|Steinbauer, MJ; Irl, S; González, JM; Breiner, F; Hernández Hernández, RM; Hopfenmüller, S; Kidane, Y; Jentsch, A; Beierkuhnlein, C: Plant invasion and speciation along elevational gradients on the oceanic island La Palma, Canary Islands, Ecology and Evolution, 7(2), 771-779 (2017)|
Background: 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. Methods: 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. Results: 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 1200 m elevation. Above that limit no non-native species were present in the studied elevational gradients. Conclusion: Ecological, anthropogenic and spatial filters control richness, diversification and invasion with elevation. With increasing 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. Increasing ecological isolation with elevation drives diversification and thus increased percentages of archipelago 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.