Fig. 5 Diagrammatic sketch of the topographic landscape in the Hengduan
Mountains (a) and the Himalayas (b) and the potential in-situdisplacement (short arrows) and long-distance dispersal (long arrows) of
caddisflies during the LGM. Different colours of the caddisflies
indicate high-elevation species (yellow) and low-elevation species
(green). During the glacial period, which means a cooler climate, a
vertical displacement along the elevational gradient (in-situdisplacement) may occur on both high- and low-elevation caddisfly
species. However, compared to the Himalayas, a wider extent of mountain
ranges along the North-South orientation in the Hengduan Mountains gives
the possibility for species to disperse further south (long-distance
dispersal). During the interglacial period, the same dispersal or
replacement may happen but in the opposite direction. Therefore,
geographic connection and isolation may repeatedly occur during climate
fluctuation, thus forming the so-called “species pump” effect and
promoting speciation or diversification, according to the MGH
(Mosbrugger et al. 2018).