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Recent studies have generated an explosion of phylogenetic and biogeographic data and have provided new tools to investigate the processes driving large-scale gradients in species diversity. Fossils and phylogenetic studies of plants and animals demonstrate that tropical regions are the source for almost all groups of organisms, and these groups are composed of a mixture of ancient and recently derived lineages. These findings are consistent with the hypothesis that the large extent of tropical environments during the past 10-50 million years, together with greater climatic stability, has promoted speciation and reduced extinction rates. Energy availability appears to only indirectly contribute to global patterns of species diversity, especially considering how some marine diversity gradients can be completely decoupled from temperature and productivity gradients. Instead, climate stability and time-integrated area together determine the baselines of both terrestrial and marine global diversity patterns. Biotic interactions likely augment diversification and coexistence in the tropics.

Many biodiversity hotspots are located in montane regions, thus, understanding the underlying mechanisms driving species assembly along elevational gradients is of major interest in ecology and biogeography. Here, we assess spatial patterns and climatic drivers, and the effects of clade age, on patterns of phylogenetic structure of ferns along the world's longest elevational gradient in the central Himalaya. We used correlation and regression analyses to relate metrics of phylogenetic structure reflecting both shallow (tip‐weighted) and deep (basal‐weighted) evolutionary histories of ferns, and their two major groups reflecting different ages (polypods representing a young clade, all other ferns representing old clades), in fifty 100‐m vertical bands to climatic factors representing different aspects of climatic conditions (mean climate, stressful climate and climate seasonality). Variation partitioning analysis was used to determine the relative importance of each group of climatic factors on phylogenetic structure. We find that the composition of fern assemblages along the Himalayan elevational gradient in Nepal shows strong signatures of evolutionary processes. In a simplified way, species‐rich assemblages at mid‐elevations are likely the result of recent radiations in combination with low extinction rates, whereas species‐poor assemblages at low elevations are composed of numerous lineages with limited radiations, and those at high elevations of few lineages, also with limited signature of recent radiations. Variables related to temperature and climatic extremes tended to play a more important role than precipitation‐ and seasonality‐related variables, respectively, in driving fern phylogenetic structure. Combining the results of ferns and angiosperms suggests that there are a few generally consistent evolutionary processes that apply to all plant groups (e.g. niche conservatism and environmental filtering), but that the specific outcomes of these processes vary with elevation, clade age and taxon.

The biogeographic affinity of a lineage leaves imprint on its niche, and influences its distribution under biotic interchange between landmasses. Since the beginning of the Quaternary, North America (a remnant of Laurasia) and South America (a remnant of Gondwana) have been united, and triggered the Great American Biotic Interchange. Based on existing knowledge, we expect more Laurasian lineages to occur at higher latitudes, in colder or drier areas; and more Gondwanan lineages to reside at lower latitudes, in hotter and wetter areas of the Americas. Moreover, the tropical niche conservatism (TNC) hypothesis states that the tropical flora be most ancient. If so, then both younger Laurasian and Gondwanan lineages would occur in regions at colder and higher latitudes. Here, we examine the latitudinal patterns of species richness and mean family age of Laurasian and Gondwanan angiosperm tree lineages in 422 forest plots distributed across the Americas, and investigate the underlying continent and climatic drivers. We found opposite latitudinal and climatic patterns for species richness of Laurasian and Gondwanan lineages, the former declined towards lower latitudes and hotter climates, whereas the latter declined towards higher latitudes and colder climates. In particular, more pronounced climatic patterns for species richness of Laurasian and Gondwanan lineages were observed in North and South America, respectively. In addition, the mean family age of Laurasian lineages declined towards higher latitudes and colder climates, and for Gondwanan lineages it also decreased towards higher latitudes in South America, hence supporting the TNC hypothesis. We suggest Laurasian and Gondwanan angiosperm tree lineages in forests of the Americas exhibit diverged climate niche preferences, perhaps partly due to diversification of the former in extratropical climates in recent geological times.

Migratory species exhibit seasonal variation in their geographic ranges, often inhabiting geographically and ecologically distinct breeding and nonbreeding areas. The complicated geography of seasonal migration has long posed a challenge for inferring the geographic origins of migratory species as well as evolutionary sequences of change in migratory behavior. To address this challenge, we developed a phylogenetic model of the joint evolution of breeding and nonbreeding (winter) ranges and applied it to the inference of biogeographic history in the emberizoid passerine birds. We found that seasonal migration between breeding ranges in North America and winter ranges in the Neotropics evolved primarily via shifts of winter ranges toward the tropics from ancestral ranges in North America. This result contrasts with a dominant paradigm that hypothesized migration evolving out of the tropics via shifts of the breeding ranges. We also show that major lineages of tropical, sedentary emberizoids are derived from northern, migratory ancestors. In these lineages, the winter ranges served as a biogeographic conduit for temperate-to-tropical colonization: winter-range shifts toward the tropics during the evolution of long-distance migration often preceded southward shifts of breeding ranges, the loss of migration, and in situ tropical diversification. Meanwhile, the evolution of long-distance migration enabled the persistence of old lineages in North America. These results illuminate how the evolution of seasonal migration has contributed to greater niche conservatism among tropical members of this diverse avian radiation.

Aim The global species richness patterns of birds and mammals are strongly congruent. This could reflect similar evolutionary responses to the Earth’s history, shared responses to current climatic conditions, or both. We compare the geographical and phylogenetic structures of both richness gradients to evaluate these possibilities. Location Global. Methods Gridded bird and mammal distribution databases were used to compare their species richness gradients with the current environment. Phylogenetic trees (resolved to family for birds and to species for mammals) were used to examine underlying phylogenetic structures. Our first prediction is that both groups have responded to the same climatic gradients. Our phylogenetic predictions include: (1) that both groups have similar geographical patterns of mean root distance, a measure of the level of the evolutionary development of faunas, and, more directly, (2) that richness patterns of basal and derived clades will differ, with richness peaking in the tropics for basal clades and in the extra‐tropics for derived clades, and that this difference will hold for both birds and mammals. We also explore whether alternative taxonomic treatments for mammals can generate patterns matching those of birds. Results Both richness gradients are associated with the same current environmental gradients. In contrast, neither of our evolutionary predictions is met: the gradients have different phylogenetic structures, and the richness of birds in the lowland tropics is dominated by many basal species from many basal groups, whereas mammal richness is attributable to many species from both few basal groups and many derived groups. Phylogenetic incongruence is robust to taxonomic delineations for mammals. Main conclusions Contemporary climate can force multiple groups into similar diversity patterns even when evolutionary trajectories differ. Thus, as widely appreciated, our understanding of biodiversity must consider responses to both past and present climates, and our results are consistent with predictions that future climate change will cause major, correlated changes in patterns of diversity across multiple groups irrespective of their evolutionary histories.

Background The broad continuum between tropical and temperate floras in Eastern Asia (EAS) are thought to be one of the main factors responsible for a prominent species diversity anomaly of temperate plants between EAS and eastern North America (ENS). However, how the broad continuum and niche evolution between tropical and temperate floras in EAS contributes to lineage divergence and species diversity remains largely unknown. Results Population genetic structure, demography, and determinants of genetic structure [i.e., isolation-by-distance (IBD), isolation-by-resistance (IBR), and isolation-by-environment (IBE)] of Machilus thunbergii Sieb. et Zucc. (Lauraceae) were evaluated by examining sequence variation of ten low-copy nuclear genes across 43 populations in southeast China. Climatic niche difference and potential distributions across four periods (Current, mid-Holocene, the last glacial maximum, the last interglacial) of two genetic clusters were determined by niche modelling. North and south clusters of populations in M. thunbergii were revealed and their demarcation line corresponds well with the northern boundary of tropical zone in China of Zhu & Wan. The divergence time between the clusters and demographic expansion of M. thunbergii occurred after the mid-Pleistocene climate transition (MPT, 0.8–1.2 Ma). Migration rates between clusters were asymmetrical, being much greater from north to south than the reverse. Significant effects of IBE, but non-significant effects of IBD and IBR on population genetic divergence were detected. The two clusters have different ecological niches and require different temperature regimes. Conclusions The north-south genetic differentiation may be common across the temperate-tropical boundary in southeast China. Divergent selection under different temperature regimes (possibly above and below freezing temperature in winter) could account for this divergence pattern. The broad continuum between tropical and temperate floras in EAS may have provided ample opportunities for tropical plant lineages to acquire freezing tolerance and to colonize the temperate regions during the late-Cenozoic global cooling. Our findings shed deeper insights into the high temperate plant species diversity in EAS.

There is a long tradition in ecology of evaluating the relative contribution of the regional species pool and local interactions on the structure of local communities. Similarly, a growing number of studies assess the phylogenetic structure of communities, relative to that in the regional species pool, to examine the interplay between broad-scale evolutionary and fine-scale ecological processes. Finally, a renewed interest in the influence of species source pools on communities has shown that the definition of the source pool influences interpretations of patterns of community structure. We use a continent-wide dataset of local ant communities and implement ecologically explicit source pool definitions to examine the relative importance of regional species pools and local interactions for shaping community structure. Then we assess which factors underlie systematic variation in the structure of communities along climatic gradients. We find that the average phylogenetic relatedness of species in ant communities decreases from tropical to temperate regions, but the strength of this relationship depends on the level of ecological realism in the definition of source pools. We conclude that the evolution of climatic niches influences the phylogenetic structure of regional source pools and that the influence of regional source pools on local community structure is strong.

Broad-scale geographical variation in species richness is strongly correlated with climate, yet the mechanisms underlying this correlation are still unclear. We test two broad classes of hypotheses to explain this pattern. Bottom-up hypotheses propose that the environment determines individual species’ ranges. Ranges then sum up to yield species richness patterns. Top-down hypotheses propose that the environment limits the number of species that occur in a region, but not which ones. We test these two classes of hypotheses using a natural experiment: seasonal changes in environmental variables and seasonal range shifts of 625 migratory birds in the Americas. We show that richness seasonally tracks the environment. By contrast, individual species’ geographical distributions do not. Rather, species occupy different sets of environmental conditions in two seasons. Our results are inconsistent with extant bottom-up hypotheses. Instead, a top-down mechanism appears to constrain the number of species that can occur in a given region.

We test for evidence of the Tropical Niche Conservatism or the Out of The Tropics hypotheses in structuring patterns of tree community composition along a 2000 + meter elevational gradient in the northern tropical Andes. By collecting and integrating data on the presence–absence of tree species within plots with phylogenetic information, we analyzed the following: (a) patterns of phylogenetic dispersion and species diversity along the elevational gradient based on indexes of net relatedness, nearest taxon relatedness, and species richness (α-diversity); and (b) the replacement of lineages along the gradient using the PhyloSorensen metric (β-diversity). More specifically, we established 20 0.25-ha permanent tree inventory plots between 750 and 2,802 m asl where all individuals with diameter at breast height (DBH) ≥ 10 cm were measured and identified. We then used a series of linear models to test for changes in a and ß diversity between plots in relation to elevation. Neither the net relatedness index nor the nearest taxon index showed a significant relationship with elevation. However, there was greater phylogenetic overdispersion at intermediate elevations; this likely reflects the mixing of species with contrasting origins from tropical and temperate lineages. β-diversity between plots was negatively related to the corresponding difference in elevation, indicating that closely related lineages occupy similar ranges of elevation and temperature. We conclude that the immigration of lineages from extra-tropical regions has significant effects in determining the phylogenetic structure of tree communities in tropical Andean forests.

Question: Global-scale forest censuses provide an opportunity to understand diversification processes in woody plant communities. Based on the climatic or geographic filtering hypotheses associated with tropical niche conservatism and dispersal limitation, we analysed phylogenetic community structures across a wide range of biomes and evaluated to what extent region-specific processes have influenced large-scale diversity patterns of tree species communities across latitude or continent. Location: Global. Methods: We generated a data set of species abundances for 21,379 angiosperm woody plants in 843 plots worldwide. We calculated net relatedness index (NRI) for each plot, based on a single global species pool and regional species pools, and phylogenetic β-diversity (PBD) between plots. Then, we explored the correlations of NRI with climatic and geographic variables, and clarified phylogenetic dissimilarity along geographic and climatic differences. We also compared these patterns for South America, Africa, the Indo-Pacific, Australia, the Nearctic, Western Palearctic and Eastern Palearctic. Results: NRI based on a global-scale species pool was negatively associated with precipitation and positively associated with Quaternary temperature change. PBD was positively associated with geographic distance and precipitation difference between plots across tropical and extratropical biomes. Moreover, phylogenetic dissimilarity was smaller in extratropical regions than in regions including the tropics, although temperate forests of the Eastern Palearctic showed a greater dissimilarity within extratropical regions. Conclusions: Our findings support predictions of the climatic and geographic filtering hypotheses. Climatic filtering (climatic harshness and paleoclimatic change) relative to tropical niche conservatism played a role in sorting species from the global species pool and shaped the large-scale diversity patterns, such as the latitudinal gradient observed across continents. Geographic filtering associated with dispersal limitation substantially contributed to regional divergence of tropical/extratropical biomes among continents. Old, long-standing geographic barriers and recent climatic events differently influenced evolutionary diversification of angiosperm tree communities in tropical and extratropical biomes.