Land snail faunas on Santa Maria (Azores): local diversity in an old, isolated and disturbed island

Sampling of land snails in 19 small sites on Santa Maria (Azores) in 2008 and 2011 yielded a total of 52 species; 26 were Macaronesian endemics, of which 23 are restricted to the Azores. These represent nearly all the described endemic fauna. Forest faunas were the richest and contained the highest proportion of endemic species. Widespread European species were the major components of assemblages in open habitats, subject to greater human disturbance, while secondary or heavily disturbed forests were intermediate. A small suite of endemic species showed no habitat preference and may represent a fauna living in relatively open conditions prior to human occupation. Within forests, congeneric species frequently occur in the same site. All seven endemic Oxychilus species recorded occurred in a single site; there is no evidence of allopatric replacement or restricted distribution other than that imposed by habitat. This may reflect the age of the island, the oldest in the archipelago. Nearly all forest endemics are found near the summit of the highest peak, a small area vulnerable to habitat destruction or climate change; even without these, there may be an extinction debt to be paid in the absence of conservation measures.