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Boughton, Elizabeth Hermanson. "Understanding plant community composition in agricultural wetlands context dependent effects and plant interactions /." Orlando, Fla. : University of Central Florida, 2009. http://purl.fcla.edu/fcla/etd/CFE0002678.
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Ratcliffe, Sophia Emma Thirza. "Competition and coexistence in experimental annual plant communities." Thesis, Imperial College London, 1999. http://hdl.handle.net/10044/1/11515.
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Gaudet, Connie Lee. "Competition in shoreline plant communities: A comparative approach." Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/6516.
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I tested the general hypothesis that competitive ability is an important determinant of pattern in shoreline plant communities. Specifically I tested four predictions generated from this general hypothesis: (1) the competitive performance of plant species is related to their distribution along natural gradients of fertility and standing crop; (2) the competitive performance of plant species is related to measurable plant traits; (3) the competitive performance of plant species is not significantly affected by changing nutrient supply; and (4) there is an "evolutionary trade-off" between nutrient stress tolerance of species and competitive performance that underlies the distribution of species along natural gradients of fertility and standing crop. These questions were posed at a broad, multi-species scale using comparative measures of competitive performance, stress tolerance, and morphology from over 40 shoreline plant species, and field distribution data from several natural shoreline communities in Ontario, Nova Scotia and Quebec. Results showed that the experimentally determined measure of the relative competitive performance of a species was significantly correlated with its position along natural gradients of fertility and standing crop; and with simple measurable plant traits, in particular above-ground biomass (r$\sb{\rm s}$ = 0.92; p .0001). Results also showed that the competitive performance of species under high and low nutrient conditions was significantly correlated after two growing seasons (r$\sb{\rm s}$ = 0.76; P .001); and that stress tolerance, measured as the relative biomass production of species under low nutrient conditions, was inversely correlated with competitive performance (r = $-$0.62, p .005).
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Heard, Matthew Spencer. "The role of invertebrate herbivory and plant competition in structuring mesic grassland communities." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390618.
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Glimskär, Anders. "Growth strategies, competition and defoliation in five grassland plants /." Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 1999. http://epsilon.slu.se/avh/1999/91-576-5465-4.pdf.
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Twolan-Strutt, Lisa. "Competition intensity and its above- and below-ground components in two contrasting wetland plant communities." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/9921.
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I used a field experiment to measure total competition intensity and its above- and below-ground components in two wetlands that represent extremes in habitat productivity: an infertile sandy shoreline and a fertile bay. Transplants of Lythrum salicaria and Carex crinita were grown with no neighbours, with roots of neighbours only and with all neighbours; their growth rates were used to estimate competition intensity. The experiment was carried out to answer the following main questions: (1) Is there a difference in total, above- and below-ground competition intensity in two wetlands that differ in standing crop? (2) Is there an effect of standing crop on total, above- and below-ground competition intensity when the data from the two wetlands are combined? Both total and above-ground competition intensity were found to be greater in the high standing crop wetland but below-ground competition did not differ between wetlands (CI$\rm\sb{TOTAL}$: p 0.00001, CI$\rm\sb{ABOVE}$: p = 0.0013 CI$\rm\sb{BELOW}$: p = 0.58). Mean total competition increased from 0.16 to 0.43, the above-ground component increased from $-$0.063 to 0.21 and the below-ground component was close to 0.20 in both wetlands. Total and above-ground competition intensity was significantly affected by standing crop in the wetlands studied but below-ground competition intensity was not (CI$\rm\sb{TOTAL}$: p = 0.0001, CI$\rm\sb{ABOVE}$: p = 0.0001, CI$\rm\sb{BELOW}$: p =0.89). The result that competition was predominantly below-ground in the low standing crop wetland supports previous work in agricultural pot experiments (Wilson 1988) and terrestrial field studies (Wilson and Tilman 1991, Putz and Canham 1992, Wilson and Tilman 1993, Wilson in press). The result that root and shoot competition were roughly equal in the high standing crop wetland is not typical of past studies. (Abstract shortened by UMI.)
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Jefferson, Lara Vanessa. "The biology and ecology of species of Maireana and Enchylaena : intra- and inter- specific competition in plant communities in the eastern goldfields of Western Australia /." Curtin University of Technology, School of Chemical and Biological Sciences, 2001. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=14451.
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Members of the family Chenopodiaceae are routinely used as colonizer plant species to rehabilitate waste and tailings materials on mine sites in the Eastern Goldfields of Western Australia. These are specifically selected for their salt and drought tolerance and also because they are representative of the surrounding natural vegetation. Where these have been sown, competition between several species has been observed. The resulting plant community structure is typically lower in species diversity than the initial seed mixture. This study aimed to determine whether competition was occurring between five of the species commonly used and some of the mechanisms that determine community structure on the rehabilitated areas of waste material. Atriplex bunburyana, Atriplex codonocarpa, Maireana brevifolia, Maireana georgei and Enchylaena tomentosa were selected for the study, which was conducted in three parts. Firstly, different plant densities and species combinations were studied in the field and in a pot trial to determine whether or not competition was occurring and to determine the resources that the plants were competing for. The results of the field trial revealed that competition was occurring, but that it formed only one component of the complex interactions between plant species, density and soil characteristics (i.e. pH and salinity). The pot trial complemented the outcome of the field trial. In addition, it showed that competition was occurring, but was even more pronounced. This was most likely due to the lack of nutrients and the limited availability of space in the pots.In the second part of this study, the ability of each species to survive and grow when subjected to adverse environmental conditions, such as low moisture availability, high salinity and low light availability, was examined in relation to competition. All five species were treated with different water regimes and soil salinity. Salt played an important role, especially for the Atriplex spp. and M. brevifolia, in ensuring survival when moisture availability was low. The effect of shade on the Maireana species and E. tomentosa was also researched after field observations suggested that M georgei was adversely affected when growing within the canopy of A. bunburyana. The pot trial showed that growth of M. georgei was affected by progressively more shade, whereas E. tomentosa was facilitated by shade. Maireana brevifolia exhibited significant tolerance to low light intensity. In the last part of this three-part study, all five chenopods were screened for allelopathy. Allelopathy may play an important role in determining community structure in successive plant generations. All chenopod species produced allelopathic substances, which were isolated from their leaves. The inhibition of seed germination was found to be speciesspecific and occurred only at certain concentrations. The seed of the Atriplex spp. was not affected by M. georgei and E. tomentosa extracts.
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Hall, Lucas Keith. "Competition Dynamics Within Communities of Desert Wildlife at Water Sources." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/6402.
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Water is a vital resource for species inhabiting arid and semi-arid regions and can shape the biotic communities that we observe. Because water is considered a limiting resource for many species in desert environments, there is the potential for competitive interactions between species to occur at or around water sources. For this dissertation I tested hypotheses related to resource competition among different species of wildlife in the Great Basin and Mojave Deserts of western Utah. Chapter one evaluated the influence of feral horses (Equus caballus) on patterns of water use by communities of native birds and mammals. Chapter two determined if feral horses competed with pronghorn (Antilocapra americana) and mule deer (Odocoileus hemionus) for access to water. In chapters one and two, we found evidence that horses compete with native wildlife for water. In chapter one, horses were associated with decreased richness and diversity of native species at water sources. Native species also had fewer visits and spent less time at water sources frequented by horses. In chapter two, we found that pronghorn and mule deer used water sources less often where horse activity was high. There were also significant differences in temporal activity for pronghorn, but not mule deer, at horse-occupied sites versus sites where horses were absent or uncommon. Our results indicated that horses spatially and temporally displaced other species at water sources providing evidence of a negative influence on how communities of native wildlife access a limited resource in an arid environment. Chapter three assessed whether dominant carnivores (coyote (Canis latrans) and bobcat (Lynx rufus)) negatively influenced the spatial use of water sources by the subordinate kit fox (Vulpes macrotis). Our results did not reveal strong negative associations between kit fox visits to water sources and visits by dominant carnivores; in fact, dominant carnivores contributed very little to the use of water by kit foxes. Instead, kit fox visits were more closely associated with habitat features at water sources. Our findings indicate that dominant carnivores are not the primary driver of use of water sources by subordinate carnivores. Chapter four evaluated whether a simulated loss of water due to climate change/increased human use would differentially affect desert bats based on flight morphology and maneuverability. When we experimentally reduced surface area of water sources, larger, less-maneuverable bats experienced a 69% decrease in drinking success and increased competition with smaller, maneuverable bats. Anticipated reductions in the sizes of water sources due to climate change may lead to species with less maneuverability being unable to access water efficiently and facing increased competition from more agile bats.
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Knudsen, Carola. "The impact of the invasive Garden lupine (Lupinus polyphyllus) on plant communities along species rich road verges." Thesis, Karlstads universitet, Avdelningen för biologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-82563.
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The Swedish Transport Administration works continuously with biological diversity. The project, “Species-rich road verges”, begun in 1995. A species-rich road verge is a road verge area that houses objects worthy of protection. It is common for a species-rich road verge to contain meadow species but on the other hand, road verges also function as new habitat for invasive species. Invasive species often tend to show faster growth and higher reproductive potential than non-invasive species and are considered to homogenize ecosystems because many native species often have difficulty competing with them. The invasive Garden lupine (Lupinus polyphyllus) can be particularly problematic at species-rich road verges, where it competes with the native flora. The purpose of the study was to investigate whether the presence of L. polyphyllus in species-rich road verges decreases plant diversity and species richness, if it changes the species composition and if it affects the vegetation height. The study also wanted to investigate if the presence of L. polyphyllus in species-rich road verges presence affects the thickness of the litter, the pH-value in the soil and the ecological indicator values. This study was conducted at 12 species rich road verges in Värmland and Örebro counties in Sweden, where vascular plants in a box of 1 m2 were inventoried along the road verges in pairs, each pair containing a plot where L. polyphyllus was present (“lupine plot”) and a plot where L. polyphyllus was absent (“control plot”). At each species-rich road verge as many pairs as the length of the road verge allowed was inventoried. Vegetation height, litter thickness and pH- value were also measured and ecological indicator values was calculated for each plot. The results suggest that the presence of L. polyphyllus decreases species richness and diversity and changes the species composition in species-rich road verges so that it becomes homogenized. Vegetation height was affected when L. polyphyllus was present, even when the species itself was not taken into the calculation. The results of this study indicate that it is important to come up with effective strategies to control and stop the spread of the invasive L. polyphyllus in species-rich road verges.Trafikverket arbetar kontinuerligt med biologisk mångfald. Projektet Artrika vägkanter började 1995. En artrik vägkant är ett vägkantsområde som hyser skyddsvärda arter. Det är vanligt att en artrik vägkant innehåller ängsarter. Vägkanter fungerar också som en ny livsmiljö för invasiva arter. Invasiva arter tenderar ofta att visa snabbare tillväxt och högre reproduktionspotential än icke-invasiva arter och anses homogenisera ekosystem då de konkurrerar ut många inhemska arter. Den invasiva blomsterlupinen (Lupinus polyphyllus) kan vara särskilt problematisk vid artrika vägkanter där den konkurrerar med den inhemska floran. Syftet med studien var att undersöka om förekomsten av L. polyphyllus i artrika vägkanter minskar växternas artrikedom och diversitet, om artsamman- sättningen förändras, om vegetationshöjden påverkas samt om abiotiska faktorer påverkas. Studien genomfördes vid 12 artrika vägkanter i Värmland och Örebro län i Sverige, där kärlväxter i en ruta på 1 m2 inventerades längs de artrika vägkanterna i par, med en lupinruta kontra en kontrollruta. Vid varje artrik vägkant inventerades så många par som vägkantens längd tillät. Vegetationshöjd, förnans tjocklek och pH-värde mättes också vid varje ruta och ekologiska indikator värden beräknades för varje ruta. Resultaten tyder på att blomsterlupinen minskar artrikedom och mångfald och att artsammansättningen i lupin rutor förändras jämfört med kontroll rutor och blir mer homogen. Vegetationshöjden påverkades av L. polyphyllus och var signifikant högre i lupinrutor jämfört med kontrollrutor även då arten L. polyphyllus inte räknades med i analysen. Resultaten av denna studie indikerar att det är viktigt att arbeta fram effektiva strategier för att kontrollera och stoppa spridningen av den invasiva L. polyphyllus i artrika vägkanter.
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Gruner, Ingrid Gerda. "Comparative Ecology and Conservation of Rare Native Broom, Carmichaelia (Fabaceae), South Island, New Zealand." Thesis, University of Canterbury. School of Forestry, 2003. http://hdl.handle.net/10092/4152.
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Using a comparative approach, the presented study explores the ecology of ten species of native New Zealand broom, Carmichaelia, and their vulnerability to competition and herbivory, with the aim of gaining a better understanding of the significance of introduced species as a threat to rare indigenous plants in New Zealand. In particular, the study focuses on the relationship between characteristics of the Carmichaelia species and their vulnerability, as well as on other factors influencing the significance of introduced species as a threat.
To gain a better understanding of the ecology of the Carmichaelia species, their current habitats and associated plant communities were investigated using quantitative-descriptive methods in the field. The effect of competition with introduced plants was studied in two glasshouse experiments, differentiating above ground competition for light from below ground competition for nutrients and water. The experiments focussed on the early life-stage
of seedling establishment of the Carmichaelia species. The impact of herbivory by introduced mammals was studied in four field-based exclosure trials, focussing on the effects on survival and reproductive activity of adult Carmichaelia plants.
The results showed that the effects of competition and herbivory vary between the different species. Furthermore, they provided a set of species characteristics that can be used as indicators to predict the vulnerability of Carmichaelia to the impact of introduced species. These indicators provide a useful tool for threatened species management, as they allow the identification of the most vulnerable species as well as the most significant threat to each species. Furthermore, the indicators can be used to group species, combining those with similar vulnerability profiles, and therefore, likely similar management needs.
However, the example of the Carmichaelia species also illustrated that the use of indicators for the vulnerability of threatened species is limited and needs to be combined with case-by-case studies to verify the actual significance of threats for each population of concern. The
vulnerability profiles derived from species’ characteristics can be used to guide such site specific
studies, ensuring they focus on the most relevant threat factors. This combination of the understanding of general patterns in the vulnerability of species with targeted species and site-specific studies will lead to increased efficiency in the conservation management of threatened plant species.
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O'Kane, Christopher Anthony John. "Elephant versus other browsers' long-term influences on savanna woodland dynamics : synergistic influences of elephant and other large mammalian herbivores on the structure and composition of woody plant communities in Hluhluwe-iMfolozi Park, South Africa." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:abf97429-a044-4a62-9e29-be45b9d689d6.
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A crucial question in the debate about reintroducing elephant culling is whether the long-term effects of elephants and mesobrowsers on woodlands are similar. Sufficiently high biomass-densities of mesobrowsers may, following reduction or removal of elephants, continue to heavily impact earlier life-history stages of a similar suite of woody plants that elephant impacted, preventing these species from maturing. Thus a similar end-point for woodland structure and composition is achieved. No study exists in the literature where woody plant and habitat utilisation of the savanna browser guild has been determined in the same locality over the same period. A review of 49 years of literature implied that the two groups impact the same core woody-species in the same habitats. Dietary and habitat utilisation of guild members was determined in Hluhluwe-iMfolozi Park, South Africa. A small suite (n = 8) of woody species formed the core diet of all guild members. Herbivores’ densities were determined using a novel GIS approach; all members of the guild showed extensive overlap in habitat use. GPS collars and a GIS were then used to detect zones of different density of impala in the landscape, thus defining, for the first time, a natural fine-grain browsing gradient. Densities of woody seedlings were significantly less (average 48% reduction) in areas of high versus low impala density. A simple browse-browser model, incorporating, in a novel approach, functional groups of plant species, was parameterised from these results and an extensive review of the literature. Outputs suggest that over the long-term (100 years), impala will have a similar impact on woodland structure as elephant. An apparently strong synergistic effect between impala and elephant impact, suggests that reduction or removal of either impala or elephant will radically reduce long-term destruction of woodlands. In smaller or medium sized reserves, where control of mesobrowser populations is practical, profitable and more acceptable than elephant culling, these findings imply a re-direction of management efforts. Management should consider the biomass-density of both groups, rather than just focus on the system’s perceived ‘keystone’ species. Such principles may also apply to temperate and other systems.
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Al, Hayek Patrick. "Roles of environmental plasticity and adaptation of nurse species from the subalpine and oromediterranean zones of the Pyrenees and the Mount-Lebanon for alpine communities structure." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0164/document.
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Les plantes en coussins sont connues pour leur capacité fondatrice de nouvel habitat pour les autres espèces. Par ailleurs, des études ont montré que la variation morphologique au sein d’espèces fondatrices peut induire une variation des effets compétiteurs sur les espèces subordonnées, ce qui peut affecter la composition des communautés. Cette thèse a pour objectif d’étudier les conséquences d’une variation intraspécifique de deux espèces fondatrices (Festuca gautieri et Onobrychis cornuta) occupant des micro-environnements contrastés dans deux systèmes montagneux [les Pyrénées (France) et le Mont-Liban (Liban),respectivement] sur les communautés végétales associées (subalpines etoroméditerranéennes, respectivement). Nous avons évalué par des approches descriptives et/ou expérimentales (jardins expérimentaux, transplantations réciproques) les contributions de la génétique et de la plasticité à la variation morphologique entre deux phénotypes de coussins (dense et lâche) pour chaque espèce fondatrice, et à leurs effets contrastés sur les espèces subordonnées. Nous avons également quantifié les effets rétroactifs de la communauté pour la reproduction des espèces fondatrices. Nos résultats montrent une contribution à la fois de la génétique et de la plasticité à la variation phénotypique. La base génétique des variations morphologiques entre les phénotypes a induit des différences héréditaires d’effets compétiteurs sur les espèces subordonnées, tout en contrecarrant l’augmentation de la compétition avec la diminution du stress – le résultat dominant dans la littérature sur les systèmes subalpins. Nous avons aussi trouvé des effets rétroactifs négatifs des espèces subordonnées pour l’espèce fondatrice, avec une diminution de la production de fleurs (par les coussins) due au nombre croissant d’espèces subordonnées. La diversité des espèces subordonnées était plus élevée dans les conditions environnementales favorables que dans les stressantes. Par conséquent, nous avons conclu que les effets génétiques surmontent les effets environnementaux, limitant la compétition dans les milieux favorables, maintenant ainsi une plus grande diversité dans ces milieux que dans les milieux stressantsAlpine cushion plants are foundation species known for their nursingability. Moreover, studies have shown that morphological variation in foundationspecies can trigger variation in competitive effects on subordinate species, likely toaffect community composition. We investigated the consequences of intraspecificvariation within two alpine cushion species (Festuca gautieri and Onobrychis cornuta)across heterogeneous environments in two mountain ranges [the Pyrenees (France)and Mount-Lebanon (Lebanon), respectively] for the associated plant communities(subalpine and oromediterranean, respectively). We assessed with observationaland/or experimental (common-gardens, reciprocal transplantation experiments)approaches the relative contribution of genetics and plasticity to the morphologicalvariation between two cushion phenotypes (tight and loose) of the foundationspecies, and to their differential effects on subordinate species. Communityfeedbacks were also quantified. Our results show that both genetics and plasticitycontributed to the phenotypic variation. The genetic basis of the morphologicaldifferences between phenotypes induced heritable differences in competitive effectson subordinate species, but however counteracted the general increase incompetition with decreasing stress dominantly found in the literature on subalpinesystems. We also found negative feedbacks of subordinates on foundation speciesfitness, with higher cover of subordinate species reducing the cushions flowerproduction. Subordinate species diversity was higher in benign than in stressedenvironmental conditions. Consequently, we concluded that genetic effects overcomethe environmental effects by limiting competition in benign physical conditions, thusmaintaining a higher diversity in benign than stressed conditions
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Spillards, D. M. "Studies of plant competition." Thesis, University of East Anglia, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.232927.
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Ferreira, Felipe Segala 1981. "Estrutura espacial de um trecho da Floresta Estacional Semidecidua no Municipio de Ipero, Estado de São Paulo." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/314965.
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Orientador: Fernando Roberto MartinsDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia
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Resumo: A distribuição das espécies nos ecossistemas florestais tropicais envolve complexas e múltiplas interações com o ambiente. A heterogeneidade ambiental pode favorecer a coexistência das espécies por criar diferentes oportunidades de nichos. Por meio dos padrões da estrutura da comunidade é possível distinguir entre os prováveis tipos de modelos de montagem da comunidade, o determinístico e o estocástico. Investigamos se em microescala a estrutura de uma comunidade de árvores estaria condicionada ao determinismo da heterogeneidade ambiental. Descrevemos a estrutura da comunidade por meio da riqueza de espécies, do índice de concentração de Simpson, da densidade e da área basal. Representamos a heterogeneidade ambiental pelo índice de convexidade (IC), pela profundidade do solo e pela percentagem de rochas expostas na superfície (rochosidade). Analisamos os dados por meio de correlações espaciais e não espaciais. Utilizamos o teste t modificado por Cliff & Ord para testar a diferença de médias entre conjuntos de dados autocorrelacionados A riqueza de espécies exibiu uma estrutura espacial que se correlacionou negativamente com a estrutura espacial do IC. A densidade não exibiu estrutura espacial, mas correlacionou-se negativamente com o IC. Não houve diferença entre as médias da riqueza de espécies, do índice de concentração de Simpson, da densidade e da área basal entre as subcomunidades côncava e convexa. A densidade média foi significativamente maior na subcomunidade côncava em relação à convexa. A profundidade do solo e a rochosidade não mostraram influência na estrutura da comunidade. Nossos resultados sugerem que a variação microtopográfica associada à sazonalidade do clima pode ter determinado a estrutura da comunidade.
Abstract: Processes of species distribution in tropical ecosystems encompass complex and multiple interactions with the environment. Environmental heterogeneity permits the coexistence of species because it creates different niche opportunities. Through the patterns revealed in the community structure it is possible to distinguish between the most likely types of community assembly, the deterministic or stochastic. We investigated whether the community structure is related to environmental determinism in microscale. We described the community structure through species richness, Simpson's index of concentration, density and basal area; and the environmental heterogeneity through microtopography variation, soil depth and rockiness. We performed spatial and non-spatial correlations and use t-test modified by Cliff & Ord to test for average differences in autocorrelated data sets. Species richness exhibited a spatial structure that correlated negatively with microtopography. Density did not exhibit spatial structure, but was positively correlated with microtopography. There was no difference between species richness of concave and convex subcommunities. Average density was greater in concave than in convex subcommunity. Soil depth and rockiness did not influence community structure. Our results suggest that the microtopography variation associated with the climate seasonality can have determined the structure of the community.
Mestrado
Biologia Vegetal
Mestre em Biologia Vegetal
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Rezki, Samir. "Structuration, dynamique et réponse des communautés microbiennes associées aux graines lors de la transmission d'agents phytopathogènes Assembly of seed-associated microbial communities within and across successive plant generations Differences in stability of seed-associated microbial assemblages in response to invasion by phytopathogenic microorganisms." Thesis, Angers, 2017. http://www.theses.fr/2017ANGE0092.
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La graine constitue le point de départ du cycle d’une plante et abrite une diversité de micro-organismes qui peuvent impacter négativement ou positivement la fitness de la plante. De plus, la graine permet la dispersion et la survie des agents phytopathogènes entre deux cycles de culture de la plante hôte. Dans ce contexte, l’objectif de ce travail était de : (i) décrypter les processus écologiques impliqués dans l’acquisition du microbiote des graines, (ii) analyser sa réponse à l’invasion par des agents phytopathogènes et(iii) suivre sa dynamique durant la germination de la graine et l’émergence de la plantule. Premièrement, nous avons analysé la structure du microbiote de graines de radis(Raphanus sativus) produites dans un même site sur trois générations successives. Ces analyses ont révélé une faible héritabilité du microbiote des graines avec peu de taxons dominants transmis d’une génération à l’autre. Ceci pourrait être expliqué par l’importance des processus neutres dans l’assemblage du microbiote des graines.Ensuite, nous avons étudié la réponse de ce microbiote à une invasion par Xanthomonas campestris pv. campestris(Xcc) et Alternaria brassicicola (Ab), deux agents phytopathogènes transmis par les graines. La transmission de Xcc aux graines n’impacte pas la composition globale du microbiote. En revanche, la transmission d’Ab modifie la structure des communautés fongiques. Ces différences de réponse sont probablement dues aux compétitions pour l’espace et les nutriments entre l’agent phytopathogène et les autres membres du microbiote. Finalement, la composition et la structure du microbiote des graines germées et des plantules ont révélé une transmission de la majorité des taxons associés à la graine y compris Xcc etAb. Globalement, les résultats de ce travail de thèse permettront à terme d’élaborer des stratégies de biocontrôle basées sur la modulation du microbiote des grainesSeed represents the initial step of the plant life cycle and harbors diverse microorganisms that can have detrimental or beneficial impacts on plant fitness. Moreover, seed represents an important means of pathogen dispersion and survival during intercrop periods. For those reasons, the aims of this work were to (i) unveil the ecological processes involved in the acquisition of the seedmicrobiota, (ii) to analyze its response against plant pathogens invasion and (iii) to monitor its dynamics during the first plant developmental stages, namely germination and emergence. First, we assessed the structure of the radish seed microbiota (Raphanus sativus) in the same experimental site across three successive plant generations. These analyses revealed a low heritability of the seed microbiota with few dominant taxa transmitted across generations. Neutral-based processes seem to be important in assembly of the seed microbiota. Second, we monitored the response of the seed microbiota to invasions by Xanthomonas campestris pv. campestris (Xcc) and Alternaria brassicicola (Ab), two seed-transmitted pathogens. While Xcc seed transmission do not change the composition of microbial communities, Ab transmission modified the structure of seed-associated fungal communities. This differences in response could be partly explained by competition for space and nutrients between the pathogenic agents and the members of the seed microbiota. Finally, composition and structure of microbial communities associated to germinating seed and seedling revealed transmission of most seed-borne microorganisms including Xcc and Ab from seed to seedling. Altogether, the results of this thesis could be helpful for designing future biocontrol strategies based on seed microbiota modulation
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Leung, Pui-chi. "Exotic plant invasion of upland plant communities in Hong Kong, China." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B36632442.
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Berglund, Linda. "Disturbance, nutrient availability and plant growth in phenol-rich plant communities /." Umeå : Dept. of Forest Vegetation Ecology, Swedish Univ. of Agricultural Sciences, 2004. http://epsilon.slu.se/s327.pdf.
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Leung, Pui-chi, and 梁佩芝. "Exotic plant invasion of upland plant communities in Hong Kong, China." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B36632442.
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Janse, van Vuuren Adriaan. "Niche occupation in biological species competition /." Link to the online version, 2008. http://hdl.handle.net/10019/753.
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Patrick, L. Brian. "Fertilization and plant litter effects on the plant and epigeal arthropod communities." [Kent, Ohio] : Kent State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1259588844.
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Thesis (Ph.D.)--Kent State University, 2009.Title from PDF t.p. (viewed April 14, 2010). Advisor: Mark W. Kershner. Keywords: biodiversity; nitrogen; fertilization; plant litter; trophic dynamics; epigeal community. Includes bibliographical references.
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Gunathilake, Hadingngnhapola Appuhamilage Jayantha. "The role of roots in plant competition." Thesis, Bangor University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305947.
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Croft, Simon Antony. "Stochastic models of plant growth and competition." Thesis, University of York, 2012. http://etheses.whiterose.ac.uk/4674/.
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Plants have been observed to show a range of plastic responses to environmental conditions. For example, the abundance and distribution of nutrients, as well as the presence and proximity of local competition, have been seen to result in changes in root proliferation and architecture. However, whilst some species have been witnessed displaying certain responses under given circumstances, experimental evidence suggests that responses to environmental factors can be far from simple, and sometimes counter-intuitive. Plant responses to components of the environment, and the benefit of such responses, are highly context sensitive. This thesis explores some of the real world complexities that result in the observed responses to hierarchical sets of environmental factors, and presents a theoretical model that seeks to elucidate the interplay between different factors and their effects on “optimal” behaviour by both individuals and populations. Starting with a simple one-dimensional model comprising a linearised approximation of a Gompertz growth function with nutrient patch dependent growth, the individual and combined effects of stochasticity in resource and competitor distribution are investigated. Complexity and functionality are progressively built up, with a resource dependent proliferation response, a scaling up into two-dimensions, and finally different intrinsic plant growth strategies trading growth rate against root system efficiency all introduced and investigated. Throughout the work presented in this thesis, complex and subtle behavioural responses and patterns emerge from seemingly simple models. The importance of stochasticity on individual and population level performance is also highlighted, and the results demonstrate the inability for mean-field approximations and expected results to capture the emergent behaviour.
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Bush, Catherine Dana. "Native seed mixes for diverse plant communities." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ28920.pdf.
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Siegwarth, Mark. "Zen and the Art of Plant Communities." University of Arizona (Tucson, AZ), 2012. http://hdl.handle.net/10150/556788.
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Cervantes, Peredo Luis Manuel. "Effects of Hemiptera on successional plant communities." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362367.
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Allan, Caroline Elizabeth. "Nitrogen fixation in riverine wetland plant communities." Thesis, University of Glasgow, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297033.
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Sutton, Julian James. "On the dynamics of annual plant communities." Thesis, University of Liverpool, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235530.
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Vonlanthen, Corinne Maria. "Alpine plant communities : ecology and species richness /." [S.l.] : [s.n.], 2005. http://www.zb.unibe.ch/download/eldiss/05vonlanthen_c.pdf.
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Shaw, Rosalind F. "Plant-herbivore interactions in montane willow communities." Thesis, University of Aberdeen, 2006. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU212664.
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This project investigated the impacts of browsing by large herbivores on all aspects of the life cycle of montane willows, using Salix arbuscula L. (Mountain Willow) as the main model species. S. arbuscula was found to be almost entirely insect pollinated, although the levels of wind pollination varied between populations. The density of nearby male plants had a positive effect on fruit set in both insect and wind pollinated catkins, but the effect was stronger in wind-only pollinated catkins. In insect pollinated catkins, catkin characteristics such as length and total number of flowers were most important in determining fruit set. Browsing was found to have both direct and indirect negative impacts on seed production in S. arbuscula, which was also highly variable between years. Direct effects included reduction of the number of inflorescences produced by browsing removal of the previous year's growth, on which most inflorescences are found. There were fewer inflorescences found per shoot on browsed plants, suggesting that browsing also reduces inflorescence production via resource limitation. Lower numbers of inflorescences per plant led to fewer pollinator visits and resulted in reduced seed production, particularly in years of poor overall production. Seed and early seedling survival were found to be strongly limited by microsite availability, as both S. arbuscula and S. lapponum required bare ground for germination and early survival. Slugs were found to have a negative impact on seedlings during the first season of growth, where as small mammals (bank voles) had a negative effect one the seedlings were larger. Growing in disturbed microsites may also favour seedling establishment through reducing the likelihood of slug and small mammal predation.
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Boughton, Elizabeth. "Understanding Plant Community Composition in Agricultural Welands: Context Dependent Effects and Plant Interactions." Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3954.
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Community composition results from an integrated combination of random processes, regional habitat spatial structure, local environmental conditions, and species interactions. For example, the outcome of plant interactions can change depending on local environmental conditions such as nutrient availability, land management, or herbivory intensity. In particular, plant interactions may vary between facilitation and competition depending on ecological context, with facilitation expected to be prevalent under stressful conditions. I present the results of four studies that address different aspects of the community assemblage and dynamics emphasizing the synergistic effect of different processes. In the first, I investigated the importance of habitat isolation in determining species richness of wetlands with contrasting land use. The second describes an experiment to test the hypothesis that plant interactions with an unpalatable plant (Juncus effusus) would range from competition in ungrazed areas to facilitation in grazed areas and predicted that facilitative effects of Juncus would differ among functional groups of beneficiary species and be strongest when grazing was intense. In the third, I examine the community composition impacts of Juncus and predicted that Juncus would preserve functional diversity in grazed wetlands but that the effects of Juncus would vary along a grazing gradient. The fourth study investigated the relative importance of competition and nutrients in determining wetland invasion in two different land use types. Broadly, I demonstrate that the importance of different processes (habitat isolation, nutrient availability, competition/facilitation) to community composition is dependent on ecological conditions. This integrated view of community dynamics is interesting from a purely ecological perspective but also can be applied to understanding ecological problems such as exotic invasions and restoration of disturbed habitats.Ph.D.
Department of Biology
Sciences
Conservation Biology PhD
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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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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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CaraDonna, Paul James, and Paul James CaraDonna. "Temporal Ecology of a Subalpine Ecosystem: Plant Communities, Plant-Pollinator Interactions, and Climate Change." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/620860.
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Ecological systems are inherently dynamic, and a primary way in which they are dynamic is through time. Individual organisms, populations, communities, species interactions, and ecosystem functions all follow a temporal progression from the past, to the present, and into the future. This temporal progression can occur over the course of minutes, hours, days, weeks, months, years, decades, or various other timescales. In this sense, temporal dynamics are an intrinsic property of all biological systems. In fact, one of the most prominent signals of recent global climate change is the significant change in the timing of biological events for a diversity of organisms. In light of this widespread pattern, there is a renewed interest in understanding the multifaceted importance of time in ecology. In this dissertation, I investigate the temporal ecology of a subalpine ecosystem, specifically focusing on flowering plant communities and plant-pollinator interactions. I examine the temporal dynamics of this system over multiple decades in response to ongoing climate change as well as over shorter time scales within a growing season. Using a 39-year record of flowering phenology, I show that species-specific shifts in the timing of flowering in response to climate change can substantially reshape a subalpine plant community over this time period. Community phylogenetic analyses reveal that these changes are largely independent of evolutionary history. Using a laboratory experiment, I show that the timing of an important harsh abiotic event-low temperatures that cause frost damage to plants-can differentially affect flowering plant species, with implications for plant demography, community structure, and interactions with pollinators. Finally, I show that plant-pollinator interactions exhibit substantial within-season temporal turnover, and that this temporal flexibility of plant-pollinator interactions from one week to the next is consistent and predictable across years. Taken together, this dissertation provides a multifaceted investigation of the temporal ecology of plant communities and plant-pollinator interactions, revealing the important consequences of ecological timing at short-term and longer-term scales.
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Prins, Natalie. "The restoration of riparian plant communities following alien plant clearing in the Western Cape." Master's thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/6164.
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Bibliography: leaves 102-118.Few of the riparian zones of the Western Cape Province, South Africa, can still be described as 'natural', as many, if not all, have been impacted upon in one way or another. They are, therefore, frequently disturbed environments that are highly susceptible to invasion by alien plants. the vegetation of riparian zones controls the flow of water, nutrients and sediments into streams. Plan communities in these habitats are often rish in species, and serve as corridor facilitating the movement of organisms.
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Marberg, Mikael. "Climate, grazing and plant interactions : Does climate and grazing shape plant interactions in alpine environments?" Thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-75722.
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Increased knowledge of plant interactions is important for our understanding of how ecosystems will respond to climate changes. Using four common low-herb and three tall- herb species as phytometers I measured the net outcome of plant interactions in an alpine environment by a neighbour removal experiment. Grazing and climate were tested as explanatory factors for differences in the outcome of plant interactions, with two altitudes representing different climates. The most important finding in this experiment is that competition is the dominating interaction among plants in this habitat, regardless of plant size, climate and grazing. Climatic exposure and grazing only influenced tall-herb species while low-herbs were mainly limited by competition, presumably for light. These results are important since facilitative interactions and net facilitation in plant communities are often reported to become more common in severe climates.
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Read, Jonathan M. "The effect of plant traits and resource supply characteristics on plant competition : a mechanistic model." Thesis, University of Stirling, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244695.
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Swedo, Barbara L. "Plant-microbe associations controls on soil bacterial community structure and consequences for aboveground plant communities /." [Bloomington, Ind.] : Indiana University, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3337259.
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Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2008.Title from PDF t.p. (viewed on Jul 28, 2009). Source: Dissertation Abstracts International, Volume: 69-12, Section: B, page: 7260. Adviser: Heather L. Reynolds.
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DeSandoli, Lisa Ann. "Restoration of plant communities to red-burned soils." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44301.
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Fire, natural or anthropogenic, is a common occurrence in the open forests and grasslands of Western North America. The effects of fire on soil and vegetation depend largely on the soil temperatures and the residence time of the burn. Generally, the more severe the fire, the more significant the changes are to soil and vegetation. The relationship between the most severe fires, or where the soil has been oxidized to a red colour, and invasive species is unknown. Resource availability may increase on these soils, leading to favourable conditions for invasive species, or the disturbance may be so severe that nothing is able to grow indefinitely.
I performed two studies to investigate the relationship between invasive species and red-burned soil. To reduce the threat of interface fires near Kamloops, BC, excess timber was harvested, piled and burned on site (pile burning), created multiple burn scars denuded of vegetation and large areas of red soil. In the first study, I investigated soil nutrient flux differences between red-burned and unburned soil using ion-exchange resin technology. I also investigated three restoration methods to control invasive species: the addition of agronomic or native seed, the addition of arbuscular mycorrhizal fungi (AMF) inoculum, and the addition of soil cover. Non-native species cover was high on red soil 2 years post-burn, which may be linked to measured increased nutrients. Only the addition of agronomic seed was successful at suppressing non-native species cover.
The second study compared the growth of native, agronomic and invasive species on unburned and red-burned soil in a greenhouse study. Soil was collected in the field and transferred to a greenhouse. Treatments were soil burning, AMF, and watering. Burning increased aboveground biomass for the native species. AMF addition increased invasive species aboveground biomass for the invasive species, but decreased biomass for agronomic and native species. Watering increased aboveground biomass for the agronomic and invasive species.
The findings here suggest that pile burning creates areas that are susceptible to colonization of non-native species. Restoration efforts should be directed at these sites as soon as possible to ameliorate the effects of invasive species colonization.
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Newton, Erika Lucie. "Plant-herbivore interactions in natural Brassica oleracea communities." Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/72253.
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Co-evolutionary interactions between plants and herbivores are suggested to be the driving force behind the high diversity observed in plant secondary metabolites. These compounds play an important role in herbivore resistance mechanisms in many plant species. An individual plant can produce and store a number of structurally different secondary compounds. Variation in plant chemical profiles is commonly observed within and between natural populations across a wide range of taxa, yet the ecological importance of this variation is still a major question in the area of plant-herbivore interactions. In this thesis I use wild cabbage (Brassica oleracea var. oleracea) plants in twelve naturally established populations to investigate plant-herbivore interactions mediated by structural variation in aliphatic glucosinolates, a class of secondary metabolites produced by the Brassicaceae. Overall, the results showed that several herbivore species respond to the genetically determined variation in glucosinolate profile, indicating that the structure of the local herbivore community can be influenced by variation in plant defence chemistry. In addition, the direction of herbivore responses to different plant chemical phenotypes differed between species. A finer scale study which focused on the interactions between an herbivore and aliphatic glucosinolate variation supported the general trend observed in the large scale study. Glucosinolate profile was also found to have an impact on plant seed set. The findings show that glucosinolate profiles may be under selection in these natural plant populations and provide some support for the role of herbivores in the maintenance of secondary metabolite diversity.
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Johnston, Mark A. "Rabbit grazing and the dynamics of plant communities." Thesis, Imperial College London, 1992. http://hdl.handle.net/10044/1/11781.
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Stonehouse, Amanda L. "The flora and plant communities of Botany Glen." Virtual Press, 2003. http://liblink.bsu.edu/uhtbin/catkey/1266033.
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Botany Glen, The James S. Wilson Memorial Sanctuary, is an 18 hectare (45 acre) forested tract located in Grant County, Indiana, adjacent to the Mississinewa River. Botany Glen is an important natural area in east central Indiana due to its relatively small size and high diversity.The flora documents 331 species and varieties of vascular plants representing 241 genera and 90 families; 158 species are recorded for the first time in Grant County. Of the 331 species listed, 67 (or 20%) are exotic. Most of these exotics have failed to penetrate the interior of the forest.Permanent monitoring plots were established in dry upland forest, floodplain forest and secondary successional forest. Data were collected from overstory, understory and herbaceous plant layers in these plots. Analysis of these data and information from the floristic inventory were utilized to describe the structure and composition of three primary plant communities. Baseline data and procedures were established for future study of this property.Department of Biology
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Jeffs, Christopher. "Natural enemies and the diversity of plant communities." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:49c80db9-6590-4e06-b86f-24d225046969.
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The processes that determine the structure of plant communities are of considerable practical and theoretical interest. Natural enemies such as herbivores, seed predators and pathogens provide one potentially important influence on plant diversity. I investigated the effects of natural enemies on plant diversity in two contrasting, species-rich plant communities (tropical forests in Panama and temperate grasslands in the UK), focusing on pre-dispersal seed predation by insects, and the mortality of seeds and seedlings caused by soil fungi. In Panama I found that pre-dispersal insect seed predators generate significant levels of mortality in multiple tropical tree species, with high heterogeneity in predation rates among individuals and at different forest sites. Insect seed predators were highly host-specific, consistent with a role in enhancing plant diversity. At Upper Seeds, a calcareous grassland site in the UK, I used manipulative experiments to show that soil fungi increase the diversity of plants propagating from soil seed banks. A parallel experiment in Panama, mimicking germination under light gap conditions, revealed differential effects of fungi among sites, with fungicide treatment appearing to increase the diversity of propagated seedlings at some sites but reducing it at others. These results suggest that the influence of soil fungi on pre-emergence mortality can alter plant diversity, even when post-emergence mortality from fungal pathogens is limited. In Panama, I also tested whether enemy-mediated mortality increases with rainfall, potentially contributing to the positive regional correlations widely observed between precipitation and plant diversity. In contrast to predictions, neither pre-dispersal insect seed predation nor the influence of soil fungi on seedling recruitment were affected significantly by site humidity, or (for soil fungi) with experimentally manipulated soil moisture levels. Overall, my results provide evidence that pre-dispersal seed predators and soil fungi can affect plant recruitment and diversity at early life stages, with potential consequences for the community structure of adult plants.
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Gauthier, Marie-Eve. "Restoring peatland plant communities on mineral well pads." Master's thesis, Université Laval, 2014. http://hdl.handle.net/20.500.11794/25320.
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Les tourbières sont largement représentées dans la région boréale de l'Alberta, mais peu est connu sur la restauration de plates-formes de forage localisées en milieux tourbeux. Deux expériences de terrain ont testées la provenance du matériel végétal (bog, écotone bog-peupleraie, fen dominé par saules-Cyperacées, riche fen arbustif, riche fen forestier) à réintroduire sur différents substrats (sciure, loam argileux, mélange sciure-loam, tourbe, microtopographie) sur d’anciennes plates-formes. Nos résultats montrent que les communautés de tourbières peuvent s’établir sur un sol minéral après transfert d’une couche muscinale. Le type de communauté végétale où les propagules sont récoltées est un facteur déterminant au succès des bryophytes à s’établir. Un amendement en tourbe facilite l’établissement des plantes. La technique de transfert de mousse est une approche prometteuse pour la restauration de fens sur plateformes pétrolières. Nous recommandons une mise à l’échelle pour tester la validité de ces méthodes de réintroduction de végétation de manière mécanisée.Peatlands are largely represented in the boreal region of Alberta but little is known about their restoration on well sites. The goal of this study is to compare plant communities and substrates in order to recover peatland vegetation. Two field experiments tested which plant communities (bog, bog-aspen ecotone, willow-sedge fen, shrubby rich fen, treed rich fen) would best regenerate on different substrate (sawdust, clay loam, mix sawdust-clay, peat, surface roughness). We found that peatland communities can establish on mineral soil after propagules transfer using the moss layer transfer technique (MLTT). The choice of plant community, where the propagules are harvested is key to bryophytes establishment. Peat amendment facilitated the plants establishment. The MLTT is a promising approach to restore fen plants on well sites. We recommend a scale-up experiment for a whole well site to test the validity of MLTT within pad removal techniques.
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Hansel, James R. "INFLUENCE OF URBANIZATION ON WOODY RIPARIAN PLANT COMMUNITIES." Miami University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=miami1113852536.
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Lee, Harold Thomas. "The effects of eutrophication on wetland plant communities." Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/6673.
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The first two parts of this study are concerned with a natural field project in which I measured specific plant traits, community state variables, species frequencies, and soil fertility in a large scale comparative study of eight Great Lakes wetlands. I asked the following questions: (1) Are there measurable, quantifiable differences between wetlands--with respect to plant traits, community state variables and fertility, and (2) Are there empirical relationships between plant traits/community state variables and fertility variables. Significant differences between four productive and four unproductive wetlands were found across all the plant traits, except rhizome diameter, all the community state variables and all the fertility variables, except nitrogen. Productive wetlands had lower species richness and were taxonomically distinct from unproductive wetlands. I found that total phosphorus was the most important independent variable and that the most important dependent variables were plant height, standing crop, and species richness. I ran a large outdoor screening experiment bioassaying 40 wetland plants, at two fertility levels, to measure a trait I call 'biomass sensitivity'. I found that all species produced more biomass in the fertile treatment. By comparing species according to the proportional 'biomass sensitivity' (P($\Delta$B)) trait, that is the proportional change in biomass between high and low nutrients, I find there are no differences between species. (Abstract shortened by UMI.)
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Irwin, Judith Ann. "Male competition and outcrossing rate in a hermaphrodite plant." Thesis, University of St Andrews, 1990. http://hdl.handle.net/10023/14400.
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The principal aim of the research presented in this thesis was to investigate factors affecting the "male competition" component of sexual selection in the hermaphroditic species, Senecio vulgaris. As male reproductive function consists of attracting pollinators and the success of pollen in contributing genes to the next generation, sexual selection will act on both the sporophytic and gametophytic stages of the life cycle. The potential for, and consequences of male competition were analysed at both pre- and post-pollination stages. A comparison of the relative attractiveness of the radiate and non-radiate morphs of S.vulgaris to pollinators revealed that in mixed stands, pollinators discriminated in favour of the radiate morph irrespective of the frequency of the two morphs in a population. Measurement of intramorph and intermorph maternal outcrossing rates showed the radiate morph always outcrossed at higher levels than the non-radiate morph. Both morphs exhibited levels of male outcrossing, the radiate morph exhibited higher levels of intramorph paternal outcrossing while non-radiate pollen was more successful than radiate pollen in intermorph crosses. The potential levels of intermorph and intramorph pollen competition experienced by the radiate and non-radiate pollen types suggest radiate pollen was subjected to greater levels of competition for access to ovules than non-radiate pollen. Examination of post-pollination events suggested that radiate pollen germinates faster than non-radiate pollen when applied to stigmas of either morph. However, no consistent evidence of radiate pollen tubes outcompeting non-radiate pollen tubes in the style and consequently fertilising a disproportionate share of available ovules was obtained. The problems associated with measuring pollen competitive ability are discussed. In addition to the research on male competition, a study was also conducted to examine the origin of the radiate morph of S.vulgaris. Morphometric and electrophoretic analyses provided strong evidence that a radiate variant from York possessed more 'squalidus-like' characters than are generally found in radiate S.vulgaris. It is suggested that this radiate form may represent an early stage in the origin of radiate S.vulgaris via introgression of S.squalidus into S.vulgaris.
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Penney, Kathy Coreen. "The effects of ozone air pollution on plant competition." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26025.
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Low levels of ozone air pollution have been shown to cause reductions in plant growth. It has been proposed that these reductions could translate into effects on a plant's competitive ability, and hence, on the inter-relationships of plants in a community.
Experiments were carried out to determine if there was an effect of low levels of ozone on intra- and inter-specific competition of barnyardgrass (BYG), redroot pigweed (RPW) and green foxtail (GFT). Three ozone treatments (a filtered air control, and 75 ppb/7 hr and 150 ppb/3.5 hr daily) were applied to monocultures and binary mixtures in replacement and additive series. The two ozone treatments represent the same ambient dose. The effects of each on the plants studied were compared and contrasted.
The order of competitive ability of the three species was found to be BYG > RPW > GFT. There were significant differences in the interaction of the species between the three ozone treatments. BYG experienced significant intra-specific competition only in the two ozone-added treatments; GFT was significantly affected by its own density only in the control. In contrast, RPW experienced significant intra-specific competition effects in all treatments.
BYG benefitted significantly from the presence of GFT in the control. A similar positive effect of GFT density on BYG yield is seen in the 150 ppb/3.5 hr treatment. It is suggested that this localized positive allelopathic effect may be due to the upward transport of a volatile compound released by GFT, or disseminated through the soil. All inter-specific competitive relations of GFT and RPW were significant in all ozone treatments.
RPW appeared to experience the most ozone effects of the three species studied. RPW and GFT in replacement series mixtures showed over-yielding in the control treatment, equal replacement in the 75 ppb/7 hr treatment and under-yielding in the 150 ppb/3.5 hr treatment. This interaction of ozone and competition treatments between RPW and GFT was significant for root dry weight per pot. BYG yield was significantly enhanced in the 75 ppb/7 hr ozone treatment over the control and 150 ppb/3.5 hr treatments. This may reflect an acclimation of BYG plants to the low (0.01-0.04 ppm) ambient background levels of ozone. The concept of an appropriate control treatment is discussed.
Although the 75 ppb/7 hr and 150 ppb/3.5 hr treatments represent the same ambient dose, the species used in this study reacted quite differently to the two treatments. Overall, the more acute 150 ppb/3.5 hr dose had a more detrimental effect on the yield variables measured for RPW and GFT, and the 75 ppb/7 hr treatment had a significant enhancing effect on BYG yield over that of the control and the 150 ppb/3.5 hr dose.
An examination of the size frequency distributions of the three species confirms that BYG is competitively dominant, whereas the GFT size distributions do not appear to be sensitive to competitive suppression. RPW displays a very skewed size frequency distribution under all treatments. It is suggested that RPW has inherent genetic variability for a wide size distribution in the populations studied. There were no ozone effects on the size frequency distributions of any species studied.Land and Food Systems, Faculty of
Graduate
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Edwards, Grant R. "The creation and maintenance of spatial heterogeneity in plant communities : the role of plant-animal interactions." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239335.
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O'Connor, Rory Charles. "Small Mammals Matter? Linking Plant Invasion, Biotic Resistance, and Climate Change in Post-Fire Plant Communities." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/5756.
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The introduction and establishment of exotic species can profoundly alter ecosystems. Two exotic species drastically changing the landscape of deserts in western North America are Bromus tectorum L. and Bromus rubens L. Through the buildup of biomass and slow decomposition rates in deserts these two exotic annual grasses can alter fire regimes that change the plant and animal community dynamics in the ecosystems. To better understand the ecological mechanisms that could restrict or alter the patterns of invasive plant establishment we established a replicated full factorial experiment in the Great Basin and Mojave Desert. The combinations of factors being manipulated are burned or intact plant communities, and presence or exclusion of small mammals. Generally invasive species establishment is thought to be a result of competitive superiority or lack of natural enemies, but if that is the case then why do not all invasive species establish and become highly abundant in their new ecosystems? To understand why some invasive species establish and others do not we monitored three dominant exotic species from the Great Basin and the Mojave Desert, B. tectorum, Halogeton glomeratus (M. Bieb.) C.A. Mey., and B. rubens. We observed that the presence of small mammals create a biotic resistance to B. tectorum, H. glomeratus, and B. rubens. This pattern was observed in both intact and burned plant communities; however, it was most prevalent in the burned plant communities. The strength of the biotic resistance on these invasive species varied between species and the years sampled. In deserts both plant and small mammal communities are tightly tied to precipitation. We wanted to understand how invasive species establishment is affected by small mammal presence after a fire disturbance, and manipulating total precipitation. Total precipitation was manipulated through three different treatments: 1) drought or 30% reduction of ambient precipitation; 2) ambient precipitation; 3) water addition or an increase of 30% ambient precipitation. We focused on B. rubens establishment in the Mojave Desert as our model organism by monitoring it beneath rain manipulation shelters nested in burned/intact and small mammal presence/absence full factorial plots. What we observed was that again small mammals created a biotic resistance on the density of B. rubens regardless of the burn or precipitation treatments. This biotic resistance also translated into decreasing B. rubens biomass and seed density. Under the drought and ambient precipitation treatments we found that small mammals kept the density and biomass equal but under increased precipitation the efficacy of biotic resistance on B. rubens density and biomass was lessened by the availability of the added water.
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Rayburn, Andrew P. "Causes and Consequences of Plant Spatial Patterns in Natural and Experimental Great Basin (USA) Plant Communities." DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/1123.
Full textAbstract:
The processes by which plant spatial patterns are formed, and the effects of those patterns on plant community dynamics, remain important areas of research in plant ecology. Plant spatial pattern formation has been linked to many ecological processes that act to structure plant communities at different spatiotemporal scales. Past studies of pattern formation are common, but recent methodological advances in data collection and analysis have permitted researchers to conduct more advanced observational studies of pattern formation in space and time. While studies of the effects of plant spatial patterns were formally rare, they have increased in the last decade as new types of experiments and analysis have been developed to better understand the myriad effects of plant patterns on community dynamics. My dissertation research examined both the causes and consequences of plant spatial patterns in the context of natural and experimental Great Basin semi-arid plant communities. In both cases, I implemented novel methodologies for data collection, experimental design, and data analysis in an attempt to address current gaps in knowledge related to the processes by which plant spatial patterns are formed, as well as the effect of plant spatial patterns on community dynamics. The results inform both basic and applied plant ecology, and set the stage for further research on the causes and consequences of plant spatial patterns in semi-arid plant communities.