The study of species diversity patterns and their causes remains a central theme of ecology. Work conducted over the last few decades has shown that both historical and ecological factors are important in determining species diversity patterns. Additionally, different causal mechanisms are important at different spatial and temporal scales. At the regional scale, species diversity patterns can best be studied in terms of three diversity components (alpha, beta and gamma). This study used the amphibians and reptiles of Costa Rica to examine these species diversity components at the regional scale. To accomplish this, existing species lists were compiled from the literature. Additionally, three herpetofaunal surveys were conducted at under surveyed sites to fill knowledge gaps. A survey of Parque Nacional Carara, a transitional zone site on Costa Rica’s central Pacific coast, gave evidence of a rich herpetofauna, containing species from both the dry tropical forest to the north and the wet lowland forest to the south. Survey results show that Carara’s herpetofaunal assemblage is more similar to that of the wet forest than the dry forest, and suggest many species from both assemblages reach their range limit at or near the park. Surveys of four sites in the eastern Área de Conservación Guanacaste showed rich herpetofaunal diversity and validated the newly purchased Rincón Rainforest as an important conservation area. A survey of Reserva Natural Absoluta Cabo Blanco provided a preliminary list of amphibian and reptile species of the lower Nicoya Peninsula and highlighted the importance of Laguna Balsitas to the local amphibian fauna. A comparison of amphibian and reptile alpha diversity among 17 sites throughout Costa Rica showed highest alpha amphibian diversity in the lowland rainforests of the Pacific versant and highest reptile alpha diversity in lowland rainforests of the Atlantic versant. An analysis of beta diversity produced dendrograms showing sites within lowland ecoregions being most similar. A Canonical Correspondence Analysis (CCA) of environmental variables showed two climate gradients, an elevation/temperature gradient and a sun/rain gradient, to be important in determining species diversity patterns for both amphibians and reptiles in Costa Rica.

Coral reefs, the planet’s most diverse marine ecosystems, are threatened globally by climate change and locally by overfishing and pollution. The dynamic partnership between coral and their endosymbiotic algae (Symbiodinium) is the foundation of all tropical reef ecosystems. Symbiodinium provide coral with nutrients for growth, but stress can break down this symbiosis, causing coral bleaching. There are also life-history trade-offs amongst Symbiodinium types - some provide coral with more nutrition, while others are better able to cope with environmental stressors. Although these symbioses are believed to be a critical element of reef resilience, little is known about how local and global stressors alter these partnerships. In this thesis, I combine synthetic literature reviews and a meta-analysis, with field research, molecular analyses, bioinformatics, and statistical analyses to investigate environmentally-driven mechanisms of change in coral-symbiont interactions with the aim of advancing understanding of how corals will adapt to the stressors they now face. First, I conducted a review of coral-Symbiodinium interactions, from molecules to ecosystems and summarized the current state of the field and knowledge gaps. Next, I conducted a meta-analysis of coral bleaching and mortality during El Niño events and created an open-source coral heat stress data product. I found that the 2015-2016 El Niño instigated unprecedented thermal stress on reefs globally, and that, across all El Niño events, coral bleaching and mortality were greater at locations with higher long-term mean temperatures. I provided recommendations for future bleaching surveys, and in a related perspectives piece, highlighted the importance of survey timing during prolonged coral bleaching events. The latter three empirical chapters are based on my six field expeditions to Kiritimati (Christmas Island). Taking advantage of the atoll’s natural ecosystem-scale experiment, I tagged, sampled and tracked over 1,000 corals across its chronic human disturbance gradient. Since corals can uptake Symbiodinium from the surrounding environment, I first investigated the effect of local disturbance and winter storm waves on Symbiodinium communities in coral, sediment, and seawater. Greater variability in Symbiodinium communities at highly disturbed sites suggests that local disturbance destabilizes symbiont community structure. Since local disturbance influences Symbiodinium community structure and coral-associated microbial communities, I next examined the covariance of coral-associated Symbiodinium and microbial communities for six coral species across Kiritimati’s disturbance gradient. Most strikingly, I found corals on Kiritimati that recovered from globally unprecedented thermal stress, experienced during the 2015-2016 El Niño, while they were still at elevated temperatures. This is notable, because no coral has previously been documented to recover from bleaching while still under heat stress. Only corals protected from local stressors exhibited this capacity. Protected corals had distinct pre-bleaching algal symbiont communities and recovered with different algal symbionts, suggesting that Symbiodinium are the mechanism of resilience and that protection governs their communities. Together, this research provides novel evidence that local protection may be more important for coral resilience than previously thought, and that variability in symbiotic and microbial communities provides a potentially flexible mechanism for corals to respond to both local and global stressors. / Graduate / 2019-11-26

abstract: First year college students have been identified as a vulnerable population for weight gain and the onset of overweight and obesity. Research regarding the gut microbiome has identified differences in the microbial composition of overweight and obese individuals compared to normal weight individuals. Dietary components like dietary fibers, act as prebiotics, or fermentable substrate, that the gut microbiota use for metabolic functions including the production of short-chain fatty acids. The objective of this longitudinal, observational study was to assess changes in the gut microbiota over time in relation to changes in fiber consumption in healthy college students at a large a southwestern university (n=137). Anthropometric and fecal samples were collected at the beginning and end of the fall and spring semesters between August 2015 and May 2016. Both alpha, within sample, diversity and beta, between sample, diversity of participant gut microbes were assessed longitudinally using non-parametric pairwise (pre-post) comparisons and linear mixed effect (LME) models which also adjusted for covariates and accounted for time as a random effect. Alpha and beta diversity were also explored using LME first difference metrics and LME first distance metrics, respectively, to understand rates of change over time in microbial richness/phylogeny and community structure. Pre-post comparisons of Shannon Diversity and Faith’s PD were not significantly different within participant groups of fiber change (Shannon diversity, p=0.96 and Faith’s PD, p=0.66). Beta diversity pairwise comparisons also did not differ by fiber consumption groups (Unweighted UniFrac p=0.182 and Bray Curtis p=0.657). Similarly, none of the LME models suggested significant associations between dietary fiber consumption and metrics of alpha and beta diversity. Overall, data from this study indicates that small changes in fiber consumption among a free-living population did not have an impact on gut microbial richness, phylogeny or community structure. This may have been due to the low intake (~15 g/d) of fiber. Further study is needed to fully elucidate the role that fiber plays in the diversity and composition of the gut microbiota, especially when delivered from a variety of food sources rather than fiber supplements. / Dissertation/Thesis / Masters Thesis Nutrition 2020

L’Amazonie occidentale héberge une biodiversité actuelle foisonnante. Si l’évolution des biomes tropicaux de basse altitude est mal documentée dans le temps profond, il semble que le Miocène ait été une période clé pour l’émergence des écosystèmes amazoniens modernes. Une phase majeure de surrection des Andes a en effet provoqué la mise en place du drainage actuel de l’Amazone au Miocène supérieur (10,5 millions d’années). Pour mieux connaître les modalités de l’émergence de la biodiversité néotropicale actuelle, acquérir une meilleure connaissance des biomes proto-amazoniens – antérieurs au Miocène supérieur – est donc crucial. Malheureusement, le registre fossile correspondant était jusqu’à présent très restreint, en particulier pour les vertébrés. En analysant l’évolution, l’écologie et la biogéographie de mésoeucrocodiliens fossiles (caïmans, gavials et sébécidés) découverts dans de nouvelles localités d’Amazonie péruvienne, le présent mémoire permet de dépeindre un épisode clé de la vie foisonnante de la “proto-Amazonie” occidentale au Miocène. La faune de crocodiles des gisements de la région d’Iquitos (13-10 Ma), au Nord-est du Pérou, représente à la fois la plus grande diversité taxonomique (sept espèces associées) et la plus grande variété de morphotypes du rostre connues pour une communauté donnée de crocodyliformes (actuels-fossiles). L’hétérogénéité dmorphologique correspondante recouvre la majeure partie du morpho-espace connu pour l’ensemble des crocodyliformes, ce qui reflète les influences conjointes d’une évolution à long terme, d’une grande abondance/variété de ressources alimentaires, et d’une ségrégation de niches dans un écosystème complexe. Outre les caïmans géants Purussaurus et Mourasuchus, tous les autres crocodiliens sont des taxons nouveaux, parmi lesquels un caïman basal—Gnatusuchus pebasensis—présentant une mandibule massive et en forme de pelle, des dents antérieures proclives et postérieures globuleuses, ainsi qu’un diastème de type « mammalien ». Cette espèce très particulière constitue un exemple extrême d’une radiation évolutive de petits caïmans durophages, associée à l’apogée des mollusques proto-amazoniens, au sein du méga-système humide Pebas. Le seul crocodilien longirostre de cette communauté est le gavialoïde le plus basal du bassin amazonien, crucial pour la reconstitution de l’écologie et du morphotype ancestraux des Gavialoidea. Une fois inclus dans des analyses phylogénétiques-morphométriques, ce nouveau taxon permet de démontrer que le patron longirostre des gavialoïdes sud-américains et indiens résulte d’une évolution convergente, dans des habitats fluviatiles.Situées à la périphérie du biome pébasien et contemporaines des assemblages d’Iquitos (fin du Miocène moyen), les localités de l’Arche de Fitzcarrald correspondent à une influence plus marquée des Andes, en termes d’environnements. Cette faune de crocodiliens inclut des sébécidés (Sebecosuchia) au crâne comprimé latéralement et des gavials dérivés et aux yeux proéminents (Gavialoidea), associés à divers caïmans (Mourasuchus, Purussaurus, Paleosuchus et Eocaiman). La composition de cet assemblage suggère la prédominance de milieux terrestres et fluviatiles dans cette région. Le contraste est fort avec la région d’Iquitos, où les faunes de crocodiles, hautement endémiques, apparaissent plutôt liées à l’existence de marécages dysoxiques typiques du méga-système Pebas. La mise en place du système de drainage transcontinental amazonien au début du Miocène supérieur a entrainé la disparition du système Pebas et le déclin de ces faunes crocodiliennes proto-amazoniennes, remplacées par des communautés dominées par des caïmans plus généralistes (notamment Caiman et Melanosuchus) et des gavials très longirostres. Plus généralement, l’essor, la persistance, puis le déclin de ces écosystèmes aquatiques miocènes à forte productivité a laissé une empreinte durable – et encore perceptible – sur la biodiversité amazonienne. / Under the influential role of the Andean range, western Amazonia developed distinctive environmental conditions that ultimately led to divergent, higher biodiversity within the Neotropics. Although this intimate geologic-biotic interaction might have produced similar phenomena in the past, our knowledge about the tropical biotic evolution occurring in close proximity to these rapid growing mountains is poorly documented in the deep time. A pivotal time interval for the emergence of the modern Amazonian ecosystems occurred during the Miocene, when major Andean uplift remodeled the landscape of the foreland basin and fostered the onset of the Amazon River System, at about 10.5 million years ago. Proto-Amazonian biotas just prior to this episode are integral to understanding origins of Neotropical biodiversity, yet vertebrate fossil evidence was extraordinarily rare thus far. By studying the evolution, ecology, and biogeography of fossil mesoeucrocodylians (caimans, gharials, and sebecids) documented in new rich paleontological sites of eastern Peru, this research provides a snapshot of the florishing Miocene life of western proto-Amazonia. The crocodylian assemblage of the Iquitos bonebeds (middle-late Miocene transition) is extraordinary in representing both the highest taxonomic diversity (with up to seven associated species) and the widest range of snout morphotypes ever recorded in any crocodyliform community, recent or extinct. The heterogeneity of snout shapes at the Peruvian Miocene localities covers most of the morphospace range known for the entire crocodyliform clade reflecting the combined influences of long-term evolution, resource abundance and variety, and niche partitioning in a complex ecosystem, with no recent equivalent. Besides the large-bodied Purussaurus and Mourasuchus, all other crocodylians in Iquitos are new taxa, including a stem caiman—Gnatusuchus pebasensis—bearing a massive shovel-shaped mandible, procumbent anterior and globular posterior teeth, and a mammal-like diastema. This unusual species is an extreme exemplar of a radiation of small caimans with crushing dentitions recording peculiar feeding strategies correlated with a peak in proto-Amazonian molluscan diversity and abundance, deep in the so-called Pebas Mega-Wetland System. The sole long-snouted crocodylian in this community is the basalmost gavialoid of the Amazonian basin, a critical taxon that offers evidence for accurately reconstructing the ancestral anatomy and ecology of this clade. Including this new species in phylogenetic-morphometric analyses suggests that the evolution of the similar rostral pattern between South American and Indian gavialoids results from parallel evolution in riverine habitats. As part of the same prevailing Pebas biome, Fitzcarrald localities correspond to coeval paleoenvironments closer to the Andean influence (13-12 Ma). This fauna includes deep-snouted sebecids (Sebecosuchia) and advanced gavialoids (Gavialoidea) with protruding eyes, associated with a wide array of caimans (Mourasuchus, Purussaurus, Paleosuchus et Eocaiman), and further suggesting the presence of terrestrial settings and fluvially-dominated ecosystems. On the other hand, the highly endemic Iquitos faunas evolved within the dysoxic marshes and swamps typical of the long-lived Pebas Mega-Wetland System (early–early late Miocene) and declined with the inception of the transcontinental Amazon drainage, favoring diversification of longirostrine crocodylians and more modern generalist-feeding caimans. Indeed, the end of the Pebas Mega-Wetland System notably resulted in the reduction of the phylogenetic and morphotypical mesoeucrocodylian proto-Amazonian diversity, designating the beginning of the modern Amazonian faunas. The rise and demise of distinctive, highly productive aquatic ecosystems substantially influenced evolution of Amazonian biodiversity hotspots of crocodylians and other organisms throughout the Neogene.

Disturbance is a central factor shaping composition, structure, and dynamics of local communities. Drying is a disturbance that occurs in aquatic ecosystems globally and can strongly influence their communities. Although the effects of drying may depend on ecosystem connectivity and the dispersal abilities of resident species, there have been no comparisons of community responses to drying between lentic and lotic ecosystems across different climates. Here, we predicted that drying would have stronger effects on aquatic communities in isolated lentic ecosystems than in dendritic lotic ecosystems, owing to the higher hydrological connectivity of the latter, and that drying would have stronger effects on passive than on active dispersers, because of the potentially higher recolonizing ability of the latter. We tested these predictions by comparing alpha diversity, phylogenetic relatedness, and beta diversity for active and passive dispersers, in both ecosystem types across five climatic regions. Drying caused greater declines in alpha diversity in lentic than in lotic ecosystems. Communities that experienced drying were more similar to one another than those of perennial sites, and this pattern was especially pronounced in lentic ecosystems. In contrast, drying did not influence the contributions of turnover and richness gradients to beta diversity. Additionally, dispersal mode did not influence community responses to drying. Relatively weaker effects of drying in lotic compared to lentic systems were likely due to the hydrological connectivity among perennial and temporary river sites, which may facilitate dispersal of organisms to escape drying and recolonize rewetted sites. Collectively, our results suggest that habitat connectivity may ameliorate (and fragmentation may worsen) the impacts of drying disturbance. This is an important finding in light of increasing drying and concomitant aquatic habitat fragmentation under global change.

No description available.

Tardigrades are microscopic organisms found in both terrestrial and aquatic environments, adapted to a wide range of environmental conditions. Despite their adaptability, tardigrade ecology, particularly their spatial distribution, remains an understudied topic. In this study, we provide a brief overview of tardigrades identified from 26 forests in Southern Chile. We represent tardigrades using Operational Taxonomic Units (OTUs) and examine their spatial distribution across multiple spatial scales. The finer scale involves individual samples (3 x 3 cm, ~9 cm2), while the larger scale encompasses the entire site from which samples were collected (10 x 10 km, 100 km2). We assessed both alpha and beta diversity at these finer and larger scales to determine the impact of these scales on their distribution. Additionally, we assessed whether geographical distances influence species turnover. Our results indicate that the composition and the assemblages of tardigrades varies greatly among samples and among sites. Different sites and scales significantly impact the spatial distribution of tardigrades. Moreover, we found nestedness was low but turnover was high across all the sites, and that geographical distance among sites does not impact turnover. Investigating how tardigrade diversity varies with scale, enhances our understanding of ecological dynamics.

Orientador: Massanori Takaki / Resumo: Grandes iniciativas mundiais no esforço de alavancar um aumento na restauração ecológica surgiram recentemente, como a Iniciativa 20 x 20 e a Bonn Challenge, que apresentam como meta conjunta restaurar 500 milhões de hectares até 2030. Assim, uma das metas da ecologia aplicada à restauração é buscar compreender as distintas maneiras pelas quais a vegetação varia durante o processo de restauração e quais fatores influenciam o aumento da riqueza de espécies regenerantes. Este trabalho teve como objetivos: (1) Compreender como variam a abundância relativa e riqueza rarefeita, quando se comparam a regeneração natural total e específica (espécies que ocorreram apenas na área de referência), nas áreas em restauração com diferentes idades. (2) Avaliar como variam a diversidade alfa e beta nas áreas em restauração com idades distintas. (3) Observar a variação na abertura do dossel nas áreas com idades distintas. (4) Analisar se as variáveis da abertura do dossel e a idade são fatores importantes no que tange à influência com o aumento da riqueza de espécies regenerantes. Nove áreas em processo de restauração, localizadas no município de Extrema (Minas Gerais), foram selecionadas com 4, 7 e 10 anos de idade e um fragmento de referência, onde ao todo, 360 parcelas foram instaladas. Em cada parcela foram mensurados todos os regenerantes entre 20 cm e 2 m de altura (ervas, trepadeiras, arbustos, arbóreas e pteridófitas). Resultados: Foram encontrados 6788 regenerantes. As herbáceas e arb... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Major global initiatives in an effort to leverage an increase in the ecological restoration areas have recently emerged, such as the 20 x 20 Initiative and the Bonn Challenge, which aim to restore together 500 million hectares by 2030. Thus, one of the goals of ecology applied to restoration is to look at the different ways in which vegetation varies during the restoration process and what factors influence the increase of regenerating species richness. This work has as objectives: (1) To understand how the relative abundance and rarefied richness vary, when comparing the total and specific natural regeneration (species that occurred only in the reference area) in restoration areas having varying ages. (2) To evaluate how alpha and beta diversity varies in areas of restoration of different ages. (3) To observe the variation in canopy opening in areas of different ages. (4) To analyze whether the variable canopy opening and age are important factors in the influence or relation with the increase of the richness of regenerating species. Nine areas aged 4,7 and 10 under restoration process were selected and a reference fragment, in which a total of 360 parcels were installed. All the areas are located in the Municipality of Extrema, Minas Gerais. In each plot was measured all regenerants between 20 cm and 2 m in height (herbs, climbers, shrubs, trees and pteridophytes). Results: 6788 regenerants were found. Herbs and trees had the highest relative abundances, general and specifi... (Complete abstract click electronic access below) / Doutor

Entender padrões de diversidade e composição de espécies ao longo de múltiplas escalas espaciais constitui um dos principais objetivos em ecologia e biogeografia. A relativa importância dos mecanismos responsáveis por estruturar as comunidades de plantas e como eles interagem para influenciar estes padrões têm sido foco de intensos debates. No presente estudo, foram utilizados dados do Inventário Florístico Florestal de Santa Catarina a fim de investigar os padrões de diversidade de espécies de árvores e suas relações com a heterogeneidade ambiental sob uma das perspectivas oriundas da teoria de metacomunidades, conhecida como “sorteio de espécies”. A predição chave deste ponto de vista é a de que a composição de espécies varia em resposta a diferenças nas condições ambientais entre manchas de hábitat. O presente estudo é focado nessa predição e objetivou entender como processos relacionados a filtros ambientais interagem direta e indiretamente sobre os padrões de diversidade em uma área de 95000 km 2 (dados de 432 unidades amostrais). Foi utilizada modelagem de equações estruturais (PLS Path Modeling), a fim de investigar os efeitos interativos da topografia, clima, balanço de água e energia e geometria das manchas de floresta sobre os padrões de alfa (α) e beta (β) diversidade de uma metacomunidade de floresta atlântica no sul do Brasil. Fatores relacionados a filtros ambientais mostraram substanciais efeitos sobre a diversidade alfa e beta. A quantidade total da variação na beta diversidade explicada pela filtragem de hábitat foi alta (64%), corroborando a predição testada no nível de metacomunidades. Os fatores mais importantes para explicar a diversidade beta foram: extremos climáticos, balanço de água e energia e alfa diversidade, enquanto tamanho da mancha e balanço de água e energia foram os fatores chaves para a alfa diversidade. O teste de Mantel parcial mostrou que os efeitos ambientais ocorrem amplamente independente de efeitos espaciais, reforçando a predição testada. O estudo provê forte suporte empírico para a predição de que a beta diversidade reflete primariamente processos determinísticos associados com o nicho das espécies e suas respostas às condições ambientais na escala espacial considerada. / Understanding patterns of species diversity and composition across multiple scales is one of the main purpose in ecology and biogeography. The relative importance of the mechanisms that structure plant communities and how they interact to influence these patterns remains a topic of hot debate. In the present study, we use data from the Forest Inventory of Santa Catarina to investigate the patterns of species diversity of subtropical Atlantic forests and its relationships with environmental heterogeneity on a metacommunity perspective (species-sorting). The key prediction of this viewpoint is that community composition varies in response to differences in environmental conditions among habitat patches. Our study focused on this perspective, aiming to understand how environmental filtering processes interact directly and indirectly on diversity patterns in an area of 95000 km 2 (data from 432 forest plots). We employed structural equation modeling (PLS Path Modeling) to disentangle the interactive effects of topography, climate, water-energy balance, and geometry of forest patches upon the alpha and beta diversity of a subtropical forest metacommunity in southern Brazil. Factors related to environmental filtering showed substantial effects upon tree alpha and beta diversity. The total amount of variation in beta diversity explained by environmental filtering was high (64%) and was even more when together with alpha diversity (73%), corroborating the prediction of species-sorting model at the metacommunity level. Climatic extremes, water-energy balance and alpha diversity were the key determinants of beta diversity and patch size and water- energy balance the key determinants of alpha diversity in the South Brazilian Atlantic forests. Partial mantel test showed that environmental effects occurred largely independent of spatial effects, reinforcing the tested prediction. Our study provides strong empirical support for the prediction that beta diversity primarily reflects deterministic factors associated with species niches and their responses to environmental conditions in the studied spatial scale.

Entender padrões de diversidade e composição de espécies ao longo de múltiplas escalas espaciais constitui um dos principais objetivos em ecologia e biogeografia. A relativa importância dos mecanismos responsáveis por estruturar as comunidades de plantas e como eles interagem para influenciar estes padrões têm sido foco de intensos debates. No presente estudo, foram utilizados dados do Inventário Florístico Florestal de Santa Catarina a fim de investigar os padrões de diversidade de espécies de árvores e suas relações com a heterogeneidade ambiental sob uma das perspectivas oriundas da teoria de metacomunidades, conhecida como “sorteio de espécies”. A predição chave deste ponto de vista é a de que a composição de espécies varia em resposta a diferenças nas condições ambientais entre manchas de hábitat. O presente estudo é focado nessa predição e objetivou entender como processos relacionados a filtros ambientais interagem direta e indiretamente sobre os padrões de diversidade em uma área de 95000 km 2 (dados de 432 unidades amostrais). Foi utilizada modelagem de equações estruturais (PLS Path Modeling), a fim de investigar os efeitos interativos da topografia, clima, balanço de água e energia e geometria das manchas de floresta sobre os padrões de alfa (α) e beta (β) diversidade de uma metacomunidade de floresta atlântica no sul do Brasil. Fatores relacionados a filtros ambientais mostraram substanciais efeitos sobre a diversidade alfa e beta. A quantidade total da variação na beta diversidade explicada pela filtragem de hábitat foi alta (64%), corroborando a predição testada no nível de metacomunidades. Os fatores mais importantes para explicar a diversidade beta foram: extremos climáticos, balanço de água e energia e alfa diversidade, enquanto tamanho da mancha e balanço de água e energia foram os fatores chaves para a alfa diversidade. O teste de Mantel parcial mostrou que os efeitos ambientais ocorrem amplamente independente de efeitos espaciais, reforçando a predição testada. O estudo provê forte suporte empírico para a predição de que a beta diversidade reflete primariamente processos determinísticos associados com o nicho das espécies e suas respostas às condições ambientais na escala espacial considerada. / Understanding patterns of species diversity and composition across multiple scales is one of the main purpose in ecology and biogeography. The relative importance of the mechanisms that structure plant communities and how they interact to influence these patterns remains a topic of hot debate. In the present study, we use data from the Forest Inventory of Santa Catarina to investigate the patterns of species diversity of subtropical Atlantic forests and its relationships with environmental heterogeneity on a metacommunity perspective (species-sorting). The key prediction of this viewpoint is that community composition varies in response to differences in environmental conditions among habitat patches. Our study focused on this perspective, aiming to understand how environmental filtering processes interact directly and indirectly on diversity patterns in an area of 95000 km 2 (data from 432 forest plots). We employed structural equation modeling (PLS Path Modeling) to disentangle the interactive effects of topography, climate, water-energy balance, and geometry of forest patches upon the alpha and beta diversity of a subtropical forest metacommunity in southern Brazil. Factors related to environmental filtering showed substantial effects upon tree alpha and beta diversity. The total amount of variation in beta diversity explained by environmental filtering was high (64%) and was even more when together with alpha diversity (73%), corroborating the prediction of species-sorting model at the metacommunity level. Climatic extremes, water-energy balance and alpha diversity were the key determinants of beta diversity and patch size and water- energy balance the key determinants of alpha diversity in the South Brazilian Atlantic forests. Partial mantel test showed that environmental effects occurred largely independent of spatial effects, reinforcing the tested prediction. Our study provides strong empirical support for the prediction that beta diversity primarily reflects deterministic factors associated with species niches and their responses to environmental conditions in the studied spatial scale.