Resource partitioning and dwarfism patterns between sympatric snakes in a micro-insular Mediterranean environment

Islands provide an evolutionary window, where a simplified natural network combined with unusual environmental conditions promote selective processes that trigger rapid changes in biological constituents of a species. The Mediterranean island of Montecristo, Italy, provides such a situation with a reduced fauna and flora compared to the mainland. We measured body size (SVL) and recorded diet of the two snake species occurring on the island, the Asp Viper (Vipera aspis) and the Western Whip Snake (Hierophis viridiflavus), and compared these data with populations of conspecifics from the mainland. Compared to mainland populations, the three principal results are: (1) no obvious niche shift along the food or habitat axes between the two snake species; (2) significant body size shift (insular dwarfism) of the whip snake by 30 %, and ca. 10 % in the viper; and (3) arboreal ambushing in the viper to add an alternative diet (birds) compared to mainland populations (more mice) to compensate for the lack of suitable micro-mammals on Montecristo Island.