Metagenomic insight into taxonomic composition, environmental filtering and functional redundancy for shaping worldwide modern non-lithifying microbial mats.

Modern microbial mats are relictual communities mostly found in extreme environments worldwide. Despite their significance as representatives of the ancestral Earth and their important roles in biogeochemical cycling, research on microbial mats has largely been localized, focusing on site-specific descriptions and environmental change experiments. Here, we present a global comparative analysis of non-lithifying microbial mats, integrating environmental measurements with metagenomic data from 62 samples across eight sites, including two new samples from the recently discovered Archaean Domes from Cuatro Ciénegas, Mexico. Our results revealed a notable influence of environmental filtering on both taxonomic and functional compositions of microbial mats. Functional redundancy appears to confer resilience to mats, with essential metabolic pathways conserved across diverse and highly contrasting habitats. We identified six highly correlated clusters of taxa performing similar ecological functions, suggesting niche partitioning and functional specialization as key mechanisms shaping community structure. Our findings provide insights into the ecological principles governing microbial mats, and lay the foundation for future research elucidating the intricate interplay between environmental factors and microbial community dynamics.

Divergence in functional traits in seven species of neotropical palms of different forest strata.

Functional traits are morphological and physiological characteristics that determine growth, reproduction, and survival strategies. The leaf economics spectrum proposes two opposing life history strategies: species with an "acquisitive" strategy grow fast and exploit high-resource environments, while species with a "conservative" strategy emphasize survival and slow growth under low resource conditions. We analyzed intra and interspecific variation in nine functional traits related to biomass allocation and tissue quality in seven Neotropical palm species from understory and canopy strata. We expected that the level of resources of a stratum that a species typically exploits would determine the dominance of either the exploitative or conservative strategy, as well as degree of divergence in functional traits between species. If this is correct, then canopy species will show an acquisitive strategy emphasizing traits targeting a larger size, whereas understory species will show a conservative strategy with traits promoting efficient biomass allocation and survival in the shade. Two principal components (57.22% of the variation) separated palm species into: (a) canopy species whose traits were congruent with the acquisitive strategy and emphasized large size (i.e., diameter, height, carbon content, and leaf area), and (b) understory species whose traits were associated with efficient biomass allocation (i.e., dry mass fraction -DMF- and tissue density). As we unravel the variation in functional traits in palms, which make up a substantial proportion of the tropical flora, we gain a deeper understanding of how plants adapt to environmental gradients.

Archaeal and Bacterial Diversity and Distribution Patterns in Mediterranean-Climate Vernal Pools of Mexico and the Western USA.

Biogeographic patterns in microorganisms are poorly understood, despite the importance of microbial communities for a range of ecosystem processes. Our knowledge of microbial ecology and biogeography is particularly deficient in rare and threatened ecosystems. We tested for three ecological patterns in microbial community composition within ephemeral wetlands-vernal pools-located across Baja California (Mexico) and California (USA): (1) habitat filtering; (2) a latitudinal diversity gradient; and (3) distance decay in community composition. Paired water and soil samples were collected along a latitudinal transect of vernal pools, and bacterial and archaeal communities were characterized using 16S rDNA sequencing. We identified two main microbial communities, with one community present in the soil matrix that included archaeal and bacterial soil taxa, and another community present in the overlying water that was dominated by common freshwater bacterial taxa. Aquatic microbial communities were more diverse in the north, and displayed a significant but inverted latitudinal diversity pattern. Aquatic communities also exhibited a significant distance-decay pattern, with geographic proximity, and precipitation explaining part of the community variation. Collectively these results indicate greater sensitivity to spatial and environmental variation in vernal pool aquatic microbial communities than in soil microbial communities. We conclude that vernal pool aquatic microbial communities can display distribution patterns similar to those exhibited by larger organisms, but differ in some key aspects, such as the latitudinal gradient in diversity.

Recent Differentiation of Aquatic Bacterial Communities in a Hydrological System in the Cuatro Ciénegas Basin, After a Natural Perturbation.

Pozas Rojas is a hydrological system comprising nine isolated shallow ponds and a deep lagoon, which were temporally merged in 2010 by increased rainfall due to a tropical cyclone. In this work, we assess which components, biotic interactions, or environment filtering effects, drive the assembly of microbial communities after a natural perturbation. Arsenic, pH, and temperature are among the most significant environmental variables between each pond, clustering the samples in two main groups, whereas microbial composition is diverse and unique to each site, with no core at the operational taxonomic unit level and only 150 core genera when studied at the genus level. Los Hundidos lagoon has the most differentiated community, which is highly similar to the epipelagic Mediterranean Sea communities. On the other hand, the shallow ponds at the Pozas Rojas system resemble more to epicontinental hydrological systems, such as some cold rivers of the world and the phreatic mantle from Iowa. Overall, despite being a sole of water body 2 years prior to the sampling, interspecific interactions, rather than environmental selection, seem to play a more important role in Pozas Rojas, bolstered by founder effects on each poza and subsequent isolation of each water body.

Altitudinal gradient drives regional and local diversity and composition patterns of epiphyllous bryophytes in ecological refuges.

'Brejos de altitude' is an ecosystem that has been subjected to severe exploitation, leading to an intense reduction in Brazil. Understanding the patterns of bryophyte diversity and composition, particularly of specialized species such as the epiphylls, to anthropic and abiotic variables is crucial for implementing protection measures. We investigated the relationship between composition and diversity of epiphyllous bryophytes and anthropic (edge effects) and abiotic (altitude) variables at local (within each 'Brejo') and regional (set of three 'Brejos') scale. Abiotic and anthropic variables were correlated with alpha and beta diversity (decomposed into species replacement and richness differences) using GLM. Their effects on species composition were evaluated using PERMANOVA. The localities at higher elevations harboured a richer bryoflora and overall beta diversity patterns were associated with altitude and locality, which acted over different scales. Regionally, the contribution of richness differences was limited with increasing altitude. Yet, dissimilarities among localities were associated with richness differences and replacement, denoting the importance of local factors. The composition was explained by local factors interacting with the regional altitudinal gradient. Anthropic activity was significant only when interacting with local factors and altitudinal gradient. Environmental filtering associated with altitude played a more important role in shaping the diversity and composition of epiphyllous bryophytes, at both regional and local scales. Each 'Brejo' acts as an ecological refuge, harbouring part of the whole environmental gradient, and presents a unique floristic composition. Moreover, partitioning beta diversity highlighted the interplay of local and regional forces shaping diversity patterns.

Modelling selection, drift, dispersal and their interactions in the community assembly of Amazonian soil mites.

Three processes can explain contemporary community assembly: natural selection, ecological drift and dispersal. However, quantifying their effects has been complicated by confusion between different processes and neglect of expected interactions among them. One possible solution is to simultaneously model the expected effects of each process within species, across communities and across species, thus providing more integrative tests of ecological theory. Here, we used generalized linear mixed models to assess the effects of selection, drift and dispersal on the occurrence probability of 135 soil oribatid mite species across 55 sites over an Amazonian rainforest landscape (64 km2). We tested for interactions between process-related factors and partitioned the explained variation among them. We found that occurrence probability (1) responded to soil P content and litter mass depending on body size and reproductive mode (sexual or parthenogenetic), respectively (selection); (2) increased with community size (drift); and (3) decreased with distance to the nearest source population, and more so in rare species (dispersal limitation). Processes did not interact significantly, and our best model explained 67% of the overall variation in species occurrence probability. However, most of the variation was attributable to dispersal limitation (55%). Our results challenge the seldom-tested theoretical prediction that ecological processes should interact. Rather, they suggest that dispersal limitation overrides the signatures of drift and selection at the landscape level, thus rendering soil microarthropod species ecologically equivalent and possibly contributing to the maintenance of metacommunity diversity.

Diversity of Gall-Inducing Insects Associated With a Widely Distributed Tropical Tree Species: Testing the Environmental Stress Hypothesis.

Abiotic factors can affect plant performance and cause stress, which in turn affects plant-herbivore interactions. The Environmental Stress Hypothesis (ESH) predicts that gall-inducing insect diversity will be greater on host plants that grow in stressful habitats. We tested this hypothesis, considering both historical and ecological scales, using the plant Copaifera langsdorffii Desf. (Fabaceae) as a model because it has a wide geographic distribution and is a super-host of gall-inducing insects. According to the ESH, we predicted that 1) on a historical scale, the diversity of gall-inducing insects will be higher in habitats with greater environmental stress and 2) on an ecological scale, gall-inducing insect diversity will be greater on plants that possess greater levels of foliar sclerophylly. We sampled gall-inducing insects on plants of C. langsdorffii in five sites with different levels of water and soil nutrient availability and separated from each other by a distance of up to 470 km. The composition, richness, and abundance of gall-inducing insects varied among study sites. Plants located in more stressful habitats had higher levels of foliar sclerophylly; but richness and abundance of gall-inducing insects were not affected by host plant sclerophylly. Habitat stress was a good predictor of gall-inducing insect diversity on a regional scale, thus corroborating the first prediction of the ESH. No relationship was found between plant sclerophylly and gall-inducing insect diversity within habitats. Therefore, on a local scale, we did not find support for our second prediction related to the ESH.

How Habitat Filtering Can Affect Taxonomic and Functional Composition of Aquatic Insect Communities in Small Amazonian Streams.

Responses in taxonomic and functional composition of communities were analysed in small Amazonian streams at the small and large scale (habitat patches, river segment scale, and catchment scale). We hypothesised that similar responses in community structure to local environmental factors were a correlation between taxonomic and functional composition. To evaluate the response of taxonomic composition to environmental variables, redundancy analysis (RDA) and RLQ analysis were performed to investigate the response of community abundance (L) as a function of the environment (R) and traits (Q). The fourth-corner analysis was applied to summarize specific interactions between environmental variables and traits. Then, community taxonomic composition was associated with models at multiple scales of habitat (i.e. riparian/channel, substrates, and water variables). Likewise, the fourth-corner tests and RLQ axes showed associations between trait composition and environmental variables related to variables, such as riparian cover and channel morphology followed by variation in substrate size and composition. Unexpectedly, these results did not show specific associations between unique environmental variables and traits. At last, results showed that local conditions of stream habitat regulated community structure and functional composition of aquatic insects. Thus, these findings indicate that the local environmental filtering appears to be strongly associated with selected species traits adapted to occur in a range of habitat conditions. Despite the low number of analysed streams, these results provide important information for understanding the simultaneous variation in functional trait composition and community composition of aquatic insect assemblages.

Linking patterns and processes of tree community assembly across spatial scales in tropical montane forests.

Many studies have tried to assess the role of both deterministic and stochastic processes in community assembly, yet a lack of consensus exists on which processes are more prevalent and at which spatial scales they operate. To shed light on this issue, we tested two nonmutually exclusive, scale-dependent hypotheses: (1) that competitive exclusion dominates at small spatial scales; and (2) that environmental filtering does so at larger ones. To accomplish this, we studied the functional patterns of tropical montane forest communities along two altitudinal gradients, in Ecuador and Peru, using floristic and functional data from 60 plots of 0.1 ha. We found no evidence of either functional overdispersion or clustering at small spatial scales, but we did find functional clustering at larger ones. The observed pattern of clustering, consistent with an environmental filtering process, was more evident when maximizing the environmental differences among any pair of plots. To strengthen the link between the observed community functional pattern and the underlying process of environmental filtering, we explored differences in the climatic preferences of the most abundant species found at lower and higher elevations and examined whether their abundances shifted along the elevation gradient. We found (1) that greater community functional differences (observed between lower and upper tropical montane forest assemblies) were mostly the result of strong climatic preferences, maintained across the Neotropics; and (2) that the abundances of such species shifted along the elevational gradient. Our findings support the conclusion that, at large spatial scales, environmental filtering is the overriding mechanism for community assembly, because the pattern of functional clustering was linked to species' similarities in their climatic preferences, which ultimately resulted in shifts in species abundances along the gradient. However, there was no evidence of competitive exclusion at more homogeneous, smaller spatial scales, where plant species effectively compete for resources.

A simulation-based framework to explore the importance of non-selection and selection processes in structuring ecological communities.

The purpose of this framework is to identify the relative importance of selection and dispersion processes in structuring ecological communities. Using a "pattern-oriented modelling" approach, it consists of five steps: (a) aggregate information from the empirical community and its environment, (b) simulate communities under different degrees of dispersal and selection, (c) select the best set of simulations into a composite model using the environmental boundary (EB) and niche breadth (NB) of each observed species, (d) validate the composite model by comparing expected and observed results from three additional community patterns and (e) classify each observed species along the selection/non-selection continuum. A free-living marine nematodes data set from a coastal bay was used as empirical example. A total of 20 parameterizations were applied varying selection and dispersion levels. In the absence of selection, species from high-dispersal parameter sets showed maximum EBs and NBs, whilst selection parameter sets generated species with narrower EB and NB values. EB and NB values declined with decreasing dispersal. The composite model encompassed 96% of the 194 nematode species and predicted all the three patterns evaluated without further calibration, i.e., they are independent: (1) abundance-rank distribution, the assemblage structures along both the (2) spatial and (3) environmental gradients. Non-selection and selection parameter sets accounted for 34% and 85% of the observed species, respectively. The main advantage of this approach is that empirical niche measurements are placed in the context of model-generated expectations, enabling a deeper understanding of community assembly processes and how they vary from species to species.

Solitary ecology as a phenomenon extending beyond insular systems: exaptive evolution in Anolis lizards.

The mechanisms driving phenotypic evolution have been of interest to biologists since Darwin. Ecological release-wherein adaptive evolution occurs following relaxation of constraining selective pressures-and environmental filtering-wherein exaptive traits allow colonization of a new area-have been studied in several insular cases. Anolis lizards, which may exist in solitude or sympatry with multiple congeners, are an excellent system for evaluating whether ecological release and environmental filtering are associated with phenotypic shifts across phylogenetic and geographical scales. Insular solitary Anolis exhibit phenotypic differentiation in body size and sexual size dimorphism-SSD-through exaptive and adaptive evolution, respectively. But, the generality of these effects has not yet been addressed. Here, we analyse the evolution of body size and SSD relative to sympatry in mainland Anolis. We found that mainland species co-occurring with few congeners exhibit uniform body size and greater SSD relative to other random mainland assemblages, consistent with the insular solitary pattern. The locations of evolutionary shifts for both traits do not coincide with evolutionary transitions to decreased levels of sympatry. These results are consistent with exaptive environmental filtering but not adaptive ecological release. Future studies should be conducted at local scales to evaluate the role of these factors in the evolution of solitary existence in mainland and island species.

Shade tolerance within the context of the successional process in tropical rain forests

Shade tolerance (the capacity to survive and grow over long periods under shade) is a key component of plant fitness and the foundation of current theories of forest succession in tropical rain forests. It serves as a paradigm to understand the optimal allocation of limited resources under dynamic light regimes. I analyze how tropical rain forest succession influences the expression of ecophysiological mechanisms leading to shade tolerance, and identify future areas that will increase our understanding of the ecological and evolutionary consequences of this phenomenon. Shade tolerance is a multivariate, continuous functional trait reflecting the growth-mortality trade-off of investing resources under limited light vs. exploiting high light conditions. I propose the life cycle successional trajectory model of Gómez-Pompa & Vázquez-Yanes as an integrative tool to understand tropical rain forest succession. This model shows how species distribute along the successional environmental gradient based on their degree of shade tolerance and represents a more integrative paradigm to understand the interface between different aspects of species diversity (ontogenetic variation and functional diversity) throughout succession. It proposes that different trait combinations determining shade tolerance are expressed at different stages of the life cycle, which affects how and when plants enter the successional trajectory. Models explaining the expression of shade tolerance (resource availability, carbon gain, CSR, resource competition) are based on whole-plant economics and are not mutually exclusive. The analysis of shade tolerance is biased towards tree seedlings in the understory of mature forests. Other life stages (juvenile and adult trees), life forms, and microhabitats throughout the forest profile are almost always excluded from these analyses. More integrative explanations based on the distribution of functional traits among species, ontogenetic stages, and the nature of the environmental gradient are being developed based on long-term data and chronosequence comparisons. In summary, shade-tolerance is a complex phenomenon, is determined by multiple characters that change ontogenetically over space and time and entails considerable plasticity. Current methods do not account for this plasticity. Understanding the nature of shade tolerance and its functional basis is critical to comprehending plant performance and improving the management, restoration and conservation of tropical rain forests given the combined threats of global warming and habitat loss.

La tolerancia a la sombra (la capacidad de sobrevivir y crecer durante largos períodos bajo sombra profunda) es un componente clave del valor adaptativo de la planta y la base de las teorías actuales de la sucesión forestal de la selva tropical. Sirve como un paradigma para entender la asignación óptima de recursos limitados bajo regímenes dinámicos de luz. En esta revisión analizo cómo la sucesión de los bosques tropicales lluviosos influye en la expresión de los mecanismos ecofisiológicos que conducen a la tolerancia a la sombra, e identifico áreas futuras que pueden aumentar nuestra comprensión de las consecuencias ecológicas y evolutivas de este fenómeno. La tolerancia a la sombra es un rasgo funcional continuo y multivariable que refleja el balance de invertir recursos bajo condiciones de luz limitada versus crecer más rápidamente en condiciones de luz intensa. Propongo el modelo de ciclo de vida a lo largo de la trayectoria de sucesión de Gómez-Pompa y Vázquez-Yanes como una herramienta integradora para entender la sucesión de la selva tropical. Este modelo muestra cómo las especies se distribuyen a lo largo del gradiente ambiental en función de su grado de tolerancia a la sombra, y representa un paradigma más integrador para comprender la interacción entre los diferentes componentes de la diversidad de especies (diversidad taxonómica y funcional y variación ontogenética) a lo largo de la sucesión. El modelo propone que las diferentes combinaciones de caracteres funcionales que determinan la tolerancia a la sombra se expresan en diferentes etapas del ciclo de vida, y afectan cómo y cuándo las plantas ingresan en el proceso de sucesión. Los modelos que explican la expresión de tolerancia a la sombra (disponibilidad de recursos, ganancia de carbono, CSR, competencia de recursos) se basan en la economía de toda la planta y no son mutuamente excluyentes. Se están desarrollando explicaciones más integradoras basadas en la distribución de caracteres funcionales entre especies, etapas ontogenéticas, y micrositios, mediante el uso de estudios de cronosecuencia y metadatos colectados a largo plazo. El análisis de la tolerancia a la sombra está sesgado hacia las plántulas de árboles y el sotobosque. Otras formas de vida y microhábitats dentro del perfil del bosque están casi excluidas de estos análisis. En resumen, la tolerancia a la sombra es un fenómeno complejo, está determinada por múltiples caracteres funcionales que cambian ontogenéticamente en el espacio y el tiempo, e implica una considerable plasticidad. Los métodos actuales no toman en cuenta esta plasticidad. Comprender la naturaleza de la tolerancia a la sombra y su base funcional es fundamental para entender el crecimiento de la planta y mejorar la gestión, restauración, y conservación de los bosques tropicales, los cuales enfrentan las amenazas combinadas del calentamiento global y la pérdida de hábitat.

Different environmental gradients affect different measures of snake ß-diversity in the Amazon rainforests.

Mechanisms generating and maintaining biodiversity at regional scales may be evaluated by quantifying ß-diversity along environmental gradients. Differences in assemblages result in biotic complementarities and redundancies among sites, which may be quantified through multi-dimensional approaches incorporating taxonomic ß-diversity (TBD), functional ß-diversity (FBD) and phylogenetic ß-diversity (PBD). Here we test the hypothesis that snake TBD, FBD and PBD are influenced by environmental gradients, independently of geographic distance. The gradients tested are expected to affect snake assemblages indirectly, such as clay content in the soil determining primary production and height above the nearest drainage determining prey availability, or directly, such as percentage of tree cover determining availability of resting and nesting sites, and climate (temperature and precipitation) causing physiological filtering. We sampled snakes in 21 sampling plots, each covering five km2, distributed over 880 km in the central-southern Amazon Basin. We used dissimilarities between sampling sites to quantify TBD, FBD and PBD, which were response variables in multiple-linear-regression and redundancy analysis models. We show that patterns of snake community composition based on TBD, FBD and PBD are associated with environmental heterogeneity in the Amazon. Despite positive correlations between all ß-diversity measures, TBD responded to different environmental gradients compared to FBD and PBD. Our findings suggest that multi-dimensional approaches are more informative for ecological studies and conservation actions compared to a single diversity measure.

Phylogenetic structure is determined by patch size in rock outcrop vegetation on an inselberg in the northern Amazon region / Estrutura filogenética é determinada pelo tamanho de manchas de vegetação sobre afloramento rochoso em um inselberg na região norte da Amazônia

Although inselbergs from around the world are iconic ecosystems, little is known on the underlying mechanisms of community assembly, especially in their characteristic patchy outcrop vegetation. Environmental constraints are expected to cause phylogenetic clustering when ecological niches are conserved within evolutionary lineages. We tested whether vegetation patches from rock outcrops of the Piedra La Tortuga Natural Monument, in the northern Amazon region, are phylogenetically clustered, indicating that environmental filtering is the dominant driver of community assemblage therein. We classified all patches according to their size as very small (< 1 m2), small (1-4 m2), medium-sized (4-8 m2), and large patches (8-15 m2). From each class, we randomly selected 10 patches, totalizing 40 patches covering 226 m2. All individuals found in the 40 isolated patches were identified to the species level. We also correlated measurements of phylogenetic community structure with patch size. We found that species from patches are restricted to the clades monocots, fabids, malvids, and lamiids. We conclude that vegetation in this rock outcrop is phylogenetically clustered. Furthermore, we found that phylogenetic turnover between pairs of patches increases with patch size, which is consistent with a scenario of higher environmental stress in smaller patches. Further research is necessary to identify nurse species in inselberg vegetation, which is pivotal for conservation and restoration of this particular ecosystem.(AU)

Ainda que os inselbergs ao redor do mundo sejam ecossistemas icônicos, pouco se sabe sobre os mecanismos subjacentes que estruturam suas comunidades vegetais, especialmente nas manchas de vegetação sobre afloramentos rochosos. Espera-se que as restrições ambientais causem agrupamento filogenético quando os nichos ecológicos são conservados dentro das linhagens evolutivas. Nós testamos se as manchas de vegetação dos afloramentos rochosos do Monumento Natural Piedra La Tortuga, no norte da região amazônica, apresentam indicadores filogenéticos de que a filtragem ambiental é o principal direcionador da estruturação da comunidade. Classificamos todas as manchas de acordo com seu tamanho como muito pequenas (<1 m2), pequenas (1-4 m2), médias (4-8 m2) e grandes (8-15 m2). Selecionamos aleatoriamente 10 manchas em cada classe de tamanho, totalizando 40 manchas cobrindo 226 m2. Todos os indivíduos encontrados nas 40 manchas foram identificados ao nível de espécie. Correlacionamos as medidas da estrutura filogenética da comunidade com o tamanho das manchas e encontramos que as espécies das manchas são restritas aos clados das monocotiledôneas, fabídeas, malvídeas e lamiídeas. Concluímos que a vegetação neste afloramento rochoso é agrupada filogeneticamente. Além disso, encontramos que o turnover filogenético entre pares de manchas aumenta com o tamanho da mancha, o que é consistente com um cenário de alto estresse ambiental nas manchas menores. São necessárias mais pesquisas para identificar espécies facilitadoras, que são fundamentais para a conservação e restauração destes ecossistemas.(AU)

Phylogenetic structure is determined by patch size in rock outcrop vegetation on an inselberg in the northern Amazon region / Estrutura filogenética é determinada pelo tamanho de manchas de vegetação sobre afloramento rochoso em um inselberg na região norte da Amazônia

Although inselbergs from around the world are iconic ecosystems, little is known on the underlying mechanisms of community assembly, especially in their characteristic patchy outcrop vegetation. Environmental constraints are expected to cause phylogenetic clustering when ecological niches are conserved within evolutionary lineages. We tested whether vegetation patches from rock outcrops of the Piedra La Tortuga Natural Monument, in the northern Amazon region, are phylogenetically clustered, indicating that environmental filtering is the dominant driver of community assemblage therein. We classified all patches according to their size as very small (< 1 m2), small (1-4 m2), medium-sized (4-8 m2), and large patches (8-15 m2). From each class, we randomly selected 10 patches, totalizing 40 patches covering 226 m2. All individuals found in the 40 isolated patches were identified to the species level. We also correlated measurements of phylogenetic community structure with patch size. We found that species from patches are restricted to the clades monocots, fabids, malvids, and lamiids. We conclude that vegetation in this rock outcrop is phylogenetically clustered. Furthermore, we found that phylogenetic turnover between pairs of patches increases with patch size, which is consistent with a scenario of higher environmental stress in smaller patches. Further research is necessary to identify nurse species in inselberg vegetation, which is pivotal for conservation and restoration of this particular ecosystem.

Ainda que os inselbergs ao redor do mundo sejam ecossistemas icônicos, pouco se sabe sobre os mecanismos subjacentes que estruturam suas comunidades vegetais, especialmente nas manchas de vegetação sobre afloramentos rochosos. Espera-se que as restrições ambientais causem agrupamento filogenético quando os nichos ecológicos são conservados dentro das linhagens evolutivas. Nós testamos se as manchas de vegetação dos afloramentos rochosos do Monumento Natural Piedra La Tortuga, no norte da região amazônica, apresentam indicadores filogenéticos de que a filtragem ambiental é o principal direcionador da estruturação da comunidade. Classificamos todas as manchas de acordo com seu tamanho como muito pequenas (<1 m2), pequenas (1-4 m2), médias (4-8 m2) e grandes (8-15 m2). Selecionamos aleatoriamente 10 manchas em cada classe de tamanho, totalizando 40 manchas cobrindo 226 m2. Todos os indivíduos encontrados nas 40 manchas foram identificados ao nível de espécie. Correlacionamos as medidas da estrutura filogenética da comunidade com o tamanho das manchas e encontramos que as espécies das manchas são restritas aos clados das monocotiledôneas, fabídeas, malvídeas e lamiídeas. Concluímos que a vegetação neste afloramento rochoso é agrupada filogeneticamente. Além disso, encontramos que o turnover filogenético entre pares de manchas aumenta com o tamanho da mancha, o que é consistente com um cenário de alto estresse ambiental nas manchas menores. São necessárias mais pesquisas para identificar espécies facilitadoras, que são fundamentais para a conservação e restauração destes ecossistemas.

Flower colour within communities shifts from overdispersed to clustered along an alpine altitudinal gradient.

Altitudinal gradients are interesting models to test the effect of biotic and abiotic drivers of floral colour diversity, since an increase in UV irradiance, decrease of pollinator availability and shifts from bee- to fly-pollination in high relative to low altitudes are expected. We tested the effect of altitude and phylogeny, using several chromatic and achromatic colour properties, UV reflectance and pollinators' discrimination capacity (Apis mellifera, Bombus terrestris, Musca domestica and Eristalis tenax), to understand the floral colour diversity in an alpine altitudinal gradient. All colour properties were weakly related to phylogeny. We found a shift from overdispersed floral colours and high chromatic contrast with the background (for bees) in the low altitude, to clustered floral colours (UV and green range for bees and flies) and clustered chromatic and achromatic properties in the high altitude. Different from flies, bees could discriminate floral colours in all altitudinal ranges. Low altitudes are likely to exhibit suitable conditions for more plant species, increasing competition for pollinators and floral colour divergence. Conversely, the increase in UV irradiance in high altitudes may filter plants with specific floral UV-reflectance patterns. Overall, floral colour diversity suggests that both biotic (pollinator fauna) and abiotic (UV irradiance) drivers shape floral communities, but their importance changes with altitude.

Human land use promotes the abundance and diversity of exotic species on Caribbean islands.

Human land use causes major changes in species abundance and composition, yet native and exotic species can exhibit different responses to land use change. Native populations generally decline in human-impacted habitats while exotic species often benefit. In this study, we assessed the effects of human land use on exotic and native reptile diversity, including functional diversity, which relates to the range of habitat use strategies in biotic communities. We surveyed 114 reptile communities from localities that varied in habitat structure and human impact level on two Caribbean islands, and calculated species richness, overall abundance, and evenness for every plot. Functional diversity indices were calculated using published trait data, which enabled us to detect signs of trait filtering associated with impacted habitats. Our results show that environmental variation among sampling plots was explained by two Principal Component Analysis (PCA) ordination axes related to habitat structure (i.e., forest or nonforest) and human impact level (i.e., addition of man-made constructions such as roads and buildings). Several diversity indices were significantly correlated with the two PCA axes, but exotic and native species showed opposing responses. Native species reached the highest abundance in forests, while exotic species were absent in this habitat. Human impact was associated with an increase in exotic abundance and species richness, while native species showed no significant associations. Functional diversity was highest in nonforested environments on both islands, and further increased on St. Martin with the establishment of functionally unique exotic species in nonforested habitat. Habitat structure, rather than human impact, proved to be an important agent for environmental filtering of traits, causing divergent functional trait values across forested and nonforested environments. Our results illustrate the importance of considering various elements of land use when studying its impact on species diversity and the establishment and spread of exotic species.

Environmental constraints on the compositional and phylogenetic beta-diversity of tropical forest snake assemblages.

The ongoing biodiversity crisis increases the importance and urgency of studies addressing the role of environmental variation on the composition and evolutionary history of species assemblages, but especially the tropics and ectotherms remain understudied. In regions with rainy summers, coexistence of tropical ectothermic species may be determined by the partitioning of the climatic niche, as ectotherms can rely on water availability and thermoregulatory behaviour to buffer constraints along their climatic niche. Conversely, tropical ectotherms facing dry summers would have fewer opportunities to climatic niche partitioning and other processes rather than environmental filtering would mediate species coexistence. We used 218 snake assemblages to quantify the compositional (CBD) and phylogenetic (PBD) beta-diversity of snakes in the Atlantic Forest (AF) hotspot, South America. We identify two AF regions with distinct climatological regimes: dry summers in the northern-AF and rainy summers in the southern-AF. While accounting for the influence of multiscale spatial processes, we disentangle the relative contribution of thermal, water-related and topographic conditions in structuring the CBD and PBD of snake assemblages, and determine the extent in which snake assemblages under distinct climatological regimes are affected by environmental filtering. Thermal conditions best explain CBD and PBD of snakes for the whole AF, whereas water-related factors best explain the structure of snake assemblages within a same climatological regime. CBD and PBD patterns are similarly explained by spatial factors but snake assemblages facing dry summers are more affected by spatial processes operating at fine to intermediate spatial scale, whereas those assemblages in regions with rainy summers have a stronger signature of coarse-scale processes. As expected, environmental filtering plays a stronger role in southern-AF than northern-AF, and the synergism between thermal and water-related conditions is the key cause behind this difference. Differences in climatological regimes within the tropics affect processes mediating species coexistence. The influence of broad-scale gradients (e.g. temperature and precipitation) in structuring tropical ectothermic assemblages is greater in regions with rainy summers where climatic niche partitioning is more likely. Our findings highlight the potential stronger role of biotic interactions and neutral processes in structuring ectothermic assemblages facing changes towards warmer and dryer climates.

Drivers of community assembly in tropical forest restoration sites: role of local environment, landscape, and space.

There is increasing recognition that community assembly theory can offer valuable insights for ecological restoration. We studied community assembly processes following tropical forest restoration efforts, using dung beetles (Scarabaeinae) as a focal taxon to investigate taxonomic and functional patterns of biodiversity recovery. We evaluated the relative importance of the local environment (i.e., canopy cover, understory cover, tree basal area, and soil texture), landscape context (i.e., habitat patch proximity and availability and percentage of surrounding area classified as natural forest or Eucalyptus spp. plantation), and space (i.e., spatial proximity of the study areas to estimate dispersal limitation or unmeasured spatially structured processes) on dung beetle species and functional trait composition across a gradient of 15 restoration sites in Brazilian Atlantic Forest. We also assessed which factors were the primary determinants in the establishment of individual dung beetle functional groups, classified according to size, food relocation habit, diet, and period of flight activity. Both species and functional trait composition were most strongly influenced by the local environment, indicating that assembly was predominantly driven by niche-based processes. Most of the variation explained by space was co-explained by local environment and landscape context, ruling out a strong influence of dispersal limitation and random colonization on assembly following restoration. In addition, nearly all of the variance explained by landscape context was co-explained by local environment, suggesting that arrival and establishment at a site depends on both local and landscape-scale environmental factors. Despite strong evidence for niche-based assembly, a large amount of variation remained unexplained in all models, suggesting that stochastic processes and/or unmeasured environmental variables also play an important role. The relative importance of local environment, landscape context, and space changed considerably when analyzing the assembly mechanisms of each functional group separately. Therefore, to recover distinct functional traits in restoration sites, it may be necessary to manipulate different components of the local environment and surrounding landscape. Overall, this study shows that assembly rules can help to better understand recovery processes, enabling improvement of future restoration efforts.

Predicting trait-environment relationships for venation networks along an Andes-Amazon elevation gradient.

Understanding functional trait-environment relationships (TERs) may improve predictions of community assembly. However, many empirical TERs have been weak or lacking conceptual foundation. TERs based on leaf venation networks may better link individuals and communities via hydraulic constraints. We report measurements of vein density, vein radius, and leaf thickness for more than 100 dominant species occurring in ten forest communities spanning a 3,300 m Andes-Amazon elevation gradient in Peru. We use these data to measure the strength of TERs at community scale and to determine whether observed TERs are similar to those predicted by physiological theory. We found strong support for TERs between all traits and temperature, as well weaker support for a predicted TER between maximum abundance-weighted leaf transpiration rate and maximum potential evapotranspiration. These results provide one approach for developing a more mechanistic trait-based community assembly theory.