Geographical patterns of ferns species diversity: comparing the latitudinal and elevational gradients to disentangle climatic drivers of species diversity

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To contribute to the increasing understanding of the geographical distribution of fern biodiversity, I aim to compare latitudinal and elevational gradients of fern species richness between the equator and 43°N on East Asian islands. Both gradients have become increasingly popular in order to disentangle the numerous potential drivers limiting the geographical distribution of species richness. By focusing specifically on the climatic component, we will answer the question: What are the main climatic constraints species have to adapt to when dispersing from the tropics to temperate climates? It is still unclear which component of climatic conditions organisms have to adapt primarily to, climatic extremes or the variation in climatic conditions (e.g. seasonality). Since they cannot be disentangled along the latitudinal gradient alone, I will use a combination of latitudinal and elevational gradients. Towards the poles, variation in climatic conditions increases but not along elevational gradients, whereas climatic extremes change the same way. This combined approach therefore allows to disentangle both factors and conclusions on the climatic constraints limiting the geographical distribution of species richness. Further these data permit to test the hypothesis that patterns of phylogenetic assemblies also reflect the evolutionary history of fern taxa in spreading from tropical-warm to high-alpine-/ temperate climates.As an outcome of a former study, 15 of the planed 20 study localities have already been sampled on the tropical part of the gradient. The proposed project will complete this data to a full latitudinal gradient up to boreal zones and is the first to directly link two basic types of gradients in order to deepen our understanding of the climatic constraints on the geographical distribuition of fern biodiversity.