Dissertations / Theses on the topic 'Facilitation and competition'
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Carlo, Joglar Tomas Ariel. "Competition and facilitation in bird-dispersed plants." Diss., Connect to online resource, 2005. http://wwwlib.umi.com/dissertations/fullcit/3178338.
Full textLucenti, Krista. "Essays on international trade: antidumping, competition, and trade facilitation." Berlin dissertation.de, 2006. http://d-nb.info/990430650/04.
Full textLucenti, Krista. "Essays on international trade : antidumping, competition and trade facilitation /." Berlin : Dissertation.de, 2008. http://www.dissertation.de/buch.php3?buch=5632.
Full textHöpfner, Ingo [Verfasser]. "Competition and facilitation among grassland plants - the role of arbuscular mycorrhiza / Ingo Höpfner." Bielefeld : Universitätsbibliothek Bielefeld, 2015. http://d-nb.info/1071651420/34.
Full textSouza, Luanne Caires da Cruz. "Facilitation and competition in coastal dunes: meta-analysis of determinants of plant interactions." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/41/41134/tde-22102018-145200/.
Full textPlantas estabelecidas nas proximidades de outras plantas podem ter sua performance afetada positiva ou negativamente por seus vizinhos, caracterizando, respectivamente, interações de facilitação e competição. Considerando que ambas as interações podem ocorrer de forma simultânea, compreender o predomínio de cada uma delas em diferentes contextos ecológicos é fundamental para o entendimento da estrutura de comunidades vegetais. De acordo com a hipótese do gradiente de estresse (HGE), a facilitação tende a predominar em ambientes mais severos, mas o balanço das interações depende ainda das características dos indivíduos envolvidos, como forma de vida e estágio ontogenético. Como condições ambientais severas e alta diversidade de formas de vida vegetais são características de planícies costeiras, o número de estudos investigando interações entre plantas tem aumentado rapidamente nesses ambientes, com conclusões aparentemente divergentes. No entanto, ainda não há uma síntese sistemática e quantitativa dos fatores que afetam o balanço entre facilitação e competição nesses ecossistemas. Nós realizamos uma meta-análise em escala global para investigar os efeitos do estresse ambiental e a influência simultânea da forma de vida e do estágio ontogenético das plantas sobre o balanço entre facilitação e competição em planícies costeiras. Utilizamos quatro variáveis de performance para estimar o balanço de interações: abundância, sobrevivência, crescimento e reprodução. Ao contrário do predito pela HGE, encontramos que impactos negativos de plantas vizinhas sobre a reprodução de outras plantas aumentam com a aridez do ambiente, mas que esse efeito não é observado para outras variáveis de performance. Nossos resultados também mostram que vizinhos lenhosos facilitam a sobrevivência de plântulas lenhosas e a reprodução de plantas herbáceas, enquanto vizinhos herbáceos facilitam o crescimento de outras herbáceas. De modo geral, o balanço das interações depende da variável de performance medida e tanto de condições ambientais quanto de características das plantas, indicando que esses fatores interagem. Tal interação e os diferentes mecanismos subjacentes à facilitação e à competição devem ser melhor investigados no futuro. A maior sobrevivência de plântulas lenhosas na presença de vizinhos lenhosos corrobora a ideia de retroalimentação positiva no processo sucessional que caracteriza o gradiente fisionômico da praia ao interior. Nossos resultados também reforçam o potencial do uso de plantas-berçários como ferramenta para restauração de planícies costeiras degradadas
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.
Full textReed, Lewis. "COMPETATIVE EVQUIVALENCY OF CULTIVAR AND NON-CULTIVAR DOMINANT GRASSES IN AN EXPERIMENTAL RESTORATION." OpenSIUC, 2010. https://opensiuc.lib.siu.edu/theses/166.
Full textWong, Carmen Monica. "Understanding disturbance, facilitation, and competition for conservation of whitebark pine in the Canadian Rockies." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42568.
Full textNascimento, Francisco J. A. "Trophic ecology of meiofauna response to sedimentation of phytoplankton blooms in the Baltic Sea /." Doctoral thesis, Stockholm : Department of Systems Ecology, Stockholm University, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-38809.
Full textAt the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: In press.
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.
Full textPh.D.
Department of Biology
Sciences
Conservation Biology PhD
Hyder, Jennifer A. "An Investigation of the Effects of Increased Tidal Inundation, Competition, and Facilitation on Salt Marsh Systems." Thesis, University of South Florida, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3700275.
Full textThe low-lying topographic nature of salt marshes makes plants in these communities particularly vulnerable to increased salinity and inundation exposure associated with sea level rise. Both increased salinity and inundation have been cited as major causes of reduced plant performance and survival in marsh and areas fringing marsh. In addition to limitations imposed by physical stress, interspecific interactions have also been shown to mediate the performance and survival of salt marsh and salt marsh fringing species. The Stress Gradient Hypothesis (SGH) postulates that species interactions shift from competitive to facilitative as stress levels increase and predicts that (a) the frequency and intensity of facilitative interactions increase as conditions become more stressful for plants and (b) the strength of competitive interactions increases as abiotic stress levels diminish. The SGH has been rigorously tested to examine how both the frequency and intensity of species interactions change under varying physical stress levels. Studies conducted in salt marsh systems have shown facilitation to be as strong of a driving force as competition in influencing plant performance and survival and have shown that while competition appears to be the pervasive force in the less physically stressful terrestrial zones fringing salt marshes, facilitation influences the performance and survival of species in harsher marsh areas. Under conditions of sea level rise, it remains unclear if the nature of interspecific interactions would shift as stress levels change. This research endeavors to examine the interplay between abiotic stresses and biotic interactions under conditions of increased salinity and inundation exposure.
The first study presented here investigated the effects of increased inundation and soil salinity associated with sea level rise on four salt marsh fringing species, and assesses how competition and facilitation impact survival of salt marsh fringing plant survival under these changing conditions. All plant species experienced reduced growth and photosynthetic inhibition below their current distributional positions, both in the presence and absence of neighboring above ground vegetation. The findings also signal a potential shift in the nature of interspecific interactions from competition to facilitation to neutral as plants begin to experience increased salt and inundation exposure.
The second study aimed to disentangle the effects of increased soil salinity and increased soil moisture on four salt marsh fringing species, and to examine the effects of plant neighbors. The results showed that fringe plants exposed to increased inundation experienced a two-fold reduction in performance and survival over 750 g pure salt addition, suggesting that inundation may be a more important limiting factor than salinity with rising sea levels. Landward transplants at the forest-fringe margin exposed to lower soil salinity and decreased inundation exhibited a three-fold increase in performance and survival when compared to controls. Neighbor manipulation studies, which consisted of trimming neighboring vegetation to ground level, again suggested that interspecific interactions in salt marsh fringing species may shift from competitive to facilitative with climate-induced sea level rise. Overall, our findings suggest that salt marsh fringing species may not be able to tolerate changing conditions associated with sea level rise and their survival may hinge on their ability to migrate towards higher elevations.
The final experiment tested the Stress Gradient Hypothesis and investigated the relative importance of facilitation and competition in a salt marsh system under varying stress levels. This study also ascertained whether salt or inundation exposure is the primary influence on salt marsh plant performance and survival. As in previous studies, our findings suggest that many salt marsh plants don't require, but merely tolerate harsher abiotic conditions. The results showed that plants at higher elevations were depressed by strong competitive pressure from neighboring fringe species while plants at lower elevations benefited from the presence of neighbors. Collectively, the results of these studies indicate that species interactions are an integral driver of plant distribution in salt marsh communities. Furthermore, our findings indicate that changing stress levels may not always result in a shift in the nature of interspecific interactions. These studies have endeavored to show that the interplay between competition and facilitation interacts with physical processes to determine the growth and performance of both fringe and marsh plant species. The paucity of studies examining the roles of species interactions and changing abiotic stress levels on multiple salt marsh and salt marsh fringing species warrants the need for additional research. The responses of salt marsh and salt marsh fringing species to sea level rise can not only serve as very valuable and sensitive indictors of climate change, but will also aid in predicting the future location of the marsh-fringe-forest ecotone, which is predicted to shift inland as sea levels continue to rise.
Hensel, Lisa E. "The Ecology and Evolution of Pollinator-mediated Interactions Among Spring Flowering Plants." Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/20186.
Full textBänsch, Svenja [Verfasser]. "Managing strawberry pollination with wild bees and honey bees: Facilitation or competition by mass-flowering resources? / Svenja Bänsch." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/1222738252/34.
Full textNilsson, Karin. "Effects of size-dependent predation and competition on population and community dynamics." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-35686.
Full textVenn, Susanna Elizabeth, and Susanna Venn@nt gov au. "Plant recruitment across alpine summits in south-eastern Australia." La Trobe University. School of Life Sciences, 2007. http://www.lib.latrobe.edu.au./thesis/public/adt-LTU20080526.160815.
Full textBao, Zhe. "Biotic Interaction of Invasive, Early-Succession Trees and Their Effects on Community Diversity: a Multi-Scale Study Using the Exotic Invasive Ailanthus altissima and the Native Robinia pseudoacacia in the Mid-Appalachian Forest of Eastern United States." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/73303.
Full textPh. D.
Sinclair, Michael N. "Facilitative and competitive tradeoffs between Morella cerifera seedlings and coastal grasses." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/5872.
Full textBalde, Alpha Bocar. "Analyse intégrée du partage des ressources (eau, azote et rayonnement) et des performances dans les systèmes de culture en relais sous semis direct en zone tropicale sub-humide." Thesis, Montpellier, SupAgro, 2011. http://www.theses.fr/2011NSAM0008/document.
Full textThis thesis dealt with characterizing and modeling the dynamics of the three principal resources which are water, nitrogen and radiation in a no-tillage relay intercropping maize-cover crop systems, under sub-humid tropical area climate. Moreover, productivity of the main crop and of the whole system and nitrogen and water flows in the soil are assessed.The study was based on an on-field approach/experimental design carried out during two crop growing seasons in Cerrados region, in Unaí (Minas Géras, Brazil) since 2007. Firstly, an experimental station was used allowing an intense effort of measurement and secondly, a whole of several farmer's fields offering a wide range of soil and climate conditions and modalities of implementation of the studied cropping systems. In the latter, main crop was maize, and intercropped cover crop was a tropical fodder crop, either leguminous, Cajanus cajan or gramineous, Brachiaria ruziziensis. Two dates of sowing, early and late were considered for the sowing of the cover crop in established maize, in the case of the experimental station. This study showed that maize yield was not significantly affected by the presence of the relay cover crops in comparison with maize as the sole crop, even when the cover crop was sown soon after maize emergence in comparison with maize sole crop. In contrast, the production of biomass by the cover crop was significantly lower when grown with maize than when it was grown as a sole crop. In the intercropped systems, when sown early, the cover crop produced higher total biomass than when sown late (20 days after maize flowering). Moreover, total aboveground biomass production of maize intercropped with a cover crop was much higher than that of any of the crops sown alone. Total biomass produced by maize and pigeon pea (Cajanus cajan) was more than double that maize grown alone. The Land Equivalent Ratio (LER) values of both maize grain yield and biomass production were higher than one, whatever the intercrop system, reaching up to 2.03 providing better available resources use efficiency by the intercropped plants. Thus, such systems permit to produce both maize grains and forage.The thesis shows also the strong variability of the production potential of these systems in farmer's fields and suggests that when water and nitrogen resources are less available than in the experimental station, competitions between maize and cover crops can reduce the agronomic performances of maize and/or the cover crop when compared to the equivalent pure sole crop. Total biomass produced by intercropping remained however higher than that of maize sole crop, except for rare exceptions where lower resources availability, sometimes accentuated by difficulties of technical practice, maize seems to suffer from stronger competition and/or the cover crop produced only very little biomass. The thesis evaluates the capacity of the STICS intercrop model, STICS-CA, to provide a finer analysis of the dynamics of the resource sharing in these systems and to estimate their agronomic performances and certain environmental impacts according to technical practices and soil and climate conditions that were different from those of our experimental station. Minor modifications and model calibration led to obtain satisfying simulations of the sole crops maize and Brachiaria and intercrop maize-Brachiaria in no-tillage under mulch. On the other hand, it was not possible to obtain satisfying simulations of sole crop maize in conventional tillage, nor of sole crop pigeon pea and intercrop maize-pigeon pea in no-tillage under mulch. The thesis provides information on the model imperfections and as well proposes improvements in terms of formalisms to take into account the mineralization of the mulch, as in terms of experimental design
Mazzochini, Guilherme Gerhardt. "Plant diversity influencing structure and functioning of Caatinga vegetation." Universidade Federal do Rio Grande do Norte, 2014. http://repositorio.ufrn.br/handle/123456789/20583.
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O estudo dos efeitos que a diversidade de esp?cies pode causar nos processos ecossist?micos tem crescido vertiginosamente nas ?ltimas duas d?cadas. Diversos trabalhos experimentais realizados no mundo todo t?m demonstrado que uma maior diversidade de plantas contribui para o aumento da produtividade de ecossistemas terrestres. Al?m disso, esse efeito pode influenciar processos em diversos n?veis tr?ficos, contribuindo assim para a estabilidade dos processos ecossist?micos a longo prazo. Paralelamente com os estudos do efeito da diversidade, muita aten??o tem sido dada para desvendar o papel das caracter?sticas funcionais das esp?cies no funcionamento dos ecossistemas. Isto porque as caracter?sticas funcionais das esp?cies t?m se mostrado importantes "pe?as" no entendimento dos efeitos que esp?cies individuais podem exercer nos ecossistemas e suas respostas ao ambiente. Nesta tese de doutorado eu explorei algumas lacunas de conhecimento dentro dessa ?rea em crescente desenvolvimento conhecida na literatura ecol?gica como "biodiversidade e funcionamento dos ecossistemas". No primeiro cap?tulo, eu busquei evid?ncias para mecanismos que podem explicar a rela??o positiva entre diversidade e funcionamento com foco em cinco mecanismos relacionados ?s intera??es entre plantas, tendo como par?metro de funcionamento a produtividade prim?ria. No segundo cap?tulo, eu utilizei t?cnicas para a estimativa de padr?es de diversidade em escalas biogeogr?ficas e bases de dados de sat?lites com longa dura??o para desvendar se a biodiversidade em escalas macroecol?gicas promove a estabilidade da produtividade dos ambientes terrestres no semi?rido brasileiro. Por fim, o objetivo do terceiro cap?tulo foi entender como a perda da cobertura vegetal origin?ria do uso da terra por comunidades tradicionais no semi?rido brasileiro influenciaria os processos de intera??es entre plantas e o papel das caracter?sticas funcionais das esp?cies nessas intera??es. Acredito que a contribui??o individual de cada cap?tulo preenche lacunas de conhecimento importantes dessa ?rea da Ecologia que ainda se encontra em expans?o.
Lett, Signe. "Mosses as mediators of climate change : implications for tree seedling establishment in the tundra." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-130942.
Full textBordron, Bruno. "Dinâmica de crescimento e funcionamento nutricional das raízes finas de Eucalyptus em função da fertilização e da associação com espécie fixadora de nitrogênio." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/11/11150/tde-20032018-175143/.
Full textThe main objective of this thesis was to better understand the functioning of Eucalyptus fine roots (diameter < 2 mm). More specifically, our work aimed at getting insights into the changes in fines roots nutrient uptake changes depending on soil depth and fertilization. Root growth dynamics was also evaluated in mixed plantations with a nitrogen fixing species to test the stress gradient hypothesis. The first chapter aimed at studying the effect of fertilization on the functional specialization of young Eucalyptus fine roots in deep soil layers (Itatinga-SP). We injected NO3-15N, Rb+ (K+) and Sr2+ (Ca2+) tracers simultaneously in a solution at 10, 50, 150 and 300 cm in depth. Determination of foliar Rb+, Sr2+ concentrations and 15N atom % made it possible to estimate the relative uptake potential (RUP), and the Specific RUP, defined as SRUP, per unit of fine root length density in the corresponding soil layer. The RUPs of NO3-15N decreased sharply with depth and the highest values of the SRUPs of NO3-15N were found at a depth of 50 cm. The SRUP of Rb+ and Sr2+ were higher at 300 cm in depth than in the topsoil with an increase in root diameter and a decrease in root tissue density with depth. The SRUP of Rb+ and Sr2+ at a depth of 300 cm was on average 88% higher for fertilized trees than for unfertilized trees. The results suggest that functional specialization of fine roots for nutrient uptake is a stable characteristic of Eucalyptus that can be enhanced by fertilization application. Chapter 2 focused on the ecological processes between Acacia mangium and Eucalyptus under a gradient of nutrient stress. Fine roots were sampled at 16 and 34 months after planting in a randomized block design with two treatments: a mixture with 50% of each species (50A:50E), with and without fertilization. For each treatment, soil samples were collected in 3 blocks at 0-15; 15-30; 30-50 and 50-100 cm at various distances of Eucalyptus and Acacia trees. During this period, two tubes of minirhizotron near eucalypt and Acacia trees in each treatment and block were used to monitoring fine roots growth and turnover. At 16 and 34 months after planting, fine root mass density (RMD) of Eucalyptus was 30% higher than of Acacia and higher in F+ than in F- in the top soil layer (0-15 cm). This result likely showed higher competition of eucalypt roots on Acacia roots in F+ than in F-. In the superficial layer, RMD of Eucalyptus in F- were higher at 34 months near Acacia trees than Eucalyptus trees, that would be consistent with greater N facilitation of Acacia on Eucalyptus in higher N-deficient environment (stress gradient hypothesis). The same N concentration in Eucalyptus leaves in both F+ and F- was also consistent with this hypothesis. Production of Eucalyptus fine roots between the two sampling dates was higher in F- than in F+ in parallel to the increase of RMD of Eucalyptus near Acacia trees. It was not possible to estimate root life span as no root mortality occurred during the study period for both species. Furthers studies should be conducted to better understand the mechanisms of tree nutrient uptake promoting a better sustainable management of forest plantations.
Brown, Joseph K. "Emergent interactions influence functional traits and success of dune building ecosystem engineers." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4111.
Full textFernandez, Marine. "Mécanismes écophysiologiques impliqués dans les interactions antagonistes entre le jeune chêne sessile (quercus petraea (Matt.) Liebl.) et la molinie bleue (Molinia caerulea (Moench) L.) : rôles des transferts d'azote, des mycorhizes et des rhizodépôts allélochimiques." Thesis, Université Clermont Auvergne (2017-2020), 2019. http://www.theses.fr/2019CLFAC053.
Full textA better understanding of plant interactions would improve the management of natural and artificial forest regeneration. It is well established that Molinia (Molinia caerulea), a monopolist species of understory, has a particularly depressive effect on young sessile oak (Quercus petraea) establishment and growth. Large capacity of Molinia in water and soil nutrients uptake leads to strong competition by resources exploitation. However, it seems that other interactions are involved in the relationship between young oak and Molinia. Thus, the allelopathic properties of Molinia have been suggested, but no study has shown such an effect on oak. Inversely, young oak seems to facilitate Molinia growth. Oak-Molinia interaction thus has the singularity of being antagonistic: the Molinia inhibits oak growth while this one favors grass growth, but the mechanisms involved are not entirely known. The aim of this thesis was to analyze the functional and ecophysiological mechanisms involved in the interactions between young sessile oak and Molinia. The experiments carried out in the thesis show that (i) oak quickly transfers nitrogen to Molinia by the underground pathways (rhizodeposition of nitrogen compounds in the soil) favoring grass growth, (ii) Molinia presence in the same pot leads to a decrease in the lateral root rate and ectomycorhization rate of oak and (iii) Molinia rhizodeposes secondary metabolites different from those of oak and have an allelopathic potential. In line with current work, the thesis puts into perspective that the chemical compounds emitted by plants in the soil act as real direct or indirect signals (via the biological communities of the soil) and induce neighbors modifications in their metabolism and / or their growth
Kinyo, Anthony Steven. "EFFECTS OF DISTANCE FROM INVASIVE LYTHRUM SALICARIA ON POLLINATOR VISITATION RATE AND REPRODUCTIVE SUCCESS IN NATIVE LYTHRUM ALATUM." University of Akron / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=akron1127925607.
Full textMaalouf, Jean-Paul. "Effets interactifs d’une sècheresse liée au changement climatique et de la gestion sur les pelouses calcaires du sud de l’Europe." Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14503/document.
Full textThis PhD aimed at testing the crossed effects of management and extreme droughts linked to climate change on plant biotic interactions, biodiversity, composition and ecosystem functions of extensive grasslands from Southern Europe, at the Western calcareous boundary of the French Central Massif. Extreme spring droughts and a mowing-based management were experimentally applied in a factorial design in the Dordogne department on two communities with contrasted soil conditions: the Mesobromion (null slope) and the Xerobromion (steep convex slope and southern exposure). Our results support theoretical models predicting a collapse of biotic interactions at the severe end of a stress gradient, especially if the system is subject to disturbance. Grassland responses were strongly dependent on local environmental conditions. Drought decreased biodiversity and altered composition in the Xerobromion community. This is explained by the combination of several constraints (experimental drought, water stress due to southern exposition and physical disturbance which induces a collapse of facilitation and an important edaphic stress) in this community. The Mesobromion community was rather affected by mowing, which increased biodiversity through a reduction of competitive graminoids cover. In Southern Europe, and in a climate change context, we recommend maintaining disturbance-based management in the Mesobromion communities and focusing on the conservation of species with a poor tolerance to drought in the Xerobromion communities
Pajunen, A. (Anu). "Willow-characterised shrub vegetation in tundra and its relation to abiotic, biotic and anthropogenic factors." Doctoral thesis, University of Oulu, 2010. http://urn.fi/urn:isbn:9789514261138.
Full textVoigtlaender, Maureen. "Produção de biomassa aérea e ciclagem de nitrogênio em consórcio de genótipos de Eucalyptus com Acacia mangium." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/11/11150/tde-04012013-105941/.
Full textEucalyptus plantations cover 20 million hectares on highly weathered soils. Eucalyptus plantations intercropped with Acacia have the potential to improve the productivity of the stand, in relation to their mono-specific plantations, through the facilitatory effect of N fixation by acacia trees. The objective was to evaluate the effect of the consortium of genotypes of Eucalyptus with Acacia mangium on the production of biomass of each species and N cycling. Four experiments were established in areas managed with eucalypts for several rotations in a randomized block design with three treatments: mono-specific acacia plantation (100A), eucalyptus (100E) and mixed plantation at 1:1 (50A:50E). The experimental areas located in different ecological conditions in the southeastern region of Brazil, in the states of São Paulo and Minas Gerais. Tree growth was measured throughout the rotation of cultivation and allometric equations of biomass and mineral mass of N have been set for each area at the end of the rotation to the compartments of the trees. Litterfall and N mineralization in situ were assessed for two years, at the end of the rotation. Concentrations of C and N in the soil were evaluated at the end of the rotation and estimated by the NIRS method (near infrared reflectance spectrometry) and calculated stocks in the soil. The symbiotic N2 fixation was estimated by the difference of the total stock of N among treatments. The wood biomass production was higher in 100E than in 50A:50E, due to lower acacia growth compared to eucalyptus climatic conditions studied. The litterfall dry mass was higher in 100E, but the average return of N from litterfall to the soil was 1.7 times higher in 100A than in 100E. The stocks of C and N in the soil were similar in the different treatments. The total stocks of C and N, with more eucalypts growth, located in Santana do Paraíso, were 30% and 50% higher relative, by less growth, located in Itatinga. The mineralization of N in the soil in 100A was twice that at 100E, and intermediate in 50A:50E, resulting from faster turnover of N in the forest floor under acacia trees. Annual N flux from litterfall at the end of the rotation was a good indicator of soil N availability in fast-growing tropical plantations. In this context, in terms of forest management, results suggest that one rotation of mono-specific N-fixing tree species (NFT) after a certain number of of eucalypt rotations could help to maintain plantation soil fertility, with a management compatible with forest company practices. Other large scale management option for management is the introduction of NFT undergrowth by commercial eucalypts. However, the success of these mixed-species plantations is largely dependt on the selected species.
Farrell, Claire. "Leaf-litter and microsite on seedling recruitment in an alley-planted E. sargentii and Atriplex spp. saline agricultural system." University of Western Australia. School of Plant Biology, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0110.
Full textPalomeque, Pesántez Fanny Ximena [Verfasser], Michael [Akademischer Betreuer] Weber, and Thomas F. [Akademischer Betreuer] Knoke. "Natural succession and tree plantation as alternatives for restoring abandoned lands in the Andes of Southern Ecuador: Aspects of facilitation and competition / Fanny Ximena Palomeque Pesantez. Gutachter: Thomas F. Knoke ; Michael Weber. Betreuer: Michael Weber." München : Universitätsbibliothek der TU München, 2012. http://d-nb.info/1031515194/34.
Full textVernay, Antoine. "De la complexité fonctionnelle et écophysiologique des ressources lumières, azote et eau dans le réseau précoce d'interactions entre le jeune chêne (Quercus petraea) et deux Poacées (D. cespitosa et M. caerulea) : conséquences pour la régénération des chênaies tempérées." Thesis, Université Clermont Auvergne (2017-2020), 2017. http://www.theses.fr/2017CLFAC081/document.
Full textTemperate forest ecosystems are prone to regeneration failures because of strong competition between understorey species and tree seedlings. This thesis aimed to improve our understanding of sessile oak seedlings (Quercus petraea) and poacea responses, both in competition among different levels of resource availabilities. Two poacea species were studied, Molinia caerulea and Deschampisa cespitosa. We focused on the role of the different resource combinations (light, water and inorganic nitrogen) on interaction variation (intensity and importance) between those species and underlying ecophysiological mechanisms. Our greenhouse and field experiments allowed us to infer a very early competition, from the first months of interaction between oak seedlings and poacea neighbours. High light level leads to stronger competition from poacea on oak seedlings, increased by nitrogen supply. Secondly nature and extent of these interactions depend on applied abiotic stress level and on considered organs. Thirdly Oak seedlings mainly respond by accumulating resources in coarse roots. These resources are remobilized next year and may have a positive carry-over effect on oak functioning if there is no water stress. Eventually we observed facilitation as well, from oak on D. cespitosa in fertilized environment. Nitrogen supply would foster oak seedling growth, increasing exudate production and root turn-over, to the benefit of D . cespitosa. The poacea would take up this extra nitrogen source for its own development. This study support the idea of including interaction effects of different abiotic factors in competition models. Silvicultural practices would also be enhanced by optimizing species coexistence in temperate forests as soon as tree seedlings and understorey species start to grow together
Forrester, David Ian, and davidif@unimelb edu au. "Mixed-species plantations of nitrogen-fixing and non-nitrogen-fixing trees." The Australian National University. Faculty of Science, 2005. http://thesis.anu.edu.au./public/adt-ANU20050202.164252.
Full textEskelinen, A. (Anu). "Plant community dynamics in tundra: propagule availability, biotic and environmental control." Doctoral thesis, University of Oulu, 2009. http://urn.fi/urn:isbn:9789514293139.
Full textPranchai, Aor. "Spatial patterns and processes in a regenerating mangrove forest." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-171569.
Full textAl, 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.
Full textAlpine 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
Monnier, Yogan. "Stratégies d'acclimatation à l'ombre et rôle des interactions plantes-plantes dans la dynamique pin-chêne en milieu méditerranéen." Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10045.
Full textDuring this work we studied the Mediterranean forest dynamic through a functional approach. Our main goal consisted to know how functional responses to light availability and biotic interactions determine the regeneration of three main species involved in this dynamic : Pinus halepensis, Quercus ilex and Quercus pubescens.A nursery experiment was set up to determine specific shade acclimatation strategies of the Aleppo pine and the Downy oak, functional tradeoffs and nutritional and ontogenetic limits of these stratgies, and the competitive and allélopathic impact on the shade induced response.Then a field experiment was set up to make a light gradient in an Aleppo pins pinewood in order to know the main positive and negative canopy effects on abiotic factors and oak seedlings development at different scales of time. Results showed that Aleppo pine exhibits a shade avoiding strategy through a strong plastic response involving functional tradeoffs, high nutritional costs, and time-limited expression. This strategy is considered as maladaptive in case of regeneration under unovercome forest canopy. Reversly, the downy oak shows a more conservative strategy through a limited plastic response to shade but a strong vulnerability to plant-plant interactions. In field conditions, Quercus pubescens and Quercus ilex seedlings showed different responses to the canopy cover, with a fewer shade tolerance in Quercus pubescens. This work help to highlight relationships between functional limits of phenotypic plasticity, shade tolerance, and regenerative success in Aleppo pine understory
McKinney, Amy Marie. "Pollinator-mediated interactions between the invasive shrub Lonicera maackii and native herbs: The roles of shade, flowering phenology, spatial scale, and floral density." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1276309342.
Full textHanton, Sheldon M. "An examination of debilitative and facilitative competitive anxiety." Thesis, Loughborough University, 1996. https://dspace.lboro.ac.uk/2134/7221.
Full textMorais, Joicy Martins. "Experimentos de remoção de plantas: abordagem cienciométrica e estudo de caso." Universidade Federal de Goiás, 2013. http://repositorio.bc.ufg.br/tede/handle/tede/3520.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
The relationships between organisms and the mechanisms that enable their coexistence are important issues in ecology. Plant removal experiments are useful to elucidate these mechanisms because its cause and effect response. This thesis aims to analyze experiments removal plants. The first paper presents a scientometric review of the literature on plant functional groups removal 1991. We verify aspects such as the number of publications and citations in journals indexed in the Web of Science, which country was made in order to detect bias and geographic gaps, which ecological effects were tested, which functional groups were removed, which removal methods and which environments were made. We found an increase in the number of publications and citations on average during this period, however, was 12 times lower than publications on functional diversity, perhaps due to the difficulty of conducting experiments. The work was mainly carried out in temperate climates where taxonomic knowledge is greater, in addition, there is a prevalence of vegetation that is most commonly removed than trees. Testing interactions, especially competition, was the main reason for removal, perhaps as a matter of historical competition is considered the interaction that influences the co-occurrence of species. The cut at ground was the major method of removing, undisturbing the soil and avoiding undesirable effects of herbicides, and few studies have been made in a greenhouse and in the natural environment at the same time, which could elucidate responses to natural conditions and at the same time responses specific interactions. In the second paper we carried a case study on removal of capim-flecha ( Tristachya leiostachya Ness.), a dominant grass in Emas National Park (ENP), and what the consequences of such removal to the co-occurring grasses. We expected that the absence of capim-flecha allow further growth of grasses, however we found no difference in mean values between treatments indicating that there is no competition influencing the abundance of capim-flecha. The historical context burned in PNE may have influenced this high dominance of capim-flecha. We believe that experiments are useful in testing interactions, especially if they are made in the natural environment and greenhouse at the same time.
As relações entre os organismos e os mecanismos que permitem sua coexistência são importantes questões em ecologia. Experimentos de remoção de plantas são úteis em elucidar esses mecanismos, devido sua capacidade de resposta do tipo causa e efeito. Esta dissertação se propõe a analisar experimentos de remoção de plantas. O primeiro artigo apresenta uma revisão cienciométrica das publicações sobre remoção de grupos funcionais de plantas, desde 1991. Verificamos aspectos como o número de publicações e citações em periódicos indexados no Web of Science, em qual país foi feito, visando detectar vieses e lacunas geográficas, quais efeitos ecológicos testados, quais grupos funcionais removidos, quais os métodos de remoção e em quais ambientes foram feitos. Encontramos um crescimento no número de publicações bem como na média de citações nesse período, contudo foi 12 vezes menor do que publicações sobre diversidade funcional, talvez devido à dificuldade de realizar experimentos. Os trabalhos foram realizados principalmente em climas temperados onde o conhecimento taxonômico é maior, além disso, há um predomínio de vegetação rasteira que é mais comumente removida do que árvores. Testar interações, principalmente competição, foi o principal motivo de remoção, talvez por uma questão histórica de competição ser considerada a interação que mais influencia a co-ocorrência de espécies. O corte rente ao solo foi o principal método de remoção, evitando revolver o solo e efeitos indesejáveis de herbicidas, e poucos trabalhos foram feitos em casa de vegetação e ambiente natural ao mesmo tempo, o que poderia elucidar respostas à condições naturais e ao mesmo tempo respostas específicas de interações. No segundo capítulo fizemos um estudo de caso sobre remoção de capim-flecha (Tristachya leiostachya Ness.), uma gramínea dominante no Parque Nacional das Emas (PNE), e quais as consequências dessa remoção para as gramíneas co-ocorrentes. Esperávamos que a ausência do capim-flecha permitiria um maior crescimento das gramíneas, contudo não encontramos diferença nos valores das médias entre os tratamentos o que indica que não há competição influenciando a abundância do capim-flecha. O contexto histórico queimadas no PNE pode ter influenciado essa alta dominância do capim-flecha. Consideramos que experimentos são úteis em testar interações, sobretudo se forem feitos em ambiente natural e casa de vegetação ao mesmo tempo.
Barbier, Nicolas Serge. "Interactions spatiales et auto-organisation des végétations semi-arides." Doctoral thesis, Universite Libre de Bruxelles, 2006. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210779.
Full textNos recherches ont été menées au sud-ouest de la République du Niger, à l’intérieur et dans les environs du parc Régional du W. Trois axes ont été explorés :(i) Une étude de la dépendance spatiale entre la structure de la végétation (biovolumes cartographiés) et les paramètres du milieu abiotique (relief, sol), sur base d’analyses spectrales et cross-spectrales par transformée de Fourier (1D et 2D). (ii) Une étude diachronique (1956, 1975 et 1996) à large échelle (3000 km²) de l’influence de l’aridité et des pressions d’origine anthropique sur l’auto-organisation des végétations périodiques, basée sur la caractérisation de la structure spatiale des paysages sur photos aériennes via la transformée de Fourier en 2D. (iii) Trois études portant sur les interactions spatiales entre individus :En premier lieu, via l’excavation des systèmes racinaires (air pulsé) ;Ensuite, par un suivi spatio-temporel du bilan hydrique du sol (blocs de gypse) ;Enfin, via le marquage de la ressource par du deutérium.
Nous avons ainsi pu établir que les végétations périodiques constituent bien un mode d’auto-organisation pouvant survenir sur substrat homogène et modulé par les contraintes climatiques et anthropiques. Un ajustement rapide entre l’organisation des végétations périodiques et le climat a pu être montrée en zone protégée. La superficie et l’organisation des végétations périodiques y ont tour à tour progressé et régressé en fonction d’épisodes secs ou humides. Par contre, en dehors de l’aire protégée, la possibilité d’une restauration du couvert semble fortement liée au taux d’exploitation des ressources végétales. Ces résultats ont d’importantes implications quant à la compréhension des interactions entre climat et écosystèmes et à l’évaluation de leurs capacités de charge. La caractérisation de la structure spatiale des végétations arides, notamment par la transformée de Fourier d’images HR, devrait être généralisée comme outil de monitoring de l’état de ces écosystèmes. Nos études portant sur les modes d’interactions spatiales ont permis de confirmer l’existence d’une facilitation à courte portée du couvert végétal sur la ressource. Cependant, cette facilitation ne semble pas s’exercer sur le terme du bilan hydrique traditionnellement avancé, à savoir l’infiltration, mais plutôt sur le taux d’évaporation (deux fois moindre à l’ombre des canopées). Ce mécanisme exclut l’existence de transferts diffusifs souterrains entre sols nu et fourrés. Des transferts inverses semblent d’ailleurs montrés par le marquage isotopique. L’étude du bilan hydrique et la cartographie du micro-relief, ainsi que la profondeur fortement réduite de la zone d’exploitation racinaire, jettent de sérieux doutes quant au rôle communément admis des transferts d’eau par ruissellement/diffusion de surface en tant que processus clé dans la compétition à distance entre les plantes. L’alternative réside dans l’existence d’une compétition racinaire de portée supérieure aux canopées. Cette hypothèse trouve une confirmation tant par les rhizosphères excavées, superficielles et étendues, que dans le marquage isotopique, montrant des contaminations d’arbustes situés à plus de 15 m de la zone d’apport. De même, l’étude du bilan hydrique met en évidence les influences simultanées et contradictoires (facilitation/compétition) des ligneux sur l’évapotranspiration.
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This PhD thesis gathers results of a research dealing with the causes of the spatial organisation of periodic vegetations. These landscape structures, featuring regular spotted, labyrinthine or banded patterns of decametric to hectometric scale, and extending over considerable areas on at least three continents, constitute a perfect study case to approach endogenous processes leading to vegetation heterogeneities. These patterns occur over homogeneous substratum, except for vegetation’s own feedbacks, and are marked by sharp ecotones and the persistence of a considerable amount of bare soil. A number of models suggested a possible case of self-organized patterning, in which the general structure would emerge from local interactions between individuals. Those models rest on the interplay of competitive and facilitative effects, relating to soil water consumption and to soil water budget enhancement by vegetation. A general necessary condition for pattern formation to occur is that negative interactions (competition) have a larger range than positive interactions (facilitation). Moreover, all models agree with the idea that patterning occurs when vegetation growth decreases, for instance as a result of reduced water availability, domestic grazing or wood cutting, therefore viewing patterns as a self-organised response to environmental constraints. However the modus operandi of the spatial interactions between individual plants remains largely to be specified.
We carried out a field research in South-West Niger, within and around the W Regional Park. Three research lines were explored: (i) The study of the spatial dependency between the vegetation pattern (mapped biovolumes) and the factors of the abiotic environment (soil, relief), on the basis of spectral and cross-spectral analyses with Fourier transform (1D and 2D). (ii) A broad scale diachronic study (1956, 1975, 1996) of the influence of aridity and human induced pressures on the vegetation self-patterning, based on the characterisation of patterns on high resolution remote sensing data via 2D Fourier transform. (iii) Three different approaches of the spatial interactions between individuals: via root systems excavation with pulsed air; via the monitoring in space and time of the soil water budget (gypsum blocks method); and via water resource labelling with deuterated water.
We could establish that periodic vegetations are indeed the result of a self-organisation process, occurring in homogeneous substratum conditions and modulated by climate and human constraints. A rapid adjustment between vegetation patterning and climate could be observed in protected zones. The area and patterning of the periodic vegetations successively progressed and regressed, following drier or wetter climate conditions. On the other hand, outside protected areas, the restoration ability of vegetation appeared to depend on the degree of vegetation resource exploitation. These results have important implications regarding the study of vegetation-climate interactions and the evaluation of ecosystems’ carrying capacities. Spatial pattern characterisation in arid vegetations using Fourier transform of HR remote sensing data should be generalised for the monitoring of those ecosystems. Our studies dealing with spatial interaction mechanisms confirmed the existence of a short range facilitation of the cover on water resource. However, this facilitation does not seem to act through the commonly accepted infiltration component, but rather on the evaporative rate (twice less within thickets). This mechanism excludes underground diffusive transfers between bare ground and vegetation. Inverse transfers were even shown by deuterium labelling. Water budget study and micro-elevation mapping, along with consistent soil shallowness, together cast serious doubts on the traditional mechanism of run-off/diffusion of surface water as a key process of the long range competition between plants. An alternative explanation lies in long range root competition. This hypothesis find support as well in the excavated root systems, shallow and wide, as in isotopic labelling, showing contaminations of shrubs located up to 15 m of the irrigated area. Water budget study also evidenced simultaneous contradictory effects (facilitation/competition) of shrubs on evapotranspiration.
Doctorat en sciences agronomiques et ingénierie biologique
info:eu-repo/semantics/nonPublished
Tur, Espinosa Cristina. "Plant-pollinator networks: incorporating individual variation and functional information." Doctoral thesis, Universitat de les Illes Balears, 2015. http://hdl.handle.net/10803/365035.
Full textLas redes complejas sirven a los ec ologos para estudiar las interacciones de polinizaci on a nivel comunitario. Actualmente, para incrementar su utilidad pr actica, es necesario construir redes que sean representaciones lo m as realistas posibles del proceso de polinizaci on. Por este motivo, esta tesis se centra en incorporar a las redes la variaci on interindividual y informaci on sobre la magnitud y el signo (positivo, neutro o negativo) de los efectos de las interacciones sobre la reproducci on de las plantas. Las especies constan de poblaciones de individuos con fenotipos, genotipos y comportamientos distintos, que por tanto pueden diferir en sus interacciones. Esta variaci on intraespec ca es relevante para muchos procesos ecol ogicos y evolutivos, pero no se ha considerado en la mayor a de estudios de redes plantapolinizador. En los cap tulos 1 y 2 se estudian las cargas pol nicas de ejemplares de insectos polinizadores en dos comunidades de monta~na en Mallorca y se construyen redes donde los nodos de los polinizadores representan individuos en lugar de especies. Esto permite incorporar la variaci on interindividual y aportar una nueva perspectiva sobre la estructura de las redes y los mecanismos que determinan las interacciones. Las redes de transporte de polen a nivel de individuo tienen una densidad de interacciones, conectancia, anidamiento y diversidad de interacciones m as baja que las mismas redes a nivel de especies, pero una modularidad mayor. Estas diferencias ocurren porque las especies de polinizadores generalistas est an formadas por individuos especialistas y heterog eneos en la utilizaci on de recursos. El grado de especializaci on individual est a asociado a la intensidad de competencia inter- e intraespec ca. Para que las redes planta-polinizador sean m as representativas de las implicaciones funcionales deben incluir medidas de los efectos de las interacciones sobre las especies o de la magnitud real en que las especies dependen de estas interacciones. La frecuencia de interacci on se considera una estimaci on v alida del efecto del polinizador sobre el exito reproductivo de la planta, aunque no aporta informaci on sobre su signo. Por ejemplo, en plantas con mecanismos de producci on de semillas independientes de los insectos (e.g. autogamia, anemogamia), las interacciones pueden tener efectos neutros sobre la reproducci on. En el cap tulo 3, para diferentes plantas de dos comunidades de estudio (costa y monta~na) se cuanti ca el grado de dependencia de polinizadores comparando experimentalmente la producci on de semillas con y sin insectos. El objetivo es determinar si las especies m as dependientes de polinizadores son tambi en las m as conectadas en las redes, con mayor centralidad, n umero y diversidad de interacciones. S olo en una de las comunidades de estudio se encuentra esta relaci on, sugiriendo que es variable en funci on del contexto comunitario. Por otro lado, hay interacciones que pueden causar efectos m as negativos que positivos sobre el exito reproductivo de las plantas. Esto puede pasar cuando los polinizadores depositan polen conespec co y heterospec co en los estigmas. La transferencia interespec ca de polen es relativamente com un, porque a menudo las especies de oraci on simult anea comparten polinizadores, y puede tener efectos perjudiciales para las plantas (e.g. p erdida de polen, obstrucci on de estigmas). En el cap tulo 4, se estudian las transferencias de polen interespec cas en tres comunidades andinas a lo largo de un gradiente altitudinal. Se construyen redes dirigidas que representan la transferencia de polen desde las especies donantes a las receptoras y a cada interacci on se le asocia un signo mostrando el efecto. Este signo se obtiene de la relaci on entre el polen conespec co y heteroespec co depositado sobre los estigmas. En todas las comunidades estudiadas, predominan las interacciones positivas y neutras, particularmente en la comunidad de mayor altitud. Esto sugiere que la facilitaci on en una comunidad puede aumentar cuando las condiciones para la polinizaci on se vuelven menos favorables.
Ecologists use network analysis to study pollination interactions at a communitywide level. The construction of plant-pollinator networks which are realistic representations of the pollination process is fundamental to increase their usefulness and ecological meaning. For that reason, this thesis focuses on incorporating to such networks individual variation and information about the magnitude and sign (positive, neutral or negative) of interaction e ects on plant reproduction. Species consist of populations of phenotypically, genetically and behaviourally diverse individuals which thus di er in their interactions and foraging decisions. Despite its relevance for many ecological and evolutionary processes, intraspeci c variation has been overlooked in most plant-pollinator network studies. In chapters 1 and 2, pollen loads of insect pollinator individuals are studied in two mountain communities of Mallorca, and networks where pollinator nodes depict individuals instead of species are built. Such approach (network downscaling) permits to account for the variation within species and provides new insights on network interaction patterns and their causal mechanisms. Pollen-transport networks at the individual level had lower linkage density, connectance, nestedness and interaction diversity, than the same networks at the species level, but higher modularity. These di erences occur because generalist pollinator species are composed of heterogeneous specialist individuals in the use of resources. The degree of individual specialization is associated with inter- and intraspeci c competition. Plant-pollinator networks which represent more accurately functional implications should include measures of interaction e ects on species or estimates of the actual degree to which species depend on such interactions. In general, interaction frequency is considered a good surrogate of the magnitude of interaction e ects, although it does not give any information about the e ect sign. For instance, in plant species with mechanisms for producing seeds independently of pollinators (e.g. autogamy, anemogamy), interactions may have a neutral reproductive e ect. In chapter 3, the degree of reproductive dependence on pollinators is quanti ed for several plant species in two study communities (coast and mountain), comparing seed set with and without insects. The objective is to determine whether plant species which depend more on pollinators are also more connected in ower-visitation networks, i.e. have high centrality, number and diversity of interactions. Such relationship is only found in one of the two study communities, which suggests that it is community-context dependent. On the other hand, there are interactions which may cause more negative than positive e ects on plant reproductive success. This may happen when owervisitors deposit both conspeci c and heterospeci c pollen on stigmas. Such interspeci c pollen transfer is common because co- owering plants often share pollinators, and can have detrimental e ects on plant tness (e.g. pollen loss and stigma clogging). In chapter 4, interspeci c pollen transfers are studied in three high-Andean communities along a mountain altitudinal gradient. Directed networks depicting pollen transfers from donor to receptor species are constructed, and a sign is associated to each network link to represent the e ect. This sign is obtained from the study of the relationship between conspeci c and heterospeci c pollen deposited on stigmas. In all study communities, facilitative and neutral pollinator-mediated interactions among plants prevail over competition, particularly in the highest elevation community. This nding suggests that pollination facilitation in communities can increase under less favourable conditions for the pollination service, supporting previous predictions of higher incidence of facilitative interactions in stressful environments.
Reberte, Cláudia Maria Chamorro. "Aspectos do princípio da facilitação da defesa do consumidor em juízo em lides individuais." Pontifícia Universidade Católica de São Paulo, 2009. https://tede2.pucsp.br/handle/handle/8518.
Full textThis study aims to examine some of the main respects the principle of facilitation of consumer protection in court, provided for by article 6, section VIII, the code of consumer protection, within the individual deal. Will address issues pertaining to competition, shifting the burden of proof, the authority of states obligations to do and not do, and the special civil courts, and how these institutions and instruments to give effect to act principle in question. The analysis takes place from the beginning governing the protective system to the consumer in the CDC, taking account of the imbalance inherent in the relationship of consumption, which stems from the situation of vulnerability of the consumer, and the difficulties for him found with regard to access to justice and their situation in judge
O presente trabalho tem por finalidade analisar alguns dos principais aspectos do princípio da facilitação da defesa do consumidor em juízo, previsto pelo art. 6º, inciso VIII, do Código de Defesa do Consumidor, no âmbito das lides individuais. Serão abordadas questões atinentes à competência, à inversão do ônus da prova, à tutela específica das obrigações de fazer e de não fazer, e aos Juizados Especiais Cíveis, e como estes institutos e instrumentos atuam para conferir efetividade ao princípio em questão. A análise desenvolve-se a partir dos princípios que regem o sistema protetivo ao consumidor, contido no CDC, levando-se em conta o desequilíbrio inerente às relações de consumo, que decorre da situação de vulnerabilidade do consumidor, e as dificuldades por ele encontradas no que respeita ao acesso à Justiça e à sua atuação em juízo
Coiffait-Gombault, Clémentine. "Règles d’assemblages et restauration écologique des communautés végétales herbacées méditerranéennes : le cas de la Plaine de La Crau (Bouches-du-Rhône, France)." Thesis, Avignon, 2011. http://www.theses.fr/2011AVIG0322/document.
Full textMediterranean herbaceous ecosystems which are characterized by a high biodiversity have been submitted to a lot of changes in use. Their conservation is not sufficient enough and ecological restoration seems to be an adapted solution to improve conservation efforts as it can mitigate damages induced by human activities. To develop restoration methods adapted to these ecosystems, preliminary researches on the different communities composing an ecosystem and the filters which are responsible for community assemblage before and after disturbance are necessary. Representative of numerous Mediterranean steppe ecosystems, the “Coussouls de Crau” and their ex-arable-fields (Bouches-du-Rhône, France) are the biological models used to identify and study the principal filters potentially responsible for organizing the plant communities. Sheep grazing, trophic changes, competition and reproduction and /or species dispersal, were identified in a first study on steppe regeneration; these filters were then the core of the following three research experiments. We carried out two in-situ restoration protocols (hay transfer and sowing foundation species) and one ex-situ experiment testing interactions between a selection of steppe species. The main results show that reproduction, seed dispersal, soil trophic level, competition, extensive sheep grazing are filters which have a determinant role in structuring the communities, in determining plant composition and partly in explaining the slow dynamics towards the reference steppe. Also, we show that filters interact between them. For applied restoration, the tested methods promote steppe vegetation come back, but in the short term (two or three years after restoration), the composition of restored areas remains different to the reference ecosystem. Even if we understand better the different factors which explain community organization, these results demonstrate that it is difficult to restore it integrally because it is not easy to manipulate and find an equilibrium between the different filters actions. Now it is necessary to continue these fundamental and applied researches, in particular on the maturation and structure of the old herbaceous plant communities
Grau, Fernàndez Oriol. "Interaccions planta-planta en gradients d'estrès en ecosistemes freds / Plant-plant interactions along stress gradients in cold ecosystems." Doctoral thesis, Universitat de Barcelona, 2013. http://hdl.handle.net/10803/101146.
Full textIn this thesis I present four chapters, and in all of them I discuss how dwarf shrubs interact with co‐occurring plants under varying regimes of stress. This research involved ecosystems of great environmental, nature conservation and ecological value, yet highly sensitive to environmental changes, in four contrasting cold regions at high altitude or high latitude. Following a latitudinal order, the selected ecosystems were: 1) a temperate alpine treeline in the Central Pyrenees; 2) a primary succession gradient in a boreal ecosystem in Finland; 3) a subarctic alpine treeline in Lapland; and 4) a high‐arctic tundra in north‐eastern Greenland. The first two chapters are based on an experimental approach and focus on how shrubs commonly found near the treeline interact with tree seedlings of treelineforming species in two contrasting environments, i.e. in a subarctic forest‐tundra ecotone in Lapland, northern Sweden, and in a more southern, temperate forestalpine pasture ecotone in the Central Pyrenees. In addition, since trees living near their limit of distribution are very sensitive to environmental changes, especially to increased temperature during the growing season (Körner 2003), we also assessed how distinct environmental change scenarios may affect tree seedling growth and survival across the ecotone. The first chapter is entitled ‘Shrub‐tree interactions and environmental changes drive treeline dynamics in the Subarctic’, where we explain the three‐year‐long experiment performed in the Abisko National Park, in the subarctic Scandes, Northern Sweden; the species studied were Betula pubescens tree seedlings and the shrub Vaccinium myrtillus. In this study we showed the importance of facilitative and competitive shrub‐tree interactions as drivers of subarctic treeline dynamics. Furthermore, we demonstrated that the great sensitivity of tree seedlings to warming had strong implications for treeline dynamics under the predicted warmer scenario at high latitudes, and we identified that complex interactions between shrubs and herbivores are critical to predicting future changes. The second chapter is entitled ‘Similar tree seedling responses to shrubs and to simulated environmental changes at Pyrenean and subarctic treelines’. Here we presented a comparison between the results obtained in the experiment presented in the first chapter and those obtained in a parallel experiment performed during a similar period near the treeline in the Alt Pirineu Natural Park, in the Central Pyrenees, Catalonia. This experiment was based on the same factorial design but with different species (i.e. Pinus uncinata tree seedlings and the shrub Rhododendron ferrugineum). To our knowledge, it is the first study which experimentally tests the responses of plants to distinct environmental scenarios in a high mountain ecosystem in the Pyrenees. In this chapter we presented some mechanisms for understanding the recently observed variability of local responses of both subarctic and alpine treelines to currently changing climate while identifying some commonalities that can be used to generalise large scale response of treelines to climate warming. The third chapter focuses on the effects of a dominant dwarf shrub (i.e. Empetrum nigrum) on Pinus sylvestris tree seedlings along a primary succession within a boreal ecosystem on an uplifting island in Bothnian Bay, Finland. This chapter is called ‘An ericoid shrub plays a dual role in recruiting both pines and their fungal symbionts along primary succession gradients’. Here we showed that facilitative and competitive effects of shrubs markedly determined tree seedling establishment and their fungal colonisation along this succession gradient, but in this chapter we did not relate these findings to any environmental changes. As far as we know, we presented the first finding that an ericoid mycorrhizal shrub may enhance both the performance of the ectomycorrhizal host tree and the tree’s fungal symbionts. The study presented in the fourth chapter was performed along a snow‐depth gradient in an extreme arctic tundra ecosystem in the Northeast Greenland National Park, the largest national park in the world. The chapter is entitled ‘Plant interactions and higharctic vegetation composition along a snow‐depth gradient in NE Greenland’. This ecosystem is probably the most sensitive and fragile among the ecosystems studied in this thesis as the eastern coast of Greenland is expected to experience substantial changes in climate due to marked changes in snow precipitation and temperature regimes (Brown and Mote 2009). Here we assessed plant species richness, establishment and composition patterns in distinct growth forms occurring in common arctic plant communities associated with varying snow‐depth during the winter season. This study will help to predict potential diversity and vegetation changes in the high Arctic if snow precipitation regime changes in the future as anticipated.
Silva, Carina Camargo. "Impacto ecológico e silvicultural do uso e colheita de eucalipto consorciado com espécies arbóreas nativas para a restauração da Mata Atlântica\"." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/11/11150/tde-01032018-171947/.
Full textThe reduction of forest cover and the intensive agricultural use of the soil result in the necessity of adopting expensive restoration interventions, which restrict the expansion of this activity and the mitigation of the impacts of human activities on biodiversity and ecosystem services. Thus, the exploitation of wood in restoration forests may be an alternative for the economic viability of this activity. Particularly noteworthy are the opportunities offered by the exploitation of short rotation exotic tree species, which anticipate the profit obtained from restoration and may contribute to the amortization of implantation costs. However, even though the intercropping with exotic trees is authorized by the current environmental legislation as a method for forest restoration, little is known concerning the possible negative effects of the use of these species in restoration models. This research aimed to evaluate the ecological and silvicultural impacts of the use and harvest of Eucalyptus temporarily mixed with native tree species in the restoration of the Atlantic Forest. We evaluated three experiments in the states of Bahia and Espírito Santo, which used Eucalyptus as a commercial pioneer species to generate income after the first rotation (around 4-5 years) and then removed from the system. Eucalyptus had no negative influence over native species\' survival and growth when compared to pure native species plantations, as well as over natural regeneration of native species in the understory. We also evaluated the impacts of harvesting Eucalyptus in two of these three experiments and found that the Eucalyptus harvesting operation causes significant damage to planted native trees and results in opening of the forest canopy (considering that Eucalyptus represents 50% of the individuals planted and 90% of the basal area), but these damages were partially minimized within only 14 months after harvesting. Thus, we conclude that for the environmental conditions evaluated, the mixture with Eucalyptus in this alternative forest restoration approach did not affect the development of native tree species neither the expression of natural regeneration, which makes its use valuable. Further studies are necessary, however, to follow the succession trajectories of forest restoration models in the medium and long runs, to validate the recommendation of their use with more consolidated scientific basis.
Mayer, Kaylea. "The facilitative effects of the acquisition of one linguistic structure on a second pedagogical implications of the competition model /." Connect to Electronic Thesis (ProQuest) Connect to Electronic Thesis (CONTENTdm), 2008. http://worldcat.org/oclc/436714825/viewonline.
Full textSteenkamp, Andre Eric. "Trade development - the impact of trade preferences in facilitating competitive Industrial development : an Agoa Case Study." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13222.
Full textThe central question and motivation behind this paper is to determine whether trade preference agreements facilitate permanent economic development, or if they merely temporarily increase the volume of exports over the period of preferential market access. The paper will evaluate this, by using the case study of the African Growth and Opportunity Act (AGOA) enacted by the United States (US) in 2000. The literature and empirical data show that exports do increase in certain cases under trade preference agreements, however what is missing to a large extent is the impact that these increased exports have on facilitating competitive industrial development through learning-by-doing spill over effects. The objective of this paper is to identity evidence which supports the notion that trade preferences have the potential to advance competitive industrial development, by specifically looking at the impact that AGOA has had on eligible Sub-Saharan African (SSA) countries exports to third countries since its enactment in 2000 as the indicator of trade induced permanent economic development. This is one indicator of many, such as labour productivity, manufacturing output, foreign direct investment, and GDP per capita which could also be used as indicators of development. The remainder of this paper is organised as follows. In the second section, a review of the theoretical and empirical literature with respect to trade preferences and specifically AGOA preferences is discussed. Section three presents an empirical analysis, firstly in terms of a graphical analysis which is then followed by an econometric analysis. The aim of the empirical analysis is to firstly understand the aggregate story of apparel exports under AGOA preferences, and secondly to test the relationship that trade preferences facilitate economic development through enhanced trade. The fourth section concludes the paper by emphasising the key findings, issues and policy recommendations of the paper.
Lin, Yue. "The role of different modes of interactions among neighbouring plants in driving population dynamics." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-105119.
Full textDiouf, Abdoulaye. "Influence du régime des feux d'aménagement sur la structure ligneuse des savanes nord-soudaniennes dans le Parc du W, Sud Ouest Niger." Doctoral thesis, Universite Libre de Bruxelles, 2012. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209610.
Full texténigmes de l'écologie des plantes. Les origines du difficile équilibre entre ces formes de vie
sur des dizaines de millions de kilomètres carrés à l'échelle mondiale sont en partie attribuées
aux perturbations fréquentes induites par les feux de végétation dont les effets varient dans
l'espace et dans le temps selon les conditions environnementales. Les résultats de recherche
dépendent de l’échelle et les conclusions tirées d’études locales sont rarement transposables à
d’autres échelles. La question du transfert d'échelle s’avère donc cruciale dans l'étude des
effets du feu, et nécessite une approche transdisciplinaire.
En raison de la variété des échelles couvertes, cette étude constitue une première dans la
confrontation de données sur l’historique des feux dérivé de l'imagerie satellitaire à des
données de terrain incluant des mesures détaillées sur la structure et la composition de
végétation, ainsi que des propriétés édaphiques et topographiques. Elle s’est focalisée sur la
composante ligneuse de par son caractère pérenne et son influence sur les processus
écologiques majeurs. Sur une zone de plus de 2000 km², le Parc National du W du Niger
(PNWN), où le feu est utilisé comme outil pour la gestion et la conservation des écosystèmes
semi-arides, une carte de l'historique des feux a été élaborée à partir d'images MODIS de 250
m de résolution spatiale et de résolution temporelle journalière couvrant une période de sept
années (2002-2009). Pour comprendre la variabilité, à la fois dans l'espace et le temps, de la
propagation du feu dans la végétation, nous avons étudié les caractéristiques de distribution
des feux en termes de régime du feu (i.e. période d'occurrence et fréquence) et de structure
spatiale (métriques paysagères). Les relations causales plausibles entre les régimes du feu, les
conditions édaphiques et topographiques à l'échelle régionale comme locale, et les
caractéristiques de la végétation ligneuse (composition et structure) ont été examinées à
travers des analyses multivariées et des modèles d'équations structurales. Nous avons aussi
examiné plus en détails les stratégies adaptatives mises en oeuvre par les ligneux, et les
interactions biologiques qui sous-tendent l'organisation spatiale des ligneux à travers une
approche des processus ponctuels.
Les résultats montrent que l'activité du feu dans le PNWN se caractérise par une hétérogénéité
spatio-temporelle induite principalement par les conditions édapho-topographiques via la
structure de la végétation ligneuse. Les feux précoces de gestion créent des pare-feux
efficaces, limitant une large extension des feux de saison tardifs. Cependant, ces feux tardifs
pourraient ne pas être aussi destructifs comme qu’on le suppose généralement. En effet,
l'adaptation des espèces aux différents régimes defeu correspond à des stratégies de croissance
contrastées. Dans le cas des feux tardifs, les surfaces terrières et hauteurs moyennes les plus
fortes sont rencontrées, permettant aux arbres de résister au feu. Quant aux zones non
affectées par les feux l'analyse "patron-processus" désigne clairement la facilitation entre
ligneux comme un processus fondamental de l'organisation spatiale périodique du couvert, une
structure émergente qui empêche le passage du feu. Bien qu’ils ne se substituent pas aux
études expérimentales, ces résultats basés sur une expérimentation naturelle à large échelle
apportent des informations nouvelles précieuses tant au niveau fondamental que pour la mise
en place d'une gestion raisonnée du PNWN.
The tree-grass equilibrium in tropical savanna is recognized as one of plant ecology's main
conundrums. The origins of the difficult balance between these life forms over tens of millions
of square kilometers worldwide are in part attributed to the frequent disturbances caused by
vegetation fires effects of which vary in space and time depending on local environmental
factors. Research results are scale-dependent and findings from local studies are rarely
transposable to higher levels of ecosystem organization. The question of scaling (scale
transfer) is therefore crucial in the study of fire effects, and requires a multidisciplinary
approach.
Because of the variety of scales covered, this study is a premiere in the confrontation of
satellite-imagery derived fire history data with detailed field data including measurements of
vegetation parameters (structure and composition), as well as soil and topographic properties.
The study focuses on the woody component, because of its perennial character and its
influence on major ecological processes. On an area of more than 2000 km², the W National
Park of Niger (WNPN) where fire is used as a tool for the management and conservation of
semi-arid ecosystems, a fire history map was elaborated from MODIS images with a 250 m
spatial resolution and a daily temporal resolution over a period of seven years (2002-2009). To
understand the variability, both in space and time, of fire propagation in vegetation, we studied
the fire distribution characteristics in terms of fire regime (i.e. timing and frequency) and
spatial structure (landscape metrics). Plausible causal relationships at regional and local scales
between fire regimes, edaphic and topographic conditions, and the woody vegetation
(composition and structure) characteristics were examined through multivariate analyses and
structural equations models. We also examined in detail the woody species adaptive strategies
as well biological interactions, which underlie their spatial organization, using point statistics.
Results show that the WNPN fire's activity is characterized by spatial and temporal
heterogeneity induced mainly by edaphic and topographic conditions via the structure of the
ligneous component. Prescribed early season fires create effective firewalls, limiting wide late
season fires. However, these late fires might not be as destructive as is commonly assumed.
Indeed, species adaptation to different fire regimes corresponds to contrasting growth
strategies. In the case of late fires, increased basal areas and mean tree heights were
encountered, enabling trees to resist fire and escape flames. As for the unburned areas, the
"pattern-process" analysis clearly indicates that facilitation between shrubs is a fundamental
process determining the woody cover periodic spatial organization, an emergent structure that
prevents fire spread.
Although they do not replace experimental studies, these results based on a large-scale natural
experiment provide valuable new information both on a fundamental level and for setting up
the rational management of the WNPN.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
Fichtner, Andreas, David I. Forrester, Werner Härdtle, Knut Sturm, and Oheimb Goddert von. "Facilitative-Competitive Interactions in an Old-Growth Forest: The Importance of Large-Diameter Trees as Benefactors and Stimulators for Forest Community Assembly." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-173653.
Full textZakrzewski, Katherine. "The Phenomenological Experience of Competitive State Anxiety for Female Beach Volleyball Players at the 2012 Olympics." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32295.
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