Abstract
AbstractAimOur objective is to analyse global‐scale patterns of mountain biodiversity and the driving forces leading to the observed patterns. More specifically, we test the ‘mountain geobiodiversity hypothesis’ (MGH) which is based on the assumption that it is not mountain‐uplift alone which drives the evolution of mountain biodiversity, but rather the combination of geodiversity evolution and Neogene and Pleistocene climate changes. We address the following questions: (a) Do areas of high geodiversity and high biodiversity in mountains overlap, that is can mountain geodiversity predict mountain biodiversity? (b) What is the role of Pleistocene climate change in shaping mountain biodiversity? (c) Did diversification rate shifts occur predominantly with the onset of more pronounced climate fluctuations in the late Neogene and Pleistocene fostering a ‘species pump’ effect, as predicted by the MGH?LocationGlobal.TaxonVascular plants.MethodsWe used generalized linear models to test to what extent vascular plant species diversity in mountains is explained by net primary productivity (NPP), geodiversity and Pleistocene climate fluctuations (i.e. changes in temperature between the Last Glacial Maximum [LGM] and today). In addition, we compiled dates of diversification rate shifts from mountain systems and investigated whether these shifts occurred predominantly before or after the global major climatic fluctuations of the late Neogene and Pleistocene.ResultsBoth NPP and elevation range show a positive relationship, whereas Pleistocene climatic fluctuations show a negative impact on plant species diversity. The availability of climatic niche space during the LGM differs markedly among mountain systems. Shifts to higher diversification rates or starts of radiations showed the highest concentration from the late Miocene towards the Pleistocene, supporting the MGH. The most commonly inferred drivers of diversification were key innovations, geological processes (uplift) and climate.Main conclusionsOur analyses point towards an important role of historical factors on mountain plant species richness. Mountain systems characterized by small elevational ranges and strong modifications of temperature profiles appear to harbour fewer radiations, and fewer species. In contrast, mountain systems with the largest elevational ranges and stronger overlap between today´s and LGM temperature profiles are also those where most plant radiations and highest species numbers were identified.
Highlights
Global comparisons of the biodiversity of mountains have fascinated natural scientists for a long time
The 1802 expedition by Alexander von Humboldt (*1769, †1859) to mount Chimborazo in the Cordillera Occidental range of the Andes led him to develop the first map of biodiversity (Humboldt, 1807; Wulf, 2016), which summarizes the vegetation and abiotic parameters of eleven elevational zones found on the Chimborazo in comparison with other mountains he had previously visited (e.g. Alps, Pyrenees, on Tenerife)
Building on Humboldts idea of exploring the relationship between geodiversity and biodiversity in mountains in particular, our study aims at providing a global comparison of mountain geodi‐ versity and vascular plant diversity, looking both at short‐term as well as long‐term processes
Summary
Global comparisons of the biodiversity of mountains have fascinated natural scientists for a long time. The inclusion of historical processes is crucial because past geological events, climatic fluctuations, biotic radiations and dispersal/migration events, in particular during the Neogene and Pleistocene, had a major impact on the present‐day distribution of biodiversity Based on this concept, Mosbrugger et al (2018) developed the ‘mountain‐geobio‐ diversity hypothesis’ (MGH) to explain the high levels of biodiversity found in the Tibeto‐Himalayan region. The MGH proposes that three boundary conditions are required to maximize the impact of mountain formation and surface uplift on regional biodiversity patterns and are key for the origination of montane biodiversity These are (a) the pres‐ ence of lowland, montane and alpine zones (full elevational zonation), (b) climatic fluctuations for a ‘species pump’ effect and (c) high‐relief terrain with environmental gradients. Did diversification rate shifts of mountain plants occur predomi‐ nantly with the onset of more pronounced climate fluctuations (wet‐dry and/or warm/cold) in the late Neogene and Pleistocene (from ca. 7 Mya) fostering a ‘species pump’ effect, as predicted by the ‘mountain‐geobiodiversity hypothesis’?
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