Shortfalls of biodiversity knowledge strongly impede effective conservation, for both species- and area-based strategies. Arid habitats (defined here as deserts to arid steppes) are often perceived as having little conservation value due to their impoverished communities. Yet, these communities are made of many endemic, specialized species with unique adaptations. Many populated arid areas are degraded due to anthropogenic activities. Arid steppes are even amongst the most threatened habitats in North Africa and the Middle East because their fertile soil make them valuable to agriculture. Small terrestrial vertebrates have generally not been integrated into conservation policies in arid areas of the Middle East and North Africa (MENA) due to a lack of knowledge on species identities and distribution in arid MENA habitats. In addition, most small vertebrates have limited dispersal abilities and are thus expected to show large species turnover between the west of the Sahara and the Arabian Peninsula and a series of recent phylogeographic studies suggest that we underestimate species-level diversity in many genera. Consequently, species' ranges, ecological niche breadths, and population sizes, are overestimated while their extinction risk and sensitivity to habitat change are underestimated. We expect many species to display smaller distribution, more specialized niches, and thus higher conservation needs than what is currently understood. The conservation values and level of endemism of the main bioregions of the MENA is probably be severely underestimated. To address these issues, we will use reptiles as models of small terrestrial vertebrates, as they often exhibit restricted dispersal, have stringent ecological requirements in terms of vegetation cover or type of substratum that makes them highly sensitive to change in land use and, like many poikilotherm species, are particularly sensitive to climate change. The project will be organized in two work packages (WPs). WP1 aims at reducing the shortfall of biodiversity knowledge at the species level. We will test two hypotheses: H1 that the number of reptile species occurring at the NA&ME is higher than the currently described ones; H2 that intra-specific genetic diversity of wide-ranging species is strongly spatially structured. WP2 aims to enhance conservation strategies through systematic conservation planning. We will test two hypotheses: H3 that phylogenetic- and genetic- diversity of reptiles is unevenly distributed across the study area; H4 that priority areas for conservation identified using phylogenetic diversity differ from the ones identified using species diversity only.