In this excerpt from Islands and Snakes authors Lillywhite and Martins explore how snakes are able to live so successfully on isolated islands.
Islands have been the subject of intense investigation — biologically and ecologically — since the time of Darwin and Wallace. Much research has focused on species assemblages and the dynamics of species richness on islands as well as other systems having geographic isolation and other characteristics similar to those of islands surrounded by water.
Since the 1960s, a robust literature on insular biology and ecology has continued to grow, with numerous investigators focusing on a variety of insular systems with attention to increasing detail concerning the requirements and dynamics of ecological factors that favor adaptation and successful existence on islands.
For many practical reasons (often with advantages), various investigators of the ecology of islands focus on taxonomic elements of fauna or flora…such approaches have intrinsic value and also provide important data for more inclusive investigations of biodiversity. Reptiles have been the frequent subject of investigations of vertebrate faunas on islands, where they are often “replacements” of endotherms as primary herbivores and top carnivores. The favorable circumstances for ectotherms versus endotherms on islands include low rates of energy expenditure relative to resources that are often scarce or limited on islands, dispersal abilities, and superior colonizing abilities. Rates of energy expenditure in terms of field metabolic rates of endothermic mammals and birds are approximately 12 and 20 times higher, respectively, than those of equivalent size, ectothermic reptiles. Reptiles, therefore, have a crucial advantage in exploiting scarce resources and building populations in circumstances that preclude, or severely challenge, the success of birds and mammals.
Snakes are very successful inhabitants of islands, and there is a very rich literature concerning the insular ecology of this group of vertebrates. An accounting of scientific articles using Google Scholar indicates that roughly 60% of the literature on islands and squamate reptiles (including Tuatara) deals with snakes. Thus, studies of snakes have contributed much to our understanding of insular ecology and are important subjects for attention to questions that might be difficult to investigate in other systems. We emphasize that there are numerous reasons why snakes are important elements of insular biotas and play critical roles on numerous islands that can offer further insights for understanding ecology of islands. Some of the more important attributes of snakes related to successful “island living” are (1) ectothermy and comparatively low energy requirements; (2) attributes favoring abilities for overwater dispersal; (3) life history features favoring comparatively rapid population growth; (4) range of body sizes favorable for inhabiting even very small islands; (5) breadth and plasticity of diet, including scavenging; (6) effective means of prey acquisition; (7) infrequent feeding on relatively large prey and “slow” digestive physiology; (8) secretive behaviors and cryptic morphologies; (9) special scansorial capabilities in many species; and (10) thermal plasticity.
Reptiles, therefore, have a crucial advantage in exploiting scarce resources and building populations in circumstances that preclude, or severely challenge, the success of birds and mammals.
The origin of snake populations in different island types differs, mainly because of variation in the origins of islands. Thus, understanding how these island types originated is crucial for understanding the diversity and biogeography of insular snakes. Land-bridge islands are originated by the variation in sea level during glaciation cycles. Most of them have been connected, disconnected, and reconnected to the mainland many times during the glaciations of the past 1.8 million years. For example, many islands in continental shelves throughout the world were connected to their respective continents during the last glacial maximum approximately 29,000 to 21,000 ybp, when sea level reached approximately 130 m below the present level. Extensive portions of continental shelves were exposed by then. When sea level rose to the present level, mountains amid these coastal lowlands became the land-bridge islands that we see today.
Continental fragments are originated by plate tectonics processes in which a portion of a continent moves away from the main portion, becoming an island. Madagascar, for instance, was part of the Gondwana supercontinent and became separated from Africa in the Late Jurassic–Early Cretaceous and from India during the Late Cretaceous. On the other hand, oceanic islands are originated mainly by volcanism in the areas of contact of tectonic plates, and they were never in contact with continents, although they may be close to them in some instances.
The favorable circumstances for ectotherms versus endotherms on islands include low rates of energy expenditure relative to resources that are often scarce or limited on islands, dispersal abilities, and superior colonizing abilities.
Snakes are found on land-bridge and oceanic islands throughout the planet — on all five continents; in all oceans; and from 42 degrees south in Tasmania, Australia, to 63 degrees north at Hitra Island, Norway. Among land-bridge islands, snakes occur on islands varying in size from 1,000 m2 (small Japanese islands in the South China Sea) to approximately 786,000 km2 (New Guinea Island) and varying in elevation from less than 1 m above sea level (ASL) on Huevos Island (Trinidad and Tobago) to almost 5,000 m ASL on New Guinea Island. Among oceanic islands, those inhabited by snakes vary in area from less than 1 km2 (e.g., many islands in the Bahamas) to more than 580,000 km2 (Madagascar) and vary in elevation from less than 5 m ASL on some small islands in the Cuban Archipelago to 3,700 m ASL on Lombok Island, Lesser Sunda Islands.
Most islands inhabited by snakes are located in the Eastern Hemisphere, where most tropical and subtropical islands are concentrated. This region harbors most groups of islands on which island snakes occur, including the Japanese and Malay archipelagoes as well as the Philippines. In the Western Hemisphere, most islands inhabited by snakes are located in the Caribbean and the Bahamas. The absolute middle latitude of islands explains just a small amount (10% or less) of the variation of snake richness on both land-bridge and oceanic islands, with islands from lower latitudes tending to harbor more species. However, using their database with islands larger than 250 km2, Pyron and Burbrink found a stronger effect of middle latitude on insular richness of snakes. Finally, the vegetation cover of islands inhabited by snakes includes most of the terrestrial vegetation types found on continents, from the dry Sonoran Desert on islands in the Sea of Cortez, Gulf of California, to the luxuriant rainforests of lowland Borneo.

Harvey B. Lillywhite is a Professor of Biology at the University of Florida, Gainesville. He has published numerous scientific articles on snakes, including those living on islands in many parts of the world. His research has been featured in Science, Nature, Scientific American, Natural History, Proceedings of the Royal Society, and many other publications. He is author of the book How Snakes Work, published by Oxford University Press in 2014.
Marcio Martins is a Professor of Ecology at the University of São Paulo, Brazil. He has published numerous scientific articles on the natural history, ecology, evolution and conservation of frogs and snakes, including studies on island snakes from Brazil and Mexico. His research has been featured in Nature Ecology & Evolution, Biological Conservation, Global Ecology and Biogeography, Oecologia, Proceedings of the Royal Society, and many other publications.

