syconium from the initiation through pre-receptive, receptive, and late inter-floral stages which act as signals/ cues for different fig wasp species. We were also interested in diel patterns of volatile emission as some fig wasp species were strictly diurnal (the pollinator, Ceratosolen fusciceps) whereas other fig wasps such as Apocryptophagus fusca were observed ovipositing even during the nocturnal hours. We identified volatiles that were specific to syconium development phase as well as to the time of day in this bouquet. α-muurolene was identified as the sesquiterpene specific to receptive-phase as well as being present only during the day thus coinciding with the diurnal pollinator arrival pattern. Volatiles such as (E)-β-ocimene were present in increasing levels across the developmental stages of the fig and thus could act as background volatiles providing suitable information to fig wasps about host plants and their phases.
Chapter 5 examines the responses of predatory and trophobiont-tending ant species to the cuticular hydrocarbon (CHC) extracts of four galler and two parasitoid fig wasp species associated with F. racemosa. Interestingly, the antennation response of both experienced and na¨ıve ants to these wasp extracts was identical indicating that prior exposure to such compounds is not necessary for eliciting such response. We also characterised these cuticular hydrocarbon extracts to find potential compounds which could as short-range cues for predatory ants. Ants were more responsive to the cuticular extracts of parasitoids rather than to those of galler wasps, implying that the CHC profile of carnivorous prey may contain more elicitors of aggressive behaviour in ants compared to herbivorous prey whose profiles may be more similar to those of their plant resources. We also find congruency between the cuticular profiles of parasitoids and their hosts suggesting that parasitoids could sequester compounds from their diet.
Important findings and conclusions of the thesis are presented in Chapter 6.
The first two parts of the appendices section discuss work carried out on alternative ways of analysing multivariate data sets such as plant volatiles and insect cuticular hydrocarbons. Appendix A details the use of Random Forests, an algorithm-based method of analysing complex data sets where there are more variables than samples, a situation akin to microarray data sets. This work illustrates the use of such techniques in chemical ecology, highlighting the potential pitfalls of classical multivariate tests and the advantages of newer more robust methods. Appendix B, an invited article following the publication of the earlier work, compares different data transformation procedures currently employed in such multivariate analysis.
Appendix C details sex-specific differences in cuticular hydrocarbons of fig wasps, using the pollinator C. fusciceps as a case study.
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Bartlett, Ryan Paul. "Ecological And Evolutionary Interactions Among Plant Resistance, Herbivores, And Predators." Diss., 2006. http://hdl.handle.net/10161/51.
Full textAbstract:
To understand how plant defensive traits will evolve, we need to consider the biotic context for plant-herbivore interactions. I investigated how predators affect selection on defensive traits in plants. First, I established the timing of resistance in three soybean genotypes. Next, I examined the combined effects of resistance and predators on plant fitness. I reared Mexican bean beetles (MBBs) with or without spined soldier bugs (SSBs) on soybeans with constitutive resistance (CR) or no resistance (NR). SSBs fed more on MBBs that fed on NR than on CR plants, and this translated into an increased fitness benefit from predators for NR plants over CR plants. Selection for some types of resistance in plants should thus be stronger with lower predation rates. Similarly, I reared MBBs with or without SSBs on soybeans with early induced resistance (EI), late induced resistance (LI), or CR. SSBs fed more on MBBs reared on LI plants than on beetles raised on CR plants, but no more on beetles reared on EI plants than on beetles reared on CR plants. LI plants were the only of the three soybean varieties to receive a fitness benefit from predators, which could help explain the evolution of this type of plant defense. The results of both experiments also suggest that predator introductions may be more beneficial to LI or NR crop plants than EI or CR crops. Finally, I present a model that determines the optimum amount of induced resistance (IR) and CR for a plant growing with and without neighbors. Unlike earlier models, our plants have a probability of being attacked that is modified by short- and long-term feedback of plant defenses to herbivores. Higher costs of defense favor IR over CR, while increasing herbivore attack rates or increasing the overall effectiveness of defense results in more CR. Plants with neighbors might be selected to evolve higher or lower levels of CR than if they were growing alone. Adding neighbors also selects for more mixed induced/constitutive strategies for all parameters. Having defended neighbors could thus be part of the reason why plants have evolved such mixed defense strategies.Dissertation
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Juenger, Thomas E. "The ecology and evolution of species interactions in the scarlet gilia, Ipomopsis aggregata, system /." 1999. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:9943081.
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Tiede, Julia. "Plant diversity and landscape-scale effects on multitrophic interactions involving invertebrates." Thesis, 2017. http://hdl.handle.net/11858/00-1735-0000-002E-E4F6-C.
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Börschig, Carmen. "Effects of land-use intensity in grasslands on diversity, life-history traits and multitrophic interactions." Doctoral thesis, 2012. http://hdl.handle.net/11858/00-1735-0000-000D-F0CE-0.
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Laurin-Lemay, Simon. "Phylogéographie comparée d’un système multitrophique : les parasitoïdes du genre Horismenus spp. ont-ils échappé au processus de domestication du haricot au Mexique?" Thèse, 2010. http://hdl.handle.net/1866/4762.
Full textAbstract:
Cette étude vise à comparer l’histoire évolutive des parasitoïdes du genre Horismenus (Hymenoptera: Eulophidae) à celle de leurs hôtes bruches (Coleoptera: Bruchidae) et plante hôte (Phaseolus vulgaris L.) cultivée dans le contexte d’agriculture traditionnelle, au sein de son centre de domestication Mésoaméricain. Nous avons analysé la structure génétique de 23 populations de quatre espèces de parasitoïdes au Mexique, en utilisant un fragment du gène mitochondrial COI afin de les comparer aux structures précédemment publiées des hôtes bruches et du haricot commun. Nous avons prédit que les structures génétiques des populations d’hôtes (bruches et plante) et de parasitoïdes seraient similaires puisque également influencées par la migration entremise par l’humain (HMM) étant donnée que les parasitoïdes se développent telles que les bruches à l’intérieur des haricots. Compte tenu des stratégies de manipulation reproductive utilisées par l’alpha-protéobactérie endosymbionte Wolbachia spp. pour assurer sa transmission, la structure génétique des populations de parasitoïdes inférée à partir du génome mitochondrial devrait être altérée conséquemment à la transmission conjointe des mitochondries et des bactéries lors de la propagation de l’infection dans les populations de parasitoïdes. Les populations du parasitoïde H. missouriensis sont infectées par Wolbachia spp. Tel que prédit, ces populations ne sont pas différenciées (FST = 0,06), ce qui nous empêche d’inférer sur une histoire évolutive parallèle. Contrairement aux bruches, Acanthoscelides obtectus et A. ovelatus, la HMM n'est pas un processus contemporain qui influence la structure génétique des populations du parasitoïde H. depressus, étant donné la forte différenciation (FST = 0,34) qui existe entre ses populations. La structure génétique observée chez H. depressus est similaire à celle de sa plante hôte (i.e. dispersion aléatoire historique à partir d'un pool génique ancestral très diversifié) et est probablement le résultat d’un flux génique important en provenance des populations de parasitoïdes associées aux haricots spontanées à proximité des champs cultivés. L’étude de l’histoire évolutive intégrant plusieurs niveaux trophiques s’est avérée fructueuse dans la détection des différentes réponses évolutives entre les membres du module trophique face aux interactions humaines et parasitaires, et montre la pertinence d’analyser les systèmes écologiques dans leur ensemble.This study aims to compare the evolutionary history of Horismenus parasitoids (Hymenoptera: Eulophidae) to that of their bruchid beetle hosts (Coleoptera: Bruchidae) and their domesticated host plant (Phaseolus vulgaris L.) in the context of traditional agriculture within their Mesoamerican center of domestication. We analyzed the genetic structure of 23 populations of four Horismenus species in Mexico using COI mitochondrial gene fragments and compared the structures to previously published data on bean plant and beetle hosts. We predicted that because parasitoids complete their development within their beetle hosts, within the bean, the genetic structure of both the host and the parasitoid would be similar and equally influenced by human-mediated migration (HMM). Furthermore, because of reproductive manipulation strategies often used by the alpha-proteobacteria endosymbionte Wolbachia spp. to ensure its transmission, the genetic structure of parasitoid populations inferred from mitochondrial genome would be bias consequently to the conjoint transmission of mitochondria and the bacteria according to propagation of the infection within parasitoids populations. The populations of H. missouriensis parasitoids are infected by Wolbachia spp. As predicted, these populations are not differentiated (FST = 0.06) which prevents us to infer on a parallel evolutionary history. Unlike their bruchids hosts, Acanthoscelides obtectus and A. ovelatus, the HMM is not a contemporary process influencing H. depressus population genetic structure according to the strong populations differentiation (FST = 0.34). The genetic structure observed within H. depressus populations is similar to that of its host plant (i.e. historical random dispersal from a highly diversified ancestral gene pool) and is probably the result of extensive gene flow from parasitoids associated with wild beans populations adjacent to crop fields. The study of evolutionary history integrating multitrophic levels has proved to be fruitful in detecting different evolutionary responses among members of the trophic module face to human and parasite interactions, but also points out the pertinence of analyzing ecological systems as a whole.
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(11186766), Geoffrey M. Williams. "Thousand Cankers Disease of Eastern Black Walnut: Ecological Interactions in the Holobiont of a Bark Beetle-Fungal Disease." Thesis, 2021.
Find full textAbstract:
Eastern black walnut (Juglans nigra L.) ranks among the most highly valued timber species in the central hardwood forest and across the world. This valuable tree fills a critical role in native ecosystems as a mast bearing pioneer on mesic sites. Along with other Juglans spp. (Juglandaceae), J. nigra is threatened by thousand cankers disease (TCD), an insect-vectored disease first described in 2009. TCD is caused by the bark beetle Pityophthorus juglandis Blackman (Corthylini) and the phytopathogenic fungus Geosmithia morbida Kol. Free. Ut. & Tiss. (Bionectriaceae). Together, the P. juglandis-G. morbida complex has expanded from its historical range in southwest North America throughout the western United States (U.S.) and Europe. This range expansion has led to widespread mortality among naïve hosts J. nigra and J. regia planted outside their native distributions.
The severity of TCD was previously observed to be highest in urban and plantation environments and outside of the host native range. Therefore, the objective of this work was to provide information on biotic and abiotic environmental factors that influence the severity and impact of TCD across the native and non-native range of J. nigra and across different climatic and management regimes. This knowledge would enable a better assessment of the risk posed by TCD and a basis for developing management activities that impart resilience to natural systems. Through a series of greenhouse-, laboratory- and field-based experiments, environmental factors that affect the pathogenicity and/or survival of G. morbida in J. nigra were identified, with a focus on the microbiome, climate, and opportunistic pathogens. A number of potentially important interactions among host, vector, pathogen and the rest of the holobiont of TCD were characterized. The holobiont is defined as the whole multitrophic community of organisms—including J. nigra, microinvertebrates, fungi and bacteria—that interact with one another and with the host.
Our findings indicate that interactions among host, vector, pathogen, secondary pathogens, novel microbial communities, and novel abiotic environments modulate the severity of TCD in native, non-native, and managed and unmanaged contexts. Prevailing climatic conditions favor reproduction and spread of G. morbida in the western United States due to the effect of wood moisture content on fungal competition. The microbiome of soils, roots, and stems of trees and seedlings grown outside the host native range harbor distinct, lower-diversity communities of bacteria and fungi compared to the native range, including different communities of beneficial or pathogenic functional groups of fungi. The pathogen G. morbida was also associated with a distinct community of microbes in stems compared to G. morbida-negative trees. The soil microbiome from intensively-managed plantations facilitated positive feedback between G. morbida and a disease-promomting endophytic Fusarium solani species complex sp. in roots of J. nigra seedlings. Finally, the nematode species Bursaphelenchus juglandis associated with P. juglandis synergizes with G. morbida to cause foliar symptoms in seedlings in a shadehouse; conversely, experiments and observations indicated that the nematode species Panagrolaimus sp. and cf. Ektaphelenchus sp. could suppress WTB populations and/or TCD outbreaks.
In conclusion, the composition, function, and interactions within the P. juglandis and J. nigra holobiont play important roles in the TCD pathosystem. Managers and conservationists should be aware that novel associations outside the host native range, or in monocultures, intensive nursery production, and urban and low-humidity environments may favor progression of the disease through the effects of associated phytobiomes, nematodes, and climatic conditions on disease etiology. Trees in higher diversity, less intensively managed growing environments within their native range may be more resilient to disease. Moreover, expatriated, susceptible host species (i.e., J. nigra) growing in environments that are favorable to novel pests or pest complexes (i.e., the western U.S.) may provide connectivity between emergent forest health threats (i.e., TCD) and native host populations (i.e., J. nigra in its native range).