title: Elevational gradients in β-diversity reflect variation in the strength of local community assembly mechanisms across spatial scales.
abstract: Despite long-standing interest in elevational-diversity gradients, little is known about the processes that cause changes in the compositional variation of communities (β-diversity) across elevations. Recent studies have suggested that β-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 β-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 β-diversity to null-model expectations. β-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 β-diversity persisted after accounting for regional variation in species pools. Moreover, the elevational gradient in β-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 β-diversity. At large spatial scales, in contrast, local assembly mechanisms were a dominant force driving changes in β-diversity. In contrast to the hypothesis that variation in species pools alone drives β-diversity gradients, we show that local community assembly mechanisms contribute strongly to systematic changes in β-diversity across elevations. We conclude that scale-dependent variation in community assembly mechanisms underlies these iconic gradients in global biodiversity.
authors: Center for Conservation and Sustainable Development, Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166, United States of America; Escuela de Biología, Pontificia Universidad Católica del Ecuador, Av. 12 de Octubre 1076 y Roca, Apdo. 17-01-2184, Quito, Ecuador.
authors: J Sebastián
authors: JS
authors: Tello
authors: Department of Biology, Washington University, St. Louis, Missouri 63130, United States of America.
authors: Jonathan A
authors: JA
authors: Myers
authors: Departamento de Biología, Área de Botánica, Universidad Autónoma de Madrid, Calle Darwin 2, 28049 Madrid, Spain.
authors: Manuel J
authors: MJ
authors: Macía
authors: Herbario Nacional de Bolivia, Campus Universitario Cota-Cota, calle 27, Correo Central Cajón Postal 10077, La Paz, Bolivia.
authors: Alfredo F
authors: AF
authors: Fuentes
authors: Herbario Nacional de Bolivia, Campus Universitario Cota-Cota, calle 27, Correo Central Cajón Postal 10077, La Paz, Bolivia.
authors: Leslie
authors: L
authors: Cayola
authors: Departamento de Biología, Área de Botánica, Universidad Autónoma de Madrid, Calle Darwin 2, 28049 Madrid, Spain; Real Jardín Botánico, Consejo Superior de Investigaciones Científicas, Plaza de Murillo 2, 28014 Madrid, Spain.
authors: Gabriel
authors: G
authors: Arellano
authors: Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166, United States of America; Department of Biology, University of Missouri, St. Louis, Missouri 63121, United States of America.
authors: M Isabel
authors: MI
authors: Loza
authors: Division of Plant Conservation and Population Biology, Department of Biology, University of Leuven, B-3001 Leuven, Belgium.
authors: Vania
authors: V
authors: Torrez
authors: Herbario Nacional de Bolivia, Campus Universitario Cota-Cota, calle 27, Correo Central Cajón Postal 10077, La Paz, Bolivia.
authors: Maritza
authors: M
authors: Cornejo
authors: Herbario Nacional de Bolivia, Campus Universitario Cota-Cota, calle 27, Correo Central Cajón Postal 10077, La Paz, Bolivia.
authors: Tatiana B
authors: TB
authors: Miranda
authors: Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166, United States of America.
authors: Peter M
authors: PM
authors: Jørgensen
mesh_terms: D000531:Altitude; D044822:Biodiversity; D058448:Biota; D001838:Bolivia; D016018:Least-Squares Analysis; D008954:Models, Biological; D018521:Plant Physiological Phenomena; D012044:Regression Analysis; D062206:Spatial Analysis; D013045:Species Specificity; D014329:Tropical Climate