Species distribution modelling to identify habitat islands suitable for narrow endemic climate relicts

Ptilostemon greuteri (Asteraceae) is one of the most fascinating narrow endemic plant species of the Mediterranean Basin. This woody broad-leaved thistle only survives in two microrefugia, distant approximately two kilometres from one another in the North-Western Sicily (Italy). Its habitat consists of NNE-facing calcareous cliffs and ledges as well as the bottom of narrow, steep and shady gorges, benefitting from the humidity rising from the sea that creates a kind of habitat islands surrounded by a contrasting climatic matrix. For this reason, P. greuteri can be considered a climate relict that persists in enclaves of benign environmental conditions within a nowadays inhospitable regional macroclimate. In order to discover previously undetected populations, and to select the most suitable translocation sites, we performed species distribution modelling using high resolution Digital Terrain Model (DTM) and other DTM-derived micro-topographic variables such as insolation, hillshade, aspect and Topographic Position Index (TPI). The species distribution model identified very few localities offering suitable conditions for the target species, and field validation of the model through field vegetation surveys confirms its reliability. Unfortunately, we did not discover any new population of P. greuteri. The first translocation activities resulted in a successful introduction of the species in a new site. Our results suggest that species distribution modelling can be a useful method to identify suitable habitat islands for translocation activities.