African and Southeast Asian Elements in the Spider Fauna of the Western Ghats of India
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African and Southeast Asian elements in the spider fauna of the Western Ghats of India Autor(en): Sudhikumar, Ambalaparambil Vasu / Maelfait, Jean-Pierre / Lens, Luc Objekttyp: Article Zeitschrift: Contributions to Natural History : Scientific Papers from the Natural History Museum Bern Band (Jahr): - (2008) PDF erstellt am: 30.09.2021 Persistenter Link: http://doi.org/10.5169/seals-787070 Nutzungsbedingungen Die ETH-Bibliothek ist Anbieterin der digitalisierten Zeitschriften. Sie besitzt keine Urheberrechte an den Inhalten der Zeitschriften. Die Rechte liegen in der Regel bei den Herausgebern. Die auf der Plattform e-periodica veröffentlichten Dokumente stehen für nicht-kommerzielle Zwecke in Lehre und Forschung sowie für die private Nutzung frei zur Verfügung. Einzelne Dateien oder Ausdrucke aus diesem Angebot können zusammen mit diesen Nutzungsbedingungen und den korrekten Herkunftsbezeichnungen weitergegeben werden. 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African and Southeast Asian elements in the spider fauna of the Western Ghats of India AMBALAPARAMBIL VASU SUDHIKUMAR1, JEAN-PIERRE MAELFAITt, LUC LENS2, FREDERIK HENDRICKX2 & POTHALIL ANTONY SEBASTIAN3 1 Department of Zoology, Christ College, Irinjalakuda, Kerala, India. PIN: 680 125 (corresponding author: [email protected]) 2 Terrestrial Ecology Unit, Department of Biology, Ghent University, K.L. Ledeganckstraat 35 B-9000 Ghent, Belgium 3 Division of Arachnology, Dept. of Zoology, Sacred Heart College, Thevara, Cochin, Kerala, India -682013 ([email protected]) Abstract Although the Western Ghats are a biodiversity hotspot in the world, the studies conducted on the faunal affinity of this region are very few and there are no studies focused on spiders. Biota of the Western Ghats is the product of extreme climatic, ecological and bio- geographical history. In this study, we tried to expose the faunal affinities of spiders distributed along this biodiversity hotspot based on their distribution throughout the world. A total of 270 species of 138 genera grouped in 39 families of spiders are so far reported from the Western Ghats of India. The biogeographical analysis revealed that a total of six genera of spiders are endemic to the Western Ghats, four genera showing affinities to the African region and 18 showing affinities to the Southeast Asian region. Another 20 genera are common to Africa, Western Ghats and Southeast Asian regions and 90 genera are cosmopolitan in distribution. These results agree with previous studies conducted on other faunal and floral elements of India, because India was part of the African continent until about 130 million years ago. It detached from there and later moved northwards and finally collided with Eurasia about 50 million years ago. In between, India was an isolated island for about 50 million years. This isolation might have lead to the creation of its unique fauna and flora. After the collision with Eurasia, the fauna of the Western Ghats underwent drastic changes due to faunal migrations between Southeast Asia and the Indian plate. There are different hypotheses explaining this migration of different animal groups through a continuous corridor of tropical evergreen forest. During this event, the Indian plate actually functioned as a "biotic ferry" which led to the spreading of African spiders to Southeast Asia. It is concluded that the spider fauna of the Western Ghats can be divided into an ancient African lineage, later Southeast Asian migrant and an endemic part. So a detailed phylogeographical approach is necessary to differentiate between these different time scale elements. INTRODUCTION mammals (Kurup 1974), birds (Ali 1935), One of the features of the biota of the Western freshwater fish (Jayaram 1974), amphibians Ghats is its strong affinity with African (Das 2002), reptiles (Daniel 2002), insects and Southeast Asian biota. There are several (Singh 1974) and plants (Mani 1974a). Fauna such cases of affinity in different taxa like and flora of the Western Ghats are an excep- 166 European Arachnology 2008 tionally interesting and challenging objective a huge share. This area is also enriched with for biogeographers due to its antiquity, large forests and therefore possesses various unique plate tectonic and palaeoclimatic assemblages of spiders. Due to high species history, and astounding array of physiognomic endemism, the Western Ghats are listed and habitat diversity (Ashton & Gunatilleke among the 34 biodiversity hotspots of the 1987). These factors have contributed to a world (Mittermeier et al. 2005). Due to the considerable diversification of biota in this paucity of workers, much of the spider region (Morley 2000). Additionally, changes diversity in the Western Ghats has remained in the extents of habitats, especially of tropical unexplored so far. As a result, the disappearance evergreen forests in space and time, have of many species remains undocumented. resulted in striking endemism in almost all The present study provides the result of taxonomic groups, inviting much debate a preliminary analysis of the faunistic affinities about processes underlying them (Swan 1993). of the spiders in the Western Ghats of Dealing with complex palaeogeographical India, which aims to demonstrate their great histories is a problem of major importance diversity and their high degree of endemism in biogeographical studies. Since the and to present a biogeographic hypothesis superposition of palaeogeographical events may of the region. produce multiple changes in species range distributions, highly complex patterns of MATERIALS AND METHODS animal and plant distributions are to be expected The Western Ghats occupy the western (Nelson & Platnick 1981; Myers & Giller part of Peninsular India, between 8° and 20° 1988). As changes may interact and produce North and between 73° to 77° East. The Western an apparent discordance between species Ghats cover a practically unbroken relief distributions, the biogeographical relationships dominating the west coast of the Indian of areas are often difficult to trace back peninsula for almost 1600 km from the river in time (McLennan & Brooks 2002; Brooks Tapti in the north to the tip of Peninsular & Van Veller 2003). The Indian subcontinent India. Zoogeographically, the Western Ghats exhibits such a complex biogeographical can be divided into three parts: a northern pattern, and several hypotheses based on division, comprising the Deccan Trap area different processes have been proposed to from the Tapti river down to 16° N, about explain the presence of Southeast Asian and the region of Goa; a central division, extending African faunal and floral elements in India from 16° N southwards and including (Mani 1974b). Some studies related this area the Kudagu and Wayanad region of south as a sister area with the Southeast Asian Karnataka and Nilgiris; and a southern region (Wallace 1876) or as sister area with the division, comprising the Anaimalai, Palani and African region (Blanford 1876). Biogeograph- Cardamom hills of Kerala (Bhimachar 1945). ically the Indian region contains a complex The Western Ghats are the main watershed assortment of barriers and dispersal routes in peninsular India from which all the principal varying in their nature as well as spatial rivers, namely Godavary, Krishna and scale to which multiple co-distributed Cauvery originate and flow east emptying taxonomic groups are unlikely to show a congruent into the Bay of Bengal. A large number of response. short perennial, torrential west flowing rivers The spiders of the Western Ghats are a also originate from it. The average height poorly worked out group compared to other of the Ghats is less than 1500 m above sea parts of the country. With respect to its level, but in the south it rises up to 2000 m geographical, climatic and ecological features, and to exceptionally high peaks of 2500 m the Western Ghats region harbours a rich and above. Along its entire length, this hill amount of arachnids of which spiders have range has only one discontinuity, the Pal- Sudhikumar et al.: African and Asian elements in spiderfauna of Western Ghats of India 167 ghat gap in Kerala, a more than 30 km wide flora and fauna. The question of whether the gap, less than 100 m above sea level (Nair links with Southeast Asia or Africa are more 1991). important has been a central aspect of this The presence of spiders, which are discussion. It culminated in the refusal of reported from the Western Ghats, in other Wallace's (1876) hypothesis that India's biota geographic regions of the world was was essentially of Southeast Asian origin, by collected