A global analysis of trait variation and evolution in climbing plants

Aim: Climbing plants (lianas, vines, scramblers) are under-represented in many global datasets that underpin knowledge in functional trait biology, important for ecological theory, conservation and predicting forest dynamics under global change. To address this omission, we tested a set of hypotheses about how the traits of climbers vary with latitude and climate and amongst major biogeographical regions of the world using a comprehensive new, global dataset. Location: Global. Methods: Data on seed mass, leaf size, specific leaf area, climbing mechanism, dispersal mode, and growth habit were compiled for 1092 species in 34 countries. For each trait we: (1) quantified the strength of latitudinal gradients using analyses across species and across evolutionary divergences, (2) examined underlying relationships between trait variation and climate variables, (3) tested for phylogenetic signal in traits (the tendency for closely related species to exhibit similar traits), and (4) compared trait variation and phylogenetic clustering between four major biogeographical regions of the world (Africa, the Americas, Asia and Australasia). Results: We found highly significant relationships between latitude and four traits (growth habit, leaf size, seed mass and specific leaf area, SLA). Leaf size, seed mass and SLA also showed significant relationships with mean annual temperature and precipitation. However, no relationship was found between dispersal mode and latitude or between climbing mechanism and latitude. These results were largely consistent in cross-species and phylogenetic analyses. All traits, except seed mass, exhibited clear differences between biogeographical regions. SLA and seed mass were the only two traits that did not present a significant phylogenetic signal. Phylogenetic clustering was detected in species from the Americas and Africa, indicating that trait conservatism is important in broad biogeographical regions. Main conclusions: The functional traits and phylogenetic patterns of climbers differ between biogeographical regions, and from other better-studied plant growth forms. Species-level trait differences may hold the key to understanding why climbers are increasing in abundance in some regions of the world, but not in others.