How can endemic proboscideans help us understand the "island rule"? A case study of Mediterranean islands

Several hypotheses have been advanced to explain size-change processes in terrestrial vertebrates on islands and in island-like ecosystems. Extinct endemic insular proboscideans are especially appropriate subjects for investigating this issue, given the frequency with which proboscideans colonised islands, and the multiple patterns in size reduction experienced by endemic taxa on different islands, as well as on a single one. To verify whether evolutionary trends in elephants from Mediterranean islands might result from predictable responses to different niche availability and selection regimes in insular and mainland environments, the body-mass (considered as the best proxy of body-size) trends in endemic species and the body-mass structure of unbalanced insular have been compared to those of coeval balanced mainland mammalian complexes. Evolutionary patterns shown by endemic elephants suggest that, in isolated environments, the body-size of small and large non-carnivorous mammals depends on parsimonious optimisation of their life-history traits (metabolic rate, age at maturation and gestation time, trophic level, home range size, population density, etc.). Accordingly, it is rational to hypothesise that insular mammals change their size, in accordance with their initial bau-plan, depending on the most appropriate “empty” niche available on the island and the size of some vacant groups of competitor species, perhaps developing novel ecological strategies