Understanding why species composition and diversity varies spatially and with environmental variation is a long-standing theme in macroecological research. Numerous hypotheses have been generated to explain species and phylogenetic diversity gradients. Much less attention has been invested in explaining patterns of beta diversity. Biomes boundaries are thought to represent major shifts in abiotic variables accompanied by vegetation patterns and composition as a consequence of long-term interactions between the environment and the diversification and sorting of species. Using North American plant distribution data, phylogenetic information and three functional traits (SLA, seed mass, and plant height), we explicitly tested whether beta diversity is associated with biome boundaries and the extent to which two components of beta diversity-turnover and nestedness-for three dimensions of biodiversity (taxonomic, phylogenetic, and functional)-are associated with contrasting environments and linked to different patterns of historical climatic stability. We found that dimensions of vascular plant beta diversity are strongly coupled and vary considerably across North America, with turnover more influential in biomes with higher species richness and greater environmental stability and nestedness more influential in species-poor biomes characterized by high environmental variability. These results can be interpreted to indicate that in harsher climates with less stability explain beta diversity, while in warmer, wetter more stable climates, patterns of endemism associated with speciation processes, as well as local environmental sorting processes, contribute to beta diversity. Similar to prior studies, we conclude that patterns of similarity among communities and biomes reflects biogeographic legacies of how vascular plant diversity arose and was shaped by historical and ecological processes.

Aim Explaining species richness gradients in space and time requires understanding the evolutionary processes that ultimately alter the number of species.Here we examine species richness differences between primary habitats (forest versus open) for Furnariides birds, a Neotropical endemic bird clade, to test three major historical hypothesesdiversification rate, out of the tropics and tropical niche conservatismand assess the role of evolutionary processes in driving the Furnariides species richness gradient.Location Neotropics. MethodsWe used phylogenetic and spatial data to tests the historical hypotheses. First, we used GeoSSE and Bayesian Analysis of Macroevolutionary Mixture models to evaluate differential diversification and dispersal rates between habitats. Second, we quantify the root distance of each species and examined the phylogenetic structure of the richness gradient and the correlation between total species richness and the richness of early-diverged and recently originated species.Results Furnariides species richness is higher in forest than in open habitats. However, we found higher speciation, extinction, and dispersal rates in open when compared to forest habitats, resulting in a higher diversification rate in open habitats and higher dispersal rate out of open habitats than into them. The phylogenetic structure of the richness gradient showed strong spatial pattern, with early diverged species richness peaking in forest habitats and driving the overall Furnariides gradient.Main conclusions The Furnariides species richness gradient results from the joint effect of differential rates of macroevolutionary processes. Our findings highlight dispersal and extinction as dominant forces driving richness differences between habitats, through the addition and extirpation of species from open to forest habitats. Differences in species richness between habitats support niche conservatism of forest habitat preferences of Furnariides species. We suggest that open habitats are effective evolutionary arenas and a key to the maintenance of bird diversity in forest habitats over evolutionary time.

Abstract.-Descriptions of intra-and interspecific variation in migratory patterns of closely related species are rare yet valuable because they can help assess how differences in ecology and life-history strategies drive the evolution of migration. We report data on timing and location of migration routes and wintering areas, and on migratory speed and phenology,