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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
271

Identification des réseaux neurobiologiques gouvernant les apprentissages ambigus chez l'abeille Apis mellifera / Identification of the neuronal circuits required for ambiguous learning in honey bees apis mellifera

Boitard, Constance 28 September 2015 (has links)
L'apprentissage associatif recouvre des niveaux variables de complexité, des tâches cognitives simples jusqu'à des tâches complexes qui nécessitent la résolution de discriminations ambigües. Cette thèse traite de deux protocoles présentant des ambigüités chez l'abeille, au cours desquels le blocage de la signalisation GABAergique des neurones récurrents sur les corps pédonculés, structures cérébrales majeures de l'apprentissage, est à l'origine de la perte de capacité de résolution ambigüe. Ces neurones, non requis pour les apprentissages simples, semblent donc indispensables à la résolution des ambigüités propres aux discriminations cognitives complexes et élaborées chez l'abeille. / Associative learning spans different levels of complexity, from simple tasks involving simple causal relationships between events, to ambiguous tasks, in which animals have to solve complex discriminations based on non-linear associative links. We focused on two protocols presenting a temporal or configural ambiguity at the level of stimulus contingencies in honey bees (\textit{Apis mellifera}). We performed selective blockades of GABAergic signalisation from recurrent feedback neurons in the mushroom bodies (MBs), higher-order insect brain structures associated with memory storage and retrieval, and found that this blockade within the MB calyces impaired both ambiguous learning tasks, although if did not affect simple conditioning counterparts. We suggest that the A3v cluster of the GABA feedback neurons innervating the MBs calyces are thus dispensable for simple learning, but are required for counteracting stimulus ambiguity in complex discriminations in honey bees.
272

Análise físico-química de amostras de méis de Apis mellifera e Meliponíneos / Physico-chemical analysis of honey samples of Apis mellifera and Meliponid

Luzimario Lima Pereira 05 November 2010 (has links)
O mel de abelhas é um produto biológico muito complexo, cuja composição varia notavelmente em função da flora visitada pelas abelhas e das condições climáticas e edáficas da região onde foi produzido. Este trabalho teve como objetivos confrontar os resultados das análises físico-químicas entre as amostras de méis produzidos em diferentes localidades do Brasil por Apis mellifera e por Meliponíneos e investigar se o mel produzido por essas abelhas nas suas diferentes regiões de origem apresenta níveis toleráveis de contaminantes inorgânicos. Para tanto, foram avaliadas 56 amostras de méis de A. mellifera e 56 amostras de méis de Meliponíneos dos Estados da Bahia, Minas Gerais, Mato Grosso do Sul, Paraíba, Piauí, Paraná, Santa Catarina e São Paulo, em relação aos seguintes parâmetros: umidade, atividade de água, viscosidade, pH, acidez livre, índice de formol, açúcares redutores, sacarose aparente, teor de cinzas, cor, condutividade elétrica, hidroximetilfurfural, atividade diastásica e metais (Hg+2, Zn+2, Cd+2, Pb+2 e Cu+2). Foi utilizada a técnica de Voltametria de Redissolução Anódica de Pulso Diferencial (DPASV) para quantificar os metais, e métodos convencionais e próprios para mel nas demais análises. Os resultados mostraram que a legislação atual, referente ao mel de A. mellifera, não é adequada para os parâmetros açúcares redutores, umidade e atividade diastásica de algumas espécies de Meliponíneos. Pôdese concluir que as espécies A. mellifera, Tetragonisca angustula, Melipona quadrifasciata, M. scutellaris, M. mandacaia, M. fasciculata, M. subnitida produzem méis com características físico-químicas diferentes e próprias de cada uma delas. Para todas as espécies avaliadas, os níveis de contaminantes inorgânicos encontrados nos méis foram toleráveis à saúde humana. Os méis produzidos por A. mellifera apresentaram variações nas características físico-químicas: atividade de água, viscosidade, acidez livre, índice de formol, açúcares redutores, condutividade elétrica, hidroximetilfurfural, atividade diastásica e o mineral zinco, em função dos diferentes locais onde foram produzidos. / The honeybee is a very complex biological product, whose composition varies markedly depending on the plant visited by the bees and the weather and soil conditions in the region where it was produced. This study aimed to compare the results of physicochemical analysis between the samples of honey produced in different locations in Brazil by Apis mellifera and Meliponid and to investigate whether honey produced by these bees, in different regions of origin, has tolerable levels of inorganic contaminants. To this end, we evaluated 56 samples of honey from A. mellifera and 56 samples of honey from Meliponid from the states of Bahia, Minas Gerais, Mato Grosso do Sul, Paraíba, Piauí, Paraná, Santa Catarina and São Paulo, for the following parameters: moisture content, water activity, viscosity, pH, free acidity, formol index, reducing sugars, apparent sucrose, ash content, color, electrical conductivity, hydroxymethylfurfural, diastase activity and metals (Hg+2, Zn+2, Cd+2, Pb+2 and Cu+2). Differential Pulse Anodic Stripping Voltammetry (DPASV) technique was used to quantify the metals, and, to the other analysis, conventional and suitable methods for honey were used. The results showed that the current legislation, referring to the honey of A. mellifera, is not appropriate for the parameters reducing sugars, moisture content and diastase activity of some species of Meliponid. It was concluded that the species A. mellifera, Tetragonisca angustula, Melipona quadrifasciata, M. scutellaris, M. mandacaia, M. fasciculata, M. subnitida produce honeys with different and specific physico-chemical characteristics. For all species studied, levels of inorganic contaminants found in honey were tolerable to human health. The honey produced by A. mellifera showed variations in physicochemical water activity, viscosity, free acidity, formol index, reducing sugars, electrical conductivity, hydroxymethylfurfural, diastase activity and the mineral zinc, depending on the different locations where they were produced.
273

Caracteriza??o de m?is brasileiros: f?sico-qu?mica, perfil de subst?ncias polares, atividade antioxidante e quimiometria / Characterization of brazilian honeys: physico-chemical, polar substances profile, antioxidant activity and chemometrics

SALGUEIRO, Fernanda Barbosa 09 March 2012 (has links)
CAPES / Honey is generally known for its therapeutic value and the determination of its main floral source allows the certification to the consumer the properties related to its origin. Thus, the aim of this work was to evaluate the quality and characterize eleven honeys from Apis mellifera from the state of Rio de Janeiro according to physico-chemical parameters, to phenolics profile, to the antioxidant activity and also through the use of chemonetric analysis applied to 1H NMR data and HPLC-DAD. Two samples of assa peixe, six samples of cambara and three samples of morr?o-de-candeia honeys from diferente regions of Rio de Janeiro were analyzed. The physico-chemical parameters determined were: HMF content and color through a spectrophotometric method, free acidity and pH. The content of free amminoacids was also determined through the c?dmium-ninhydrine together with total proteins via the Bradford method. The antioxidant ability of honeys and their extracts was qualitatively determined through the total phenolics content using the Folin-Denis method. Total flavonoids were determined by the complexation method with aluminium chloride. The quantitative antioxidant activity of honeys was determined by the trapping of the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) radical, by trapping of the ABTS.+ radical and also by the iron reduction method (FRAP). The identification and quantitation of polyphenols in the extracts were done by HPLC-PDA. The use of multivariate analysis for the 1H NMR data and HPLC enabled the distinction of the honeys analyzed in this work. Thus, the use of 1H NMR and HPLC data combined with multivariate analysis may be employed as a new strategy for the fast and non-destructive typification of Brazilian honeys. / No mercado, m?is s?o conhecidos pelo seu poder terap?utico e a designa??o de sua principal fonte floral permite atestar ao consumidor as propriedades de sua origem. Assim, o objetivo deste trabalho foi avaliar a qualidade e caracterizar onze m?is de Apis mellifera provenientes do Estado do Rio de Janeiro, por meio de par?metros f?sico-qu?micos, do perfil de subst?ncias fen?licas, de seus potenciais antioxidantes, al?m de usar m?todos quimiom?tricos aplicados aos dados de RMN de 1H e CLAE-DAD. Para tanto, utilizou-se duas amostras de mel de assa peixe, seis de cambar? e tr?s de morr?o de candeia de diferentes munic?pios do Rio de Janeiro. Os par?metros f?sico-qu?micos avaliados foram: teor de HMF e a cor utilizando m?todo espectrofotom?trico, acidez livre e pH. Al?m dessas determina??es, o conte?do de amino?cidos livre foi avaliado pelo m?todo de c?dmio-ninidrina, e prote?nas totais pelo m?todo de Bradford. A capacidade antioxidante dos m?is e de seus extratos foi avaliada qualitativamente atrav?s do conte?do de fen?licos total pelo m?todo de Folin-Denis, e de flavon?ides total pelo m?todo de complexa??o com cloreto de alum?nio. A quantifica??o do potencial antioxidante foi realizada pela captura do radical 2,2-difenil-1-picril-hidrazil (DPPH), captura do radical livre ABTS.+, al?m do m?todo de redu??o do ?on f?rrico (FRAP). A identifica??o e quantifica??o das subst?ncias polifen?licas dos extratos foi feita por cromatografia l?quida de alta efici?ncia com detector de arranjo de diodos (CLAE-DAD). A aplica??o da an?lise multivariada aos dados de RMN de H e de CLAE-DAD distinguiu os m?is de assa peixe, cambar? e morr?o de candeia produzidos no Estado do Rio de Janeiro. Assim, o uso de RMN de 1H e CLAE-DAD combinado com a quimiometria pode ser uma nova estrat?gia para tipifica??o de m?is brasileiros de forma r?pida e n?o destrutiva.
274

Modelo matem?tico para a simula??o da produ??o de mel em munic?pios do Rio de Janeiro / Mathematical models for the honey production simulation in municipalities of Rio de Janeiro

AQUINO, Renato Machado 29 April 2015 (has links)
Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2018-05-18T18:24:16Z No. of bitstreams: 1 2015 - Renato Machado Aquino.pdf: 1434016 bytes, checksum: 3679650b2f036e3b85b93c090450ba7d (MD5) / Made available in DSpace on 2018-05-18T18:24:16Z (GMT). No. of bitstreams: 1 2015 - Renato Machado Aquino.pdf: 1434016 bytes, checksum: 3679650b2f036e3b85b93c090450ba7d (MD5) Previous issue date: 2015-04-29 / Brazil and Argentina amongst the world?s ten leading countries in honey exports. The two countries share in this commodity exports was about US$ 220 million dollars in 2011. Argentina is one of the world?s greatest producers, having reached 83,121 tons that year. That means that apiculture is a relevant activity to both countries? agrobusiness network. All this amount of production and equivalente input were consequence of the joint effort of producers, research centres and development agencies. Thus, mathematical models which may allow a better understanding of honey production over time, under many factors influence, might be na important planning tool for the many actors involved in this scene. The aim of this work is to develop mathematical models, defined by ordinary differential equations, whose numerical solutions and parameters may allow one to have information about a certain municipality?s honey production. The central hipotesis is that it is possible to assess and predict a municipality?s honey production, by using mathematical models. A secondary hipotesis would be that these models? paremeters could be important indices to this productive activity. The models deveploped here were based in Lucas Growth Model, which takes into account that human capital as an endogenous fundamental growth component. The parameter rescue and the models numerical solving were implemented through a software in Fortran 95 programming language. The software main guideline was to allow solutions to the models so that it was possible to offer anoptimalmuniciplaity?s honey production description, in a certain time period. The solution fitting of the system of differential equaions which define the models was made through a nonlinear least squares method. The solver to this method was BOBYQA, a software presented in Powell (2009). This algorithm was developed in Fortran 77, is derivative free and accepts box constraints. The model validation was made in two steps: in the first it was validated gedanken honey production data. In the second the models were applied to eightenn municipalities which represented honey production in Rio de Janeiro State microregions. Fifteen among the researched had good model fitting. There was no fitting in three cases of anomalous production.This way, the results allow one to conclude that the developed models may be efficient instruments to honey agorbusiness managers, by allowing good production predictions under certain conditions and crop estimate in harvest periods. Moreover, they may start important research about technology and productivity in this economic activity. / Brasil e Argentina est?o entre os dez maiores exportadores mundiais de mel. A atividade de exporta??o desse produto rendeu aos dois pa?ses, em 2011, algo em torno de US$ 224 milh?es. A Argentina ? um dos primeiros produtores mundiais, tendo produzido 83.121 toneladas, em n?meros de 2011. Isso significa que a apicultura ? uma atividade de vulto para o universo do agroneg?cio de ambos os pa?ses. Todo esse volume de produ??o e o montante angariado pelos dois pa?ses s?o frutos do esfor?o conjunto de produtores, centros de pesquisa e ?rg?os de fomento etc. Portanto, modelos matem?ticos que possibilitem melhor compreens?o do comportamento da produ??o de mel ao longo do tempo, sob a influ?ncia de diversos fatores, podem ser importantes instrumentos de planejamento para diversos atores nesse cen?rio. O objetivo deste trabalho ? desenvolver modelos matem?ticos, definidos por sistemas de equa??es diferenciais ordin?rias, cujas solu??es num?ricas e par?metros possam permitir a obten??o informa??es a respeito da produ??o de mel de determinadalocalidade.A hip?tese central ? a de que ? poss?vel prever e avaliar a produ??o de dada localidade, utilizando modelos matem?ticos. Uma hip?tese secund?ria seria a de que os par?metros desses modelos poderiam ser importantes indicadores a respeito da atividade produtiva.Os modelos aqui elaborados tiveram como base o Modelo de Lucas para o crescimento econ?mico de longo prazo, que leva em conta o capital humano como elemento end?geno fundamental de crescimento. A recupera??o dos par?metros e a obten??o das solu??esnum?ricas para os modelos foram implementadas atrav?s de software na linguagem Fortran 95.O princ?pio norteador do software foi o de fornecer solu??es para os modelos que oferecessem uma descri??o ?tima da produ??o de uma certa localidade, durante um certo per?odo de tempo.Para os ajustes da solu??o do sistema de equa??es diferenciais que definem os modelos, foi utilizado um m?todo dos quadrados m?nimos n?o linear. O solver para este m?todo foi o algoritmo apresentado em Powell (2009), denominado BOBYQA. Esse algoritmo foi escrito em Fortran 77, sendo livre de derivadas e aceitando restri??es de caixa. A valida??o do modelo foi feita em duas etapas: na primeira,ajustou-se o modelo adadosgedanken de produ??o de mel. Na segunda etapa os modelos foram aplicados ? produ??o de dezoito munic?pios representativos, em produ??o mel?fera, das microrregi?es em que o Estado do Rio de Janeiro est? dividido. Houve bom ajuste dos modelos em 15 dos munic?pios pesquisados. S? n?o houve ajuste nos tr?s casos em que a produ??o mostrou-se an?mala. Dessa forma, os resultados permitem concluir que os modelos desenvolvidos podem servir de instrumento eficaz para os gestores do agroneg?cio do mel, podendo inclusive fornecer boas previs?es de produ??o sob certas condi??es e estimativas de safra em per?odos de colheita. Al?m do mais, podem abrir front importante de pesquisa a respeito da tecnologia e produtividade empregadas nesta atividade econ?mica.
275

Causes and consequences of individual forager variability in social bees / Analyse des causes et conséquences de la diversité dans les stratégies de butinage de pollinisateurs sociaux

Klein, Simon 26 January 2018 (has links)
Chez les pollinisateurs sociaux, comme l'abeille domestique (Apis mellifera L.) et le bourdon terrestre (Bombus terrestris L.), mes deux modèles d'étude, différents individus sont spécialisés dans différentes tâches. Il est admis que différents types de comportement de butinage contribuent à une optimisation des performances de la colonie. Actuellement, les populations de pollinisateurs sont exposées à des stress environnementaux, qui sont connus pour perturber le comportement des individus en visant directement leur cognition. Il est ainsi crucial de mieux comprendre comment les colonies d'abeilles et de bourdons maintiennent une activité de butinage efficace, et quels sont les effets de stress environnementaux sur les butineuses. Dans cette thèse, j'ai donc examiné les différentes stratégies de butinage pour différentes sources de nourriture, pollen et nectar, et les variabilités interindividuelles dans le comportement de butinage. Je me suis aussi intéressé à l'impact de stress tels que les pesticides sur l'efficacité de butinage. J'ai utilisé la technologie RFID pour suivre le comportement des abeilles tout au long de leur vie. J'ai trouvé que les colonies d'abeilles et de bourdons reposent sur un petit groupe d'individus très actifs qui fournissent la majorité de la nourriture pour la colonie. Chez les abeilles, ces individus très actifs sont aussi plus efficaces pour collecter nectar et pollen. J'ai aussi identifié l'existence de différentes stratégies pour la collecte de pollen ou de nectar. Ensuite, j'ai pu montrer que les bourdons ont des différences interindividuelles très marquées dans un test de navigation, une tâche cruciale dans le comportement de butinage. Finalement, j'ai testé l'effet néfaste de pesticides sur l'apprentissage visuel chez l'abeille. Cette thèse a pour but de mieux comprendre les causes de vulnérabilité des pollinisateurs aux stress environnementaux. Mes résultats soulignent le besoin de considérer la diversité comportementale comme une adaptation des espèces de pollinisateurs sociaux, mais aussi comme une potentielle cause de vulnérabilité de la colonie vis-à-vis des stress. / In social insects, such as bees, different individuals specialise in the collection of different resources, and it is assumed that natural behavioural variability among foragers contributes to a self-organised optimisation of colony performance. Currently, bee populations are facing an increasing number of environmental stressors, known to disturb the behaviour of individuals, presumably upon their impact on cognitive capacities. Hence it is important to learn more about how stressors impact on individual foraging behaviour to understand how a colony maintains effective nutrition and development. In this thesis in cognitive ecology, I examined the different foraging strategies for the different macronutrient sources, pollen and nectar, and the inter-individual variation in bee foraging performance. I also looked at how stressors, such as pesticides, can impact on bee foraging efficiency. I compared two social Hymenoptera that vary in their level of social complexity: the European honey bee (Apis mellifera L.) and the buffed-tailed bumblebee (Bombus terrestris L.). I used Radio Frequency Identification (RFID) to automatically track the foraging behaviour of bees throughout their life. I found that honey bee and bumblebee colonies rely on a subset of very active bees to supply the whole colony needs. In honey bees, these foragers are more efficient and collect more pollen. I also identified different strategies for pollen or nectar collection in both species. Using manipulative experiments, I then showed that bees exhibit consistent inter-individual different behaviours in a spatial learning task and that pesticides impair visual learning. My thesis aims at better explaining the causes of vulnerability of pollinators to sublethal pesticides and other environmental stressors. The results highlight the need for considering behavioural diversity as an adaptation for social insects, as well as a potential dimension of colony-level vulnerability to environmental stressors that can impair the whole colony nutritional balance.
276

Forrageamento estacional da Apis mellifera L., 1758 (Hymenoptera : Apidae) e identificação da florada apícola de importância nectífera e polinífera em Jaboticabal, São Paulo, Brasil /

Doreto, Hanay dos Santos. January 2019 (has links)
Orientador: Eduardo Custódio Gasparino / Resumo: As abelhas Apis mellifera L. (1758) são consideradas os principais polinizadores das plantas com flores e também uma das espécies mais produtoras de mel. Devido o amplo número de espécies vegetais que utilizam para a obtenção de alimento e matéria-prima, a identificação botânica do mel é fundamental para a classificação da florada em monofloral ou silvestre. Para isso, a técnica da melissopalinologia utiliza da análise das características morfológicas externas dos grãos de pólen presentes no mel. O presente estudo objetivou analisar o comportamento estacional de forrageamento de colmeias de Apis mellifera por meio da identificação dos tipos polínicos nectíferos e poliníferos presentes no mel. As coletas do mel foram realizadas entre outubro de 2017 a agosto de 2018 nas estações primavera, verão, outono e inverno no Setor de Apicultura da Faculdade de Ciências Agrárias e Veterinárias, FCAV/UNESP Campus de Jaboticabal, São Paulo, Brasil onde três colmeias de abelhas Apis mellifera estavam instaladas. Para a extração dos grãos de pólen e montagem das lâminas a metodologia clássica da melissopalinologia e a técnica clássica de acetólise foram empregadas. Ao todo, foram encontrados 42 tipos polínicos, distribuídos em 24 famílias botânicas. Alguns tipos foram observados em todas as estações: Alternanthera (Amaranthaceae), Cecropia (Urticaceae), Mimosa (Fabaceae) e Myrtaceae (Myrtaceae), mas também houve a ocorrência de tipos exclusivos das estações: Aloe, Bignoniaceae, Byrsonima, D... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Apis mellifera L. (1758) bees are considered the main pollinators of flowering plants and also one of the most honey-producing species. Because of the large number of plant species they use to obtain food and raw materials, the botanical identification of honey is fundamental for the classification of flowering as monofloral or wild. For this, the melissopalynology technique uses the analysis of the external morphological characteristics of pollen grains present in honey. The present study aimed to analyze the seasonal foraging behavior of Apis mellifera hives by identifying the nectiferous and polyniferous pollen types present in honey. Honey was collected between October 2017 and August 2018 in the spring, summer, autumn and winter seasons at the Setor de Apicultura da Faculdade de Ciências Agrárias e Veterinárias, FCAV/UNESP Campus de Jaboticabal, São Paulo, Brazil where three hives of Apis mellifera bees were installed. For the extraction of pollen grains and slide assembly the classical melissopalynology methodology and the classical acetolysis technique were employed. In all, 42 pollen types were found, distributed in 24 botanical families. Some types were observed in all seasons: Alternanthera (Amaranthaceae), Cecropia (Urticaceae), Mimosa (Fabaceae) and Myrtaceae (Myrtaceae), but there were also unique types of seasons: Aloe, Bignoniaceae, Byrsonima, Daustinia, Eucalyptus, Euphorbiaceae, Machaerium, Mangifera, Pseudobombax, Sapindus, Solanum and Tabebuia in spring; An... (Complete abstract click electronic access below) / Mestre
277

Use Of Multi-walled Carbon Nanotubes In Matrix Solid Phase Dispersion Extraction Combined With Gas Chromatography

Njie, Njaw 01 June 2008 (has links) (PDF)
The use of Multi-Walled Carbon Nanotubes (MWCNT) as solid sorbent in Matrix Solid-Phase Dispersion (MSPD) extraction and preconcentration method was presented to determine some commonly used organophosphorus insecticides/OPIs in honey samples using a Gas Chromatography Flame Ionization Detector (GC-FID). OPIs are poisonous compounds used to kill insects and rodents by affecting their nervous system. The limit of detections obtained after MSPD extraction were 7.0 ng/g for Malathion, Malaoxon and Fenitrothion and 33.3 ng/g for Isomalathion. The recovery of the insecticides from spiked honey, ranged from 83.6% to 103.3% with % RSD ranged from 9.8% to 12.3% (n=3). The correlation coefficient (R2) of the calibration data varied from 0.9945 to 0.9987. Standard addition method was utilized to examine matrix-induced effects on analyte peaks, and to demonstrate the efficiency of the method. The MSPD extraction was successfully applied for the analysis of four honey samples but no insecticide residues were detected.
278

alpha- Dicarbonyle in Lebensmitteln und glucosehaltigen Lösungen der Peritonealdialyse

Weigel, Kai 11 October 2004 (has links) (PDF)
Das Vorkommen von alpha-Dicarbonylverbindungen werden in 2 Schwerpunkten dokumentiert. Zum einen werden mehrere Honige auf Ihren Gehalt an 3-DG, GO und MGO neben HMF analysiert und die Bildung wärend einer Lagerung beobachtet. Zum anderen wird die Entstehung von alpha-Dicarbonylen und anderen cytotoxischen Glucoseabbauprodukten bei der Behandlung von Lösungen der Peritonealdialyse mit hohen Druck beobachtet.
279

Biotic and abiotic controls on carbon dynamics in a Central Texas encroaching savanna

Thijs, Ann 16 January 2015 (has links)
Anthropogenic activities are responsible for increases in atmospheric CO₂ and climate change. These increases are partly counterbalanced by natural processes, such as carbon uptake in land surfaces. These processes are themselves subject to climate change, creating a coupled carbon-climate system. I investigated the carbon sink that woody encroachment represents, using a Central Texas savanna as study site, and studied how climatic factors influence this carbon sink. Woody plant encroachment, a worldwide structural change in grassland and savanna ecosystems, alters many ecosystem properties, but the net effect on the carbon balance is uncertain. Woody encroachment represents one of the key uncertainties in the US carbon balance, and demands a more detailed understanding. To come to a process-based understanding of the encroachment effect on carbon dynamics, I analyzed patterns of carbon exchange using eddy-covariance technology. I expected the imbalance between carbon uptake and release processes associated with the encroaching trees specifically, to be responsible for the carbon sink. I also expected that the sink would vary in time, due to strong links between carbon fluxes and soil water in this semi-arid ecosystem. I further studied the ecophysiology of the dominant species, as well as soil respiration processes under different vegetation types, and scaled these findings in space and time. I found that the ecosystem was a significant carbon sink of 405 g C m⁻² yr⁻¹. The encroaching trees increased photosynthesis by 180% and decreased soil respiration by 14%, compared to the grassland, resulting in a strong carbon sink due to the encroachment process. The encroaching process also altered carbon dynamics in relation to climatic drivers. The evergreen species Ashe juniper effectively lengthened the growing season and widened the temperature range over which the ecosystem acts as a carbon sink. The drought resistance of the encroaching trees reduced the sensitivity of this savanna to drought. I conclude that encroachment in Central Texas savannas increased the carbon sink strength by increasing the carbon inputs into the ecosystem. Woody encroachment also reduced the sensitivity to climatic drivers. These two effects constitute a direct effect, as well as a negative feedback to the coupled carbon-climate system. / text
280

Sleeping in a society : social aspects of sleep within colonies of honey bees (Apis mellifera)

Klein, Barrett Anthony 02 August 2011 (has links)
Sleep is a behavioral condition fraught with mystery. Its definition—either a suite of diagnostic behavioral characters, electrophysiological signatures, or a combination of the two—varies in the literature and lacks an over-arching purpose. In spite of these vagaries, sleep supports a large and dynamic research community studying the mechanisms, ontogeny, possible functions and, to a lesser degree, its evolution across vertebrates and in a small number of invertebrates. Sleep has been described and examined in many social organisms, including eusocial honey bees (Apis mellifera), but the role of sleep within societies has rarely been addressed in non-human animals. I investigated uniquely social aspects of sleep within honey bees by asking basic questions relating to who sleeps, when and where individuals sleep, the flexibility of sleep, and why sleep is important within colonies of insects. First, I investigated caste-dependent sleep patterns in honey bees and report that younger workers (cell cleaners and nurse bees) exhibit arrhythmic and brief sleep bouts primarily while inside comb cells, while older workers (food storers and foragers) display periodic, longer sleep bouts primarily outside of cells. Next, I mapped sleep using remote thermal sensing across colonies of honey bees after introducing newly eclosed workers to experimental colonies and following them through periods of their adult lives. Bees tended to sleep outside of cells closer to the edge of the hive than when asleep inside cells or awake, and exhibited caste-dependent thermal patterns, both temporally and spatially. Wishing to test the flexibility of sleep, I trained foragers to a feeder and made a food resource available early in the morning or late in the afternoon. The bees were forced to shift their foraging schedule, which consequently also shifted their sleep schedule. Finally, I sleep-deprived a subset of foragers within a colony by employing a magnetic “insominator” to test for changes in their signaling precision. Sleep-deprived foragers exhibited reduced precision when encoding direction information to food sources in their waggle dances. These studies reveal patterns and one possible purpose of sleep in the context of a society. / text

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