Amazon tree dominance across forest strata.

The forests of Amazonia are among the most biodiverse plant communities on Earth. Given the immediate threats posed by climate and land-use change, an improved understanding of how this extraordinary biodiversity is spatially organized is urgently required to develop effective conservation strategies. Most Amazonian tree species are extremely rare but a few are common across the region. Indeed, just 227 'hyperdominant' species account for >50% of all individuals >10 cm diameter at 1.3 m in height. Yet, the degree to which the phenomenon of hyperdominance is sensitive to tree size, the extent to which the composition of dominant species changes with size class and how evolutionary history constrains tree hyperdominance, all remain unknown. Here, we use a large floristic dataset to show that, while hyperdominance is a universal phenomenon across forest strata, different species dominate the forest understory, midstory and canopy. We further find that, although species belonging to a range of phylogenetically dispersed lineages have become hyperdominant in small size classes, hyperdominants in large size classes are restricted to a few lineages. Our results demonstrate that it is essential to consider all forest strata to understand regional patterns of dominance and composition in Amazonia. More generally, through the lens of 654 hyperdominant species, we outline a tractable pathway for understanding the functioning of half of Amazonian forests across vertical strata and geographical locations.

Vascular flora and phytogeographical links of the Carabaya Mountains, Peru / Flora vascular y conexiones fitogeográficas de las montañas Carabaya, Perú

Studies of floristic composition and plant species richness in tropical mountains support their recognition as areas of high biological diversity, and therefore of their importance for plant conservation. Here, we present data on the flora of the high Andes of eight sites centered in the Carabaya mountains, and also provide a floristic comparison with nine other floras within Peru and northern Bolivia. The study area includes 506 species of vascular plants, grouped in 203 genera and 66 families. The highest species richness was found in two families: Asteraceae and Poaceae, which collectively encompass 37% of all species. Other important families were Caryophyllaceae, Fabaceae, Malvaceae, Brassicaceae, Caprifoliaceae, Gentianaceae, Plantaginaceae and Cyperaceae. The most diverse genera wereSenecio, Calamagrostis, Poa and Nototriche. Perennial herbs were the dominant growth form. The vascular flora of the Carabaya Mountains is closely related to those of other regions of southern Peru. Also, more than half of all vascular plants registered for the Carabaya Mountain occur in the Andean region of Bolivia, which shows the undoubted geophysical and phytogeographical connection of the Carabaya and the Bolivian Apolobamba Mountains. This study also shows that there is still a need for more extensive plant collecting and future exploration, since the Carabaya, as other parts of Peru’s high Andes are subject of dramatic change that may threaten these plant populations.

Los estudios sobre la composición florística y riqueza de especies en montañas tropicales apoyan su reconocimiento como áreas de alta diversidad biológica, y, por tanto, de su importancia para la conservación. En este trabajo presentamos datos sobre la flora altoandina de ocho sitios localizados en la Cordillera de Carabaya, proveemos también una comparación florística con otros nueve lugares tanto en Perú como en el norte de Bolivia. El área de estudio incluye 506 especies de plantas vasculares, reconocidas en 203 géneros y 66 familias. Las tasas más altas de riqueza de especies se hallan en dos familias: Asteraceae y Poaceae, que colectivamente abarcan el 37% de todas las especies. Otras familias importantes fueron Caryophyllaceae, Fabaceae, Malvaceae, Brassicaceae, Caprifoliaceae, Gentianaceae, Plantaginaceae y Cyperaceae. Los géneros más diversos fueron Senecio, Calamagrostis, Poa y Nototriche. La forma de crecimiento predominante fueron las hierbas perennes. La flora vascular de la Cordillera Carabaya está muy relacionada con otras regiones del sur de Perú. Además, más de la mitad de todas las plantas vasculares registradas para la Cordillera Carabaya se encuentran en la región andina de Bolivia, lo que demuestra la indudable conexión geofísica y fitogeográfica entre las cordilleras Carabaya y Apolobamba de Bolivia. Este estudio también demuestra la necesidad de una extensa colección botánica y futura exploración, desde que Carabaya, como otras partes de los altos Andes del Perú, están sujetos a cambios dramáticos que amenazan las poblaciones de esas plantas.

An integrated assessment of the vascular plant species of the Americas.

The cataloging of the vascular plants of the Americas has a centuries-long history, but it is only in recent decades that an overview of the entire flora has become possible. We present an integrated assessment of all known native species of vascular plants in the Americas. Twelve regional and national checklists, prepared over the past 25 years and including two large ongoing flora projects, were merged into a single list. Our publicly searchable checklist includes 124,993 species, 6227 genera, and 355 families, which correspond to 33% of the 383,671 vascular plant species known worldwide. In the past 25 years, the rate at which new species descriptions are added has averaged 744 annually for the Americas, and we can expect the total to reach about 150,000.

Linking environmental filtering and disequilibrium to biogeography with a community climate framework.

We present a framework to measure the strength of environmental filtering and disequilibrium of the species composition of a local community across time, relative to past, current, and future climates. We demonstrate the framework by measuring the impact of climate change on New World forests, integrating data for climate niches of more than 14000 species, community composition of 471 New World forest plots, and observed climate across the most recent glacial-interglacial interval. We show that a majority of communities have species compositions that are strongly filtered and are more in equilibrium with current climate than random samples from the regional pool. Variation in the level of current community disequilibrium can be predicted from Last Glacial Maximum climate and will increase with near-future climate change.

Elevational gradients in ß-diversity reflect variation in the strength of local community assembly mechanisms across spatial scales.

Despite long-standing interest in elevational-diversity gradients, little is known about the processes that cause changes in the compositional variation of communities (ß-diversity) across elevations. Recent studies have suggested that ß-diversity gradients are driven by variation in species pools, rather than by variation in the strength of local community assembly mechanisms such as dispersal limitation, environmental filtering, or local biotic interactions. However, tests of this hypothesis have been limited to very small spatial scales that limit inferences about how the relative importance of assembly mechanisms may change across spatial scales. Here, we test the hypothesis that scale-dependent community assembly mechanisms shape biogeographic ß-diversity gradients using one of the most well-characterized elevational gradients of tropical plant diversity. Using an extensive dataset on woody plant distributions along a 4,000-m elevational gradient in the Bolivian Andes, we compared observed patterns of ß-diversity to null-model expectations. ß-deviations (standardized differences from null values) were used to measure the relative effects of local community assembly mechanisms after removing sampling effects caused by variation in species pools. To test for scale-dependency, we compared elevational gradients at two contrasting spatial scales that differed in the size of local assemblages and regions by at least an order of magnitude. Elevational gradients in ß-diversity persisted after accounting for regional variation in species pools. Moreover, the elevational gradient in ß-deviations changed with spatial scale. At small scales, local assembly mechanisms were detectable, but variation in species pools accounted for most of the elevational gradient in ß-diversity. At large spatial scales, in contrast, local assembly mechanisms were a dominant force driving changes in ß-diversity. In contrast to the hypothesis that variation in species pools alone drives ß-diversity gradients, we show that local community assembly mechanisms contribute strongly to systematic changes in ß-diversity across elevations. We conclude that scale-dependent variation in community assembly mechanisms underlies these iconic gradients in global biodiversity.

Limited sampling hampers "big data" estimation of species richness in a tropical biodiversity hotspot.

Macro-scale species richness studies often use museum specimens as their main source of information. However, such datasets are often strongly biased due to variation in sampling effort in space and time. These biases may strongly affect diversity estimates and may, thereby, obstruct solid inference on the underlying diversity drivers, as well as mislead conservation prioritization. In recent years, this has resulted in an increased focus on developing methods to correct for sampling bias. In this study, we use sample-size-correcting methods to examine patterns of tropical plant diversity in Ecuador, one of the most species-rich and climatically heterogeneous biodiversity hotspots. Species richness estimates were calculated based on 205,735 georeferenced specimens of 15,788 species using the Margalef diversity index, the Chao estimator, the second-order Jackknife and Bootstrapping resampling methods, and Hill numbers and rarefaction. Species richness was heavily correlated with sampling effort, and only rarefaction was able to remove this effect, and we recommend this method for estimation of species richness with "big data" collections.

Functional trait space and the latitudinal diversity gradient.

The processes causing the latitudinal gradient in species richness remain elusive. Ecological theories for the origin of biodiversity gradients, such as competitive exclusion, neutral dynamics, and environmental filtering, make predictions for how functional diversity should vary at the alpha (within local assemblages), beta (among assemblages), and gamma (regional pool) scales. We test these predictions by quantifying hypervolumes constructed from functional traits representing major axes of plant strategy variation (specific leaf area, plant height, and seed mass) in tree assemblages spanning the temperate and tropical New World. Alpha-scale trait volume decreases with absolute latitude and is often lower than sampling expectation, consistent with environmental filtering theory. Beta-scale overlap decays with geographic distance fastest in the temperate zone, again consistent with environmental filtering theory. In contrast, gamma-scale trait space shows a hump-shaped relationship with absolute latitude, consistent with no theory. Furthermore, the overall temperate trait hypervolume was larger than the overall tropical hypervolume, indicating that the temperate zone permits a wider range of trait combinations or that niche packing is stronger in the tropical zone. Although there are limitations in the data, our analyses suggest that multiple processes have shaped trait diversity in trees, reflecting no consistent support for any one theory.

Habitat area and climate stability determine geographical variation in plant species range sizes.

Despite being a fundamental aspect of biodiversity, little is known about what controls species range sizes. This is especially the case for hyperdiverse organisms such as plants. We use the largest botanical data set assembled to date to quantify geographical variation in range size for ~ 85 000 plant species across the New World. We assess prominent hypothesised range-size controls, finding that plant range sizes are codetermined by habitat area and long- and short-term climate stability. Strong short- and long-term climate instability in large parts of North America, including past glaciations, are associated with broad-ranged species. In contrast, small habitat areas and a stable climate characterise areas with high concentrations of small-ranged species in the Andes, Central America and the Brazilian Atlantic Rainforest region. The joint roles of area and climate stability strengthen concerns over the potential effects of future climate change and habitat loss on biodiversity.

Beta-diversity in temperate and tropical forests reflects dissimilar mechanisms of community assembly.

Site-to-site variation in species composition (ß-diversity) generally increases from low- to high-diversity regions. Although biogeographical differences in community assembly mechanisms may explain this pattern, random sampling effects can create this pattern through differences in regional species pools. Here, we compared assembly mechanisms between spatially extensive networks of temperate and tropical forest plots with highly divergent species pools (46 vs. 607 species). After controlling for sampling effects, ß-diversity of woody plants was similar and higher than expected by chance in both forests, reflecting strong intraspecific aggregation. However, different mechanisms appeared to explain aggregation in the two forests. In the temperate forest, aggregation reflected stronger environmental correlations, suggesting an important role for species-sorting (e.g. environmental filtering) processes, whereas in the tropics, aggregation reflected stronger spatial correlations, more likely reflecting dispersal limitation. We suggest that biogeographical differences in the relative importance of different community assembly mechanisms contribute to these striking gradients in global biodiversity.

Passifloraceae endémicas del Perú

La familia Passifloraceae es reconocida en el Perú por presentar tres géneros y 95 especies (Brako & Zarucchi, 1993; Ulloa Ulloa et al., 2004), la mayoría bejucos y lianas. En este trabajo reconocemos 24 especies y siete taxones subespecíficos como endemismos peruanos, todas en el género Passiflora. Los taxones endémicos se encuentran principalmente en las regiones Bosques Muy Húmedos Montanos y Bosques Húmedos Premontanos, entre los 700 y 2850 m de altitud. Cinco especies endémicas se encuentran dentro del Sistema Nacional de Áreas Naturales Protegidas por el Estado.

The Passifloraceae are represented in Peru by three genera and 95 species (Brako & Zarucchi, 1993; Ulloa Ulloa et al., 2004), mainly vines and lianas. Here we recognize as Peruvian endemics 24 species and seven infra-specific taxa, all in the genus Passiflora. These endemic taxa are found mainly in Very Humid Montane and Very Humid Premontane Forests regions, between 700 and 2850 m elevation. Five endemic taxa are recorded in the Peruvian System of Protected Natural Areas.