Le début de l’adolescence est une période de changements rapides où la détresse psychologique et l’expérimentation de la marijuana sont choses fréquentes. Certaines études longitudinales ont démontré que ces deux phénomènes ont tendance à se manifester conjointement tandis que d’autres n’ont pu observer de tel lien. Ces résultats divergents suggèrent que plusieurs questions persistent concernant la nature de cette relation. Cette thèse a pour objectif d’explorer la consommation de marijuana et la détresse psychologique en début d’adolescence afin de mieux saisir les changements à travers le temps, ainsi que d’examiner si ces deux problématiques évoluent conjointement et s’influencent réciproquement. Un échantillon de 448 adolescents garçons et filles fréquentant deux écoles secondaires de Montréal, ont été suivi de secondaire I à secondaire III. De 1999 à 2001, les participants ont complété un questionnaire à chaque année de l’étude incluant des mesures portant sur la consommation de marijuana et la détresse psychologique (IDPESQ-14). Un modèle de mixture semi-paramétrique (Nagin, 2005) a été utilisé afin d’identifier les trajectoires développementales de la consommation de marijuana et de détresse psychologique. Des analyses ont également été effectuées afin d’établir les liens d’appartenance entre chacune des trajectoires de consommation identifiées et la détresse psychologique lors de la première année de l`étude, ainsi qu’entre chacune des trajectoires de détresse psychologique et la consommation de marijuana en première année du secondaire. Finalement, des analyses de trajectoires jointes ont été effectuées afin de déterminer l’interrelation entre la consommation de marijuana et la détresse psychologique. Les résultats de notre étude suggèrent qu’il existe une grande hétérogénéité au niveau de la consommation de marijuana et la détresse psychologique. Trois trajectoires développementales ont été identifiées pour la consommation de marijuana: consommation légère, consommation grandissante et consommation élevée et stable. Trois trajectoires ont également été observées pour la détresse psychologique : basse, moyenne et élevée. Nos résultats démontrent la présence d’un lien entre la détresse psychologique rapportée lors de la première année de l’étude et les trajectoires de consommation problématiques. Ce lien a également été observé entre la consommation de marijuana rapportée lors de première année de l’étude et les trajectoires problématiques de détresse psychologique. Les analyses de trajectoires jointes démontrent la présence d’une concordance entre la consommation de marijuana et la détresse psychologique. Cette interrelation est toutefois complexe puisque les trajectoires de détresse psychologique élevée sont associées à un niveau de consommation de marijuana plus problématique mais l’inverse de cette association est moins probable. Notre étude met en lumière la nature asymétrique de la concordance entre la consommation de marijuana et la détresse psychologique. / Early adolescence is period of rapid changes where psychological distress and marijuana use experimentation are common occurrences. Longitudinal studies examining the association between these two phenomena have provided mixed results and many questions prevail regarding the nature of this association. The purpose of this study is to examine the patterns of co-occurrence between marijuana use and psychological distress in early adolescence. A sample of 448 adolescent boys and girls attending two high schools in Montreal, Canada was followed from Grade 7 to 9. From 1999 to 2001, the participants completed an annual survey which included measures of marijuana use and psychological distress (IDPESQ-14). Using a semi-parametric group based modeling strategy, the study has for objectives to establish the developmental trajectories of marijuana use and psychological distress in early adolescence, to explore how marijuana use or psychological distress measured at baseline is associated with various developmental trajectories and to examine the interrelationship of these two phenomena as they concurrently develop over the span of our study. Our results provide evidence that marijuana use and psychological distress are phenomena with great heterogeneity as they develop over time. We identified 3 trajectories of marijuana use: Light Users, Increasers and High Chronics and 3 trajectories of psychological distress: Low, Medium and High. Our findings also demonstrate that adolescents who reported psychological distress at baseline were more likely to follow problematic trajectories of marijuana use when compared to light users and the reverse of the association was also true since adolescent who reported marijuana use at baseline were more likely to follow an elevated trajectory of psychological distress. Our joint trajectory analysis demonstrated that the developmental patterns of co-occurrence of marijuana use and psychological distress are complex. Our study provides evidence that adolescents following a trajectory of elevated psychological distress are at increased risk of also following a trajectory of elevated marijuana use but adolescents following a problematic trajectory of marijuana use are not necessarily at greater risk of following an elevated trajectory of psychological distress. Our study highlights the presence of an asymmetrical relationship between marijuana use and psychological distress in early adolescence.

Over the past 100–150 years Texas rangelands have dramatically changed from native open savannahs to dense woodlands. On the Edwards plateau, a major management concern is the increasing encroachment of Ashe juniper (Juniperus ashei). Preceding an anticipated brush management program, I investigated the presence, co-occurrence, and habitat relationships of 7 breeding bird species in the Leon River Watershed in central Texas, USA: black-capped vireo (Vireo atricapillus), golden-cheeked warbler (Dendroica chrysoparia), northern bobwhite (Colinus virginianus), white-eyed vireo (Vireo griseus), Bell’s vireo (Vireo bellii), painted bunting (Passerina ciris), and brown-headed cowbird (Molothrus ater). Vegetation characteristics were compared between sites occupied by each species and unoccupied sites using univariate analysis. Models for predicting species site occupancy were developed (using logistic regression) based on habitat characteristics correlated with the presence of each species. Two species of special concern, the endangered black-capped vireo and golden-cheeked warbler occupied 5.6% of sites and 13.8% of sites respectively, while the brood parasite brown-headed cowbird was the most widespread, occupying 86.8% of sites. Species co-occurrence patterns revealed significant associations between the golden-cheeked warbler and each of 5 other species. For most species, variables included in habitat models could be explained by knowledge of species known habitat associations. For example, the black-capped vireo was positively associated with increasing low-growing (<1.5 m) hardwood cover and with Low Stony Hill ecological sites. The golden-cheeked warbler was positively associated with increasing density of larger juniper trees, increasing variability in vertical vegetation structure, and decreasing midstory canopy of deciduous nonoaks (e.g., cedar elm [Ulmus crasifolia]). It also preferred Low Stony Hill and Steep Adobe ecological sites. Site occupancy seemed to be driven by variables that describe overall vegetation structure. In particular, cover of low-growing non-juniper vegetation and juniper tree density appeared to be important in determining site occupancy for several species. Although the models constructed were not very robust, resource managers can still benefit from such models because they provide a preliminary examination of important controlling variables. Managing rangelands to maintain or restore a mosaic of juniper patches and open shrublands are likely to help meet the habitat requirements of these bird communities.

This thesis is motivated by the need for scalable and reliable methods and technologies that support the construction of network data based on information from text data. Ultimately, the resulting data can be used for answering substantive and graph-theoretical questions about socio-technical networks. One main limitation with constructing network data from text data is that the validation of the resulting network data can be hard to infeasible, e.g. in the cases of covert, historical and large-scale networks. This thesis addresses this problem by identifying the impact of coding choices that must be made when extracting network data from text data on the structure of networks and network analysis results. My findings suggest that conducting reference resolution on text data can alter the identity and weight of 76% of the nodes and 23% of the links, and can cause major changes in the value of commonly used network metrics. Also, performing reference resolution prior to relation extraction leads to the retrieval of completely different sets of key entities in comparison to not applying this pre-processing technique. Based on the outcome of the presented experiments, I recommend strategies for avoiding or mitigating the identified issues in practical applications. When extracting socio-technical networks from texts, the set of relevant node classes might go beyond the classes that are typically supported by tools for named entity extraction. I address this lack of technology by developing an entity extractor that combines an ontology for sociotechnical networks that originates from the social sciences, is theoretically grounded and has been empirically validated in prior work, with a supervised machine learning technique that is based on probabilistic graphical models. This thesis does not stop at showing that the resulting prediction models achieve state of the art accuracy rates, but I also describe the process of integrating these models into an existing and publically available end-user product. As a result, users can apply these models to new text data in a convenient fashion. While a plethora of methods for building network data from information explicitly or implicitly contained in text data exists, there is a lack of research on how the resulting networks compare with respect to their structure and properties. This also applies to networks that can be extracted by using the aforementioned entity extractor as part of the relation extraction process. I address this knowledge gap by comparing the networks extracted by using this process to network data built with three alternative methods: text coding based on thesauri that associate text terms with node classes, the construction of network data from meta-data on texts, such as key words and index terms, and building network data in collaboration with subject matter experts. The outcomes of these comparative analyses suggest that thesauri generated with the entity extractor developed for this thesis need adjustments with respect to particular categories and types of errors. I am providing tools and strategies to assist with these refinements. My results also show that once these changes have been made and in contrast to manually constructed thesauri, the prediction models generalize with acceptable accuracy to other domains (news wire data, scientific writing, emails) and writing styles (formal, casual). The comparisons of networks constructed with different methods show that ground truth data built by subject matter experts are hardly resembled by any automated method that analyzes text bodies, and even less so by exploiting existing meta-data from text corpora. Thus, aiming to reconstruct social networks from text data leads to largely incomplete networks. Synthesizing the findings from this work, I outline which types of information on socio-technical networks are best captured by what network data construction method, and how to best combine these methods in order to gain a more comprehensive view on a network. When both, text data and relational data, are available as a source of information on a network, people have previously integrated these data by enhancing social networks with content nodes that represent salient terms from the text data. I present a methodological advancement to this technique and test its performance on the datasets used for the previously mentioned evaluation studies. By using this approach, multiple types of behavioral data, namely interactions between people as well as their language use, can be taken into account. I conclude that extracting content nodes from groups of structurally equivalent agents can be an appropriate strategy for enabling the comparison of the content that people produce, perceive or disseminate. These equivalence classes can represent a variety of social roles and social positions that network members occupy. At the same time, extracting content nodes from groups of structurally coherent agents can be suitable for enabling the enhancement of social networks with content nodes. The results from applying the latter approach to text data include a comparison of the outcome of topic modeling; an efficient and unsupervised information extraction technique, to the outcomes of alternative methods, including entity extraction based on supervised machine learning. My findings suggest that key entities from meta-data knowledge networks might serve as proper labels for unlabeled topics. Also, unsupervised and supervised learning leads to the retrieval of similar entities as highly likely members of highly likely topics, and key nodes from text-based knowledge networks, respectively. In summary, the contributions made with this thesis help people to collect, manage and analyze rich network data at any scale. This is a precondition for asking substantive and graph-theoretical questions, testing hypotheses, and advancing theories about networks. This thesis uses an interdisciplinary and computationally rigorous approach to work towards this goal; thereby advancing the intersection of network analysis, natural language processing and computing.

Protein sequences are essential for encoding molecular structures and functions. Consequently, biologists invest substantial resources and time discovering functional patterns in proteins. Using high-throughput technologies, biologists are generating an increasing amount of data. Thus, the major challenge in biosequencing today is the ability to conduct data analysis in an effi cient and productive manner. Conserved amino acids in proteins reveal important functional domains within protein families. Conversely, less conserved amino acid variations within these protein sequence patterns reveal areas of evolutionary and functional divergence. Exploring protein families using existing methods such as multiple sequence alignment is computationally expensive, thus pattern search is used. However, at present, combinatorial methods of pattern search generate a large set of solutions, and probabilistic methods require richer representations. They require biological ground truth of the input sequences, such as gene name or taxonomic species, as class labels based on traditional classi fication practice to train a model for predicting unknown sequences. However, these algorithms are inherently biased by mislabelling and may not be able to reveal class characteristics in a detailed and succinct manner. A novel pattern representation called an Aligned Pattern Cluster (AP Cluster) as developed in this dissertation is compact yet rich. It captures conservations and variations of amino acids and covers more sequences with lower entropy and greatly reduces the number of patterns. AP Clusters contain statistically signi cant patterns with variations; their importance has been confi rmed by the following biological evidences: 1) Most of the discovered AP Clusters correspond to binding segments while their aligned columns correspond to binding sites as verifi ed by pFam, PROSITE, and the three-dimensional structure. 2) By compacting strong correlated functional information together, AP Clusters are able to reveal class characteristics for taxonomical classes, gene classes and other functional classes, or incorrect class labelling. 3) Co-occurrence of AP Clusters on the same homologous protein sequences are spatially close in the protein's three-dimensional structure. These results demonstrate the power and usefulness of AP Clusters. They bring in similar statistically signifi cance patterns with variation together and align them to reveal protein regional functionality, class characteristics, binding and interacting sites for the study of protein-protein and protein-drug interactions, for diff erentiation of cancer tumour types, targeted gene therapy as well as for drug target discovery.

Le début de l’adolescence est une période de changements rapides où la détresse psychologique et l’expérimentation de la marijuana sont choses fréquentes. Certaines études longitudinales ont démontré que ces deux phénomènes ont tendance à se manifester conjointement tandis que d’autres n’ont pu observer de tel lien. Ces résultats divergents suggèrent que plusieurs questions persistent concernant la nature de cette relation. Cette thèse a pour objectif d’explorer la consommation de marijuana et la détresse psychologique en début d’adolescence afin de mieux saisir les changements à travers le temps, ainsi que d’examiner si ces deux problématiques évoluent conjointement et s’influencent réciproquement. Un échantillon de 448 adolescents garçons et filles fréquentant deux écoles secondaires de Montréal, ont été suivi de secondaire I à secondaire III. De 1999 à 2001, les participants ont complété un questionnaire à chaque année de l’étude incluant des mesures portant sur la consommation de marijuana et la détresse psychologique (IDPESQ-14). Un modèle de mixture semi-paramétrique (Nagin, 2005) a été utilisé afin d’identifier les trajectoires développementales de la consommation de marijuana et de détresse psychologique. Des analyses ont également été effectuées afin d’établir les liens d’appartenance entre chacune des trajectoires de consommation identifiées et la détresse psychologique lors de la première année de l`étude, ainsi qu’entre chacune des trajectoires de détresse psychologique et la consommation de marijuana en première année du secondaire. Finalement, des analyses de trajectoires jointes ont été effectuées afin de déterminer l’interrelation entre la consommation de marijuana et la détresse psychologique. Les résultats de notre étude suggèrent qu’il existe une grande hétérogénéité au niveau de la consommation de marijuana et la détresse psychologique. Trois trajectoires développementales ont été identifiées pour la consommation de marijuana: consommation légère, consommation grandissante et consommation élevée et stable. Trois trajectoires ont également été observées pour la détresse psychologique : basse, moyenne et élevée. Nos résultats démontrent la présence d’un lien entre la détresse psychologique rapportée lors de la première année de l’étude et les trajectoires de consommation problématiques. Ce lien a également été observé entre la consommation de marijuana rapportée lors de première année de l’étude et les trajectoires problématiques de détresse psychologique. Les analyses de trajectoires jointes démontrent la présence d’une concordance entre la consommation de marijuana et la détresse psychologique. Cette interrelation est toutefois complexe puisque les trajectoires de détresse psychologique élevée sont associées à un niveau de consommation de marijuana plus problématique mais l’inverse de cette association est moins probable. Notre étude met en lumière la nature asymétrique de la concordance entre la consommation de marijuana et la détresse psychologique. / Early adolescence is period of rapid changes where psychological distress and marijuana use experimentation are common occurrences. Longitudinal studies examining the association between these two phenomena have provided mixed results and many questions prevail regarding the nature of this association. The purpose of this study is to examine the patterns of co-occurrence between marijuana use and psychological distress in early adolescence. A sample of 448 adolescent boys and girls attending two high schools in Montreal, Canada was followed from Grade 7 to 9. From 1999 to 2001, the participants completed an annual survey which included measures of marijuana use and psychological distress (IDPESQ-14). Using a semi-parametric group based modeling strategy, the study has for objectives to establish the developmental trajectories of marijuana use and psychological distress in early adolescence, to explore how marijuana use or psychological distress measured at baseline is associated with various developmental trajectories and to examine the interrelationship of these two phenomena as they concurrently develop over the span of our study. Our results provide evidence that marijuana use and psychological distress are phenomena with great heterogeneity as they develop over time. We identified 3 trajectories of marijuana use: Light Users, Increasers and High Chronics and 3 trajectories of psychological distress: Low, Medium and High. Our findings also demonstrate that adolescents who reported psychological distress at baseline were more likely to follow problematic trajectories of marijuana use when compared to light users and the reverse of the association was also true since adolescent who reported marijuana use at baseline were more likely to follow an elevated trajectory of psychological distress. Our joint trajectory analysis demonstrated that the developmental patterns of co-occurrence of marijuana use and psychological distress are complex. Our study provides evidence that adolescents following a trajectory of elevated psychological distress are at increased risk of also following a trajectory of elevated marijuana use but adolescents following a problematic trajectory of marijuana use are not necessarily at greater risk of following an elevated trajectory of psychological distress. Our study highlights the presence of an asymmetrical relationship between marijuana use and psychological distress in early adolescence.

情感運算引領人機互動開創一新的研究發展領域，通過各種能觀測人類情感表達的工具來計算不同表達方式的情感蘊含；另一方面，拜發展急速的網路媒體所賜，大量文字成為線上傳遞訊息便捷又有效率的方式，因此，各類富含情感的文字能夠被搜集成為情感分析運算的語料；而近年來跨領域研究的盛行，促成許多不同學科間的對話，也將各種技術帶入不同的領域知識範疇中，開啟創新研究的可能；有如資訊領域的社會網路分析(Social Network Analysis)技術套用到語言文字的研究上，使得大量語料的分析能夠更快速的達成。 本研究針對英文的情歌歌詞進行字詞共現網絡(Word Co-Occurrence Network)的分析，將字彙之間的概念關聯，和歌詞文本隱喻分析的結果作一比較，以評估字詞共現網絡作為隱喻表達分析工具的潛能，提供不同角度的情感語意探勘方法，作為情感溝通上的一項貢獻。 / Affective computing explore a new research field, human different emotional expression could be calculated through types of affection detection tool. On the other hand, “word” as a convenience communication medium through the online media, lead lots of entailment affection word to be the affective computing analysis corpus. Interdisciplinary cooperation researches prevail among different academic field to initiate innovation study. Applying Social Network Analysis (SNA) information technique to semantic research as an example, make the large corpus analysis to be more efficiency. In this research, Word Co-Occurrence Network was used to explore the specific meaning of the lyrics to observe what the content represent affective concepts in western classical love songs, and evaluated the potential of Word Co-Occurrence Network to be a new concept relation analysis tool by compared with the content analysis data.

Child maltreatment is not a new issue. It has existed in various forms in every society since the early days in history. However, it is only in the past four decades that abuse and neglect of children has attracted widespread interest among health professionals and the general public. There is now a large body of evidence that identifies four main maltreatment forms: physical, sexual, emotional maltreatment and neglect. Child maltreatment is a substantial public health problem, as it is associated with immediate and long-term health problems. Most research into child maltreatment has been conducted in English-speaking, developed countries. Although there has been a small but steady increase in the number of studies from less developed countries over the past decade, there remains a relative dearth of research in these populations, especially in Asia. Over the years, most research projects around the world tend to be focused on only one type of child maltreatment (usually either child sexual abuse or child physical maltreatment), and many studies do not examine risk factors in depth, or address the possible outcomes of various forms of maltreatment. Children have always held a very important place in the culture and traditions in Vietnam. In 1989, Vietnam was the first Asian country and the second country in the world to sign and ratify the United Nations Convention on the Rights of the Child. Since then Vietnam has adopted various measures to promote children's rights and particularly children's rights to be protected from abuse and exploitation. Despite strong political support for the rights of children, there is little formal research into child maltreatment. From the small amount of available evidence and media reports, it appears that children in Vietnam are vulnerable to maltreatment, just as they are all over the world. It is clear that information about the extent and health consequences of different forms of child maltreatment from scientifically sound studies is still far from sufficient. Thus, more research is essential to ensure effective and culturally appropriate responses to protect children from maltreatment. The primary aim of this research was to examine the nature and co-occurrence of four forms of child maltreatment including sexual, physical, emotional maltreatment and neglect among Vietnamese secondary and high school adolescents in both urban and rural settings, and determine the extent to which such adverse experiences impact on self-reported health risk behaviours and physical and mental health. A mixed methods design including qualitative interviews and focus group discussions, and a cross-sectional survey was employed in this study. Incorporation of qualitative inquiry added a cultural dimension on child maltreatment and informed to develop appropriate quantitative measures. Following 8 focus group discussions and 16 in-depth interviews as well as a pilot study of 299 adolescents in Vietnamese schools, a cross-sectional survey of 2,591 adolescents randomly selected from eight secondary and high schools in one urban district and one rural district was undertaken between 2004 and 2005. Data were collected by self-administered questionnaires in class rooms. Key information included demographics, family characteristics and environment, and four scales measuring sexual abuse, emotional and physical maltreatment and neglect as well as standard brief assessments of health related risk behaviours, mental and general physical health. The study clearly revealed that experiences of different forms and co-occurrence of child maltreatment among school adolescents were prevalent in Vietnam. The prevalence estimates of at least one type of physical and emotional maltreatment, neglect and sexual abuse were 47.5%, 39.5%, 29.3% and 19.7% respectively. A significant proportion of respondents (41.6%) was exposed to more than one form of child maltreatment, of which 14.5% and 6.3% experienced three or four maltreatment forms. Results from multivariate logistic regression analyses showed that the prevalence of child physical and emotional maltreatment and neglect among adolescents was not statistically different between urban and rural districts. However, children from rural schools were more likely to report unwanted sexual experiences than their counterparts in urban schools. There was no significant gender difference in reports of adverse sexual experiences. In contrast, girls were more likely to report emotional maltreatment and neglect whereas boys were more likely to experience physical maltreatment. Furthermore, family environment assessed by parental quarrelling, fighting, perceived quality of parental relationship and emotional support appeared to be the most consistent factors significantly predicting each form of child maltreatment. After controlling for a wide range of potential confounding factors, many significant correlates between each type of maltreatment, each level of maltreatment co-occurrence and each health risk behaviour were found. In general, the pattern of correlations between child maltreatment and health risk behaviours was similar for females and males. Emotional maltreatment significantly correlated with most behaviours examined. Physical maltreatment seems more likely to be associated with involvement in physical fights and being threatened. Sexual abuse was significantly related to smoking, drinking, being drunk, and involvement in fighting. Statistically significant associations between neglect and self-harm such as involvement in fighting, feeling sad and hopeless, suicidal thoughts and attempts were found. Clearly, co-occurrence of child maltreatment was significantly associated with almost all examined health risk behaviours and a dose-response relationship was observed in most of the dependent variables. Regarding continuous measures of mental and physical health, multivariate regression analyses revealed that presence of four types of child maltreatment explained a small but significant proportion of variance (from 5% to 9%), controlling for a wide range of background variables. Additionally, while each form of child maltreatment had independent effects on depression, anxiety problems, low self-esteem and poor physical health emotional maltreatment appeared to be the strongest influence on mental and physical health of both female and male adolescents. Analysis of variance also clearly suggested that exposure to increasing numbers of maltreatment forms significantly increased the risk of mental and physical health problems in a dose-response fashion. The present study extends a small body of previous research examining poly-victimization in developed nations to an Asian country. The data contribute new knowledge on cross-cultural child maltreatment problems. Considerable commonalities as well as some differences in the findings in Vietnam compared with earlier research were found. One important conclusion concerns the significant independent associations between various types of child maltreatment, as well as the cumulative effects of poly-victimization on a wide range of health risk behaviours, depression, anxiety, self-esteem, and general physical health. This pioneering research in Vietnam provides timely and substantial evidence that can be used to raise public awareness of the nature of child maltreatment and the harmful effects of not only sexual and physical abuse but also other forms of emotional maltreatment and neglect which have not received attention before. These results from a community-based sample have demonstrated the urgent need for prevention programs. The current study provides an impetus for more comprehensive research in this sensitive area in the near future so that culturally and politically relevant evidence-based responses to child maltreatment can be developed in Vietnam.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais / Ants that collect nectar from plants bearing extrafloral nectaries (EFN) can defend them against the attacks of herbivores. Many cases of this food-for-protection mutualism have been described and the next step is to understand the mechanisms that structure these interactions. In this study, this issue was addressed through field observations and experiments on ant behaviour in studies compiled into five chapters. Specifically, we evaluated the plant\'s investment in attracting ants (nectar quality) and the competitive relationship between ants (resource dominance hierarchies) as structuring mechanisms of ant-plant interactions. The entire study took place in areas of the ecosystem known as Rupestrian Fields, located in Ouro Preto (Brazil), between June 2011 and March 2014. In Chapter 1, we observe that ant-plant interaction network in Rupestrian Fields is nested and generalized as expected for mutualisms, but differs from ant-hemipteran network, its ecological equivalent, despite both share ant species interactions. In Chapter 2, we delve into the study of the effect of resources in interaction frequency, and we showed that the quality more than quantity of nectar determines the pattern of interaction between plants (10 species) and ants (32 species), as well as the benefits of this interaction (conditional outcomes). In the Chapter 3, we focus on the ants to demonstrate, using paired encounters, that ants species are organized in dominance hierarchies based on aggressiveness. This hierarchies affects the numerical dominance based on territoriality and, more importantly, in the dominance of interactions and nectar. Keeping this line of thought, we demonstrated in Chapter 4 that not all ants that collect nectar really protect the plant against herbivores but only the ecological dominant and highly interacted species. Finally, we close the thesis demonstrating in Chapter 5 that the ant species interacted with plants during the day are not the same at night, but this diurnal-nocturnal turnover does not affect the structure of the interactions by only changing the dominant species. This study brings behavioural and empirical evidences on the importance of the identity of the ant species and its ecological dominance, as well the effect of the nectar quality, for the structure of ant-plant interactions and effectiveness of mutualisms. / As formigas que recolhem o néctar das plantas com nectários extraflorais (EFN) podem defendê-las contra ataques de herbívoros. Muitos casos desse tipo de mutualismo foram descritos mas ainda é preciso entender os mecanismos que estruturam essas interações. Neste estudo, esse problema foi abordado através de observações de campo e experimentos sobre o comportamento das formigas compilados em cinco capítulos. Especificamente, foi avaliado o investimento da planta em atrair formigas (qualidade do néctar) e a relação competitiva entre formigas pelo néctar (hierarquias de dominância) como mecanismos estruturadores das interações formiga-planta (partição das interações). Todo o estudo ocorreu em áreas do ecossistema Campo Rupestre, localizadas em Ouro Preto (Brasil), de junho de 2011 a março de 2014. No Capítulo 1, observamos que redes de interação formiga-planta em Campo rupestre é aninhada e generalizada como esperado para mutualismos, mas difere da rede formiga-hemíptero, seu equivalente ecológico, apesar de compartilharem as mesmas espécies de formigas interagentes. No Capítulo 2, nós aprofundamos no efeito dos recursos estruturando interações, e mostramos que a qualidade mais do que a quantidade de néctar determina o padrão de interação entre formigas (32 espécies) e plantas (10 espécies), bem como os benefícios desta interação (benefícios condicionais). No Capítulo 3, nós demonstramos através de encontros interespecíficos pareados que as formigas são organizadas em hierarquias de dominância comportamental baseadas em agressividade. Essa hierarquia afeta a dominância numérica por territorialidade e, mais importante, o domínio das interações e do néctar. Mantendo esta linha de pensamento, demonstramos no Capítulo 4 que nem todas as formigas que coletam néctar realmente protegem a planta contra herbívoros mas somente as espécies dominantes e altamente interagidas. Finalmente, fechamos a tese demonstrando no Capítulo 5 que as espécies de formiga que interagem com as plantas durante o dia não são o mesmo à noite, mas esta rotatividade diurno-noturno não afeta a estrutura das interações devido a troca específica da formiga dominante. Este estudo traz evidências comportamentais e empíricas sobre a importância da identidade de espécies de formiga e sua dominância ecológica, assim como da qualidade do recurso, para a estrutura de rede da formiga-planta e eficácia do mutualismo. / Doutor em Ecologia e Conservação de Recursos Naturais

Maize is the principal staple food/feed crop exposed to mycotoxins, and the co-occurrence of multiple mycotoxins and their metabolites has been well documented. Dietary (co)-exposure to mycotoxins is associated with human and animal health concerns as well as economic losses. The present thesis aims to apply a holistic approach for the risk assessment of mycotoxin mixtures in food and feed, i.e. from fungal production and occurrence to harmonised risk characterisation. This was done in three folds. Firstly, available environmental, ecological, and agronomic factors that may affect the relative abundance of co-occurring mycotoxins in the contaminated crops were collected from peer-reviewed literature, with focus on maize (Chapter I). Secondly, (co-)occurrence data on mycotoxins in core cereals was extracted from available articles in the scientific literature and analysed to estimate potential pattern of co-exposure in humans and animals (Chapter II). Finally, Chapter III investigates the applicability of the EFSA guidance to multiple mycotoxins through a scenario of possible co-exposure in humans and animals, using maize as a case study. In particular, a human and animal risk assessment to mycotoxin mixture in maize was conducted using a modelled component-based approach for selected mixture of mycotoxins, that, according to our data, co-occur in maize based feed and food products. / Maize is the principal staple food/feed crop exposed to mycotoxins, and the co-occurrence of multiple mycotoxins and their metabolites has been well documented. Dietary (co)-exposure to mycotoxins is associated with human and animal health concerns as well as economic losses. The present thesis aims to apply a holistic approach for the risk assessment of mycotoxin mixtures in food and feed, i.e. from fungal production and occurrence to harmonised risk characterisation. This was done in three folds. Firstly, available environmental, ecological, and agronomic factors that may affect the relative abundance of co-occurring mycotoxins in the contaminated crops were collected from peer-reviewed literature, with focus on maize (Chapter I). Secondly, (co-)occurrence data on mycotoxins in core cereals was extracted from available articles in the scientific literature and analysed to estimate potential pattern of co-exposure in humans and animals (Chapter II). Finally, Chapter III investigates the applicability of the EFSA guidance to multiple mycotoxins through a scenario of possible co-exposure in humans and animals, using maize as a case study. In particular, a human and animal risk assessment to mycotoxin mixture in maize was conducted using a modelled component-based approach for selected mixture of mycotoxins, that, according to our data, co-occur in maize based feed and food products.

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