title: Plant invasion and speciation along elevational gradients on the oceanic island La Palma, Canary Islands.
abstract: Ecosystems that provide environmental opportunities but are poor in species and functional richness generally support speciation as well as invasion processes. These processes are expected not to be equally effective along elevational gradients due to specific ecological, spatial, and anthropogenic filters, thus controlling the dispersal and establishment of species. Here, we investigate speciation and invasion processes along elevational gradients. We assess the vascular plant species richness as well as the number and percentage of endemic species and non-native species systematically along three elevational gradients covering large parts of the climatic range of La Palma, Canary Islands. Species richness was negatively correlated with elevation, while the percentage of Canary endemic species showed a positive relationship. However, the percentage of Canary-Madeira endemics did not show a relationship with elevation. Non-native species richness (indicating invasion) peaked at 500 m elevation and showed a consistent decline until about 1,200 m elevation. Above that limit, no non-native species were present in the studied elevational gradients. Ecological, anthropogenic, and spatial filters control richness, diversification, and invasion with elevation. With increase in elevation, richness decreases due to species-area relationships. Ecological limitations of native ruderal species related to anthropogenic pressure are in line with the absence of non-native species from high elevations indicating directional ecological filtering. Increase in ecological isolation with elevation drives diversification and thus increased percentages of Canary endemics. The best preserved eastern transect, including mature laurel forests, is an exception. The high percentage of Canary-Madeira endemics indicates the cloud forest's environmental uniqueness-and thus ecological isolation-beyond the Macaronesian islands.
authors.affiliation: Department of Biogeography Bay CEER University of Bayreuth Bayreuth Germany; Section Ecoinformatics & Biodiversity Department of Bioscience Aarhus University Aarhus Denmark.
authors.forename: Manuel J
authors.initials: MJ
authors.lastname: Steinbauer
authors.affiliation: Department of Biogeography BayCEER University of Bayreuth Bayreuth Germany.
authors.forename: Severin D H
authors.initials: SD
authors.lastname: Irl
authors.affiliation: Departamento de Botánica, Ecología y Fisiología Vegetal Universidad de La Laguna San Cristóbal de La Laguna Tenerife Spain.
authors.forename: Juana María
authors.initials: JM
authors.lastname: González-Mancebo
authors.affiliation: Swiss Federal Research Institute WSL Birmensdorf Switzerland; Department of Ecology and Evolution University of Lausanne Lausanne Switzerland.
authors.forename: Frank T
authors.initials: FT
authors.lastname: Breiner
authors.affiliation: Departamento de Botánica, Ecología y Fisiología Vegetal Universidad de La Laguna San Cristóbal de La Laguna Tenerife Spain.
authors.forename: Raquel
authors.initials: R
authors.lastname: Hernández-Hernández
authors.affiliation: Department of Animal Ecology and Tropical Biology University of Würzburg Würzburg Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Hopfenmüller
authors.affiliation: Department of Biogeography BayCEER University of Bayreuth Bayreuth Germany.
authors.forename: Yohannes
authors.initials: Y
authors.lastname: Kidane
authors.affiliation: Department of Disturbance Ecology Bay CEER University of Bayreuth Bayreuth Germany.
authors.forename: Anke
authors.initials: A
authors.lastname: Jentsch
authors.affiliation: Department of Biogeography BayCEER University of Bayreuth Bayreuth Germany.
authors.forename: Carl
authors.initials: C
authors.lastname: Beierkuhnlein
keywords: alien species; altitudinal gradient; colonization; diversification; diversity; endemism; exotic; high‐elevation ecosystems; island biogeography