Scales of marine endemism in oceanic islands and the Provincial-Island endemism

Oceanic islands are remote environments commonly harboring endemic species, which often are unique lineages originated and maintained by a variety of ecological, biogeographical and evolutionary processes. Endemic species are found mostly in a single oceanic island or archipelago, however, a great number of species can be considered multiple-island endemics, i.e. species found on multiple oceanic islands that still have a restricted distribution. The geographic criteria chosen to classify endemic species has a direct impact on the endemism rate of islands, and many studies have used multiple scales of endemism (single and multiple-island endemics), which has historically influenced wide-scale comparisons. In this perspective, we accessed the importance of single and multiple-island endemic species to the biodiversity of oceanic islands, introducing the concept of Provincial-island endemism as an additional strategy to standardize biogeography studies.