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Item type:Publication, The evolutionary assembly of forest communities along environmental gradients: recent diversification or sorting of pre-adapted clades?(John Wiley and Sons Inc, 2021-12-01)Recent studies have demonstrated that ecological processes that shape community structure and dynamics change along environmental gradients. However, much less is known about how the emergence of the gradients themselves shape the evolution of species that underlie community assembly. In this study, we address how the creation of novel environments leads to community assembly via two nonmutually exclusive processes: immigration and ecological sorting of pre-adapted clades (ISPC), and recent adaptive diversification (RAD). We study these processes in the context of the elevational gradient created by the uplift of the Central Andes. We develop a novel approach and method based on the decomposition of species turnover into within- and among-clade components, where clades correspond to lineages that originated before mountain uplift. Effects of ISPC and RAD can be inferred from how components of turnover change with elevation. We test our approach using data from over 500 Andean forest plots. We found that species turnover between communities at different elevations is dominated by the replacement of clades that originated before the uplift of the Central Andes. Our results suggest that immigration and sorting of clades pre-adapted to montane habitats is the primary mechanism shaping tree communities across elevations.1 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Wood density variation across an Andes-to-Amazon elevational gradient(2024-12-18)1. Understanding how functional traits are related to species diversity and ecosystem properties is a central goal of ecology. Wood density is a trait that integrates many aspects of plant form and function and is highly variable among species. Previous studies of wood density across elevational gradients have been based on limited sampling and have reported declines with increasing elevation, though even this simple pattern remains unknown, much less its underlying functional and evolutionary relationships. 2. Here, we use one of the longest and most speciose elevational gradients in the world, extending from the Andean tree line to the Amazon basin, to test the extent to which elevation, species composition, phylogenetic affinity, and forest structure determine variation in wood density. Using field-collected wood samples and global databases, we assigned wood density to 1231 species and 31,330 stems across 41 (47.5 ha) mature forest plots arrayed across a 3,500 m vertical gradient. 3. Our results show that mean wood density, either weighted by abundance, basal area, or species, was highly variable but tended to decline from low to middle elevations and increase again from mid-elevations to the tree line. As a result of this non-linearity, forests at the Andean tree line had higher wood density than their lowland Amazon counterparts. We observed an abrupt transition in wood density at the lower limit of persistent cloud formation (cloud base), where the lowest wood density values were found. The decline of wood density is attributed to a significant shift in life forms, with an abundance of tree ferns at middle elevations and a higher probability of landslides and disturbances favoring a suite of traits associated with low wood density, such as softer wood and higher elasticity. Species turnover explained most of the among-species variation across the gradient, with elevation having no consistent effect on within-species variation in wood density. 4. Together, both gradual compositional changes and sharp local changes in the importance of non-dicot life forms, such as arborescent ferns and palms, define patterns of forest-level carbon density, with wood density per se controlling ecosystem properties across the Andes-to-Amazon elevational gradient. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Historical Assembly of Andean Tree Communities(Multidisciplinary Digital Publishing Institute (MDPI), 2023-10-01)Patterns of species diversity have been associated with changes in climate across latitude and elevation. However, the ecological and evolutionary mechanisms underlying these relationships are still actively debated. Here, we present a complementary view of the well-known tropical niche conservatism (TNC) hypothesis, termed the multiple zones of origin (MZO) hypothesis, to explore mechanisms underlying latitudinal and elevational gradients of phylogenetic diversity in tree communities. The TNC hypothesis posits that most lineages originate in warmer, wetter, and less seasonal environments in the tropics and rarely colonize colder, drier, and more seasonal environments outside of the tropical lowlands, leading to higher phylogenetic diversity at lower latitudes and elevations. In contrast, the MZO hypothesis posits that lineages also originate in temperate environments and readily colonize similar environments in the tropical highlands, leading to lower phylogenetic diversity at lower latitudes and elevations. We tested these phylogenetic predictions using a combination of computer simulations and empirical analyses of tree communities in 245 forest plots located in six countries across the tropical and subtropical Andes. We estimated the phylogenetic diversity for each plot and regressed it against elevation and latitude. Our simulated and empirical results provide strong support for the MZO hypothesis. Phylogenetic diversity among co-occurring tree species increased with both latitude and elevation, suggesting an important influence on the historical dispersal of lineages with temperate origins into the tropical highlands. The mixing of different floras was likely favored by the formation of climatically suitable corridors for plant migration due to the Andean uplift. Accounting for the evolutionary history of plant communities helps to advance our knowledge of the drivers of tree community assembly along complex climatic gradients, and thus their likely responses to modern anthropogenic climate change.