. Bonner zoologische Monographien. Zoology. 33 ly isolated but situated further west (river gorge between Dhaulagiri and Annapurna). Today there is no longer an exchange of individuals between the populations W (S Dolpo) and E (Thakkhola) of Dhaulagiri (P. rufonuchalis) or W (Thakkhola) and N (Manang) of An- napurna (C. himalayana) - even though these areas are less than 100 km apart. Movement between them is prevented by unforested sections to the north of the main chain and mon- soon-influenced forest formations to the south. The two nuthatches Sitta leucopsis and S. cashmirensis, moving in
. Bonner zoologische Monographien. Zoology. 33 ly isolated but situated further west (river gorge between Dhaulagiri and Annapurna). Today there is no longer an exchange of individuals between the populations W (S Dolpo) and E (Thakkhola) of Dhaulagiri (P. rufonuchalis) or W (Thakkhola) and N (Manang) of An- napurna (C. himalayana) - even though these areas are less than 100 km apart. Movement between them is prevented by unforested sections to the north of the main chain and mon- soon-influenced forest formations to the south. The two nuthatches Sitta leucopsis and S. cashmirensis, moving in from the west, have not even colonized Thakkhola, although their habitat requirements would be well satisfied by the presence of highly differentiated coni- fer forests. Why is this? During a postglacial warm phase pine and birch forests grew in S Tibet, enabhng the migration of aridity-loving faunal elements N of the mountain crest. Under present-day climatic conditions, the link has been broken (Li Tianchi 1988, fide Mie- he 1991). This old bridging function of the Himalayas is still more impressive in another example: Sitta leucopsis, Certhia himalayana and also Aegithalos niveogularis live in the dry W Himalayas and separately in mountains of SW China to the east of the Himalayas (Fig. 100), where they again occupy regions of reduced monsoon influence. The vegetation that once bridged the gap is no longer discernible, not even remnants in the form of ade- quate forest islands. Comparable W-E disjunctions of the Himalayan flora are also regar- ded as secondary, relatively recent and a result of climatic change (Miehe 1993). The Tibetan Himalayas This region is an alpine semidesert in the rain shadow of the main Himalayan chain; it ex- tends northward to the oasis of the Tsangpo River. Only a small part of this subdivision of. : Inner Hinialu\as. Upper Kali Gandaki Valley, Titi Lake, looking eastward from Titi village, slopes with Pinus wallichiana forest, 2700 m, Musta
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Keywords: ., bookcentury1900, bookcollectionbiodiversity, booksubjectzoology
