Journal Article

Plant invasion and speciation along elevational gradients on the oceanic island La Palma, Canary Islands

Jentsch, Anke, Steinbauer, Manuel J., Hernández‐Hernández, Raquel, Hopfenmüller, Sebastian, Irl, Severin D. H., Beierkuhnlein, Carl, González‐Mancebo, Juana María, Breiner, Frank T., Kidane, Yohannes

2017

Overview

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. Ecological, anthropogenic, and spatial filters control plant richness, diversification, and establishment of non‐native species on the oceanic island La Palma. Increase in ecological isolation with elevation likely drives diversification and thus above average numbers of endemics at high elevations. We argue that unsuitable environmental conditions and lower human influences are responsible for the absence of non‐native species at elevations above 1200 m.

• Publisher: John Wiley & Sons, Inc,John Wiley and Sons Inc
• Subject: alien species / altitudinal gradient / Anthropogenic factors / Cloud forests / colonization / Dispersal / diversification / diversity / Ecological effects / Ecological monitoring / Elevation / Endemic species / endemism / exotic / Filters / Filtration / Forests / Herbivores / high‐elevation ecosystems / Indigenous species / Introduced species / Invasive species / island biogeography / Islands / Marine ecosystems / Native species / Original Research / Plant species / Speciation / Species richness / Species-area relationship