ORIGINAL PAPER Preliminary conservation status and needs of an oceanic island fauna: the case of Seychelles insects Justin Gerlach Received: 31 January 2008 / Accepted: 5 March 2008 / Published online: 19 March 2008 Ó Springer Science+Business Media B.V. 2008 Abstract Islands are generally reported to have much higher extinction rates and levels of threat than continental areas. This perception is based largely on studies of ver- tebrates. A recent assessment of the biodiversity of the Seychelles islands enables the status of a range of taxo- nomic groups to be compared. A high proportion of the fauna is found to be threatened, with Dictyoptera being the most threatened insect order (51% of 34 native species) followed by Orthoptera (47% of 68 species). Lower levels of threat are found in Diptera (28% of 562 species), Der- maptera (24% of 21 species) and Lepidoptera (21% of 517 species). Differences between the orders relate mainly to distribution patterns, with the most threatened orders hav- ing the highest proportions of endemic and restricted range species. The main threats for most orders are habitat deterioration due to invasion by introduced plant species, sea level rise and climate change. These threat factors are different from those reported to affect vertebrates, which are generally considered to be threatened by introduced predators resulting in critically low population sizes. These findings indicate that conservation sources would be more useful and cost effective for insect conservation if directed to habitat maintenance and restoration rather than to alien predator control. Keywords Climate change Á Conservation Á Insects Á Invasive species Á Seychelles Introduction It is widely accepted that island ecosystems are particularly vulnerable to extinction (Mueller-Dombois 1981; Loope and Mueller-Dombois 1989; D’Antonio and Dudley 1995); in support of this is the high rate of extinction of birds and reptiles on islands, compared to continental areas (Baille et al. 2004), with high susceptibility to invasion by alien species (Donlan et al. 2003a; Reaser et al. 2007). Although this is well established in literature there have been no comprehensive surveys of the status of island biodiversity, with studies limited to vertebrates, some plant groups and a small number of conspicuous invertebrate taxa. The invertebrates reported are mainly molluscs threatened with particular invasive predators (Hadfield et al. 1993; Coote and Loeve 2003) and large, charismatic insects such as the New Zealand Weta (Sherley 1998) and the Fregate island giant tenebrionid beetle (Polposipus herculeanus) (Fergu- son and Pearce-Kelly 2005). In 2000–2005 the Indian Ocean Biodiversity Assess- ment (IOBA) provided a comprehensive survey of the biodiversity of the Seychelles islands. This is producing a series of taxonomic reviews and Red List assessments of all the species recorded in Seychelles. These assessments provide a comprehensive review of the status of the insect fauna, allowing this to be compared to existing assessment of the vertebrate fauna in order to answer the question of whether or not island faunas are particularly vulnerable or whether this is an artefact of the small size of vertebrate island populations. The Red Listing process is ongoing. The orders that have been completed are evaluated here. The Seychelles islands comprise 115 islands in the western Indian Ocean. These form two main groups; the northern granitic islands and the southern, coralline islands. The southern islands are less than 10 m above J. Gerlach (&) Nature Protection Trust of Seychelles, 133 Cherry Hinton Road, Cambridge CB1 7BX, UK e-mail: jstgerlach@aol.com 123 J Insect Conserv (2008) 12:293–305 DOI 10.1007/s10841-008-9156-3