Mountain biodiversity and elevational gradients

Pteridophyte species richness in the central Himalaya is limited by cold climate extremes at high elevations and rainfall seasonality at low elevations

“…As a result, in Africa, species richness decreases from the equatorial wet tropics toward the desert zones, although mean and extreme temperatures increase (Kreft & Jetz, 2007 ). This demonstrates two crucial facts, namely that precipitation is a vital resource gradient and that temperature in contrast is a regulator gradient (Vetaas, 2021 ). Thermal energy regulates liquid water availability by evapotranspiration where both high and low values will transform the liquid water into either gas or solid ice, respectively (O'Brien, 1993 , 2006 ).…”

“…As a result, in Africa, species richness decreases from the equatorial wet tropics toward the desert zones, although mean and extreme temperatures increase (Kreft & Jetz, 2007). This demonstrates two crucial facts, namely that precipitation is a vital resource gradient and that temperature in contrast is a regulator gradient (Vetaas, 2021).…”

“…Most importantly, many of the potential underlying causes that covary along latitudinal gradients (e.g., history, climate, time since glaciation) do not covary when one considers several elevational gradients in combination (Körner, 2007 ; Sanders & Rahbek, 2012 ). Further, geographical distances are much shorter along elevational gradients, so that dispersal limitation and geographical barriers play a lesser role, implying that species distributions along an elevational gradient are expected to reflect their climatic niches more directly than along a latitudinal gradient (Qian et al, 2020 ; Vetaas, 2021 ). Different elevational gradients in many mountain systems across the world may therefore be considered as replicates in hypothesis testing (Vetaas, 2021 ).…”

“…Further, geographical distances are much shorter along elevational gradients, so that dispersal limitation and geographical barriers play a lesser role, implying that species distributions along an elevational gradient are expected to reflect their climatic niches more directly than along a latitudinal gradient (Qian et al, 2020 ; Vetaas, 2021 ). Different elevational gradients in many mountain systems across the world may therefore be considered as replicates in hypothesis testing (Vetaas, 2021 ). Because many of the biodiversity hotspots across the world are located in montane regions (Myers et al, 2000 ), understanding the underlying mechanisms driving species diversity patterns along elevational gradients is of major interest in ecology and biogeography (Fjeldså et al, 2012 ; Rahbek et al, 2019 ).…”

Water and energy availability mediate biodiversity patterns along an elevational gradient in the tropical Andes

“…Eleven of the world’s biodiversity hotspots are located in tropical montane ecosystems (Malhi et al, 2010), with the tropical Andes hotspot—the most biodiverse on the planet—hosting one‐sixth of all plant species in the world (Myers et al, 2000). The study of elevational gradients has a long and rich history and remains at the forefront for deepening current understanding of patterns in biodiversity, ecosystem functioning and how species respond to climate change (Antonelli et al, 2018; Bhatta et al, 2021; Bhattarai & Vetaas, 2006; Malhi et al, 2010; McCain & Grytnes, 2010; Vetaas, 2021). There is mounting evidence that tropical biota are more sensitive than species from high latitudes to climate and land‐use change, highlighting the importance of tropical mountains as potential refugia for biodiversity (Feeley et al, 2020; Malhi et al, 2010; Rahbek et al, 2019).…”