The Socotra Archipelago is a unique hotspot of biodiversity, particularly for terrestrial reptiles (28 endemic out of 31 native species) whose ecology is known only in general terms. We describe the ecological preference and the daily activity of 21 species of terrestrial reptiles, geckos, lizards, skinks, snakes and chameleon, from the largest island of the archipelago. The database includes 6950 records collected by 260 standardized transects from 2007 to 2013. The sister species Haemodracon riebeckii–H. trachyrhinus with very distinct body sizes, overlapped in their distribution but segregated by habitat and substrate. Three pairs of sister species with great phylogenetic afnity and similar morphology (Pristurus insignis–P. insignoides; Pristurus guichardi–P. obsti; Hemidactylus dracaenacolus–H. granti) were only partially segregated by distribution, habitat, substrate and body size, in the order of decreasing frequency. On the contrary, the other, phylogenetically more distant species of geckos, widely distributed and less similar in morphology, overlapped completely in their habitat use and distributional range. Such patterns suggest that strictly related species reduced their competition by segregation in diferent habitats and temporal niches and by non-overlapping distribution within the relatively small island of Socotra. On the other hand, the activity rhythm was similar within each genus. The unique biodiversity of Socotra endured up to present, thanks to a human impact lower than for most other inhabited islands, but the pace of change has accelerated recently. Conservation measures are urgent, particularly for the species of endemic geckos with a distribution range as small as 10 km2 .
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