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1
Delalandre, Léo. "Relations traits-environnement chez les végétaux : du cycle de vie des organismes au cycle de vie des données." Electronic Thesis or Diss., Université de Montpellier (2022-....), 2024. http://www.theses.fr/2024UMONG001.
Abstract:
L’écologie comparative a mis en évidence des associations récurrentes entre les traits fonctionnels des plantes et leur environnement. Ces relations peuvent varier selon le niveau d’organisation considéré – au sein des espèces, entre les espèces, et entre groupes d’espèces –, mais cette dépendance demeure peu étudiée. Une distinction fondamentale dans les théories de l’histoire de vie est effectuée entre espèces annuelles (réalisant leur cycle de vie en une année) et pérennes (cycle de vie sur plus d’une année, avec généralement plusieurs événements de reproduction). Les annuelles et les pérennes herbacées diffèrent quant à leur fonctionnement (vitesse de croissance, investissement dans la production de graines, allocation aux racines, etc.). Cependant, bien qu’elles coexistent fréquemment, peu d’études considèrent les potentielles différences dans les relations traits-environnements entre ces deux groupes. L’objectif de cette thèse est de comprendre les spécificités des variations des traits des plantes annuelles en fonction de la disponibilité en ressources du milieu, à partir de mesures in situ et en jardin commun.Nous avons étudié des communautés de parcours ovins des Grands Causses, où annuelles et pérennes coexistent dans deux conditions environnementales contrastées : i) fertilisation et forte perturbation, et ii) sol pauvre et perturbation mois intense. Nous montrons que les variations des traits liés à la vitesse de croissance et à la densité des tissus foliaires sont plus faibles chez les annuelles que chez les pérennes. Ceci s’explique par (a) un remplacement d’espèces plus élevé chez les pérennes, et (b) la présence d’espèces présentant de plus grandes différences de valeurs de traits entre environnements chez les pérennes. Les variations intraspécifiques sont identiques entre les deux groupes d’espèces. Les mesures effectuées au cours de de ce premier volet ont permis de compléter une base de données de traits en cours de développement. A cette occasion, j’ai contribué à la structuration de cette base par un travail de gestion des données, visant à proposer des modalités de partage des données de traits fonctionnels et des variables environnementales associées ; une synthèse de ce travail est proposée. Dans un second temps, nous avons analysé la variabilité intraspécifique chez les annuelles de ces communautés, afin de tester son origine (génétique ou plastique), d’identifier les traits les plus variables en réponse à la fertilisation, et de comparer cette variabilité entre espèces. Trente populations ont été cultivées en jardin commun, avec une fertilisation faible ou élevée. Les résultats indiquent que i) les variations de traits observées in situ sont vraisemblablement d’origine plastique ; ii) la plasticité est faible sur les traits morphologiques des feuilles et des racines, mais forte sur l’allocation de la biomasse et la teneur en azote ; iii) les espèces préférentes pour des milieux riches en nutriments sont plus plastiques sur leur teneur en azote.Enfin, un travail de revue de la littérature a été engagé de manière à déterminer quels traits sont déterminants pour les herbacées annuelles et pérennes, en raisonnant sur les composantes de la démographie (reproduction, croissance, survie), dont l’importance diffère selon le cycle de vie. Nous proposons un article d’opinion visant à proposer comment mieux intégrer le cycle de vie et les trait morpho-physio-phénologiques communément mesurés.Cette thèse propose une étude des relations entre traits fonctionnels et environnement à différents niveaux d’organisation : entre cycles de vie, entre espèces, et au sein des espèces. Elle met en évidence que les relations trait-environnement peuvent varier entre ces niveaux, s’inscrivant dans un regain d’intérêt pour la prise en compte de la dépendance au contexte en écologie comparativeComparative ecology has highlighted recurring associations between plant functional traits and their environment. These relationships may vary depending on the level of organization considered – within species, between species, and among groups of species – but this dependency remains poorly studied. A fundamental distinction in life history theories is made between annual species (completing their life cycle in one year) and perennial species (life cycle over more than one year, usually with multiple reproductive events). Annual and perennial herbaceous plants differ in their functioning (growth rate, investment in seed production, allocation to roots, etc.). However, despite their frequent coexistence, few studies have considered potential differences in trait-environment relationships between these two groups. The objective of this thesis is to understand the specific variations in the traits of annual plants depending on resource availability, based on in situ measurements and in a common garden setting.We studied herbaceous communities in the Grands Causses, where annuals and perennials coexist in two contrasting environmental conditions: i) fertilization and high disturbance, and ii) poor soil and less intense disturbance. We show that variations in traits related to growth rate and leaf tissue density are lower in annuals than in perennials. This is explained by (a) a higher species turnover in perennials, and (b) the presence of species with larger differences in trait values between environments in perennials. Intraspecific variations are identical between the two groups of species. Measurements made during this first part were used to complete a trait database under development. On this occasion, I contributed to the structuring of this database through data management work, aiming to propose modalities for sharing functional trait data and associated environmental variables; a synthesis of this work is proposed.Secondly, we analyzed intraspecific variability in annuals from these communities, in order to test its origin (genetic or plastic), to identify the most variable traits in response to fertilization, and to compare this variability between species. Thirty populations were grown in a common garden, with low or high fertilization. The results indicate that i) the observed trait variations in situ are likely of plastic origin; ii) plasticity is low in morphological leaf and root traits but high in biomass allocation and nitrogen content; iii) species preferring nutrient-rich environments are more plastic in their nitrogen content.Finally, a literature review was undertaken to determine which traits are determinant for annual and perennial herbaceous plants, reasoning on demographic components (reproduction, growth, survival), the importance of which differs according to the life cycle. We propose an opinion article aiming to better integrate life cycle and commonly measured morpho-physio-phenological traits.This thesis proposes a study of the relationships between functional traits and the environment at different levels of organization: between life cycles, between species, and within species. It highlights that trait-environment relationships can vary between these levels, fitting into a renewed interest in context dependency in comparative ecology
2
Heilmayer, Olaf. "Environment, adaptation and evolution: scallop ecology across the latitudinal gradient = Umwelt, Anpassung und Evolution: Ökologie der Jakobsmuscheln im latitudinalen Gradienten /." Bremerhaven : Alfred-Wegener-Inst. für Polar- und Meeresforschung, 2004. http://www.gbv.de/dms/bs/toc/385417098.pdf.
3
Danczak, Robert E. "Dynamics in Microbial Ecology Across an Environmental Stability Gradient." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1530878203337741.
4
Leandro, Sérgio Miguel Franco Martins. "Environmental forcing of an estuarine gradient of zooplankton abundance and production." Doctoral thesis, Universidade de Aveiro, 2008. http://hdl.handle.net/10773/936.
Abstract:
Doutoramento em BiologiaOs copépodes são pequenos e frágeis crustáceos que constituem um dos grupos de organismos metazoários mais abundantes do mundo. Em ambientes marinhos e estuarinos, os copépodes assumem um papel de extrema relevância ao nível das cadeias tróficas, nomeadamente na transferência de matéria e energia de níveis tróficos inferiores (fitoplâncton) para níveis tróficos superiores (ex. larvas de peixe). A importância ecológica dos copépodes reflecte-se no elevado número de citações constantes no ISI Web of Knowledge (7716 citações entre 1969 e 2006) e no destaque que os mesmos continuam a possuir em estudos recentes de planctologia marinha e estuarina. Esta dissertação teve como objectivos principais (1) descrever variações espacio-temporais em termos de abundância e biomassa de populações estuarinas de copépodes da Ria de Aveiro (Portugal) e a sua relação com parâmetros hidrológicos (salinidade, temperatura, clorofila a e precipitação; (2) comparar as taxas de crescimento e desenvolvimento de populações alopátricas de copépodes; (3) definir modelos de crescimento dependentes da temperatura para as formas juvenis (nauplius e copepoditos) de Acartia tonsa; (4) avaliar o forçamento ambiental na distribuição e abundância de populações de Acartia e (5) calcular taxas de produção secundária potenciais para as populações de Acartia. Numa primeira fase, foi objecto de estudo a comunidade de copépodes estuarinos, para a qual foram descritos os padrões temporais de abundância e biomassa e obtidas estimativas de produção secundária. Os resultados obtidos neste estudo permitiram concluir que, entre outros aspectos, a abundância e biomassa da comunidade de copépodes da Ria de Aveiro se encontra significativamente correlacionada de modo positivo com a salinidade e com a temperatura da água. As estimativas das taxas de produção secundária derivadas da aplicação de modelos gerais de crescimento mostraram ser algo diferentes, sendo a estimativa dada pelo modelo de Hunthey & Lopez (1992) mais elevada do que a obtida pelo modelo de Hirst & Bunker (2003). O crescimento e desenvolvimento de espécies de Acartia foram estudados sob condições controladas em termos de alimento e temperatura, de forma a serem definidos modelos de crescimento dependentes da temperatura. A partir destes estudos concluiu-se que as populações alopátricas possuem diferentes respostas à temperatura. Além deste aspecto, também se observou que, pelo menos no caso da A.tonsa, as taxas de crescimento das formas juvenis (nauplius e copepoditos) estimadas in situ ou sob condições saturantes de alimento são similares. resumo O forçamento ambiental das populações de Acartia no Canal de Mira foi avaliado através de uma análise de componentes principais (ACP), que permitiu a análise simultânea das alterações espaciais e temporais das diferentes populações. Esta análise identificou três zonas distintas no estuário com base na abundância de Acartia spp.. Para cada zona, análises de correlação com diferentes desfasamentos temporais entre as variáveis ambientais e a abundância de copépodes, permitiram detectar a existência de forçamentos ambientais específicos, assim como um efeito positivo da biomassa fitoplanctónica na abundância do zooplâncton verificada meses mais tarde. Esta tese demonstrou igualmente a grande importância que as populações de Acartia, especialmente a mais abundante – A. tonsa – assumem na transferência de matéria e energia no ambiente planctónico da Ria de Aveiro (Portugal).
Copepods are small fragile and tiny crustaceans that form one of the world’s most abundant groups of metazoan organisms. In estuarine and marine environments copepods assume a key role in what trophic chains are concerned, namely in the transfer of matter and energy from lower trophic levels (phytoplankton) to higher trophic levels (ex. fish larvae). Copepods ecological importance is proven by the high number of quotations in ISI Web of Knowledge (7716 quotations between 1969 and 2006) and in the significance that they still have concerning current studies on estuarine and marine planktonic studies. The main goals of the present thesis were (1) to characterize and to describe the spatialtemporal patterns of abundance, biomass and production of the estuarine copepod community from Ria de Aveiro (Portugal) and its relationship with hydrological data (salinity, temperature, chlorophyll a and rainfall regime); (2) to compare growth and developmental rates of allopatric copepod populations; (3) to define temperature dependent growth models for nauplii and copepodites of Acartia tonsa; (4) to evaluate environmental forcing on the distribution and abundance of Acartia populations; and (5) to estimate potential secondary production rates of Acartia populations. In a first stage estuarine copepods community was studied, time patterns of abundance and biomass having been described and estimates of secondary production having been obtained. Results achieved by this study have led us to the conclusion that, among other aspects, abundance and biomass of the copepods community in Ria de Aveiro is positively correlated with water salinity and temperature. Estimates of secondary production rates deriving from the use of general growth models were different, the estimate obtained by Hunthey & Lopez (1992) model being higher than the one resulting from the Hirst & Bunker (2003) one. In order to define specific temperature-dependent copepod growth models, the growth and development of Acartia species were studied under controlled conditions of food and temperature. From those studies it was concluded that allopatric populations have different temperature responses. Additionally, it was also observed that, at least for A.tonsa, the growth rates of nauplii and copepodites at saturated food conditions and in situ conditions of food are similar. Environmental forcing of Acartia populations in Canal de Mira was evaluated by means of 3-mode PCA, which analyses simultaneously spatial and temporal changes of multispecies assemblages. This analysis identified three distinct zones along the estuary based on Acartia spp. abundance. For each zone time-lagged correlations between environmental variables and copepods abundance indicated that different zones were forced by different combinations of variables and the existence of delayed effects of phytoplanktonic biomass on the abundance of A.tonsa. This thesis also demonstrated the high importance that Acartia populations, in particular the most abundant A.tonsa, assume on the transfer of matter and energy in the planktonic realm of Ria de Aveiro (Portugal).
5
Hall, David. "Tracing selection and adaptation along an environmental gradient in Populus tremula." Doctoral thesis, Umeå : Institutionen för Ekologi, miljö och geovetenskap, Umeå universitet, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-30123.
6
Choboter, Paul F. "Forced Rossby waves in a zero absolute vorticity gradient environment." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ37107.pdf.
7
Öhlund, Gunnar. "Ecological and evolutionary effects of predation in environmental gradients." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-59465.
Abstract:
Understanding species interactions and how they affect densities and distributions of organisms is a central theme in ecological research. Studying such interactions in an ecosystem context is challenging as they often depend on species-specific characteristics and rates that not only change during the ontogeny of an organism, but also are affected by the surrounding environment. This thesis focuses on two separate questions and study systems that highlight different aspects of how effects of predation can depend on environmental conditions. In the first part of the thesis, we studied how temperature affects attack rate and handling time, two ecological rates with profound importance for predator-prey dynamics. Using a metaanalysis, we first show that the currently dominating model for temperature dependence in predator-prey interactions, i.e. the Arrhenius equation, has weak support in available empirical literature. This suggests that we need new rules for how and when we can generalize on the temperature-dependence of intake rates. We then use a simple model and a series of experiments to demonstrate that differences in the relative physiological capacity between predator and prey can impose strong non-linear effects on temperature-response curves of attack rate. In the second part of the thesis, we study the role of predation along a benthic-pelagic habitat gradient in promoting divergence and resource polymorphism among prey. We show that presence of a large piscivorous predator, the northern pike (Esox lucius), induces dwarfs, giants or divergence into both ecotypes in populations of European whitefish (Coregonus lavaretus) depending on lake characteristics. Using dated introductions of whitefish as controlled natural experiments, we show that pike presence induces rapid life history divergence between pelagic and littoral habitat use strategies, and that this divergence can translate into partial reproductive isolation in a matter of decades. Our results demonstrate the potential for thresholds in a crucial ecological rate, setting the stage for tipping points with potentially far reaching implications for effects of warming on predator prey dynamics and ecosystem stability. Moreover, they illustrate the potentially drastic consequences of such tipping points by demonstrating the importance of a single predator species as a driving force behind the creation and maintenance of biodiversity in a natural system.
8
Ghisbain, Pierre. "Application of a gradient-based algorithm to structural optimization." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/47758.
Abstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2009.Includes bibliographical references (leaves 175-180).
Optimization methods have shown to be efficient at improving structural design, but their use is limited in the engineering practice by the difficulty of adapting state-of-the-art algorithms to particular engineering problems. This study proposes the use of a robust gradient-based algorithm, whose adaptation to a variety of design problems is more straightforward. The algorithm was first applied to truss geometry and beam shape optimization, both forming part of the increasingly popular class of structural form-finding problems. The results showed that the gradient-based method is an appropriate tool for defining shapes in structures. The robustness of the algorithm was verified, as a series of structural configurations were treated with similar efficiency. The gradient-based method was also applied to a more traditional structural design problem through the optimization of a steel girder, resulting in a hybrid scheme featuring a truss stiffener. Throughout the study, emphasis was laid on the practical computer implementation of the gradient-based algorithm in interaction with structural analysis tools.
by Pierre Ghisbain.
S.M.
9
ASSISI, Mario Benedetto. "Wall(les)s, liminal environments between inside and outside." Doctoral thesis, Università degli studi di Ferrara, 2017. http://hdl.handle.net/11392/2488264.
Abstract:
Wall(les)s is a research on architectural unconventional boundaries. Starting from the wall system, the thesis investigates solutions where its thickness becomes a place of relationship between the parts, generating hybrid territories and contents.
The technological development and the obsession for security, comfort and energy performance of buildings, has further extended the contents of the limit, marking a shift from monolithic wall to a more layered and complex configuration. Moreover a huge amount of devices takes part of it and manages the exchange between the inside and the outside: natural and artificial thermal insulation, double and triple air chambers, heat exchangers, controlled mechanical ventilation, biometric and electronic access devices. The evolution and progress behind the constituent components of our buildings did not have the same impact in terms of typology and space organisations.
To rethink the limit as a spatial threshold is to realise that inside and outside are not separable by just one wall or frame, and as such, numerous territorialities, scales, continuity and discontinuity, transparency and opacity in between can be integrated.
An overall reflection on it, as a unifying element can call for a new integration between the parts unveiling unconventional relations between interior and exterior spaces, architecture and technology.Wall(les)s è una ricerca sui limiti architettonici non convenzionali. Attraverso una lettura per sottosistemi, l’obiettivo è di indagare potenzialità nascoste negli intervalli di spazio tra i vari strati che compongono il sistema parete. Essa nel tempo ha assunto vari significati legati alla protezione, la sicurezza e il comfort segnando un passaggio dalla parete monolitica ad una configurazione sempre più stratificata e complessa, dove ogni elemento svolge una funzione specifica pur mantenendo compatto l’insieme. Il paradigma della sostenibilità e dei cambiamenti climatici impone strategie di riduzione dei consumi energetici, spesso esplicitati attraverso miglioramenti della componentistica degli edifici ma senza nessuna conseguenza in termini architettonici e spaziali. Isolamenti termici naturali ed artificiali, doppie e triple camere d’aria, impianti meccani ed elettrici e ventilazione meccanica controllata sono solamente alcuni dei dispositivi che regolano lo scambio tra interno ed esterno. Interrogandosi sulla profondità e la composizione della parete, la ricerca mette in luce idee e interventi capaci di dare spessore agli intervalli di spazio nascosti facendoli diventare luoghi dell’abitare intermedio, ambiguo e indeterminato. La parete intesa come elemento di organizzazione architettonica e spaziale ma allo stesso tempo come dispositivo di gestione climatica potrebbe richiamare a una nuova unione tra architettura e tecnologia, tra spazio e impianto.
10
Owings, Paul C. "High Gradient Magnetic Separation of nanoscale magnetite." Thesis, Kansas State University, 2011. http://hdl.handle.net/2097/12020.
Abstract:
Master of ScienceDepartment of Civil Engineering
Alexander P. Mathews
Nanoscale magnetite is being examined for possible uses as an adsorbent of heavy metals and for the enhancement of water treatment processes such as stripping of trichloroethylene (TCE) from contaminated water supplies and wastewaters. Methods for recovering nanoscale magnetite must be developed before the particles can be used in water treatment processes. This is necessary because expelling high amounts of particles into the environment will be unacceptable and costly; if captured they can be reused; additionally, they could potentially cause environmental impacts due to their stability in an aqueous environment and possible toxicity. Nanoscale magnetite is superparamagnetic, so it has a high magnetic susceptibility, and hence it is very attracted to magnetized materials. Utilizing the magnetic properties of magnetite may be one possible means of separating the particles from a treatment process. High Gradient Magnetic Separation (HGMS) has been studied for the separation of micron and even tenths of a micron size particles, but there is little experimental data for HGMS of nanoscale magnetite. This research looks to filter nanoscale magnetite through a HGMS and determine the capture efficiency of the filter. Subsequently, the filter was backwashed to determine particle recover efficiencies. The flow rate was adjusted to determine the dependency of particle capture efficiency on cross sectional velocity through the filter. Additionally, particle loading was changed to better understand the correlation of particle loading with capture efficiency. Filtrations for nanoscale magnetite dispersed with sodium tripolyphosphate were also completed as well as filtrations of nanoscale magnetite coated with silica and magnetite silica composites. Experimental data in this research indicates that magnetite nanoparticles can be captured at 99.8% efficiency or higher in a well-designed filtration system. Capture efficiencies around 99.8% have been found for magnetite. The silica coated magnetite and magnetite silica composites were captured at efficiencies as high as 96.7% and 97.9%, respectively. The capture efficiency of the dispersed magnetite is lower than non-dispersed magnetite and most promising at relatively low fluid flow velocities and particle loadings. The maximum capture efficiency for dispersed magnetite particles was 90.3%. Both magnetite and dispersed magnetite were successfully recovered using backwash at pH of 10 to 11.
11
Wiryono, Wiryono. "A Gradient Analysis of the Soil-Vegetation Complex in the Neotoma Valley." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1392019873.
12
Tsai, Chih-Wei. "Riverine thermal environment and ecological function across a rural-urban gradient." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/5279/.
13
Peltzer, Duane Adolph. "Variation in plant interactions along experimental and natural environmental gradients." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0018/NQ54678.pdf.
14
Hennige, S. J. "Photoacclimation and adaptation of hermatypic coral species across environmental gradients." Thesis, University of Essex, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496253.
Abstract:
Light is often the most abundant resource within the nutrient poor waters surrounding coral reefs. Consequently, both photoacclimation and photoadaptation of the host and Symbiodinium play a crucial role in ensuring coral success. This thesis systematically examined responses (phenotypic and genotypic) of hermatypic corals across environmental gradients by 1) characterising variability between different isolated Symbiodinhim types under different light regimes, 2) examining the role of the host in photoacclimation using laboratory and in situ transplant experiments, and 3) assessing photoacclimation and photoadaptation strategies in four key coral species across habitats to determine key drivers of coral distribution.
15
Doxford, S. W. "Plant population responses to environmental change and the role of biotic interactions along environmental gradients." Thesis, University of Sheffield, 2012. http://etheses.whiterose.ac.uk/3246/.
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Burns, Marcelo Dias de Mattos. "Consequências da barragem eclusa do canal São Gonçalo para a ictiofauna do sistema patos - mirim." reponame:Repositório Institucional da FURG, 2010. http://repositorio.furg.br/handle/1/4269.
Abstract:
Tese(doutorado) - Universidade Federal do Rio Grande, Programa de Pós–Graduação em Oceanografia Biológica, Instituto de Oceanografia, 2010.Submitted by Cristiane Gomides (cristiane_gomides@hotmail.com) on 2013-12-15T18:51:27Z No. of bitstreams: 1 Marcelo Dias de Mattos Burns.pdf: 3987125 bytes, checksum: f6bba28caf87e1a5ccc3cca6e2beadf7 (MD5)
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O presente estudo teve como objetivo investigar as consequencias da construção Barragem Eclusa na estrutura das assembléias de peixes marinha, estuarina e de água doce que habitam o sistema lagunar Patos-Mirim. A área de estudo foi o Canal São Gonçalo, o qual interliga a Lagoa dos Patos com a Lagoa Mirim. As amostragens foram conduzidas mensalmente durante os anos de 2005 (12 meses), 2006 (6 meses), 2007 (12 meses) e 2008 (2 meses) abrangendo a região sudoeste do Canal denominada de limnica, sem a presença de salinidade, e na região nordeste, com influência sazonal da salinidade. As amostragens foram realizadas com métodos ativos de pesca: Arrasto de praia em profundidades (1,5m) e o Arrasto de fundo, em profundidades (>2m) totalizando 384 e 768 amostras, respectivamente. O trabalho foi dividido em três capítulos: I) Evidência de Fragmentação de Habitat afetando a movimentação de peixes entre as Lagoas Patos – Mirim, no Sul do Brasil; II) Distribuição espacial da assembléia de peixes em uma região de transição entre o estuário da Lagoa dos Patos e a Lagoa Mirim, Canal São Gonçalo, RS, Brasil; III) Padrões Ambientais influenciando a similaridade espacial da assembléia de peixes em uma região de transição entre estuário e água doce. No total foram capturadas 98 espécies, com 52.020 indivíduos no arrasto de praia e 155.972 indivíduos no arrasto de fundo. Os principais resultados demonstram que as conseguencias da Barragem Eclusa provocaram uma mudança na condição ambiental deste Sistema Lagunar envolvendo três aspectos para assembléia de peixes: i) a perda de habitat para as espécies Marinho Vagante, Estuarino Dependente e Estuarino Residente, ii) o Aumento do habitat para as espécies Primárias e Secundárias de água doce na região da Lagoa Mirim e iii) a fragmentação do habitat para as espécies Primárias e Secundárias de água doce entre as regiões Limnica e Estuarina do Canal. As medidas propostas para mitigar o impacto da Barragem Eclusa estão relacionadas a aumentar a passagem das espécies Estuarino Dependente para região Límnica do Canal São Gonçalo para a Lagoa Mirim, via o aperfeiçoamento da operação do sistema de comportas da Barragem Eclusa.
The present study aimed to investigate the consequences of the São Gonçalo channel dam-lock in the structure of the marine, estuarine and freshwater fish assemblies that inhabit the Patos-Mirim lagoon system. The study area was the São Gonçalo channel that connects the Patos Lagoon with the Mirim Lagoon. Sampling took place monthly during years 2005 (12 months), 2006 (6 months), 2007 (12 months) and 2008 (2 months), covering the southwestern part of the channel – the limnic region without salinity, and the northeastern part, influenced by saline waters. Samples were taken by means of active gears: beach-seine in depth up to 1.5 m and bottom-trawl at depth higher than 2 m, totaling 384 and 768 samples, respectively. The present wor was divided in three chapters: I) Evidence of habitat fragmentation affecting fish movement between Patos and Mirim coastal Lagoons in Soutthenr Brazil, II) Spatial distribution of the fish assembly in a transition zone between Patos Lagoon's e estuary and Mirim Lagoon: São Gonçalo channel, RS, Brazil; III) Environmental patterns influencing the spatial similarity of the fish assembly of a transition zone between estuarine and freshwater. In total, 98 species, with 52,020 individuals were collected by the beach-seine and 155,972 by bottom-trawl. Main results demonstrate that the building of the dam-lock caused a change in the environment of this lagunar system with three aspects: i) habitat loss for the marine vagrant, the estuarine-resident and the estuarine-depentent species, ii) an increase of habitat for primary and secondary freshwater species in the Mirim lagoon region, and iii) habitat fragmentation for primary and secondary freshwater species in the limnic and estuarine regions of the channel. The proposed measures to mitigate the impact of the dam-lock are related to increase the passage of estuarine-dependent species towards the limnic region of São Gonçalo channel and to Mirim lagoon, by improving the operation of the dam-lock gates.
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Martins, Lucia Helena Baggio. "Atributos edáficos do gradiente de declividade em floresta ombrófila mista alto-montana, no Planalto Catarinense." Universidade do Estado de Santa Catarina, 2015. http://tede.udesc.br/handle/handle/604.
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Previous issue date: 2015-03-06Upper montane ecosystems have been highlighted by environmental functionality, supplying ecosystem services due to its high capacity of water and carbon storage besides the endemism of species. From the edaphic perspective, these regions stand out for lower decomposition rate of organic material and the predominance of less developed and acid soils with high capacity of carbon storage. Its soil variability and properties related to the upper layer as carbon and nutrients cycling and water dynamics are related to the slope. Associated with these characteristics, according to the steep slope, upper montane ecosystems show lower resilience and fragility to unplanned human interventions. The objectives of this research was: to characterize slope and morphology of the soil related to drainage and total organic carbon content; to describe physical and chemical properties of the soil according to slope gradient and contents and fractions of soil organic carbon, in a fragment of upper montane mixed-rain forest, in Urupema SC. This research is presented in three chapters; firstly, presents relationship between slope, soil morphology and organic carbon contents; secondly, characterizes soil physical and chemical properties; and finally, analyzes contents and fractions of soil organic carbon in slope gradient under native forest areas. Soil was sampled into four transects across the slope, subdivided in plots of 10 m x 20 m, amounting 55 plots. The evaluated attributes werealtitude, slope, drainage, depth, stoniness and soil color, in surface horizon. For the chemical analysis were determined pH in CaCl2, extracting acidity (Al+3 e H+), exchangeable cations (Ca⁺², Mg⁺² and K⁺), available phosphorus and total organic carbon (TOC). The sum of exchangeable bases (SB) and cation exchange capacity (CEC) were calculated. The particulate fraction of carbon (POC) was determined and the fraction associated to minerals (COAM), was calculated by the difference between TOC and COP. Physical analysis were macro, micro and total porosity and soil resistance to penetration. The analysis of humin fractions (H), humic acid (HA), fulvic acids (FA) was performed in the layer 0 to 10 cm. It was calculated the relation among humin fractions, C humic acid and C fulvic acid (FAH-C/ C-FAF) and, the C alkaline extract (AE-C = C+C fulvic acid humic acid) with C from humin fraction (C-EA/ C-HUM). To evaluate the litterfall, composed litter samples from each plot of the four transect were collected. Relations among variables were determined through principal compounds analysis (PCA). The studied soils mainly occurred under steep slope areas, and that condition justifies the occurrence of rocky and shallow soils. Thinner soils were classified as Humic Lithic Dystrudept. Soils from higher altitudes with lower slope and better drainage showed higher TOC values, being classified as Humic Dystrupept. Soils from higher areas, with lower slope have lower acidity level and fertility when compared with soils under steep slope condition, lower altitude and moderately deep soil profile. The Humic Dystrupept are more fertile, showed high organic carbon content and had more litter quantity. They presented predominance of humin, indicating greater organic material humification, so reflecting the influence of weather conditions, altitude, slope and vegetation on total organic carbon dynamics
Ecossistemas alto-montanos têm sido destacados pela funcionalidade ambiental, podendo suprir serviços ecossistêmicos, devido à elevada capacidade de armazenamento de água e carbono, além do endemismo de espécies. Do ponto de vista edáfico, essas regiões se destacam pela menor taxa de decomposição da matéria orgânica e predomínio de solos pouco desenvolvidos e ácidos, com alta capacidade de estoques de carbono. Nestes, a variabilidade de solo e atributos relacionados à camada superficial, como ciclagem de carbono e nutrientes e dinâmica da água é condicionada pelo relevo. Associado a essas características, em função do relevo ondulado, os ecossistemas alto-montanos apresentam baixa resiliência e fragilidade as intervenções antrópicas não planejadas. Os objetivos do trabalho foram: caracterizar relevo e morfologia do solo, relacionados à drenagem e ao teor de carbono orgânico total; caracterizar os atributos físicos e químicos do solo em função do gradiente de declividade e caracterizar os teores e frações do carbono orgânico do solo em fragmento de Floresta Ombrófila Mista Alto-Montana, no município de Urupema SC. Este trabalho e foi apresentado em três capítulos, sendo o primeiro abordando relações entre relevo, morfologia e teores de carbono orgânico do solo, o segundo caracterizando atributos físicos e químicos do solo e o terceiro analisando teores e frações do carbono orgânico do solo em gradiente de relevo em áreas de floresta nativa. Os solos foram amostrados em quatro transectos, subdividos em parcelas de 10 m x 20 m, totalizando 55 parcelas. Para as análises químicas e físicas o solo foi coletado nas profundidades de 0 a 10, 10 a 30 e 30 a 50 cm. Os atributos avaliados foram altitude, declividade, drenagem, profundidade, pedregosidade e cor do solo, no horizonte superficial. As análises químicas foram pH em CaCl2, acidez extraível (Al+3 e H+), cátions trocáveis (Ca⁺², Mg⁺² e K⁺), fósforo disponível e carbono orgânico total (COT). A soma de bases trocáveis (S) e capacidade de troca catiônica (CTC) foram calculadas. Foi determinada a fração do carbono particulado (COP) e a fração associada aos minerais (COAM), calculada pela diferença entre o COT e o COP. As análises físicas foram macro e microporosidade, porosidade total e resistência à penetração do solo. As frações huminas (H), ácidos húmicos (AH), ácidos fúlvicos (AF) foram analisadas apenas na camada de 0 a 10 cm. Foram calculadas as relações C ácido húmico e C ácido fúlvico (C-AH/C-AF) e, C do extrato alcalino (C-EA= C ácido fúlvico + C ácido húmico) com o C da fração humina (C-EA/CH). Para estimar a serapilheira foram coletadas amostras compostas em cada parcela. As relações entre as variáveis foram determinadas pela análise de componentes principais (ACP). Os solos estudados ocorrem predominantemente em relevo ondulado. Essa condição justifica a ocorrência de solos rasos, com afloramentos de rocha. Os solos mais rasos foram enquadrados como Neossolos Litólicos Distróficos. Os solos nas cotas mais elevadas, menos declivosas e com boa drenagem apresentaram mais COT e foram classificados como Cambissolos Húmicos Distróficos. Os solos das áreas de maior altitude, em topografia mais plana são menos ácidos e tem baixa fertilidade, quando comparados com os solos localizados em topografia mais inclinada, com menor altitude e maior profundidade. Os Cambissolos são mais férteis apresentam maior teor de COT e serapilheira. Além disso, apresentaram predomínio de humina, indicando maior humificação da matéria orgânica, o que denota a influencia das condições climáticas, altitude, topografia e vegetação na dinâmica do carbono orgânico total
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Kenly, Travonya L. "Variability in Invertebrate Trophic Networks along Stream Nutrient Gradients." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1525715627495345.
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Viegas, Gustavo. "Estrutura da assembleia de besouros scarabaeinae (coleoptera: scarabaeidae) em floresta ripária com diferentes situações de conservação na bacia hidrográfica do R io dos Sinos, no Sul do Brasil." Universidade do Vale do Rio dos Sinos, 2012. http://www.repositorio.jesuita.org.br/handle/UNISINOS/3595.
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FUNDEPE - Fundação Universitária para Desenvolvimento do Ensino e da Pesquisa
Petrobras - Petróleo Brasileiro S. A.
A economia humana, saúde e bem estar são intimamente ligados com a funcionalidade do ecossistema. Como interface entre os ecossistemas aquáticos e terrestres, os habitats ripários são um importante componente na paisagem para muitas espécies. Estudos sobre os padrões das comunidades de insetos em florestas tropicais são extremamente necessários para identificar as conseqüências da fragmentação do hábitat na biota, e auxiliar planos de conservação. Scarabaeinae representa um grupo de insetos globalmente distribuídos, contudo, tanto sua biologia como ecologia são pouco conhecidas para a maioria das espécies. Os rola-bostas são importantes organismos decompositores, envolvidos em muitas funções do ecossistema. Além disso, esses insetos são muito sensíveis à destruição do hábitat, mostrando padrões de organização distintos entre áreas degradadas quando comparados com contínuos florestais. Este estudo teve como objetivo: 1) realizar um inventário da diversidade da fauna de Scarabaeinae e de suas guildas funcionais em ambiente ripário; 2) analisar a dinâmica temporal da comunidade de rola-bostas ao longo de um ciclo anual em florestas ripárias; e 3) avaliar a influência das diferentes condições de conservação da vegetação ripária na riqueza, abundância e composição de Scarabaeinae em uma bacia hidrográfica no Sul do Brasil. O presente estudo foi realizado em florestas ripárias de arroios de segunda ordem com diferentes condições de conservação na porção superior bacia hidrográfica do Rio dos Sinos, na região Sul do Brasil. Foram alocadas armadilhas de queda com iscas de fezes humanas e carne suína em decomposição, em quatro coletas durante um ciclo anual (2010-2011) em quatro pontos em cada um de três arroios. Um total de 1289 besouros foi coletado, distribuídos em 29 espécies de 11 gêneros. As espécies classificadas como paracoprídeas e telecoprídeas predominaram na comunidade. A riqueza e a composição de besouros variaram entre os pontos com diferentes situações de conservação da vegetação ripária ao longo do período, sendo que a riqueza foi maior na primavera e no verão, bem como nos pontos mais conservados da vegetação ripária. Os rola-bostas parecem indicar grande variabilidade ambiental, e por isso, conhecer as espécies características de cada tipo de ambiente, bem como obter o entendimento das relações entre suas funções ecológicas e os serviços ecossistêmicos que executam é de vital importância para manejos futuros dos ecossistemas. Junto com outros grupos de invertebrados, estes besouros podem prover uma representação taxonômica mais ampla no desenvolvimento de práticas e políticas conservacionistas. Neste sentido, este estudo contribui com informações tanto sobre a abrangência da validade dos conhecimentos sobre Scarabaeinae para as regiões subtropicais, como também na obtenção de conhecimentos para a região Neotropical.
The human economy, health and well being are intimately connected with the functionality of the ecosystem. As the interface between terrestrial and aquatic ecosystems, riparian habitats are an important component in the landscape for many species. Studies on the patterns of insect communities in tropical rainforests are extremely necessary to identify the consequences of habitat fragmentation on the biota, and assist conservation plans. Scarabaeinae represents a group of insects globally distributed, however both its biology as well as ecology are unknown for most species. The dung beetles are important decomposer organisms, involved in many ecosystem functions. Moreover, these insects are very sensitive to habitat destruction, showing patterns of organization distinguished between degraded when compared to continuous forest. This study had as aim: 1) perform an inventory of the diversity of the Scarabaeinae fauna and their functional guilds in riparian forest ecosystem; 2) analyze the temporal dynamics of dung beetles community by along an annual cycle in riparian forests; and 3) evaluate the influence of different conditions of conservation of riparian vegetation in the richness, abundance and composition of Scarabaeinae in a hydrographic basin in Southern Brazil. This study was performed in riparian forests of second-order streams with different conditions on the upper portion of hydrographic basin of the Rio dos Sinos, in Southern Brazil. Pitfall traps baited with human feces and rotting pork were placed in four samplings during an annual cycle (2010-2011) at four places in each of three streams. A total of 1289 beetles were collected, distributed in 29 species of 11 genera. The species classified as paracopríds and telecopríds predominated in the community. The beetle richness and composition varied among sites with different situations of conservation of riparian vegetation throughout the period, and the richness was highest in spring and summer, as well as in the most conserved riparian vegetation. The dung beetles seem to indicate great environmental variability, and therefore know the species characteristics of each type of environment, as well as gain an understanding of the relationships between ecological functions and ecosystem services that run is of vital importance for future management of ecosystems. Together with other groups of invertebrates, these beetles can provide a broader taxonomic representation in the development of practices and conservation policies. Thus, this study provides information both about the scope of the validity of knowledge about dung beetles to the subtropics, as well as in obtaining knowledge for the Neotropical region.
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Gray, Miranda M. "Genomic differentiation of big bluestem (Andropogon gerardii) along the Great Plains’ environmental gradient." Thesis, Kansas State University, 2012. http://hdl.handle.net/2097/14626.
Abstract:
Master of ScienceDepartment of Plant Pathology
Eduard D. Akhunov
Loretta C. Johnson
Big bluestem (Andropogon gerardii Vitman) is an ecologically dominant grass of the North American grasslands with precipitation-dependent productivity. However, climatic predictions for big bluestem’s dominant range in the Great Plains include increased periods of drought. The main objectives of this research were to determine the extent of neutral and non-neutral genetic differentiation and diversity among putative big bluestem ecotypes using amplified fragment length polymorphism (AFLP) markers. This is the first study of both neutral and non-neutral genetic diversity of big bluestem which also includes source populations of well-described ecotypes studied in reciprocal common gardens. A total of 378 plants were genotyped from 11 source prairies, originating from one of three ecoregions (Central Kansas, Eastern Kansas, and Illinois). Using two AFLP primer sets, 387 polymorphic markers (error rate 9.18%) were found. Un-rooted neighbor joining tree and principle-component analyses showed continuous genetic differentiation between Kansas and Illinois putative ecotypes, with genetic overlap occurring between Kansas ecotypes. Analysis of molecular variance showed high diversity within-prairie sites (80%) relative to across-prairies (11%), and across- ecoregions (9%) (p<0.001). Within-prairie genetic diversity levels were similar among ecoregions (84-92%), with the highest genetic variation maintained in Illinois prairies (92%). Population structure analyses supported K=6 genetic clusters across the environmental gradient, with Kansas prairies belonging to three main genetic groups, and Illinois prairies having largely divergent allele frequencies from Kansas prairies. Interestingly, BAYESCAN analysis of the three putative ecotypes identified eight F[subscript]ST-outlier AFLP loci under potential diversifying selection. Frequency patterns of loci under diversifying selection were further linked to geo-environmental descriptors including precipitation, temperature severity, diurnal temperature variation, prairie location, and elevation. The observed allele frequency divergence between Kansas and Illinois ecotypes suggests tallgrass restorations should consider possible maladaptation of non-local ecotypes and genetic swamping. However, high within-prairie genetic variation may help individual big bluestem populations withstand climatic variability.
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Anderson, Philippa Mary Levick. "The impact of grazing along an environmental gradient in the Kamiesberg, South Africa." Doctoral thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/6221.
Abstract:
Includes abstract.Includes bibliographical references (p. 175-200).
The Kamiesberg Mountain range, which is situated within the arid Succulent Karoo biome, South Africa, is internationally-recognised for its high conservation value and forms the study site for this project. The Kamiesberg is straddled by the Leliefontein communal area, which has been stocked for many years at twice the rate of the adjacent private rangelands. This presents an opportunity to test whether and how high stock numbers impact on vegetation. In the literature the drivers of rangeland ecology are discussed predominantly in the context of the equilibrium versus non-equilibrium debate, where density-dependent or climatic factors influence the vegetation respectively. Recent dissatisfaction with these paradigms has lead to the exploration of models better placed to incorporate the complex dynamics of rangelands.
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Sgarbi, Luciano Fabris. "Determinantes da raridade das espécies e seus efeitos sobre a estrutura de comunidades biológicas." Universidade Federal de Goiás, 2018. http://repositorio.bc.ufg.br/tede/handle/tede/8612.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
A recurrent pattern seen in nature is that species vary in abundance among sites, being common in a few sites and rare at the majority of sites. This intraspecific distribution of abundance, in turn, generates an excess of rare species in biological communities. This excess may cause problems in data analyses as datasets include many zeros. In this thesis I studied the causes of species rarity and how the excess of rare species influence the detection of patterns at the community level. In the first chapter I observed that species classified as rare were common in other habitat types, in other sites elsewhere, and in other years. However, among these three factors, the rarity was explained mainly by the habitat type. In the second chapter I observed that species tend to become rarer as they distance themselves (above, below or in both directions) from their optimal elevation. This pattern was quite robust and independent of taxonomic group or geographic region. In the third chapter, I observed that remotion of rare species in general did not have effects on the recovery of community structure patterns. In addition, the effect of that remotion of rare species was similar to that observed for the common species exclusion or random species exclusion.
Um padrão repetidamente observado na natureza é que as espécies variam em abundância entre os locais, sendo que em poucos locais a espécie é abundante, enquanto que na maioria a espécie é rara. Esta distribuição intraespecífica de abundância, por sua vez, gera um padrão recorrente que é o excesso de espécies raras nas comunidades biológicas. Este excesso de espécies raras pode complicar análises ao nível de comunidade visto que produzem conjuntos de dados com muitos zeros. Nesta tese busquei entender quais são as causas para a raridade das espécies e como excesso de espécies raras influência a detecção de padrões ao nível de comunidades. No primeiro capítulo observei que espécies classificadas como raras, foram comuns em outros habitats, em outros locais e em outros anos. No entanto, entre estes três fatores, a raridade foi melhor explicada pelo tipo de habitat em que ela foi amostrada. No segundo capítulo observei que as espécies tendem a se tornar mais raras conforme elas se distanciam (acima, abaixo ou em ambas as direções) de sua elevação ótima. Este padrão foi bastante robusto pois foi independente do grupo taxonômico ou da região geográfica. No terceiro capítulo, observei que a remoção das espécies raras têm pouco efeito na recuperação dos padrões de estrutura das comunidades. Além disso, o efeito da remoção de espécies raras foi similar ao observado quando exclui as espécies comuns, ou exclui as espécies de forma aleatória.
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LeBlanc, Denis R. "Density and recharge effects during the Cape Cod natural-gradient tracer test." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/84242.
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Hall, Aaron. "The environmental gradients and plant communities of Bergen Swamp, N.Y., USA /." Link to online version, 2005. https://ritdml.rit.edu/dspace/handle/1850/1121.
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Airi, Valentina <1979>. "Reproduction of Mediterranean zooxanthellate and azooxanthellate scleractinian corals along environmental gradients." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6425/1/PhDThesis_Airi.pdf.
Abstract:
Despite extensive studies focus mainly on sexual reproductive characteristics in tropical scleractinian species, there is limited knowledge on temperate regions. The Mediterranean is a biodiversity hotspot under intense pressure from anthropogenic impacts. Climatic models further predict that the Mediterranean basin will be one of the most impacted regions by the ongoing warming trend. This makes it a potential model of more global patterns to occur in the world’s marine biota, and a natural focus of interest for research on climate. The present research contributed to increase data on reproductive modes and sexuality of temperate scleractinian corals, highlighting their developmental plasticity, showing different forms of propagation and different responses to environmental change. For the first time, sexuality and reproductive mode in Caryophyllia inornata were determined. An unusual embryogenesis without a clear seasonal pattern was observed, suggesting the possibility of an asexual origin. Sexual reproduction of Astroides calycularis was governed by annual changes in seawater temperature, as observed for other Mediterranean dendrophylliids. Defining the reproductive biology of these species is the starting point for studying their potential response to variations of environmental parameters, on a global climate change context. The results on the influence of temperature on reproductive output of the zooxanthellate (symbiosis with unicellular algae) Balanophyllia europaea and the non-zooxanthellate Leptopsammia pruvoti suggest that the latter may be quite tolerant to temperature increase, since the zooxanthellate species resulted less efficient at warm temperatures. A possible explanation could be related to their different trophic system. In B. europaea thermal tolerance is primarily governed by the symbiotic algae, making it more sensitive to temperature changes. On the contrary, the absence of symbionts in L. pruvoti might make it more resistant to temperature. In a progressively warming Mediterranean, the efficiency on scleractinian reproduction could be influenced in different ways, reflecting their extraordinary adaptability.
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Airi, Valentina <1979>. "Reproduction of Mediterranean zooxanthellate and azooxanthellate scleractinian corals along environmental gradients." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6425/.
Abstract:
Despite extensive studies focus mainly on sexual reproductive characteristics in tropical scleractinian species, there is limited knowledge on temperate regions. The Mediterranean is a biodiversity hotspot under intense pressure from anthropogenic impacts. Climatic models further predict that the Mediterranean basin will be one of the most impacted regions by the ongoing warming trend. This makes it a potential model of more global patterns to occur in the world’s marine biota, and a natural focus of interest for research on climate. The present research contributed to increase data on reproductive modes and sexuality of temperate scleractinian corals, highlighting their developmental plasticity, showing different forms of propagation and different responses to environmental change. For the first time, sexuality and reproductive mode in Caryophyllia inornata were determined. An unusual embryogenesis without a clear seasonal pattern was observed, suggesting the possibility of an asexual origin. Sexual reproduction of Astroides calycularis was governed by annual changes in seawater temperature, as observed for other Mediterranean dendrophylliids. Defining the reproductive biology of these species is the starting point for studying their potential response to variations of environmental parameters, on a global climate change context. The results on the influence of temperature on reproductive output of the zooxanthellate (symbiosis with unicellular algae) Balanophyllia europaea and the non-zooxanthellate Leptopsammia pruvoti suggest that the latter may be quite tolerant to temperature increase, since the zooxanthellate species resulted less efficient at warm temperatures. A possible explanation could be related to their different trophic system. In B. europaea thermal tolerance is primarily governed by the symbiotic algae, making it more sensitive to temperature changes. On the contrary, the absence of symbionts in L. pruvoti might make it more resistant to temperature. In a progressively warming Mediterranean, the efficiency on scleractinian reproduction could be influenced in different ways, reflecting their extraordinary adaptability.
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Nilsson-Örtman, Viktor. "Thermal adaptation along a latitudinal gradient in damselflies." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-62276.
Abstract:
Understanding how temperature affects biological systems is a central question in ecology and evolutionary biology. Anthropogenic climate change adds urgency to this topic, as the demise or success of species under climate change is expected to depend on how temperature affects important aspects of organismal performance, such as growth, development, survival and reproduction. Rates of biological processes generally increase with increasing temperature up to some maximal temperature. Variation in the slope of the initial, rising phase has attracted considerable interest and forms the focus of this thesis. I explore variation in growth rate-temperature relationships over several levels of biological organization, both between and within species, over individuals’ lifetime, depending on the ecological context and in relation to important life history characteristics such as generation length and winter dormancy. Specifically, I examine how a clade of temperate damselflies have adapted to their thermal environment along a 3,600 km long latitudinal transect spanning from Southern Spain to Northern Sweden. For each of six species, I sampled populations from close to the northern and southern range margin, as well from the center of the latitudinal range. I reared larvae in the laboratory at several temperatures in order to measure indiviudal growth rates. Very few studies of thermal adaptation have employed such an extensive sampling approach, and my finding reveal variation in temperature responses at several levels of organization. My main finding was that temperature responses became steeper with increasing latitude, both between species but also between latitudinal populations of the same species. Additional genetic studies revealed that this trend was maintained despite strong gene flow. I highlight the need to use more refined characterizations of latitudinal temperature clines in order to explain these findings. I also show that species differ in their ability to acclimate to novel conditions during ontogeny, and propose that this may reflect a cost-benefit trade-off driven by whether seasonal transitions occur rapidly or gradually during ontogeny. I also carried out a microcosm experiment, where two of the six species were reared either separately or together, to determine the interacting effects of temperature and competition on larval growth rates and population size structure. The results revealed that the effects of competition can be strong enough to completely overcome the rate-depressing effects of low temperatures. I also found that competition had stronger effects on the amount of variation in growth rates than on the average value. In summary, my thesis offers several novel insights into how temperature affects biological systems, from individuals to populations and across species’ ranges. I also show how it is possible to refine our hypotheses about thermal adaptation by considering the interacting effects of ecology, life history and environmental variation.
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Liautaud, Kevin. "Community stability and turnover in changing environments." Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30264.
Abstract:
Les communautés d'êtres vivants peuvent elles êtres considérées comme des organismes complexes, ou au contraire comme de simples groupes d'espèces, individuelles ? Cette question est à l'origine de nombreux débats en écologie, ces deux visions impliquant notamment des prédictions très différentes dans les patrons spatiaux et temporels de communautés. Lorsque l'environnement change graduellement dans l'espace ou dans le temps, la vision individualiste implique des changements graduels dans la composition des communautés, tandis que la vision du "super-organisme" prédit des changements davantage abrupts. L'objectif principal de cette thèse est de comprendre et déterminer sous quelles conditions ces différents types de réponse des communautés aux changements de l'environnement peuvent advenir. Dans une première partie, nous étudions le rôle que la compétition inter-spécifique peut jouer dans l'émergence de différents patrons spatiaux de communautés. Nous étudions notamment les conditions théoriques sous lesquelles la compétition peut faire apparaître des patrons graduels ou discontinus dans la composition des espèces. Dans une deuxième partie, nous étudions l'influence des interactions entre les espèces et leur environnement sur les patrons spatiaux de communautés. Nous montrons notamment comment des phénomènes de construction de niche peuvent mener à l'émergence de changements brutaux dans la composition des communautés, mais également dans les conditions de l'environnement. Enfin, dans une dernière partie, nous illustrons le rôle que peut jouer la biodiversité dans la protection des écosystèmes face à des effondrements écologiques, et notamment le rôle que peut jouer la biomasse dans cette protectionThe question whether communities should be viewed as superorganisms or loose collections of individual species has been the subject of a long-standing debate in ecology. Each view implies different spatial and temporal community patterns. When environment gradually changes in space or in time, the organismic view predicts that species turnover is discontinuous, while the individualistic view predicts gradual changes in species composition. The main objective of this thesis is to understand the theoretical conditions under which these various types of community response can occur. First, I study the role of interspecific competition can play in the emergence of various spatial community patterns. I investigate the theoretical conditions in competition under which smooth or discrete spatial patterns can emerge. Then, I study how interactions between species and their environment can lead to various community patterns in space. I notably show how ecological niche construction can lead to the emergence of abrupt changes in species composition and in the environment, and the role biodiversity plays therein. Finally, I focus on the role biodiversity can play against ecosystem collapse. In this section, I illustrate how diversity loss, through its effects on total biomass, can lead to ecosystem collapse
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Fowler, Robert Edward. "An investigation into bee assemblage change along an urban-rural gradient." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5823/.
Abstract:
Urban densification and a rise in human population call for greater investigation into how the urban-rural gradient can influence bees and their pollination services. This thesis aimed to further current knowledge by: (i) sampling bee assemblages along the urban-rural gradient in Birmingham, UK; (ii) increasing documentation of bee traits associated with pollen carryover; (iii) incorporating a trait-based analysis to bee assemblage change along the urban-rural gradient; (iv) testing whether the pollination services along the same gradient varied between land-use types and (v) investigating the provisioning and reproductive success of bees in the urban environment. This thesis supports previous evidence of species-specific variation by urbanisation and shows how trait composition and trait diversity are influenced by bee assemblage change along the urban-rural gradient. However, this recorded assemblage and trait variation appeared not to alter seed-set in Campanula glomerata between urban and rural areas. I also found that nutritional quality could play an important role in provisioning rate in the solitary bee \(Osmia\) \(bicornis\), with greater offspring produced in sites where more protein was found in provisioned pollen in urban areas. Furthermore, the inter-specific variation in pilosity (which could have an important role to play in pollen carryover and subsequent pollination) can be explained by body size and species’ pollen transport adaptation. From this work, I suggest trait based analysis could be a common framework for future studies to measure bee assemblage change between urban and rural areas. Moreover, this research builds on previous work which suggests that particular traits affect pollen transport and subsequent pollination, and that further detailed study could give clues as to how changing bee assemblages could influence pollination.
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Foust, Christy M. "Population Genetics and Epigenetics of Two Salt Marsh Plant Species along an Environmental Gradient." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5947.
Abstract:
Phenotypic plasticity is the ability of a given genotype to exhibit different phenotypes in response to environmental variables, which can impact population level processes. Plasticity of ecologically-relevant traits is important to an organism’s environmental response; however, the underlying mechanisms of plasticity are largely unknown. Ecological epigenetics may offer mechanisms (e.g. DNA methylation) underlying phenotypic plasticity. Epigenetics can be defined as the underlying molecular mechanisms that allow one genotype to exhibit different phenotypes. Differential DNA methylation is one epigenetic mechanism that has been correlated with a number of ecologically-relevant traits; including, differential herbivory in Viola cazorlensis, spinescence in Ilex aquifolium, flower morphology in Linaria vulgaris, and fitness in Arabidopsis thaliana. The epigenetic correlations with traits found in these studies are interesting, but they are also partially confounded by a potential correlation between genetic and epigenetic variation.
Teasing apart the correlation between genetic and epigenetic variation is one of the challenges within ecological epigenetics. This correlation has resulted in epigenetic variation being partitioned into three types by researchers: obligate, facilitated, and pure. Changes in obligate epigenetic variation are directly correlated with genetic variation. Changes in pure epigenetic variation are completely independent from genetic variation. Changes in facilitated epigenetic variation are partially dependent on genetic variation, but the outcome of the phenotype is context-dependent based on environmental conditions. Since our predictions about the outcome of phenotypic variation are driven largely by population genetics theories, which make no room for variation that operates in non-Mendelian ways, epigenetics research needs to utilize unique ways to tease apart the interaction between genetic and epigenetic variation where facilitated or pure epigenetic variation exists outside of the realm of population genetics theory.
To address these issues, I performed a literature review and two research-based studies. In Chapter 1 I performed a literature review on the topic of population epigenetics addressing the correlation with genetic variation and recommending an extension to the Modern Synthesis to accommodate the non-Mendelian nature of DNA methylation. While population genetics has approximately 85-years of data to support it, epigenetics is beginning to show some of the limitations associated with predictions made using populations genetics models. One of these limitations is that population genetics as defined by the Modern Synthesis does not allow for violations of Mendelian genetics (i.e. random assortment and segregation of alleles). This limitation does not allow for phenotypic variation that is directly due to environmental conditions; however, recent ecological epigenetics data shows that this can, indeed, occur. Within this review I propose epigenetic questions that we should focus on at the population level, and I make recommendations for how to approach these questions in future studies.
In the second and third research-based chapters, I investigated whether an independent component of epigenetic variation was correlated with habitat, while controlling for a correlation with genetic variation, for Spartina alterniflora and Borrichia frutescens, respectively. Previous work has shown that there is no consistent genetic response to environment in these species. I, therefore, hypothesized that there would be a significant epigenetic correlation with habitat instead. To test this hypothesis, I collected leaf samples from five different sites for each species on Sapelo Island, GA. Within each site I established three 10m transects (n=20 for each microhabitat) in low, middle, and high marsh microhabitats, respectively. Plants of both species exhibit different phenotypes for height (tall, intermediate, short, respectively) based on their location within the marsh. I screened AFLP and methylation-sensitive AFLP (MS-AFLP) markers for genetic and epigenetic variation, respectively. I used a variety of statistical tests to attempt to tease apart a potential correlation between genetic and epigenetic variation and found that when genetic population structure is controlled for, significant epigenetic population structure persists across all populations for S. alterniflora and within 3 of 5 populations for B. frutescens. These results suggest that regulation of certain genomic elements via DNA methylation may play an important role in dealing with environmental variables. To fully determine the significance of these findings, future studies should examine the interaction between environmentally-mediated epigenetic variation and gene expression to determine its importance to phenotypic plasticity and habitat differentiation.
The body of work I produced supports that epigenetics may play a role in environmental response in populations within relatively small spatial scales. I used a combination of statistical tests to control for potential correlations with genetic variation which allowed me to see patterns that may normally be hidden. These findings expand upon traditional views of evolution by suggesting that environment can play a role in phenotypic variation, and other research supports that the variation due to epigenetic mechanisms can be inherited in future generations. Much of the current epigenetic research is based upon studies involving model species in highly controlled studies. While this research is been incredibly informative about some of the mechanisms underlying epigenetics, to fully understand the role of epigenetics to environmental response and evolution we must pair these data with field studies of non-model organisms. Only then will we begin to see the full role of epigenetics in organisms.
31
Council, Gregory W. (Gregory Wayne). "Solute dispersion in groundwater : the synergistic effect of heterogeneity and hydraulic gradient variability." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/38028.
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Schmadel, Noah M. "Quantifying Surface Water and Groundwater Interactions in a High-Gradient Mountain Stream for Solute Transport." DigitalCommons@USU, 2009. https://digitalcommons.usu.edu/etd/486.
Abstract:
A study reach in a mountain stream highly influenced by groundwater was selected to test common data collection strategies used to characterize and quantify groundwater exchange processes necessary to predict solute transport. The data types collected include: high frequency discharge estimates with the use of rating curves, dilution gauging techniques with instantaneous tracer experiments, groundwater table and stream water surface elevations, vertical head gradients, and hydraulic conductivity estimates. The first two data types were categorized as stream gauging and the remaining three data types as site characterization. The stream gauging data were used to quantify net changes in stream discharge at a reach scale with rating curve predictions and dilution gauging. Each method resulted in opposite net changes at this scale. An error analysis regarding rating curve predictions and dilution gauging suggested that neither method detected groundwater exchange at this scale due to discharge estimates being statistically the same. The error in rating curve predictions was estimated using a 95% joint confidence region of model parameters and the error in dilution gauging was estimated using a first order error analysis. Dilution gauging was also performed at a sub-reach scale to quantify net changes and indicated the groundwater exchange was highly spatially variable, which was not concluded at the reach scale. To quantify a water balance more representative of the exchanges occurring, gross gains and gross losses were quantified by measuring tracer mass recoveries and were found to occur in every sub-reach. However, the error analysis concluded that nearly half of the changes were not significant, which emphasized the importance of quantifying error in stream gauging techniques used to understand surface water-groundwater interactions.
The site characterization data were used to test and verify the water balance results by providing information regarding general trends and spatial variability of surface water-groundwater interactions. This study proved that one data type is not adequate to clearly characterize and quantify surface water-groundwater interactions and researchers must exercise caution when interpreting results from different data types at varying spatial scales.
33
Yanos, Casey Lee. "Effects of Productivity Gradients on Fish Community Structure in Lake Erie." University of Toledo / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1483546630641725.
34
Eltaher, Hoda M. M. A. "Gradient delivery of bioactive molecules across porous hydrogels." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/31697/.
Abstract:
Tissue regeneration approaches involve the recreation of biochemical and mechanical cues dictating tissue fate. Gradients of chemical cues are common in the natural microenvironment and are usually accompanied with gradual changes in cellular responses. Consequently, thorough understanding of biomolecule gradient development, their effective concentrations and the corresponding cellular responses as a function of time and space are essential for efficient design of scaffolds for biomedical applications. Here, we developed a compartmental diffusion model to study the development and measurement of biomolecule gradients. The model was validated to ensure effective spatiotemporal measurements of diffusing species within three-dimensional (3D) hydrogels. Results confirmed that the factors regulating the diffusing molecules’ behaviour in hydrogel matrices were dependant on the size of the diffusing species and the interaction with the matrix. The source compartment was subsequently replaced by polymeric particulate depots with tuneable characteristics to maintain structural protein stability and provide controlled temporal release of proteins and the diffusion through the hydrogel compartment was accordingly monitored. Glycosaminoglycan enhanced transduction (GET) technology was employed to study 3D gradient transduction of reporter protein in cell-laden hydrogels and to examine the effect of cells on the diffusion of biomolecules. Results demonstrated that cellular uptake of GET proteins altered the diffusion pattern as compared to acellular scaffolds and cells themselves acted as a sink that maintained steep GET protein gradients over the 5 mm wide scaffold. Furthermore, the synergistic combination of poly-arginine cell penetrating peptide (CPP) together with the cell membrane binding peptide using the GET technology demonstrated significant intracellular transduction in a gradient fashion in comparison to CPP alone. Employing GET technology and the compartmental diffusion model in the gradient delivery of the transcription factor MyoD to cell-laden hydrogels, resulted in directing the cells towards myogenic differentiation. However, the gradient pattern of differentiation was not clearly observed due to the limited number of genes examined. In conclusion, the model can be employed for the effective spatiotemporal gradient delivery of functional proteins to achieve the tissue complexity observed in the native tissues.
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Herfindal, Ivar. "Life history consequences of environmental variation along ecological gradients in northern ungulates." Doctoral thesis, Norwegian University of Science and Technology, Department of Biology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-706.
Abstract:
Temporal and spatial variation in the environment can influence the performance of individuals in wild ungulate populations. Of particular importance is an understanding of the mechanisms that shape variation in individual body mass, because several important life history traits are directly related to body mass. Body mass is one of the first traits that is influenced by environmental variation, and often the effect operates through variation in the components of the foraging niche of ungulates. In this thesis, I aim to demonstrate how measurements of environmental variation relate to variation in the foraging niche of ungulates. Furthermore, I aim to explore how variation in ungulate life history traits relates to these variables, and finally, how the management of ungulates could benefit from the incorporation of knowledge about the effects of environmental variation on population dynamics. I use weather observations, large-scale climate indices, and indices of environmental phenology based on satellite-derived vegetation indices (NDVI) to analyse the effect of environmental variation on plants and body mass in moose (Alces alces) and roe deer (Capreolus capreolus) populations.
The environmental variables that explained most of the variation in plant performance, measured as radial growth in common juniper (Juniper communis) also explained variation in ungulate body mass. These variables were related to conditions in spring and early summer. Plant growth was low in cold summers, and in spring where the green-up curve as measured by change in photosynthetic activity during spring was moderate. Such growing conditions are recognised to increase the quality of the plants as forage for ungulates. Consequently, moose body mass in autumn showed the opposite pattern than juniper to environmental conditions, indicating that quality of plants, rather than the quantity, is an important component in temperate ungulate foraging niche. Further, regional variation in moose body mass was associated with environmental variables related to forage quality. Roe deer body mass was associated with availability of forage during winter, and not with factors related to summer conditions. Factors related to forage quantity neither influenced temporal nor spatial variation in body mass in the two species.
Accordingly, it appears that both weather observations and satellite-derived vegetation indices are able to effectively predict variation in plant performance related to variation in foraging conditions for ungulates. The variation in forage quality in space and time created variation in body mass between populations and between cohorts within a population. Further, the variation in body mass between moose population, caused by variation in the foraging conditions, predicted how the populations differentially respond to the effects of environmental stochastisity. In populations with a high mean body mass, or a low density relative to plant biomass production, available resources buffered environmental stochastisity, and were less influenced by environmental variation than populations with relatively fewer resources available.
If wildlife managers fail to incorporate the effects of environmental variation on population performance, e.g. on the recruitment rate, the population may show unexpected and large fluctuations in size. Therefore, managers should attempt to incorporate knowledge of recent environmental conditions on the population when setting harvesting quotas.
In face of the large variation in environmental conditions experienced by the ungulate populations in Norway, and the fact that responses to environmental variation varies between populations, management should be regionally adapted, and aim to incorporate variation in vital rates caused by environmental conditions. This is likely to create more stable and predictable populations. In face of the predicted climate and landscape changes in Norwegian forests, environmental variables, e.g. from satellite-derived vegetation indices, have the potential to be a powerful tool for a sustainable management of ungulate populations. Consequently, such information should be incorporated into the management of ungulates in order to a) obtain a management of ungulate populations that is adapted to regional mechanisms of environmental variation, and b) acquire a management that is sustainable in face of future change in climate and landscape that may vary regionally. This calls for a regional differentiation in management strategies.
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Lindgren, Beatrice. "Adaptation Along Environmental Gradients: an Evaluation of Physiological Mechanisms and Ecological Constraints." Doctoral thesis, Uppsala University, Department of Ecology and Evolution, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8310.
Abstract:
For ectotherms living in seasonal environments, time available for development and growth is often constrained by the length of the growth season. Declining season length towards higher latitudes often select for latitudinal clines in development and growth rates, exhibiting increasing growth and developmental rates towards the north. However, the physiological and ecological factors enabling these clines are poorly understood.
Our study system included eight populations of Rana temporaria along a 1500 km latitudinal gradient. We found increased growth rates in populations at higher latitudes to be the result of higher growth efficiency, partly due to increased relative gut length. Populations with higher growth rates also exhibited lower standard metabolic rates, implying that fast-growing individuals are able to achieve high growth rates by spending less energy on maintenance metabolism under low activity conditions.
Predator densities, and antipredatory defenses in prey, are assumed to decrease towards higher latitudes. While all study populations responded to predator presence by decreasing activity and foraging, high latitude populations maintained higher activity levels in the presence of the predator. In trials with a free-ranging predator, high latitude tadpoles experienced higher mortality than those from the low latitudes. The higher activity level in the northern populations increases mortality under predation risk, but is probably needed to maintain high growth and development rates.
When competing over resources, tadpoles from the low latitude population were inferior competitors, as indicated by their longer development time when raised together with high latitude tadpoles. We found no effect of latitude on size-corrected burst speed. The general effect of predator presence on burst speed depended on food availability, with well fed tadpoles being faster in the absence, and food restricted being faster in the presence of a predator.
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Tolman, Deborah A. "Environmental Gradients, Community Boundaries, and Disturbance the Darlingtonia Fens of Southwestern Oregon." PDXScholar, 2004. https://pdxscholar.library.pdx.edu/open_access_etds/3013.
Abstract:
The Darlingtonia fens, found on serpentine soils in southern Oregon, are distinct communities that frequently undergo dramatic changes in size and shape in response to a wide array of environmental factors. Since few systems demonstrate a balance among high water tables, shallow soils, the presence of heavy metals, and limited nutrients, conservative efforts have been made to preserve them. This dissertation investigates the role of fire on nutrient cycling and succession in three separate fens, each a different time since fire. I specifically analyze the spatial distributions of soil properties, the physical and ecological characteristics of ecotones between Jeffrey pine savanna and Darlingtonia fens, and the vegetation structure of fire-disturbed systems. Soil, water, and vegetation sampling were conducted along an array of transects, oriented perpendicular to community boundaries and main environmental gradients, at each of the three fens. Abrupt changes in vegetation, across communities, were consistently identified at each of the three sites, although statistical analysis did not always identify distinct mid-canopy communities. Below-ground variables were likewise distinguished at the fen and savanna boundary for two of the three sites. At the third site, discontinuities did not align with the fen boundaries, but followed fluctuations in soil NH4. My results suggest that below-ground discontinuities may be more important than fire at preserving these uniquely-adapted systems, while vegetation undergoes postfire succession from fen to mid-canopy to savanna after approximately 100 years since fire. Although restoration of ecosystem structure and processes was not the primary focus of this study, my data suggest that time since fire may drive ecosystem processes in a trajectory away from the normal succession cycle. Moreover, time since fire may decrease overall vigor of Darlingtonia populations.
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BENELLI, Sara. "Hot moments and hot spots of benthic nitrogen cycling along environmental gradients." Doctoral thesis, Università degli studi di Ferrara, 2019. http://hdl.handle.net/11392/2487919.
Abstract:
In shallow water ecosystems the functioning of benthic compartment depends on the interactions between the physico-chemical environment and the community of micro and macroorganisms. This environment displays steep redox gradients and multiple interfaces, where fully oxic layers may be adjacent to sulfidic sediments. The biological communities have evolved adaptations creating a network of coupled processes and multiple feedbacks. The sedimentary environment is complex and difficult to colonize but is full of opportunities for organisms, as it may be more stable than the water column, and it may receive a large flux of energy. It is also challenging for scientists, as sediment can be manipulated in laboratory in order to validate key ecological questions generally addressed in terrestrial environments, among which those related to diversity and functioning relationships.
This PhD thesis investigates some aspects of the benthic system functioning (bsf) along gradients including light, nutrient availability and those of species or functional diversity. The ecological interactions between trophic levels and physical environment create the complexity, whereas the functioning here refers to organic matter mineralization, nutrient cycling and transport across sediment-water interface. Benthic animals create horizontal and vertical heterogeneities in sediments and affect the benthic-pelagic coupling through their bioturbation activities. Bioturbation affects the heterotrophic component of benthic system but also primary producers growth. The main aim of the thesis is to understand the effects of microbes, macrofauna and primary producers on benthic system processes along multiple environmental gradients. The general hypothesis is that a complex benthic system exploits better the available resources by increasing nutrient recycling and decreasing nutrient import or loss.
The thesis is divided in five chapters that revise the effects of complexity on ecosystem functioning. Traditionally processes were studied along gradients of decreasing species and functional diversity. Results from these experiments were usually characterized by unidirectional large fluxes of energy and matter. Recently, researches have begun to apply more complex approaches that usually include both the experimental and modelling tools.
After a brief overview of the ecological research over the last few decades (Chapter 1), I introduce three experimental works in which the effects of the heterotrophic component on bsf was investigated (Chapter 2). These studies demonstrate that benthic invertebrates are drivers of biogeochemical processes, by controlling the fate of organic matter and nutrients as well as fluxes of nutrients between sediment and water. However, in natural environments their large effects could be smoothed in presence of primary producers that assimilate nutrients from both the water column and the sediment. The co-occurrence of macrofauna and benthic primary producers was therefore investigated by means of two experiments. They demonstrated that process stimulation is species-specific and benthic microalgae can act as a buffer for regenerated nutrients (Chapter 3). Finally, I investigated interactions among multiple trophic levels along a gradient of inorganic N availability and organic matter content (Chapter 4). In a eutrophic site the co-occurrence of two different primary producers and macrofauna groups increased the recycling of nutrients within the system, suggesting a better exploitation of N sources. Results highlight the important role of macrofauna as facilitator of N availability in the benthic and pelagic compartments. On the contrary, microbial N fixation was the most important process that sustained primary production under oligotrophy. Primary producers N requirements suppressed N loss via denitrification. In the last chapter I draw the main conclusions of my work and some aspects that could be developed in the future (Chapter 5).In sistemi acquatici poco profondi il funzionamento del comparto bentonico dipende dalle interazioni tra ambiente fisico-chimico e comunità di micro e macrorganismi. Questo ambiente presenta ripidi gradienti di ossido-riduzione e interfacce multiple, dove strati di sedimento completamente ossidati possono confinare con strati sulfidici. Le comunità biologiche si sono adattate a vivere in queste condizioni creando una rete di processi accoppiati e di feedback multipli. Il sedimento è un ambiente complesso e difficile da colonizzare ma è pieno di opportunità per gli organismi, in quanto può essere più stabile della colonna d’acqua e ricevere elevati flussi di energia. Inoltre il sedimento, che può essere facilmente manipolato in laboratorio, può essere utilizzato dagli ecologi per rispondere a domande sulla diversità ed il funzionamento di un ecosistema. Questa tesi di dottorato ha lo scopo di investigare alcuni aspetti del funzionamento del sistema bentonico in relazione a gradienti di luce, disponibilità di nutrienti e biodiversità. Le interazioni ecologiche tra i livelli trofici e l’ambiente fisico creano la complessità del sistema mentre per funzionamento si intende la mineralizzazione della sostanza organica ed il trasporto dei nutrienti all’interfaccia acqua-sedimento. Gli animali creano eterogeneità orizzontali e verticali nei sedimenti ed influenzano l’accoppiamento bentonico-pelagico attraverso le loro attività di bioturbazione, le quali influenzano la componente eterotrofa del sistema bentonico ma anche la crescita di produttori primari. Lo scopo della tesi è di capire gli effetti di batteri, macrofauna e produttori primari sui processi del sistema bentonico in relazione a gradienti ambientali. L’ipotesi è che un sistema bentonico complesso sfrutti meglio le risorse disponibili aumentando il riciclo dei nutrienti e diminuendo gli import o le perdite. La tesi è divisa in 5 capitoli che esaminano gli effetti della complessità sul funzionamento di un ecosistema. Tradizionalmente i processi biogeochimici erano studiati con approcci semplificati in cui un singolo processo veniva messo in relazione alla biomassa crescente di una specie ed i risultati erano caratterizzati da elevati flussi unidirezionali di energia. Recentemente i ricercatori hanno cominciato ad utilizzare approcci sperimentali più complessi che includono anche l’utilizzo di modelli. Dopo una breve sintesi della ricerca ecologica degli ultimi decenni (Capitolo 1), introduco 3 lavori sperimentali in cui si investigano gli effetti della componente eterotrofa sul funzionamento del sistema bentonico (Capitolo 2). Questi studi dimostrano che la macrofauna guida i processi controllando il destino della sostanza organica e dei flussi di nutrienti. Negli ambienti naturali però questi flussi possono essere attenuati dai produttori primari che assimilano i nutrienti dalla colonna d’acqua e dal sedimento. La copresenza di macrofauna e produttori primari è stata investigata mediante 2 esperimenti che dimostrano che la stimolazione dei processi è specie-specifica e che le microalghe bentoniche possono agire da tampone per i nutrienti rigenerati (Capitolo 3). Infine, ho analizzato le interazioni tra più livelli trofici in relazione alla disponibilità di azoto (N) e di sostanza organica (Capitolo 4). In un sito eutrofico, la copresenza di produttori primari e macrofauna aumenta il riciclo di nutrienti all’interno del sistema, suggerendo un migliore sfruttamento delle risorse. I risultati evidenziano l’importante ruolo della macrofauna nel rendere più disponibile l’azoto. Diversamente, in un ambiente oligotrofico la fissazione batterica di N è il processo più importante che sostiene la produzione primaria mentre la perdita di N per denitrificazione è azzerata. Nel capitolo 5 riporto le principali conclusioni del mio lavoro e alcuni aspetti della ricerca che possono essere sviluppati in futuro.
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Ruhl, Nathan A. "The Lotic-Lentic Gradient in Reservoirs and Estuaries." Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1339177201.
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Ngeleza, Eric B. "Modification of gradient winds by dissected topography in the vicinity of the Jonkershoek Valley." Master's thesis, University of Cape Town, 1993. http://hdl.handle.net/11427/13420.
Abstract:
Includes bibliography.The pilot balloon runs and synoptic charts show that mountain and valley winds at the Jonkershoek valley correspond with the west to east ridging of anticyclones over the South Western Cape. Saddles between the South Atlantic and South Indian anticyclones are particularly conducive to the development of well established local wind circulations at Jonkershoek. Gradient winds during the occurrence of saddles are shown to be light and variable. Deep gradient southeasterlies undergo an acceleration to the lee of the ridges resulting in strong airflow at the Jonkershoek valley bottom. The topography at Jonkershoek is shown not have any meaningful modifying effect on the gradient northwesterlies.
41
Poulin, Nolan. "Proactive Planning through Active Policy Inference in Stochastic Environments." Digital WPI, 2018. https://digitalcommons.wpi.edu/etd-theses/1267.
Abstract:
In multi-agent Markov Decision Processes, a controllable agent must perform optimal planning in a dynamic and uncertain environment that includes another unknown and uncontrollable agent. Given a task specification for the controllable agent, its ability to complete the task can be impeded by an inaccurate model of the intent and behaviors of other agents. In this work, we introduce an active policy inference algorithm that allows a controllable agent to infer a policy of the environmental agent through interaction. Active policy inference is data-efficient and is particularly useful when data are time-consuming or costly to obtain. The controllable agent synthesizes an exploration-exploitation policy that incorporates the knowledge learned about the environment's behavior. Whenever possible, the agent also tries to elicit behavior from the other agent to improve the accuracy of the environmental model. This is done by mapping the uncertainty in the environmental model to a bonus reward, which helps elicit the most informative exploration, and allows the controllable agent to return to its main task as fast as possible. Experiments demonstrate the improved sample efficiency of active learning and the convergence of the policy for the controllable agents.
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Koller, Eva Katharina. "Impacts of environmental change on subarctic dwarf shrub communities : landscape gradient and field manipulation approaches." Thesis, University of Sheffield, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557953.
Abstract:
Global warming is predicted to be most severe at high latitudes, where cold-adapted ecosystems may be vulnerable to change and carbon-rich soils are a source of green- house gas emissions and positive feedback to climate. This makes ecological responses of arctic ecosystems to climate change a pressing concern. Usually, responses to climate change factors are addressed by short-term experimental manipulation, which can be misleading when trying to predict long-term responses. In this thesis, this was addressed by studying the growth responses of three ubiquitous subarctic dwarf shrubs to higher temperatures, earlier snow melt and higher nutrient availability using a combination of detailed study of an environmental gradient and long-term (18 years) field manipulation of temperature and nutrient availability. The most important findings were: i) Contrary to current opinion, delays in snow melt timing did not considerably affect dwarf shrub phenology, and the timing of leaf bud burst did not influence total summer shoot growth ii) Widespread P limitation (rather than N limitation) of growth was found in all studied species. This coincided with strong P immobilization in soils. Accordingly, soil P availability was strongly correlated with growth in deciduous shrubs. If climate change induces higher N mineralization, P may become limiting to plant growth and hence be more important than N in mediating arctic plant responses to global change iii) Leaf N and P per shoot were closely correlated with growth. In the deciduous species, there was more shoot growth per unit leaf N under warming, indicating that in a future, warmer climate, nutrient availability may have to increase by very little to increase productivity in deciduous shrubs. This provides insight into the mechanisms driving the increase in deciduous shrub abundance in arctic ecosystems in the last 50 years. This work suggests that further research on the arctic phosphorus cycle and its responses to climate change is urgently needed for better predictions of the response of arctic ecosystems to climate change.
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White, Philip B., De Gevel Saskia L. Van, Henri D. Grissino-Mayer, Lisa B. LaForest, and Georgina G. Deweese. "Climate Response Of Oak Species Across An Environmental Gradient In The Southern Appalachian Mountains, USA." Tree-Ring Society, 2011. http://hdl.handle.net/10150/622636.
Abstract:
We investigated the climatic sensitivity of oak species across a wide elevation range in the
southern Appalachian Mountains, an area where greater knowledge of oak sensitivity is desired. We developed three tree-ring chronologies for climatic analyses from oak cores taken from the Jefferson National Forest, Virginia, and Great Smoky Mountains National Park, Tennessee. We statistically compared the three chronologies with monthly climatic data from 1930 to 2005. The results of our analyses suggest that oak species in the southern Appalachian Mountains require a cool, moist summer for above average-growth to occur. The climate signal increased in duration from high to low elevational and latitudinal gradients, indicating a strong moisture-preconditioning signal during the previous fall at our lowest elevation site. A notable finding of this research was the degree of responsiveness in oaks that are growing in forest interior locations where strong climate sensitivity would not be expected because of the effects of internal stand dynamics. Furthermore, the relationships between evapotranspiration rates and the geographic factors of elevation, latitude, and aspect influence the climate signals at the three sites. Our research suggests that oaks located in a warm and xeric climate experience more physiological stress and put forth a more varied climatic response.
44
Kolbe, Sarah E. "Forest ecosystem response to environmental pressures along an urban-to-wildland gradient in southwestern Ohio." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352993756.
45
Jones, David. "PATTERNS OF ABUNDANCE ACROSS AN URBAN-RURAL GRADIENT FOR COMMONLY FOUND INDIGENOUS ARTHROPODS." VCU Scholars Compass, 2009. http://scholarscompass.vcu.edu/etd/1814.
Abstract:
Abstract Proof of concept for a continuous environmental sampling methodology that employs common terrestrial arthropods as environmental samplers was tested by analyzing pitfall, malaise and black light captures over a six month period over a replicated urban-suburban-rural gradient in Central Virginia. All arthropods captured at the nine sites were identified and assigned to aquatic, vegetation, or soil groups based on their association with these microhabitats. To offset variability in arthropod life history patterns and species abundance within habitat types, arthropod categories based on presence/absence data over the six month period were constructed to provide for sampling reliability within each microhabitat type. Arthropod categories ranged from single abundant species and families to synthetic groupings based on microhabitat associations (e.g., “soil beetles”), all of which could be easily identified. Mean weekly captures of individuals in each resulting category were compared within and among the nine sites using GLM or ranks analyses. Overall and weekly mean capture rates in the aquatic (two categories), soil (seven categories) and vegetation (11 categories) microhabitats were similar within each habitat type. With the exception of the two aquatic category members (midges and caddisflies), overall, monthly and weekly mean capture rates of all arthropod categories were highest in suburban and lowest in urban habitats. Results demonstrate reliability of the arthropod categories constructed and provide ground truthing for a continuously deployable and user-friendly arthropod-based system for monitoring environmental agents.
46
Downard, Giselle Teresa 1966. "Bird-habitat relationships along a vegetation gradient in desert grasslands of the southwest." Thesis, The University of Arizona, 1998. http://hdl.handle.net/10150/278668.
Abstract:
During winter 1996-1997 and summer 1997, I studied bird assemblages along a vegetation gradient in desert grasslands of southeast Arizona and southwest New Mexico. A gradient of increasing woody cover and decreasing grass cover best described the variance in vegetation characteristics among sites. At larger scales of observation, I found woody plant characteristics had a large effect on the presence and distribution of individual species and assemblages. At finer scales of analysis, I found a greater proportion of relationships between birds and particular plant species. Bird species richness was positively related to shrub species richness during winter. I observed greater between season shifts in bird species richness among sites with >1.0% woody cover. Total bird abundance varied little between seasons except at sites with 1.0% woody cover. Woody plant levels below 10% and 20% are likely to increase populations of plains and semidesert grassland bird communities respectively.
47
Redar, Sean Patrick. "Low temperature tolerance for Artemisia tridentata seedlings over an elevation gradient." CSUSB ScholarWorks, 2000. https://scholarworks.lib.csusb.edu/etd-project/1760.
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Bründl, Aisha Colleen. "Investissement parental le long d'un gradient altitudinal chez la mésange bleue (Cyanistes caeruleus)." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30265/document.
Abstract:
Dans cette thèse, j'examine la dynamique de l'investissement parental et la fitness chez la mésange bleue eurasienne (Cyanistes caeruleus) dans les Pyrénées françaises, et j'évalue les différences potentielles dues à un gradient altitudinal qui crée une variation de "dureté" environnementale. J'ai utilisé de données observationnelles et expérimentales, recueillies de plus de 500 nids de mésanges bleues. Les conditions de reproduction sont " plus dures " en cas de températures plus froides et d'une élévation croissante. J'ai trouvé que l'altitude croissante conduit à une diminution du succès de l'éclosion. Néanmoins, la taille des couvées et la mortalité des couvées sont comparables à travers le gradient. Je suggère que les décisions initiales en matière de procréation, telles que le moment et la quantité de progéniture, déterminent fortement le succès d'une tentative de reproduction. Ces résultats ont des implications pour notre compréhension du succès de reproductionIn this thesis, I examine parental investment and fitness in the Eurasian blue tit (Cyanistes caeruleus) in the French Pyrenees and assess potential differences due to an altitudinal gradient that creates variation in environmental "harshness". I used observational and experimental data, collected from over 500 blue tit nests. Breeding conditions are "harsher" due to colder temperatures with increasing elevation. I found that increasing altitude leads to decreased hatching success. Nevertheless, clutch size and brood mortality is comparable across the gradient. I suggest that initial reproductive decisions such as timing and amount of offspring produced heavily shape the success of a reproductive attempt. These results have implications for understanding reproductive success
49
Kiker, Taylor Wilson. "Dissolved Organic Carbon and Dissolved Inorganic Carbon along an Urbanization Gradient in Charlotte, North Carolina." Thesis, The University of North Carolina at Charlotte, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10928077.
Abstract:
Streams and rivers are an integral component of the freshwater carbon cycle as they provide the lateral transport of carbon from terrestrial environments to the ocean. Urbanization is one of the fastest growing land uses and it has major impacts on streams and rivers. This study examined twenty-eight watersheds varying in land uses from pre-restoration forested to urban in Charlotte, North Carolina. Their impervious cover ranged from 0.5–55%. The objective of this study was to examine alterations to freshwater carbon processes among watersheds of various land uses in multiple streams in Mecklenburg County, Charlotte, NC.
Surface water was collected at each site in addition to discharge measurements. Water quality parameters were analyzed including: DOC concentration, Specific UV Absorbance of DOC, DIC concentration, alkalinity concentration, δ 13C-DIC, major cations (Na+, K+, Mg 2+, and Ca2+), and anions (F–, Cl–, PO43–, NO 3–and SO42–). DOC concentration ranged from 1.1–18 mg/L and SUVA values ranged from 0.2–18 L/mg*m. Alkalinity concentrations ranged from 0.1–3.8 meq/L and DIC concentrations ranged from 0.2–3.8 mM. δ13C-DIC values ranged from –18.0‰ to –7.4‰. Overall, DOC concentrations and SUVA values had weak negative relationships with percent impervious cover. DIC concentrations, alkalinity concentrations, δ13C-DIC values, all cations, and F–, Cl– , and SO42– had strong positive relationships with percent impervious cover. PO43– and NO 3– had weak correlations with percent impervious cover. The increase in DIC, alkalinity, δ13C-DIC, and cations with high impervious cover was largely due to the increased chemical weathering of concrete materials in urban areas.
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Ferreira, Paulo Sérgio Monteiro. "Cactáceas do semiárido paraibano: Padrões de estrutura e diversidade." Universidade Estadual da Paraíba, 2015. http://tede.bc.uepb.edu.br/tede/jspui/handle/tede/2253.
Abstract:
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
The study of how species behave in relation to environmental gradients is an established tool in the ecology, being investigated since the pioneering studies in this field. Cactaceae is established as an important constituent family of plant communities of the Brazilian semiarid, and the change in the distribution of many genres and modes of life of this family coincides with the transition between wet and dry environments. In this context, this study aimed to test the hypothesis that the structure and diversity of cactaceas communities will be differentiated in relation to different areas of the semiarid of Paraiba, because the genera and species of this family present distinct environmental preferences. To carry out the study were selected four areas (A1, A2, A3 and A4) with pluviometric precipitations decreasing (650, 550, 450 and 350 mm respectively) in the semiarid of Paraiba. We assessed a total of 3,660 individuals of Cactaceae, distributed in six species: Cereus jamacaru DC., Melocactus zehntneri (Britton & Rose) Luetzelb, Opuntia inamoena K. Schum, Pilosocereus gounellei (F. A. C. Weber) Byles & G. D. Rowley, Pilosocereus pachycladus F. Ritter and Tacinga palmadora (Britton & Rose) N.P. Taylor & Stuppy. A1 presented 196 individuals divided into three species (C. jamacaru, O. inamoena and P. pachycladus); A2 was represented by 642 individuals, A3 presented 1,447 individuals and A4 1,375 individuals divided among the six species mentioned. The cactaceas species demonstrated patterns of Importance Value Index (IVI) and Relative Volume (VR) between the different areas. A1 presented the highest individuals (mean height = 4.96 m) and with bigger DAS (mean DAS = 13,34 cm), and having the largest volume of cactaceas (21.42 m 3 ); A2 showed more diversity (H '= 1.39) and equability (J' = 0.83); A3 had the lowest values of DAS (mean DAS = 4.33 cm), height (mean height= 0.85 m), diversity (H'= 0.58), equability (J'= 0.39) and volume of cactaceas (4.92 m ); and A4 presented, in most cases, intermediate values between A2 and A3. The greatest richness and abundance of species were related to the locations with low rainfall and more clayey soils had greater diversity of cactaceas. The nMDS (non-Metric Multidimensional Scaling) produced by the environmental variables separated the samples into four groups and the cluster analysis showed differentiated configurations of these attributes within their own areas. The groups differed significantly according to the permutation of Monte Carlo test that were between the Areas 1 and 2; 1 and 4; 2 and 4; and 3 and 4. Of these environmental variables, the predictive model given by BIO-ENV (Biotic-Environmental) suggested that the percentage of clay in the soil and EVI (Enhanced Vegetation Index) are those that best explain the variations of cactaceas communities. The CCA diagram (Canonical Correspondence Analysis), produced 3 with the predicted variables by BIO-ENV showed that the cactacea species that occurring in of Paraiba semiarid have different environmental preferences, revealing that the species P. pachycladus and C. jamacaru were positively related to areas with higher indices of EVI and rainfall; M. zehntneri and P. gounellei adapted better in areas with soils with higher proportion of clay and silt; O. inamoena, was negatively related with higher proportions of medium sand; and T. palmadora, showed no patterns related to variables given by the BIOENV. The significant correlations between the axes of the CCA and the attributes of the structure of the species (abundance, height and DAS), were some times moderate (r 0.40 to 0.69) and most of the times stronger (r ≥ 0.70) and the species that presented best linear associations with the variables tested were M. zehntneri, P. gounellei and P. pachycladus.
O estudo de como as espécies se comportam em relação aos gradientes ambientais é uma ferramenta estabelecida na ecologia, sendo investigado desde os estudos pioneiros nesse campo. Cactaceae, estabelece-se como uma importante família constituinte das comunidades vegetais do semiárido brasileiro, e a mudança na distribuição de muitos gêneros e formas de vida dessa família coincide com a transição entre ambientes secos e úmidos. Nesse contexto, o presente estudo buscou testar a hipótese de que a estrutura e diversidade das comunidades de cactáceas serão diferenciadas em relação às diferentes áreas do semiárido paraibano, pelo fato dos gêneros e espécies dessa família apresentarem preferências ambientais distintas. Para a realização do estudo foram selecionadas quatro áreas (A1, A2, A3 e A4) com precipitações pluviométricas decrescentes (650, 550, 450 e 350 mm respectivamente) no semiárido paraibano. Foram aferidos ao todo 3.660 indivíduos de Cactaceae, distribuídos em seis espécies: Cereus jamacaru DC., Melocactus zehntneri (Britton & Rose) Luetzelb, Opuntia inamoena K. Schum, Pilosocereus gounellei (F. A. C. Weber) Byles & G. D. Rowley, Pilosocereus pachycladus F. Ritter e Tacinga palmadora (Britton & Rose) N.P. Taylor & Stuppy. A1 apresentou 196 indivíduos divididos em três espécies (C. jamacaru, O. inamoena e P. pachycladus); A2 foi representada por 642 indivíduos, A3 apresentou 1.447 indivíduos e A4 1.375 indivíduos divididos entre as seis espécies citadas. As espécies de cactáceas demonstraram padrões de Índice de Valor de Importância (IVI) e Volume Relativo (VR) distintos entre as Áreas. A1 apresentou os indivíduos mais altos (Alt. med. = 4,96 m) e de maior DAS (DAS med. = 13,34 cm), possuindo também o maior volume de cactáceas (21,42 m 3 ); a A2 demonstrou maior diversidade (H’ = 1,39) e equabilidade (J’ = 0,83); A3 apresentou os menores valores de DAS (DAS med. = 4,33 cm), altura (Alt. med.= 0,85 m), diversidade (H’ = 0,58), equabilidade (J’ = 0,39) e volume de cactáceas (4,92 m ); já A4 apresentou, na maioria das vezes, valores intermediários entre A2 e A3. As maiores riquezas e abundâncias estiveram relacionadas aos locais de menores precipitações e os solos mais argilosos foram os que comportaram maior diversidade de cactáceas. O nMDS (Escalonamento Multidimensional não-Métrico) produzido através das variáveis ambientais separou as amostras em quatro grupos e a análise de agrupamento demonstrou configurações diferenciadas desses atributos dentro das próprias Áreas. Os grupos que diferiram estatisticamente segundo a permutação do teste de Monte Carlo foram entre as Áreas 1 e 2; 1 e 4; 2 e 4; e 3 e 4. Destas variáveis ambientais, o modelo preditivo dado pelo BIO-ENV (Biotic-Environmental) sugeriu que a % de Argila no solo e o EVI (Índice de Vegetação 3 Aprimorada) são as que melhor explicam a variação das comunidades de cactáceas. O diagrama de CCA (Análise de Correspondência Canônica), produzido com as variáveis preditas pelo BIO-ENV, demonstrou que as espécies de cactáceas ocorrentes no semiárido paraibano apresentam preferências ambientais distintas, revelando que as espécies P. pachycladus e C. jamacaru foram positivamente relacionadas às áreas com maiores índices de EVI e Precipitação; M. zehntneri e P. gounellei, foram melhor adaptadas a habitarem em ambientes com solos com maior proporção de Argila e Silte; O. inamoena, esteve negativamente relacionada às maiores proporções de Areia média; e T. palmadora, não demonstrou padrões relacionados as variáveis dadas pelo BIO-ENV. As correlações significativas entre os eixos da CCA e os atributos da estrutura das espécies (abundância, altura e DAS), foram algumas vezes moderadas (r 0,40-0,69) e na maioria das vezes fortes (r ≥ 0,70) e as espécies que apresentaram melhores associações lineares com as variáveis testadas foram M. zehntneri, P. gounellei e P. pachycladus.