Aim: To identify and evaluate the environmental properties of the Mediterranean islands that make them a suitable habitat for their endemic lizards. This would represent an important improvement in our knowledge and would assist the conservation of these lizards, which are threatened by both the expansion of mainland species and the increasing intensity of human disturbance on these islands.

Location: Mediterranean Basin.

Methods: I assessed the environmental associations of 50 species of lizard (19 endemic) across 552 Mediterranean islands using outlying mean index analysis. The strength of the response of each species was assessed using binomial generalized linear models.

Results: The presence of endemic species is positively correlated with the distance of the island from the mainland. Island connectivity is also positively correlated with an increased presence of endemic lizards, but not with an increased presence of mainland species (those with exclusive or mainly continental natural distribution). In addition, island size, temperature, and vegetation productivity are positively correlated with the presence of mainland species. Outlying mean index (OMI) analysis showed that the endemic species occupy niche positions that are similar to the average environmental conditions in the archipelago, but frequently without using the entire range of niches. The mainland species usually occur in more peripheral positions in the environmental space, except for some highly expansive species.

Conclusions: Lizards that are endemic to the Mediterranean islands were found to be present on a large number of islands within an archipelago, but they quickly disappear as the conditions change, largely because of human activity. Large islands act as population reservoirs for mainland species, facilitating secondary colonization of peripheral islets.