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With a new focus on flow regulation by the Tennessee Valley Authority (TVA) in reservoir tailwaters, it is now possible to recover many mussel species that once occurred in these reaches. Before flows can be modified to create habitat for freshwater mussels, suitable microhabitat conditions must be defined. In this study, I used multiple approaches to define suitable microhabitats for species in the free-flowing upper Clinch River, Virginia and Tennessee, where reproducing mussel populations persist. During summer low flows in 2003 and 2004, I measured flow and substrate conditions in over 1000 microhabitat patches (0.25 m² quadrat samples) across five river reaches. Flow characteristics and embeddedness were significantly different between microhabitats occupied and unoccupied by the most abundant species (MRPP, p < 0.05). Comparison of simple and multiple logistic regression models with Akaike's Information Criteria (AIC) demonstrated that increasing Fleisswasserstammtisch (FST) hemisphere number (a measure of shear stress), decreasing degree of embeddedness, and increasing mean column velocity best explained species occurrences in a microhabitat patch. Subtle differentiation in habitat use among species was observed; however, most species appeared to be microhabitat generalists. Species were grouped into three habitat guilds using corresponding canonical analysis and cluster analysis: fast-flow specialists (FFS), fast-flow generalists (FFG), and slow-flow tolerant (SFT). I used the same data set to develop and test transferability of Habitat Suitability Criteria (HSC) for three habitat guilds and seven species of adult freshwater mussels. Nonparametric tolerance limits were used to define the range of suitable and optimal habitat during summer low flows. Optimal habitat was defined as those ranges of FST hemisphere number, mean column velocity, and embeddedness occupied by the central 50% of independent observations for a species or guild, whereas suitable habitat was defined by those ranges occupied by the central 90% of observations. The transferability of criteria to other reaches of the Clinch River was assessed using one-sided Chi-square tests. Criteria developed for the fast-flow specialist (FFS) and fast-flow generalist (FFG) guilds, as well as most criteria for species in those guilds, transferred to destination reaches. In contrast, criteria developed for the slow-flow tolerant (SFT) guild and individual constituent species consistently failed to transfer. Criteria for FFS and FFG guilds and their constituent species should be incorporated into flow simulation models such as PHABSIM to gauge the effect of minimum flows on mussel habitat quality and quantity. These criteria could also be used to determine suitable sites for mussel translocations. However, my criteria require further testing in other rivers before they can be transferred beyond the Clinch River. Behavior and physiological responses to laboratory manipulations of flow velocity and substrate particle size were used to elucidate microhabitat preferences of Actinonaias pectorosa, Potamilus alatus, and Ptychobranchus subtentum. These species appeared less stressed in the fastest flow treatment, demonstrating significantly higher oxygen consumption and oxygen-to-nitrogen (O:N) ratios than in slower flow treatments. Only P. alatus demonstrated a preference for substrate particle size, and consistently selected finer particle sizes. Actinonaias pectorosa and P. subtentum demonstrated preference for fast-flow microhabitats by readily burrowing in those conditions, while abandoning slow-flow conditions. The lack of preference for substrate particle size demonstrated by A. pectorosa and P. subtentum supports conclusions of previous studies that substrate particle size is of little or secondary importance for explaining mussel microhabitat use. These results, along with previous studies in the Clinch River, demonstrate that the stable habitats of riffles and runs; characterized by fast flows during summer low flows, low percent bedrock, and low embeddedness, are the most suitable habitats for mussel assemblages. To create and maintain suitable habitat conditions in tailwaters, releases should maintain flow over riffles at a minimum depth of no less than 30 cm in riffles that provide higher shear stress conditions (FST number > 7) and velocities (> 0.70 m/s). Periodic releases that are sufficient to transport silt and sand, but not high enough to transport larger substrate should be adequate to maintain substrates with a low degree of embeddedness. Doing so would create suitable habitat for all mussels, from the most to least specialized. Additionally, HSC developed for FFS and FFG guilds can be used to determine suitable destination sites for translocations of species belonging to these guilds. / Master of Science

The freshwater pearl mussel Margaritifera margaritifera is an endangered bivalve which is usually regarded as sedentary, although individual movement has been observed both vertically and horizontally. Little is known about the causes and rates of mussel movement. The objective of this study was to test the effect of microhabitat characteristics on the horizontal movement distance and rates of freshwater pearl mussels. A total of 120 mussels (length range 40–59 mm) were marked individually with passive integrated transponder tags, placed in stream microhabitats differing in their sediment composition and monitored biweekly over a period of 10 weeks. Mussels situated in sand-dominated habitats had a significantly higher mean movement rate (3.2 ± 4.2 cm/day, mean ± SD) than mussels situated in gravel-dominated (1.9 ± 2.7 cm/day) or stone-dominated habitats (1.8 ± 3.2 cm/day). The direction of the movements appeared random; however, an emigration from sandy habitats was observed, probably to avoid dislodgment from these hydraulically unstable habitats. This study demonstrates that freshwater pearl mussels can actively emigrate from unsuitable microhabitats. Once suitable streams with respect to physical, chemical, and biological quality were identified, it is therefore only necessary to identify suitable mesohabitats (area of 10–30 m²) when reintroducing or relocating mussels.

Made available in DSpace on 2017-07-10T18:13:27Z (GMT). No. of bitstreams: 1 Fernanda de A Gurski.pdf: 1608576 bytes, checksum: 475c7482fe1de32140a798e3ebb23954 (MD5) Previous issue date: 2011-08-12 / The heterogeneity of substrate in streams promotes the colonization and diversity of benthic organisms. Among them, Chironomidae larvae are one of the most abundant in aquatic ecosystems. This study aimed at determining the composition, richness, diversity and the existence of distribution patterns of Chironomidae larvae in different microhabitats of preserved streams of Atlantic Forest. Samplings were performed in February and August 2010, with a Surber-type sampler. The environmental variables analyzed were not significantly different between sampled streams, but the taxonomic richness of Chironomidae larvae was distinct between the microhabitats. In the total, 6,429 Chironomidae larvae were identified and classified into 96 taxa belonging to the subfamilies Chironominae, Tanypodinae and Ortocladiinae. The analyses of density, richness, evenness and diversity, in relation to the months, sites and microhabitats, have pointed out statistically significant differences in the larval distribution for the different microhabitats. Among them, the highest richness was observed in the deposits of litter, and the highest number of exclusive species took place in the pool regions. Thus, the composition and structure of the Chironomidae assemblage is directly related to the availability and heterogeneity of habitats in streams. / A heterogeneidade de substratos em riachos favorece a colonização e diversidade dos organismos bentônicos. Entre estes, as larvas de Chironomidae são uns dos mais abundantes em diversos ecossistemas aquáticos. Este trabalho teve como objetivo determinar a composição, a riqueza, a diversidade e a existência de padrões na distribuição de larvas de Chironomidae, em diferentes microhabitats de riachos preservados da Mata Atlântica. As coletas foram realizadas em fevereiro e agosto de 2010, com um amostrador tipo Surber. As variáveis ambientais analisadas não foram significativamente diferentes entre os riachos amostrados, porém a riqueza taxonômica de larvas de Chironomidae foi distinta entre os microhabitats. Foram identificadas 6.469 larvas de Chironomidae distribuídas em 96 táxons pertencentes às subfamílias Chironominae, Tanypodinae e Ortocladiinae. As análises de densidade, riqueza, equitabilidade e diversidade desta assembleia em relação aos meses, pontos e microhabitats indicaram diferenças, estatisticamente significativas, na distribuição das larvas apenas para os diferentes microhabitats. Entre eles, a maior riqueza foi observada nos depósitos de folhiços e os maiores números de espécies exclusivas ocorreram nas regiões de remansos. Assim, a composição e estrutura da assembleia de Chironomidae está diretamente relacionada à disponibilidade e à heterogeneidade de habitats em riachos.

Le concept d’habitat, qui définit le lieu de vie des organismes par des conditions abiotiques et biotiques, est déterminant pour étudier les relations entre les organismes et leur environnement. La sélection d’habitat est le processus à travers lequel l’organisme va choisir l’habitat où il se trouve en fonction des différents habitats disponibles autour de lui. Cette sélection va dépendre d’un choix individuel, qui est propre à l’organisme (ex. son comportement), et d’un choix commun, qui est observable chez des organismes qui partagent des traits communs (ex. les individus d’une même espèce). Les modèles spécifiques de sélection d’habitat cherchent à expliquer et prédire ce choix commun, et sont notamment utilisés pour les cours d’eau dans les outils d'aide à la définition de débits écologiques. Pour les poissons de rivière, la plupart des modèles spécifiques à l’échelle du microhabitat sont peu transférables à d’autres rivières. En effet, ils sont construits à partir de données d’abondance échantillonnées dans le même site pendant quelques campagnes. Afin d’améliorer la qualité prédictive de ces modèles, j’ai développé une approche prometteuse de modélisation multi-sites et multi-campagnes permettant à la fois de considérer la réponse non linéaire de la sélection et la surdispersion des données d’abondance. A partir de suivis individuels par télémétrie, j’ai montré la pertinence des modèles de sélection spécifiques malgré la forte variabilité individuelle observée. Finalement, la sélection d’habitat étant dépendante de processus structurant les communautés et agissant à l’échelle du paysage, telle que la dispersion des individus, j’ai mis en évidence l’intérêt d’utiliser des techniques légères d’échantillonnage comme les observations par plongée pour caractériser les structures des communautés et leurs répartitions spatiales. Ces techniques permettront alors d’étudier l’influence des processus du paysage sur les modèles de sélection d’habitat / The habitat concept, which defines the place where organisms live, is composed by abiotic and biotic conditions and differs for examples between species or activities. The habitat selection is the process where organisms choose the habitat to live in function of all habitats available around them. This habitat selection depends on an individual choice related to the organism, for example its behavior and a common choice related to organisms sharing common traits as individuals from the same species. Specific habitat selection models are developed to understand and represent this common choice and used to build ecological flow tools. For freshwater fish, most of specific habitat selection models have low transferability between reaches and rivers. Indeed, they are built from abundance data and sampled in the same study reach during few numbers of surveys. In order to improve predictive quality of models, I developed an attractive modelling approach, both multi-reach and multi-survey, involving the non-linear response of habitat selection and abundance data overdispersion. Then, despite the high individual variability of habitat selection, I showed, from telemetry data, the relevance of developing specific habitat selection models. Finally, as the habitat selection is also depending on processes which influence community structures at the landscape scale (e.g. dispersal), I demonstrate the benefits of sampling methods such as snorkeling to characterize community structures and their longitudinal distributions at a large spatial scale. These techniques will allow studying the influence of landscape processes on habitat selection models.

The range of a species often extends across a diverse landscape, necessitating that individuals make different movement and habitat decisions, despite consistent food and shelter requirements. Great Basin gophersnakes (Pituophis catenifer deserticola) are threatened in Canada, where they occur at the northern extent of their range in southern interior river valleys of British Columbia such as the Okanagan Valley. I followed 39 radio-transmittered adult gophersnakes at four sites in the Okanagan, to obtain information on life history, movement and range patterns, and habitat use. Habitat selection and movement patterns exhibited by gophersnakes differed between study sites, sexes, and months, indicating that snake choice varies depending on resources and life history traits. Despite these fine-grain differences, males moved more than females in the spring. In addition to this, females moved more than males in the summer and fall. Differences in movement and range were apparent among the study sites. Habitat selection differed by study site, however rock-outcrops were consistently selected overall. Microhabitat selection varied, but retreat sites including logs, rocks, and holes in the ground, were consistently located closer than random. Hibernation sites in the south Okanagan were in rock features, while in the north Okanagan a good proportion were in rodent burrows in hillsides. Hibernation site fidelity was low, and annual reproduction was common. Oviposition sites were on south-facing slopes of moderate grade with little to moderate grass cover. Three ecdysis periods were observed when most or all transmitter-equipped snakes shed their skin. These findings will be very valuable to species conservation goals in British Columbia when developing guidelines on the habitats and sizes of areas to protect. With an iii understanding of the movement and ranges patterns exhibited by individuals, the area required to sustain a healthy population of gophersnakes can be determined. Knowledge of the habitats and microhabitats gophersnakes select makes it possible to identify and protect important areas at sites known to contain gophersnakes, including the Vaseux, Ripley, and Vernon study sites. Characterization of hibernation and oviposition sites allows surveys to identify these areas in locations that may support gophersnakes. Finally, identification of the timing of various important life history behaviours means human disturbance can be avoided during mating and oviposition periods, especially on sites such as Vernon, where land is used for multiple purposes.

The range of a species often extends across a diverse landscape, necessitating that individuals make different movement and habitat decisions, despite consistent food and shelter requirements. Great Basin gophersnakes (Pituophis catenifer deserticola) are threatened in Canada, where they occur at the northern extent of their range in southern interior river valleys of British Columbia such as the Okanagan Valley. I followed 39 radio-transmittered adult gophersnakes at four sites in the Okanagan, to obtain information on life history, movement and range patterns, and habitat use. Habitat selection and movement patterns exhibited by gophersnakes differed between study sites, sexes, and months, indicating that snake choice varies depending on resources and life history traits. Despite these fine-grain differences, males moved more than females in the spring. In addition to this, females moved more than males in the summer and fall. Differences in movement and range were apparent among the study sites. Habitat selection differed by study site, however rock-outcrops were consistently selected overall. Microhabitat selection varied, but retreat sites including logs, rocks, and holes in the ground, were consistently located closer than random. Hibernation sites in the south Okanagan were in rock features, while in the north Okanagan a good proportion were in rodent burrows in hillsides. Hibernation site fidelity was low, and annual reproduction was common. Oviposition sites were on south-facing slopes of moderate grade with little to moderate grass cover. Three ecdysis periods were observed when most or all transmitter-equipped snakes shed their skin. These findings will be very valuable to species conservation goals in British Columbia when developing guidelines on the habitats and sizes of areas to protect. With an iii understanding of the movement and ranges patterns exhibited by individuals, the area required to sustain a healthy population of gophersnakes can be determined. Knowledge of the habitats and microhabitats gophersnakes select makes it possible to identify and protect important areas at sites known to contain gophersnakes, including the Vaseux, Ripley, and Vernon study sites. Characterization of hibernation and oviposition sites allows surveys to identify these areas in locations that may support gophersnakes. Finally, identification of the timing of various important life history behaviours means human disturbance can be avoided during mating and oviposition periods, especially on sites such as Vernon, where land is used for multiple purposes.

Made available in DSpace on 2015-04-17T14:55:29Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2364966 bytes, checksum: d7434af52b65fc72aebc83b04b51d289 (MD5) Previous issue date: 2012-07-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / We investigated the contribution of ecological and historical factors in determining patterns of lizard assemblage structure from an Atlantic forest fragment, analyzing microhabitat use, diet composition and morphology. We collected the lizards with pitfall traps, glue traps and active visual search. We recorded 16 species belonging to eight families. The principal components analysis revealed a cluster in morphological space of Teiidae species and moderate in Gymnophthalmidae, suggesting the importance of historical factors in the morphology of these species. The null model showed that the assemblage is structured based on microhabitat use, but not in diet composition. Patterns of structure found in microhabitat use, as well as, the absence of pattern in prey selection seems to be determined by the evolutionary history of species, being competitive interactions not determinant, which is supported by the results of canonical phylogenetic ordination that revealed the significant influence of the historical aspects, related to the phylogenetic relationships of species, in microhabitat use in Teiidae, as well as, in diet composition of Iguania. / Foi investigada a contribuição dos fatores ecológicos e históricos, na determinação dos padrões de estruturação da taxocenose de lagartos de um fragmento de floresta atlântica, analisando parâmetros de utilização do espaço, composição da dieta e morfometria das espécies. A coleta dos lagartos foi realizada através da utilização de armadilhas e de procura visual ativa. Foram registradas 16 espécies pertencentes a 8 famílias. A análise de componentes principais revelou um agrupamento no espaço morfológico de espécies pertencentes à família Teiidae e moderado para Gymnophthalmidae, sugerindo a ação de fatores históricos na morfologia das espécies. Os modelos nulos mostraram que a comunidade está estruturada com relação à utilização dos microhábitats disponíveis, mas não em relação à composição da dieta. Os padrões de estruturação encontrados na utilização do espaço, assim como, a ausência de padrão na seleção das presas, parecem ser determinados pela história evolutiva das espécies, não revelando interações competitivas presentes, o que é corroborado pela ordenação canônica filogenética que revelou a influência significativa dos aspectos históricos, relacionados às relações filogenéticas das espécies, na utilização do espaço pela família Teiidae, assim como na composição alimentar de Iguania.

Uma das mais relevantes perspectivas que buscam explicar como as comunidades ecológicas se organizam é a teoria do nicho, que se divide em duas linhas de pesquisa com filosofias opostas. A primeira enfatiza que diferenças nas características funcionais de organismos permitem sua coexistência, enquanto que a segunda avalia até que ponto membros de uma mesma comunidade tendem a exibir similaridade em seus atributos funcionais. Uma variedade de métodos analíticos tem sido desenvolvida para avaliar mecanismos ligados a cada um dos processos. Explorando o padrão de distribuição de atributos de comunidades, a limitação de similaridade resulta em divergência de atributos, enquanto a ação local de filtros ambientais em geral produz convergência de atributos. Nesse sentido, o método para discriminação de padrões de organização por convergência ou por divergência de atributos no contexto de metacomunidades é de grande valor. Nesta dissertação, tal abordagem é utilizada para a avaliação de padrões de convergência e de divergência de atributos de plantas arbóreas juvenis em manchas florestais. Não incluímos informação filogenética ou de espécies a fim de avaliarmos até que ponto uma abordagem plenamente funcional pode explicar padrões de comunidades. O trabalho foi desenvolvido na Serra do Sudeste do RS, que consiste em um mosaico campo-floresta relativamente bem conservado. Algo instigante na Serra do Sudeste é a presença das coníferas Araucaria angustifolia (Bertol.) Kuntze e Podocarpus lambertii Klotzsch ex Endl. em várias manchas florestais, espécies reconhecidas como características da Floresta com Araucária do Planalto Sul-Brasileiro. Tal ocorrência vem sendo discutida há muitas décadas na literatura, mas nenhum estudo ecológico feito nessas áreas foi publicado ainda. Assim, nesta dissertação, tive como objetivos avançar na teoria relacionada à organização de comunidades e obter dados de qualidade para a avaliação continuada da dinâmica ecológica por trás dos mosaicos campo-floresta com presença de A. angustifolia na Serra do Sudeste. Os resultados encontrados revelaram padrões tanto de convergência quanto de divergência de atributos. A abordagem inteiramente funcional utilizada neste trabalho foi muito útil para a inferência de prováveis mecanismos de nicho envolvidos na organização das comunidades de árvores juvenis. Nós defendemos que a análise de dados de atributos referentes ao nível de indivíduos em um contexto de metacomunidades é a melhor maneira de explorar diretamente como a convergência e a divergência de atributos realmente se comporta ao longo de um dado gradiente. Com relação ao limite austral da distribuição de Araucaria angustifolia, caso as áreas da Serra do Sudeste sejam consideradas nativas, haveria uma ocorrência disjunta da espécie e, talvez, do tipo vegetacional Floresta com Araucária. Esse tema é especialmente importante no que concerne a uma possível migração da espécie ou mesmo da flora típica da formação rumo ao sul, ou alternativamente a uma possível evidência remanescente de que a espécie ou mesmo de que a formação tenham ocorrido continuamente até essas latitudes, talvez há centenas de milhares de anos atrás. A resolução desse mistério, entretanto, provavelmente só seja alcançada através de estudos paleopolínicos e genéticos. De qualquer forma, tais áreas devem ser protegidas, já que seu desconhecimento por grande parte da comunidade científica facilita a negligência de sua conservação. / Ecologists have considered niche theory one of the most relevant perspectives attempting to explain ecological community assembly. It is divided in two research programs with opposed philosophies. The first emphasises that differences in functional attributes of organisms enable their coexistence, whereas the second evaluate to which extent members of a same community tend to exhibit similarity regarding their functional traits. A variety of analytical methods have been developed for assessing mechanisms related to each of these processes. By exploring the trait distribution pattern in communities, it is generally accepted that the local action of environmental filters generates a pattern of trait convergence, whereas limiting similarity leads to trait divergence. In this sense, the method for discriminating traitconvergence and trait-divergence assembly patterns in the metacommunity context is of great value. In this dissertation, such approach is used for evaluating convergence and divergence patterns of tree sapling traits in forest patches in the Serra do Sudeste region of Rio Grande do Sul state, southern Brazil. We did not include phylogenetic or species identity information in the analysis since we wanted to evaluate to which extent an entirely functional approach could explain community patterns. The study was carried out in Serra do Sudeste, which consists of a forest-grassland mosaic relatively well conserved. Something puzzling in Serra do Sudeste is the presence of conifers such as Araucaria angustifolia (Bertol.) Kuntze and Podocarpus lambertii Klotzsch ex Endl. in several forest patches. These species are characteristic of the Araucaria forest occurring in the South-Brazilian Plateau. Such occurrence has been matter of a long-lasting debate in the regional literature, but no ecological study done in these areas has been published yet. In this dissertation I aimed at advancing on the theoretical bases of community assembly and at gathering data for continuously evaluating the ecological dynamics of the forest-grassland mosaics with presence of A. angustifolia in Serra do Sudeste. The results revealed both trait convergence and divergence patterns, which indicated mechanisms for the assembly of tree sapling communities. The entirely functional approach applied here was very useful to infer probable mechanisms underlying community assembly. We argue that the use of individual-based trait information in a metacommunity context is the best way to directly explore how trait convergence and trait divergence behave along a given gradient. With regard to the austral boundary of Araucaria angustifolia distribution, if the patches of Serra do Sudeste are considered native, there would be a disjunct occurrence of the species and perhaps of the vegetational type Araucaria forest. This issue is especially important regarding a possible migration of the species or even of the typical associated flora southwards, or alternatively, regarding a possible relict evidence that the species had continuously occurred along such latitudes in a remote past. Nonetheless, the resolution of this puzzle probably only will be achieved through genetic and paleopollen studies. Anyway, such areas must be protected as their omission in important scientific studies facilitates the negligence of their conservation.

Uma das mais relevantes perspectivas que buscam explicar como as comunidades ecológicas se organizam é a teoria do nicho, que se divide em duas linhas de pesquisa com filosofias opostas. A primeira enfatiza que diferenças nas características funcionais de organismos permitem sua coexistência, enquanto que a segunda avalia até que ponto membros de uma mesma comunidade tendem a exibir similaridade em seus atributos funcionais. Uma variedade de métodos analíticos tem sido desenvolvida para avaliar mecanismos ligados a cada um dos processos. Explorando o padrão de distribuição de atributos de comunidades, a limitação de similaridade resulta em divergência de atributos, enquanto a ação local de filtros ambientais em geral produz convergência de atributos. Nesse sentido, o método para discriminação de padrões de organização por convergência ou por divergência de atributos no contexto de metacomunidades é de grande valor. Nesta dissertação, tal abordagem é utilizada para a avaliação de padrões de convergência e de divergência de atributos de plantas arbóreas juvenis em manchas florestais. Não incluímos informação filogenética ou de espécies a fim de avaliarmos até que ponto uma abordagem plenamente funcional pode explicar padrões de comunidades. O trabalho foi desenvolvido na Serra do Sudeste do RS, que consiste em um mosaico campo-floresta relativamente bem conservado. Algo instigante na Serra do Sudeste é a presença das coníferas Araucaria angustifolia (Bertol.) Kuntze e Podocarpus lambertii Klotzsch ex Endl. em várias manchas florestais, espécies reconhecidas como características da Floresta com Araucária do Planalto Sul-Brasileiro. Tal ocorrência vem sendo discutida há muitas décadas na literatura, mas nenhum estudo ecológico feito nessas áreas foi publicado ainda. Assim, nesta dissertação, tive como objetivos avançar na teoria relacionada à organização de comunidades e obter dados de qualidade para a avaliação continuada da dinâmica ecológica por trás dos mosaicos campo-floresta com presença de A. angustifolia na Serra do Sudeste. Os resultados encontrados revelaram padrões tanto de convergência quanto de divergência de atributos. A abordagem inteiramente funcional utilizada neste trabalho foi muito útil para a inferência de prováveis mecanismos de nicho envolvidos na organização das comunidades de árvores juvenis. Nós defendemos que a análise de dados de atributos referentes ao nível de indivíduos em um contexto de metacomunidades é a melhor maneira de explorar diretamente como a convergência e a divergência de atributos realmente se comporta ao longo de um dado gradiente. Com relação ao limite austral da distribuição de Araucaria angustifolia, caso as áreas da Serra do Sudeste sejam consideradas nativas, haveria uma ocorrência disjunta da espécie e, talvez, do tipo vegetacional Floresta com Araucária. Esse tema é especialmente importante no que concerne a uma possível migração da espécie ou mesmo da flora típica da formação rumo ao sul, ou alternativamente a uma possível evidência remanescente de que a espécie ou mesmo de que a formação tenham ocorrido continuamente até essas latitudes, talvez há centenas de milhares de anos atrás. A resolução desse mistério, entretanto, provavelmente só seja alcançada através de estudos paleopolínicos e genéticos. De qualquer forma, tais áreas devem ser protegidas, já que seu desconhecimento por grande parte da comunidade científica facilita a negligência de sua conservação. / Ecologists have considered niche theory one of the most relevant perspectives attempting to explain ecological community assembly. It is divided in two research programs with opposed philosophies. The first emphasises that differences in functional attributes of organisms enable their coexistence, whereas the second evaluate to which extent members of a same community tend to exhibit similarity regarding their functional traits. A variety of analytical methods have been developed for assessing mechanisms related to each of these processes. By exploring the trait distribution pattern in communities, it is generally accepted that the local action of environmental filters generates a pattern of trait convergence, whereas limiting similarity leads to trait divergence. In this sense, the method for discriminating traitconvergence and trait-divergence assembly patterns in the metacommunity context is of great value. In this dissertation, such approach is used for evaluating convergence and divergence patterns of tree sapling traits in forest patches in the Serra do Sudeste region of Rio Grande do Sul state, southern Brazil. We did not include phylogenetic or species identity information in the analysis since we wanted to evaluate to which extent an entirely functional approach could explain community patterns. The study was carried out in Serra do Sudeste, which consists of a forest-grassland mosaic relatively well conserved. Something puzzling in Serra do Sudeste is the presence of conifers such as Araucaria angustifolia (Bertol.) Kuntze and Podocarpus lambertii Klotzsch ex Endl. in several forest patches. These species are characteristic of the Araucaria forest occurring in the South-Brazilian Plateau. Such occurrence has been matter of a long-lasting debate in the regional literature, but no ecological study done in these areas has been published yet. In this dissertation I aimed at advancing on the theoretical bases of community assembly and at gathering data for continuously evaluating the ecological dynamics of the forest-grassland mosaics with presence of A. angustifolia in Serra do Sudeste. The results revealed both trait convergence and divergence patterns, which indicated mechanisms for the assembly of tree sapling communities. The entirely functional approach applied here was very useful to infer probable mechanisms underlying community assembly. We argue that the use of individual-based trait information in a metacommunity context is the best way to directly explore how trait convergence and trait divergence behave along a given gradient. With regard to the austral boundary of Araucaria angustifolia distribution, if the patches of Serra do Sudeste are considered native, there would be a disjunct occurrence of the species and perhaps of the vegetational type Araucaria forest. This issue is especially important regarding a possible migration of the species or even of the typical associated flora southwards, or alternatively, regarding a possible relict evidence that the species had continuously occurred along such latitudes in a remote past. Nonetheless, the resolution of this puzzle probably only will be achieved through genetic and paleopollen studies. Anyway, such areas must be protected as their omission in important scientific studies facilitates the negligence of their conservation.