Nas últimas duas décadas estudos empíricos têm demonstrado a importância da facilitação entre plantas, especialmente sob condições ambientais severas. Tal constatação inspirou a proposição da hipótese do gradiente de estresse (HGE), um modelo conceitual que prediz que a freqüência relativa entre facilitação e competição deve variar inversarmente ao longo de um gradiente de estresse, sendo a facilitação mais comum sob condições extremamente severas. As restingas (ou planícies costeiras arenosas) são ambientes caracterizados por condições ambientais limitantes para o desenvolvimento das plantas, fazendo-se então um ambiente propício para o predomínio de facilitação. Além disso, o gradiente de intensidade de estresse e perturbação relacionado à distância do mar faz ainda deste ecossistema um modelo ideal para testar a HGE. O objetivo geral desta tese foi estudar facilitação entre plantas de restinga através dos seguintes objetivos específicos: i) Apresentar uma revisão sistemática dos trabalhos já publicados sobre facilitação entre plantas de restinga em escala mundial, assim como investigar, através de meta-análise, que fatores influenciam a presença e intensidade da facilitação entre plantas; ii) Testar se os padrões de associação espacial entre árvores adultas isoladas e plantas de distintas formas de vida se alteram ao longo de um gradiente ambiental praia-interior, conforme esperado pela HGE; iii) Testar a HGE através de experimentos de campo envolvendo transplante da espécie potencialmente beneficiada, assim como manipulação de recurso limitante ao longo do gradiente praia-interior; iv) Testar se o sombreamento é um mecanismo de facilitação na restinga. Para os testes empíricos (objetivos ii-iv), as observações e experimentos foram realizados em um gradiente de restinga arbustiva do Parque Estadual da Ilha do Cardoso (PEIC) localizado em Cananéia, São Paulo, Brasil. Os resultados indicaram que: i) diversas condições e aspectos da facilitação entre plantas de planícies costeiras têm sido pouco exploradas, como por exemplo, há poucos estudos nas regiões tropicais e poucos estudos que consideraram estágios de vida de semente ou de adultos da espécie alvo da interação. Dentre os estudos publicados, fatores como precipitação, região geográfica e estágio de vida da planta alvo definitivamente influenciam a existência e magnitude da facilitação entre plantas de restinga; ii) para a maioria das formas de vida, o padrão de associação espacial com árvores adultas não se altera ao longo do gradiente ambiental conforme predito pela HGE. Apenas árvores jovens apresentam associação espacial positiva com árvores adultas, o que sugere efeito de planta-berçário entre árvores da restinga arbustiva; iii) tanto a intensidade quanto a importância da interação entre árvores foram negativamente relacionadas ao estresse, rejeitando então a proposição clássica da HGE. Além disso, o sinal da interação foi dependente do estágio de vida da espécie alvo, uma vez que a presença do adulto vizinho foi predominantemente negativa sobre o estágio de semente mas positiva sobre a sobrevivência das plântulas; iv) o efeito de planta-berçário entre árvores da restinga é, pelo menos parcialmente, explicado pelo sombreamento gerado pela copa da espécie facilitadora. Dessa forma, concluimos que a facilitação via sombreamento é uma interação relevante entre árvores adultas e jovens na restinga. Entretanto, ao contrário do previsto pela HGE, o efeito de planta-berçário tende a ser mais intenso em condições ambientais mais amenas. Estes resultados sugerem a existência de um ciclo de retroalimentação positiva gerado a partir do estabelecimento das primeiras árvores isoladas. Este ciclo positivo apresenta implicações importantes para a compreensão da organização estrutural da vegetação da restinga arbustiva, em que moitas de espécies lenhosas estão distribuídas em uma matriz predominantemente herbácea. Adicionalmente, a facilitação entre árvores e sua dependência em relação às condições ambientais locais devem ser mecanismos essenciais para explicar o gradiente de fisionomias vegetacionais sobre os cordões arenosos, a qual inicia-se em uma vegetação aberta e termina em uma floresta, assim como para entender a dinâmica temporal desta vegetação ao longo do tempo. Por fim, nossos resultados também apresentam implicações práticas, relacionadas ao uso potencial de plantas-berçário e mímicos de sombra como técnicas de manejo para aumentar o estabelecimento de mudas transplantadas em projetos de restauração de restingas arbustivo-arbóreas. / In the last two decades, empirical studies have shown the importance of plant interaction, especially under harsh environmental conditions. These observations led to the proposition of the stress gradient hypothesis (SGH), a conceptual model predicting that the relative frequency of facilitation and competition will vary inversely across gradients of stress, with facilitation being the dominant interaction under highly stressful conditions. Coastal dunes (known as restinga in Brazil) are environments with limiting conditions for plant performance, which makes them suitable for facilitation predominance among plant interactions. Furthermore, there is a gradient of stress and disturbance related to the presence of the sea, making this environment an ideal model to test the SGH. The general goal of this thesis was to study plant facilitation in coastal dunes with the following specific objectives: i) to perform a systematic review of published studies on plant facilitation in costal dunes around the world as well as to investigate, using a meta-analysis approach, factors that affect the existence and magnitude of plant facilitation; ii) to test if spatial association between isolated adult trees and understory plants of distinct life forms changes along a beach-to-inland gradient, as expected by the SGH; iii) to test the SGH through field experiments involving target species transplantation coupled with manipulation of limiting resource along a beach-to-inland gradient; iv) to test if shading is a facilitation mechanism in coastal dunes. The empirical tests (objectives ii-iv) were conducted in an open scrub coastal dune located at Ilha do Cardoso State Park, Cananéia, São Paulo, Brazil. Our results indicate that: i) several aspects and conditions of plant facilitation in coastal dunes have been little studied. For instance, few studies were conducted in tropical regions and few of them studied the effect of neighbor presence on seed and adult life stage of the target species. Precipitation, geographic region and target life stage affect the existence and magnitude of plant facilitation; ii) For most of the understory life forms, the spatial association between adult trees and understor plants do not change along the environmental gradient as predicted by the SGH. Among all life forms, only young trees were positively associated with adult trees, suggesting a nurse plant effect among trees in coastal dunes; iii) Both intensity and importance of the interaction among trees were negatively related to stress, rejecting the classic proposition of the SGH. Furthermore, the signal of the net interaction depends on the life stage of the target species since the adult neighbor had mostly negative effects on target species seeds but positive effects on seedlings survival; iv) The nurse plant effect among trees was, at least partly, due to the shading provided by the facilitator crown. Overall, we concluded that facilitation driven by shade is a relevant interaction between adult and young trees in the studied coastal dune. However, contrary to what was expected by the early propositions of the SGH, the observed nurse plant effect tends to be more intense under mild conditions. Our results suggest a positive feedback relationship started with the establishment of the first isolated trees. This positive feedback has important implications to understand the vegetation organization on open scrub vegetation, where patches of woody species are scattered in a matrix of herbaceous plants. Furthermore, the facilitation between trees and their dependency on local environmental conditions could be fundamental to explain the gradient of vegetation physiognomies from open vegetation to forest observed along the beach-to-inland gradient, as well as to understand the dynamics of this vegetation over time. Finally, our results also have practical implications, highlighting the potential use of nurse plants and artificial shade as techniques to restore shrubland or forest physiognomies in coastal dunes.

Neste trabalho, avaliamos como arbustos pioneiros regulam comunidades lenhosas em uma restinga subtropical. Arbustos têm grande capacidade de modificar ecossistemas, pois alteram o fluxo de nutrientes e água do solo, aprisionam sementes transportadas por água ou vento sob suas copas, e oferecem recursos a dispersores. A combinação desses processos leva ao surgimento de ilhas de fertilidade em áreas de vegetação herbácea, aumentando a diversidade local. Interações biológicas são fatores determinantes na coexistência de espécies nessas ilhas arbustivas. Portanto, utilizamos atributos vegetativos de arbustos e distância filogenética média (MPD) entre as espécies para avaliar como a riqueza, a abundância e a diversidade (i.e. Entropia Quadrática de Rao, EQR) são reguladas em moitas de restinga. Também comparamos esses mesmos parâmetros nas áreas de vegetação predominantemente herbácea circundantes às ilhas arbustivas. A fim de entender a estruturação filogenética nesse ambiente, calculamos o net relatedness index (NRI) de cada moita. Nossos dados reforçam a importância de arbustos pioneiros sobre a vegetação de áreas predominantemente campestres devido à sua capacidade de modificar o micro-habitat sob suas copas e pelas interações com espécies que colonizam as ilhas arbustivas. / In this work we tested how pioneer shrubs regulate community structure in woody islands of a subtropical sand-dune (restinga) environment. Shrubby species show a great ability to modify ecosystems, since they change the flux of nutrients and water in the soil, they retain under their crowns seeds carried by water or wind, and the seeds in turn attract new dispersers. The combination of these processes leads to the formation of fertility islands in areas with herbaceous vegetation, increasing the local diversity. Biological interactions are determinant factors in the coexistence of species in these shrubby islands. So we used vegetative traits of shrubs and mean phylogenetic distance (MPD) between species to evaluate how richness, abundance and diversity, i.e., Rao‟s quadratic entropy (RQE), are regulated in sand-dune woody islands. We also evaluated the same parameters in the surrounding areas with predominantly herbaceous vegetation. In order to understand the phylogenetic structuring in this environment we estimated the net relatedness index (NRI) in each woody thicket. Our data reinforce the importance of pioneer shrubs in a matrix of the predominantly open grassland vegetation because of their ability to modify the microhabitat under their crowns and their interactions with other species which colonize the shrubby islands.

Neste trabalho, avaliamos como arbustos pioneiros regulam comunidades lenhosas em uma restinga subtropical. Arbustos têm grande capacidade de modificar ecossistemas, pois alteram o fluxo de nutrientes e água do solo, aprisionam sementes transportadas por água ou vento sob suas copas, e oferecem recursos a dispersores. A combinação desses processos leva ao surgimento de ilhas de fertilidade em áreas de vegetação herbácea, aumentando a diversidade local. Interações biológicas são fatores determinantes na coexistência de espécies nessas ilhas arbustivas. Portanto, utilizamos atributos vegetativos de arbustos e distância filogenética média (MPD) entre as espécies para avaliar como a riqueza, a abundância e a diversidade (i.e. Entropia Quadrática de Rao, EQR) são reguladas em moitas de restinga. Também comparamos esses mesmos parâmetros nas áreas de vegetação predominantemente herbácea circundantes às ilhas arbustivas. A fim de entender a estruturação filogenética nesse ambiente, calculamos o net relatedness index (NRI) de cada moita. Nossos dados reforçam a importância de arbustos pioneiros sobre a vegetação de áreas predominantemente campestres devido à sua capacidade de modificar o micro-habitat sob suas copas e pelas interações com espécies que colonizam as ilhas arbustivas. / In this work we tested how pioneer shrubs regulate community structure in woody islands of a subtropical sand-dune (restinga) environment. Shrubby species show a great ability to modify ecosystems, since they change the flux of nutrients and water in the soil, they retain under their crowns seeds carried by water or wind, and the seeds in turn attract new dispersers. The combination of these processes leads to the formation of fertility islands in areas with herbaceous vegetation, increasing the local diversity. Biological interactions are determinant factors in the coexistence of species in these shrubby islands. So we used vegetative traits of shrubs and mean phylogenetic distance (MPD) between species to evaluate how richness, abundance and diversity, i.e., Rao‟s quadratic entropy (RQE), are regulated in sand-dune woody islands. We also evaluated the same parameters in the surrounding areas with predominantly herbaceous vegetation. In order to understand the phylogenetic structuring in this environment we estimated the net relatedness index (NRI) in each woody thicket. Our data reinforce the importance of pioneer shrubs in a matrix of the predominantly open grassland vegetation because of their ability to modify the microhabitat under their crowns and their interactions with other species which colonize the shrubby islands.

Nas últimas duas décadas estudos empíricos têm demonstrado a importância da facilitação entre plantas, especialmente sob condições ambientais severas. Tal constatação inspirou a proposição da hipótese do gradiente de estresse (HGE), um modelo conceitual que prediz que a freqüência relativa entre facilitação e competição deve variar inversarmente ao longo de um gradiente de estresse, sendo a facilitação mais comum sob condições extremamente severas. As restingas (ou planícies costeiras arenosas) são ambientes caracterizados por condições ambientais limitantes para o desenvolvimento das plantas, fazendo-se então um ambiente propício para o predomínio de facilitação. Além disso, o gradiente de intensidade de estresse e perturbação relacionado à distância do mar faz ainda deste ecossistema um modelo ideal para testar a HGE. O objetivo geral desta tese foi estudar facilitação entre plantas de restinga através dos seguintes objetivos específicos: i) Apresentar uma revisão sistemática dos trabalhos já publicados sobre facilitação entre plantas de restinga em escala mundial, assim como investigar, através de meta-análise, que fatores influenciam a presença e intensidade da facilitação entre plantas; ii) Testar se os padrões de associação espacial entre árvores adultas isoladas e plantas de distintas formas de vida se alteram ao longo de um gradiente ambiental praia-interior, conforme esperado pela HGE; iii) Testar a HGE através de experimentos de campo envolvendo transplante da espécie potencialmente beneficiada, assim como manipulação de recurso limitante ao longo do gradiente praia-interior; iv) Testar se o sombreamento é um mecanismo de facilitação na restinga. Para os testes empíricos (objetivos ii-iv), as observações e experimentos foram realizados em um gradiente de restinga arbustiva do Parque Estadual da Ilha do Cardoso (PEIC) localizado em Cananéia, São Paulo, Brasil. Os resultados indicaram que: i) diversas condições e aspectos da facilitação entre plantas de planícies costeiras têm sido pouco exploradas, como por exemplo, há poucos estudos nas regiões tropicais e poucos estudos que consideraram estágios de vida de semente ou de adultos da espécie alvo da interação. Dentre os estudos publicados, fatores como precipitação, região geográfica e estágio de vida da planta alvo definitivamente influenciam a existência e magnitude da facilitação entre plantas de restinga; ii) para a maioria das formas de vida, o padrão de associação espacial com árvores adultas não se altera ao longo do gradiente ambiental conforme predito pela HGE. Apenas árvores jovens apresentam associação espacial positiva com árvores adultas, o que sugere efeito de planta-berçário entre árvores da restinga arbustiva; iii) tanto a intensidade quanto a importância da interação entre árvores foram negativamente relacionadas ao estresse, rejeitando então a proposição clássica da HGE. Além disso, o sinal da interação foi dependente do estágio de vida da espécie alvo, uma vez que a presença do adulto vizinho foi predominantemente negativa sobre o estágio de semente mas positiva sobre a sobrevivência das plântulas; iv) o efeito de planta-berçário entre árvores da restinga é, pelo menos parcialmente, explicado pelo sombreamento gerado pela copa da espécie facilitadora. Dessa forma, concluimos que a facilitação via sombreamento é uma interação relevante entre árvores adultas e jovens na restinga. Entretanto, ao contrário do previsto pela HGE, o efeito de planta-berçário tende a ser mais intenso em condições ambientais mais amenas. Estes resultados sugerem a existência de um ciclo de retroalimentação positiva gerado a partir do estabelecimento das primeiras árvores isoladas. Este ciclo positivo apresenta implicações importantes para a compreensão da organização estrutural da vegetação da restinga arbustiva, em que moitas de espécies lenhosas estão distribuídas em uma matriz predominantemente herbácea. Adicionalmente, a facilitação entre árvores e sua dependência em relação às condições ambientais locais devem ser mecanismos essenciais para explicar o gradiente de fisionomias vegetacionais sobre os cordões arenosos, a qual inicia-se em uma vegetação aberta e termina em uma floresta, assim como para entender a dinâmica temporal desta vegetação ao longo do tempo. Por fim, nossos resultados também apresentam implicações práticas, relacionadas ao uso potencial de plantas-berçário e mímicos de sombra como técnicas de manejo para aumentar o estabelecimento de mudas transplantadas em projetos de restauração de restingas arbustivo-arbóreas. / In the last two decades, empirical studies have shown the importance of plant interaction, especially under harsh environmental conditions. These observations led to the proposition of the stress gradient hypothesis (SGH), a conceptual model predicting that the relative frequency of facilitation and competition will vary inversely across gradients of stress, with facilitation being the dominant interaction under highly stressful conditions. Coastal dunes (known as restinga in Brazil) are environments with limiting conditions for plant performance, which makes them suitable for facilitation predominance among plant interactions. Furthermore, there is a gradient of stress and disturbance related to the presence of the sea, making this environment an ideal model to test the SGH. The general goal of this thesis was to study plant facilitation in coastal dunes with the following specific objectives: i) to perform a systematic review of published studies on plant facilitation in costal dunes around the world as well as to investigate, using a meta-analysis approach, factors that affect the existence and magnitude of plant facilitation; ii) to test if spatial association between isolated adult trees and understory plants of distinct life forms changes along a beach-to-inland gradient, as expected by the SGH; iii) to test the SGH through field experiments involving target species transplantation coupled with manipulation of limiting resource along a beach-to-inland gradient; iv) to test if shading is a facilitation mechanism in coastal dunes. The empirical tests (objectives ii-iv) were conducted in an open scrub coastal dune located at Ilha do Cardoso State Park, Cananéia, São Paulo, Brazil. Our results indicate that: i) several aspects and conditions of plant facilitation in coastal dunes have been little studied. For instance, few studies were conducted in tropical regions and few of them studied the effect of neighbor presence on seed and adult life stage of the target species. Precipitation, geographic region and target life stage affect the existence and magnitude of plant facilitation; ii) For most of the understory life forms, the spatial association between adult trees and understor plants do not change along the environmental gradient as predicted by the SGH. Among all life forms, only young trees were positively associated with adult trees, suggesting a nurse plant effect among trees in coastal dunes; iii) Both intensity and importance of the interaction among trees were negatively related to stress, rejecting the classic proposition of the SGH. Furthermore, the signal of the net interaction depends on the life stage of the target species since the adult neighbor had mostly negative effects on target species seeds but positive effects on seedlings survival; iv) The nurse plant effect among trees was, at least partly, due to the shading provided by the facilitator crown. Overall, we concluded that facilitation driven by shade is a relevant interaction between adult and young trees in the studied coastal dune. However, contrary to what was expected by the early propositions of the SGH, the observed nurse plant effect tends to be more intense under mild conditions. Our results suggest a positive feedback relationship started with the establishment of the first isolated trees. This positive feedback has important implications to understand the vegetation organization on open scrub vegetation, where patches of woody species are scattered in a matrix of herbaceous plants. Furthermore, the facilitation between trees and their dependency on local environmental conditions could be fundamental to explain the gradient of vegetation physiognomies from open vegetation to forest observed along the beach-to-inland gradient, as well as to understand the dynamics of this vegetation over time. Finally, our results also have practical implications, highlighting the potential use of nurse plants and artificial shade as techniques to restore shrubland or forest physiognomies in coastal dunes.

Neste trabalho, avaliamos como arbustos pioneiros regulam comunidades lenhosas em uma restinga subtropical. Arbustos têm grande capacidade de modificar ecossistemas, pois alteram o fluxo de nutrientes e água do solo, aprisionam sementes transportadas por água ou vento sob suas copas, e oferecem recursos a dispersores. A combinação desses processos leva ao surgimento de ilhas de fertilidade em áreas de vegetação herbácea, aumentando a diversidade local. Interações biológicas são fatores determinantes na coexistência de espécies nessas ilhas arbustivas. Portanto, utilizamos atributos vegetativos de arbustos e distância filogenética média (MPD) entre as espécies para avaliar como a riqueza, a abundância e a diversidade (i.e. Entropia Quadrática de Rao, EQR) são reguladas em moitas de restinga. Também comparamos esses mesmos parâmetros nas áreas de vegetação predominantemente herbácea circundantes às ilhas arbustivas. A fim de entender a estruturação filogenética nesse ambiente, calculamos o net relatedness index (NRI) de cada moita. Nossos dados reforçam a importância de arbustos pioneiros sobre a vegetação de áreas predominantemente campestres devido à sua capacidade de modificar o micro-habitat sob suas copas e pelas interações com espécies que colonizam as ilhas arbustivas. / In this work we tested how pioneer shrubs regulate community structure in woody islands of a subtropical sand-dune (restinga) environment. Shrubby species show a great ability to modify ecosystems, since they change the flux of nutrients and water in the soil, they retain under their crowns seeds carried by water or wind, and the seeds in turn attract new dispersers. The combination of these processes leads to the formation of fertility islands in areas with herbaceous vegetation, increasing the local diversity. Biological interactions are determinant factors in the coexistence of species in these shrubby islands. So we used vegetative traits of shrubs and mean phylogenetic distance (MPD) between species to evaluate how richness, abundance and diversity, i.e., Rao‟s quadratic entropy (RQE), are regulated in sand-dune woody islands. We also evaluated the same parameters in the surrounding areas with predominantly herbaceous vegetation. In order to understand the phylogenetic structuring in this environment we estimated the net relatedness index (NRI) in each woody thicket. Our data reinforce the importance of pioneer shrubs in a matrix of the predominantly open grassland vegetation because of their ability to modify the microhabitat under their crowns and their interactions with other species which colonize the shrubby islands.

Bien que les interactions biotiques soient connues pour être déterminantes dans l’établissement des espèces, il est encore difficile de savoir quels facteurs sont impliqués dans l’équilibre entre interaction positive et interaction négative. Il est de fait difficile de savoir sous quelles conditions les interactions biotiques peuvent favoriser ou empêcher la régénération des espèces. Cette thèse vise à étudier le rôle des interactions biotiques d'arbustes avec des semis de chêne sur la régénération de trois espèces de chênes sur les forêts des dunes côtières d'Aquitaine en testant comment l’effet net de ces interactions varie le long d’un gradient d’aridité, sur deux étages de canopée et en fonction des stratégies fonctionnelles de trois espèces de Chêne dans un contexte de changement global. Ce travail a été effectué en utilisant deux approches, une approche descriptive en utilisant un patron de points répartis dans l’espace et une approche expérimentale en transplantant les semis cibles. Les résultats montrent que la variation spatiale, en terme d’interactions biotiques, est fortement corrélée avec la sévérité environnementale, avec des interactions entre jeunes pousses de chêne très sensibles aux sécheresses estivales et aux trouées dans les canopées. Les interactions testées étaient de nature facilitatrice dans les plots découverts dans les dunes sèches du nord de Soulac et tournaient à la compétition sous le couvert forestier dans les dunes plus humides du sud, à Seignosse. La nature des interactions était constant entre les stratégies fonctionnelles des espèces cibles de chêne. Les résultats de cette thèse montrent de manière générale une confirmation de la formulation originale du SGH qui prédit une augmentation de la facilitation en lien avec une augmentation de la sévérité environnementale et souligne le fait que la réduction du stress hydrique atmosphérique par des arbustes est nécessaire à la régénération des semis de chêne. Dans cette perspective, le sylviculteur doit conserver les arbustes du sous-étage, en particulier dans les trouées, afin de permettre une meilleure régénération des plants de chêne. Cette thèse met en évidence la nécessaire considération des interactions biotiques dans la régénération du chêne dans les actuelles sévères conditions climatiques et le rôle prépondérant de ces interactions dans la réponse aux changements climatiques futurs probables dans cette région Aquitaine. / Although biotic interactions are known to be important determinants of species establishment, it is uncertain what factors determine the net balance between positive and negative interactions thus, under what conditions biotic interactions could enhance or impede species regeneration. Bien que les interactions biotiques soient connues pour être This thesis aims to study the role of biotic interactions of shrubs with oak seedlings for regeneration of three oak species on the Aquitaine coastal dune forests, by testing how the net effect of these interactions vary along aridity gradient, between two overstory canopies and in respect to the functional strategies of three oak species in the context of climate change. This was done by using two approaches, descriptive approach using spatial point pattern data and experimental approach by transplanting the target seedlings. The results show that the spatial variation in the nature of biotic interactions is strongly relate to environmental severity conditions, where the shrub-oak seedling interactions were very sensitive to increasing summer drought and canopy opening, the interactions strength was facilitative under gap plots in the dry northern dunes in Soulac and switch on competitive under forest plots in the wet southern dunes in Seignosse. The nature of the interactions was constant across the functional strategies of the targets species of oak. For the most part, results of this thesis show general support to the original formulation of SGH which predicts increasing facilitation with increasing severity and underscore the fact that atmospheric water stress reduction by shrubs is required for oak seedling regeneration. In this perspective, silviculturist should conserve understory shrubs, in particular in gaps, in order to allow a better regeneration niche of oak seedlings. This thesis highlights the importance of considering biotic interactions in oak regeneration under current harshness climatic conditions and with expectation to have an ambitious role in alleviation future climatic change consequence in this region.

Entender os processos que definem a montagem de comunidades é uma das questões centrais na ecologia. A influência de processos como o filtro ambiental e a competição pode ser observada na diversidade funcional das comunidades vegetais. A competição, através da exclusão competitiva, limita a similaridade de estratégias presentes na comunidade. O filtro ambiental, por outro lado, restringe as espécies que estão aptas a se estabelecer no local, diminuindo a diversidade funcional. É razoável pressupor que a influência desses processos varia em gradientes ambientais, onde o filtro ambiental exercerá maior influência em locais mais estressantes, e a competição, em locais menos estressantes. O objetivo deste trabalho é compreender a influência do filtro ambiental e da competição na diversidade funcional numa comunidade vegetal em um gradiente de estresse. Esperamos uma relação inversa entre diversidade funcional e estresse. O gradiente de estresse estudado ocorre na restinga do Parque Estadual da Ilha do Cardoso (Cananéia - SP). Amostramos 41 parcelas, com 104 espécies de plantas vasculares. Focamos a diversidade funcional em três dimensões: forma de vida, área foliar e atributos associados ao espectro de economia foliar (LES). Representamos o filtro ambiental utilizando variáveis edáficas associadas às restrições na restinga. Utilizamos a classificação de estratégias de Grime (CSR) para extrair o componente associado à competitividade de cada espécie, e a partir dela calculamos a média ponderada de cada parcela (CWM), para representar a competição. Construímos modelos lineares mistos (LMM) representando diferentes hipóteses relativas à diversidade funcional e selecionamos os melhores modelos pelo critério de Akaike (AIC). Avaliamos a diversidade funcional através das métricas: riqueza funcional (FRic), dispersão funcional (FDis) e CWM, que foram incluídas separadamente como respostas nos modelos. Na seleção de modelos o CWM de cada atributo, FRic das formas de vida e FRic para todos os atributos foram preditos pelo filtro ambiental. O FRic do LES, FRic da área foliar e todas FDis tiveram como modelo mais plausível o nulo, descartando a influência da competição e do filtro ambiental nesses componentes da diversidade funcional. A concentração em determinadas estratégias ao longo do gradiente explica a ausência de diferença na dispersão funcional. Inferimos que o filtro ambiental restringe certas estratégias, diminuindo a riqueza funcional ou deslocando o espaço funcional das comunidades. A ausência da competição afetando a diversidade funcional sugere que a limitação de similaridade exerce pouca influência na comunidade estudada, ou que a consequência da limitação de similaridade é compensada por outros processos / Understanding processes underlying community assembly is one of the main questions in community ecology. The influence of processes such as environmental filtering and competition can be observed in patterns of functional diversity patterns in plant communities. Competition, through competitive exclusion, limits similarities in ecological strategies in a given community. Environmental filtering, on the other hand, constrains the species that can be established in a given community, restricting the functional diversity. One can reasonably predict that the influence of such processes changes across environmental gradients, where the environmental filtering will exert more influence in more stressful environments, whereas competition will exert more influence in less stressful places. This study aimed to understand the influence of environmental filtering and competition on functional diversity in a plant community across a stress gradient. We expected an inverse relationship between functional diversity and stress. The stress gradient studied occurs in the restinga of the Cardoso Island State Park (Cananeia, SP). We sampled 41 sites, in which we found 104 species of vascular plants. We measured three traits: life form, leaf area and leaf economic spectrum (LES). We represented the environmental filter using edaphic variables that represent restinga environmental restrictions. We used Grime\'s strategies classification (CSR), to extract the component related to competitiveness of each species, and therefore, calculated the competition community weighted mean (CWM) of each plot as proxy of competition. We built linear mixed models (LMM) to represent different hypothesis related to functional diversity and selected the best models by Akaike Criterion (AIC). We evaluated functional diversity through three response variables in the models: functional richness (FRic), functional dispersion (FDis) and CWM. In the model selection of CWM for each trait, FRic for life form and FRic for all traits were predicted by the environmental filtering. The FRic of LES, FRic of leaf area and all models of FDis had the null model as the most plausible, discarding the influence of competition and environmental filter in functional diversity. The fact that there is a concentration of abundance around certain strategies explains why there is no difference in functional dispersion. We infer that environmental filter restricts some strategies, reducing functional richness or displacing functional space of the communities. The absence of competition affecting functional diversity suggests that limiting similarity exerts little influence on community assembly in the studied gradient, or that the consequences of similarity limitation is compensated by other process

Entender os processos que definem a montagem de comunidades é uma das questões centrais na ecologia. A influência de processos como o filtro ambiental e a competição pode ser observada na diversidade funcional das comunidades vegetais. A competição, através da exclusão competitiva, limita a similaridade de estratégias presentes na comunidade. O filtro ambiental, por outro lado, restringe as espécies que estão aptas a se estabelecer no local, diminuindo a diversidade funcional. É razoável pressupor que a influência desses processos varia em gradientes ambientais, onde o filtro ambiental exercerá maior influência em locais mais estressantes, e a competição, em locais menos estressantes. O objetivo deste trabalho é compreender a influência do filtro ambiental e da competição na diversidade funcional numa comunidade vegetal em um gradiente de estresse. Esperamos uma relação inversa entre diversidade funcional e estresse. O gradiente de estresse estudado ocorre na restinga do Parque Estadual da Ilha do Cardoso (Cananéia - SP). Amostramos 41 parcelas, com 104 espécies de plantas vasculares. Focamos a diversidade funcional em três dimensões: forma de vida, área foliar e atributos associados ao espectro de economia foliar (LES). Representamos o filtro ambiental utilizando variáveis edáficas associadas às restrições na restinga. Utilizamos a classificação de estratégias de Grime (CSR) para extrair o componente associado à competitividade de cada espécie, e a partir dela calculamos a média ponderada de cada parcela (CWM), para representar a competição. Construímos modelos lineares mistos (LMM) representando diferentes hipóteses relativas à diversidade funcional e selecionamos os melhores modelos pelo critério de Akaike (AIC). Avaliamos a diversidade funcional através das métricas: riqueza funcional (FRic), dispersão funcional (FDis) e CWM, que foram incluídas separadamente como respostas nos modelos. Na seleção de modelos o CWM de cada atributo, FRic das formas de vida e FRic para todos os atributos foram preditos pelo filtro ambiental. O FRic do LES, FRic da área foliar e todas FDis tiveram como modelo mais plausível o nulo, descartando a influência da competição e do filtro ambiental nesses componentes da diversidade funcional. A concentração em determinadas estratégias ao longo do gradiente explica a ausência de diferença na dispersão funcional. Inferimos que o filtro ambiental restringe certas estratégias, diminuindo a riqueza funcional ou deslocando o espaço funcional das comunidades. A ausência da competição afetando a diversidade funcional sugere que a limitação de similaridade exerce pouca influência na comunidade estudada, ou que a consequência da limitação de similaridade é compensada por outros processos / Understanding processes underlying community assembly is one of the main questions in community ecology. The influence of processes such as environmental filtering and competition can be observed in patterns of functional diversity patterns in plant communities. Competition, through competitive exclusion, limits similarities in ecological strategies in a given community. Environmental filtering, on the other hand, constrains the species that can be established in a given community, restricting the functional diversity. One can reasonably predict that the influence of such processes changes across environmental gradients, where the environmental filtering will exert more influence in more stressful environments, whereas competition will exert more influence in less stressful places. This study aimed to understand the influence of environmental filtering and competition on functional diversity in a plant community across a stress gradient. We expected an inverse relationship between functional diversity and stress. The stress gradient studied occurs in the restinga of the Cardoso Island State Park (Cananeia, SP). We sampled 41 sites, in which we found 104 species of vascular plants. We measured three traits: life form, leaf area and leaf economic spectrum (LES). We represented the environmental filter using edaphic variables that represent restinga environmental restrictions. We used Grime\'s strategies classification (CSR), to extract the component related to competitiveness of each species, and therefore, calculated the competition community weighted mean (CWM) of each plot as proxy of competition. We built linear mixed models (LMM) to represent different hypothesis related to functional diversity and selected the best models by Akaike Criterion (AIC). We evaluated functional diversity through three response variables in the models: functional richness (FRic), functional dispersion (FDis) and CWM. In the model selection of CWM for each trait, FRic for life form and FRic for all traits were predicted by the environmental filtering. The FRic of LES, FRic of leaf area and all models of FDis had the null model as the most plausible, discarding the influence of competition and environmental filter in functional diversity. The fact that there is a concentration of abundance around certain strategies explains why there is no difference in functional dispersion. We infer that environmental filter restricts some strategies, reducing functional richness or displacing functional space of the communities. The absence of competition affecting functional diversity suggests that limiting similarity exerts little influence on community assembly in the studied gradient, or that the consequences of similarity limitation is compensated by other process

Positive biotic interactions such as mutualism, commensalism and facilitation are ubiquitous in nature, but historically have received considerably less research attention than negative interactions such as competition, predation and parasitism. The paucity of research on positive interactions is particularly evident in stream ecosystems and in vertebrate communities. Stream fishes clearly provide an ideal system for advancing research on positive interactions. Many minnows (Cyprinidae) of eastern North America engage in a potentially mutualistic reproductive interaction known as nest association, in which individuals of one species (nest associates) spawn in nests constructed by host species. In nest association, hosts provide unsilted gravel substrate for spawning nest associates, and increased parental care to associate broods. High associate: host egg ratios can create a dilution effect, reducing the probability that host eggs will be preyed upon by egg predators. Nest associative interactions are common, but are relatively understudied compared to other interactions among stream fishes. The goals of this study were to apply general ecological models to this novel system to (a) gain new insight into the mechanisms structuring nest associative stream fish communities, and (b) to use inference from stream fish communities to potentially expand and improve the general ecological models. These goals required completion of three objectives, including (1) examining the influence of abiotic and biotic contexts on reproductive behavior and fitness outcomes between a cyprinid host and associate, using the biological markets model to generate predictions; (2) examining the utility of the nest web framework (previously only used for cavity nesting vertebrate communities) and the stress gradient hypothesis (previously applied almost exclusively to plant communities) for predicting which associate species spawn on nests built by various nest building species, and the consequences of these choices, respectively; and (3) using two-species occupancy modeling to determine the relative influence of biotic interactions and habitat covariates on the co-occurrence of a host and two nest associates. To accomplish these goals, I conducted a large-scale experiment to manipulate presence of mutualists (Nocomis leptocephalus, host; Chrosomus oreas, associate), egg predators (biotic context) and habitat quality (abiotic context). I conducted behavioral nest observations and conducted repeated stream fish stream fish community surveys to collect demographic data. I constructed a nest web from observational data, and implemented structural equation modeling through an information-theoretic framework to identify nest web plausibility across a large spatial extent. I tested some predictions of the stress gradient hypothesis by regressing juveniles-per-nest and a metric of cyprinid community structure on a composite measure of physical stress (scaled gradients of catchment-scale agricultural land use and catchment area). I used two-species occupancy modeling to model co-occurrence of N. leptocephalus hosts and two associates, C. oreas and Clinostomus funduloides, and used an information-theoretic framework to compare hypotheses representing the importance of biotic interactions, habitat covariates or both at determining species co-occurrence. Results corroborated some (but not all) model predictions, and identified room for improvement in each of the general models. Nest associative spawning by C. oreas was not context dependent; C. oreas did not spawn in the absence of a reproductively active male N. leptocephalus at any treatment level. However, the net fitness outcome of host and associate species was mutualistic, and the interaction outcome switched from commensalistic to mutualistic with abiotic context. N. leptocephalus reproductive success was improved by C. oreas presence in less-silted habitats, but not in heavily-silted habitats. This is most likely because broods were subject to predation in both habitat types, but were also negatively affected by siltation in silted habitats. Accordingly, egg dilution by associates was not sufficient to support a mutualistic relationship in less favorable habitats. Results suggest that the biological markets model may be a useful tool for predicting fitness outcomes of nest associative mutualism, but may not be as useful for predicting the behavioral outcomes of obligate mutualisms. Future applications of the biological markets model should carefully consider species traits, specifically the degree to which trading behavior is obligate for participants. Future work with this model will yield more insight by considering highly facultative associates. Nest webs constructed from nest observational data suggested an interaction topology in which strong (nearly-obligate) associates relied most frequently on N. leptocephalus nests, and less frequently on nests constructed by Campostoma anomalum. Weak (facultative) associates were seldom associated with nests constructed by either species, and probably spawned before hosts began nesting activity. Structural equation models corroborated this topology throughout the New River basin, although some less-supported model evidence specified some nest association by weak associates. Juveniles-per-nest of strong associates responded positively to physical stress, while this metric for other cyprinid reproductive groups showed no relationship. Proportional representation of Nocomis and strong associates also increased predictably with physical stress. This study suggests that the nest web framework can be informative to systems outside the ones for which it was developed; future studies may be able to use this framework to better understand the role of habitat-modifying species in communities other than cavity nesting terrestrial vertebrates and nest associative stream fishes. This work extended the nest web framework by (a) modeling the outcomes of interactions instead of the interactions themselves, and (b) by using structural equation modeling to test nest web predictions with an information-theoretic framework. This study also suggests that the stress gradient hypothesis can be useful for understanding interaction dynamics in vertebrate communities; this represents the first direct evidence that this model can be used in vertebrate communities. Further, I demonstrate that the stress gradient hypothesis may be extended to predict community structure. However, more research in a diversity of systems will be needed to determine the extent to which this can be applied. This study provides some of the first evidence of large-scale positive co-occurrence patterns in vertebrates. However, the precise roles of habitat covariates and biotic interactions were species-specific. Occupancy results suggest that co-occurrence between N. leptocephalus and nest associate C. funduloides is driven only by reproductive behavioral interactions. Alternatively, evidence suggests that co-occurrence between N. leptocephalus and C. oreas is driven by both nest association and habitat covariates. That two-species occupancy modeling can be a useful tool for comparing difficult-to-test hypotheses involving biotic interactions at large spatial scales. This study represents the first quantitative, multi-scale treatment of positive interactions in stream ecosystems. This study demonstrates that applying general ecological models to stream fish communities can yield new insights about both the study system and the models themselves. While models of negative interactions, food webs and dispersal have been applied to stream fishes, we stand to gain much ground by also considering positive biotic interactions. In doing so, stream fish ecologists will also be able to contribute to the advancement of general ecology, and thus raise awareness for these understudied ecosystems and taxa. / Ph. D.