Vipers on Islands: Ecology, Evolution, and Conservation
Departamento de Ecologia Instituto de Biociências Universidade de São Paulo São Paulo SP, Brazil
About 100 species of vipers occur on 300 islands throughout the world. About half (51%) of these islands are oceanic and half (49%) are continental (or land-bridge). The size of islands inhabited by vipers vary from tiny (0.038 km2) to very large (743,330 km2), and elevation varies from 1 to 4095 m a.s.l. Up to eight vipers may be found in sympatry in continental islands, with Sumatra (8 spp.), Taiwan (7), Sri Lanka (6), and Borneo (6) being the richest islands regarding vipers. In oceanic islands, up to 5 species occur in sympatry, with Langkawi (Malaysia) being the richest one (5 spp.). Vipers occur in 1 (45 spp.) to 34 islands (Vipera ammodytes). About 20% of island vipers (19 spp.) are endemics to a single island, and an additional 11 species occur only in islands. Both island area and island maximum elevation (a proxy for habitat diversity) explain very little of the variation in viper richness (only 5% and 8%, respectively). The origin of vipers on islands is related to the type of island where they occur. Vipers from continental islands are probably relictual portions from once widespread populations on exposed continental shelf during Pleistocene glaciations. On the other hand, viper populations from most oceanic islands probably resulted from colonization-driven processes. Similar biotic conditions on islands inhabited by vipers apparently led to several cases of convergent evolution. Of 62 species of island vipers present in the IUCN red list, seven are listed as threatened (15% of all threatened vipers in the list), two as Near Threatened,” and one as Data Deficient. Illegal captures, habitat loss, fire, and drought are the main threats to island vipers. A global conservation action plan is urgently needed for island vipers.