Abstract
AbstractAimAlpine ecosystems differ in area, macroenvironment and biogeographical history across the Earth, but the relationship between these factors and plant species richness is still unexplored. Here, we assess the global patterns of plant species richness in alpine ecosystems and their association with environmental, geographical and historical factors at regional and community scales.LocationGlobal.Time periodData collected between 1923 and 2019.Major taxa studiedVascular plants.MethodsWe used a dataset representative of global alpine vegetation, consisting of 8,928 plots sampled within 26 ecoregions and six biogeographical realms, to estimate regional richness using sampleâbased rarefaction and extrapolation. Then, we evaluated latitudinal patterns of regional and community richness with generalized additive models. Using environmental, geographical and historical predictors from global raster layers, we modelled regional and community richness in a mixedâeffect modelling framework.ResultsThe latitudinal pattern of regional richness peaked around the equator and at midâlatitudes, in response to current and past alpine area, isolation and the variation in soil pH among regions. At the community level, species richness peaked at midâlatitudes of the Northern Hemisphere, despite a considerable withinâregion variation. Community richness was related to macroclimate and historical predictors, with strong effects of other spatially structured factors.Main conclusionsIn contrast to the wellâknown latitudinal diversity gradient, the alpine plant species richness of some temperate regions in Eurasia was comparable to that of hyperdiverse tropical ecosystems, such as the pĂĄramo. The species richness of these putative hotspot regions is explained mainly by the extent of alpine area and their glacial history, whereas community richness depends on local environmental factors. Our results highlight hotspots of species richness at midâlatitudes, indicating that the diversity of alpine plants is linked to regional idiosyncrasies and to the historical prevalence of alpine ecosystems, rather than current macroclimatic gradients.
Highlights
More than 200 years after the attempt by Alexander von Humboldt to formulate a unified theory of the natural world, understanding the global patterns of diversity remains one of the greatest challenges in biogeography and macroecology (Brummitt et al, 2020; Keil & Chase, 2019; Kier et al, 2005; Kreft & Jetz, 2007; Kreft et al, 2008; Weigelt et al, 2016)
We used a dataset representative of global alpine vegetation, consisting of 8,928 plots sampled within 26 ecoregions and six biogeographical realms, to estimate regional richness using sample-Âbased rarefaction and extrapolation
We found that the Pamir and Altai Mountains (Eastern Palaearctic) exhibited regional richness comparable to the pĂĄramos, representing hotspots of alpine plant diversity outside the tropics
Summary
More than 200 years after the attempt by Alexander von Humboldt to formulate a unified theory of the natural world, understanding the global patterns of diversity remains one of the greatest challenges in biogeography and macroecology (Brummitt et al, 2020; Keil & Chase, 2019; Kier et al, 2005; Kreft & Jetz, 2007; Kreft et al, 2008; Weigelt et al, 2016). Besides having a lower energy input compared with the lowlands, alpine ecosystems are highly heterogeneous in their topoclimates (Quinn, 2008), which might weaken the correlation between latitude and primary productivity (Testolin et al, 2020) For these reasons, plant diversity in alpine areas might decouple from major climatic gradients. Following the ecological principle of the speciesâÂarea relationship (Lomolino, 2000b) and its application to the theory of island biogeography (MacArthur & Wilson, 1967), the extent of alpine habitats and their isolation could have affected rates of colonization, speciation and extinction of plants (Heaney, 2000; Steinbauer et al, 2016) These processes might have resulted in biodiversity patterns linked to the historical and current abundance of alpine habitats at the global scale. We evaluate how those patterns and drivers change between regional and community levels and how they relate to hotspots of alpine plant diversity recognized at the global scale
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