|Irl, S; Harter, D; Steinbauer, M; Puyol Gallego, D; Fernández-Palacios, JM; Jentsch, A; Beierkuhnlein, C: Climate vs. topography – spatial patterns of plant species diversity and endemism on a high-elevation island, Journal of Ecology, 103, 1621-1633 (2015), doi:10.1111/1365-2745.12463 [Link]|
1.Climate and topography are among the most fundamental drivers of plant diversity. Here, we assess the importance of climate and topography in explaining diversity patterns of species richness, endemic richness and endemicity on the landscape scale of an oceanic island, and evaluate the independent contribution of climatic and topographic variables to spatial diversity patterns. 2.We constructed a presence/absence matrix of perennial endemic and native vascular plant species (including subspecies) in 890 plots on the environmentally very heterogeneous island of La Palma, Canary Islands. Species richness, endemic richness and endemicity were recorded, interpolated and related to climate (i.e. variables describing temperature, precipitation, variability and climatic rarity) and topography (i.e. topographic complexity, solar radiation, geologic age, slope and aspect). We used multi-model inference, spatial autoregressive models, variance partitioning and linear regression kriging as statistical methods. 3.Species richness is best explained by both climatic and topographic variables. Topographic variables (esp. topographic complexity and solar radiation) explain endemic richness and climatic variables (esp. elevation/temperature and rainfall seasonality) explain endemicity. Spatial patterns of species richness, endemic richness and endemicity were in parts geographically decoupled from each other. 4.Synthesis. We identify several topography-dependent processes ranging from evolutionary processes (micro-refugia, in situ speciation, pre-adaptation to rupicolous conditions, dispersal limitations) to human-induced influences (introduced herbivores, fire, land use) that possibly shape the endemic richness pattern of La Palma. In contrast, climate mainly drives endemicity, which is connected to ecological speciation and specialisation to local conditions. We highlight the importance of incorporating climatic variability into future studies of plant species diversity and endemism. The spatial incongruence in hotspots of species richness, endemic richness and endemicity emphasize the need for an integrated conservation approach acknowledging different diversity measures to protect the complete spectrum of diversity. High-elevation islands such as La Palma are highly suitable to study drivers of diversity and endemism, as they offer environmental gradients of continental magnitude on the landscape scale of a single climatic mini-continent and a large array of in situ-speciated endemics.
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