Reptiles are declining worldwide at an alarming rate (Gibbons et al. 2000, Böhm et al. 2013) and, along with amphibians, are considered among the most threatened vertebrate groups (Stuart et al. 2008, Hof et al. 2011). The decline of reptiles has been induced by a variety of threats such as habitat loss, degradation and fragmentation, pet trade, invasive species, pollution and diseases (Gibbons et al. 2000, Cox and Temple 2009). Currently, it is considered that climate changes severely affect reptiles (Böhm et al. 2013). Therefore, we need to assess the potential impacts of the forecasted global changes by assessing anticipated changes in the ecological niche of species. Although complex species distribution models have been developed, with some managing to predict the species ecological niches from just a few known localities (Phillips et al. 2006, Peterson et al. 2011), we still face difficulties to accurately assess the impact of these future threats. Among the limitations encountered when modeling ecological niches is the quality of the biological data used to train the models, which is the first condition to meet certain standards (Pineda and Lobo 2009). Data quality issues are triggered by use of improper spatial resolution, misidentification, missing data, and the lack of a proper sampling design (Araújo and Guisan 2006, Peterson et al. 2011). In this manner, it is mandatory to check for any bias in the sampling effort when mapping species distribution (e.g., Proess 2003, Loureiro et al. 2010).

Romania has five biogeographic regions (i.e., Alpine, Continental, Pannonian, Black Sea, and Steppic) out of the nine regions recognized by the European Union (Cogălniceanu and Cogălniceanu 2010, Iojă et al. 2010, Evans 2012). Romania still maintains a significant proportion of habitats with high conservation value, such as boreal coniferous forests, mesophilous, hygrophilous and xerothermic broadleaved forests, grassland and shrubby ecosystems. There is also a rich diversity of aquatic ecosystems including mountain springs and rivers, river floodplains, glacial lakes, coastal wetlands and bogs (Rey et al. 2007).

The diversity of reptiles is surprisingly high for a country with a mostly temperate and continental climate. There are 23 reptile species in Romania, out of which 12 species reach the limit of their geographic range (i.e., Testudo hermanni, Testudo graeca, Ablepharus kitaibelii, Lacerta trilineata, Podarcis tauricus, Podarcis muralis, Eremias arguta, Darevskia praticola, Eryx jaculus, Dolichophis caspius, Elaphe sauromates, Vipera ammodytes), while other two species are near their range edge in Romania (i.e., Zamenis longissimus, Vipera ursinii) (Gasc et al. 1997).

No updated distribution maps have been published since the publication of the milestone volume on Reptiles in the series Fauna of Romania fifty-two years ago (Fuhn and Vancea 1961), despite a substantial increase in the inventory effort over the following years. However, there are published papers compiling species distributions of single species such as Darevskia praticola (Sós et al. 2012), Vipera ursinii (Krecsák and Zamfirescu 2008), Natrix tessellata (Strugariu et al. 2011), Emys orbicularis (Sós 2011), Testudo hermanni (Rozylowicz and Dobre 2010), Eryx jaculus (Krecsák and Iftime 2006), or restricted to particular geographical areas (e.g., Ghira et al. 2002, Covaciu-Marcov et al. 2006).

We here present an updated overview of the distribution and diversity of reptiles in Romania. The aims of our study are to (1) map the distribution of reptile species in Romania and (2) analyze the spatial pattern of distribution data.

We here present the first comprehensive distribution database of the reptile species occurring in Romania. We fulfilled the major requirements of data quality by (1) filtering the large amount of data for doubtful and erroneous records, (2) aggregating the known localities to a fine resolution of 25 km², and (3) assessing the bias in sampling effort and thus providing useful information for further analyses.

We addressed a series of issues related to the quality and relevance of occurrence records. The most conspicuous issue was the overall biased density of records, which might appear due to differences in species detectability. For instance, our database showed that the snake species with low detectability (Hartel et al. 2009, Durso et al. 2011) had a low number of occurrences despite their wide range. Notable exceptions are the grass snake and the dice snake (genus Natrix), both of them being active during the day and easy to identify. The higher detectability of most lizards and both tortoise species resulted in a large number of occurrences and thus, more detailed distribution maps.

Another issue of concern was misidentification (e.g., Török 2012), due to difficulties in distinguishing the actual species based only on sightings. For example, it is rather difficult to distinguish among green lizards, especially between Lacerta viridis and Lacerta trilineata and we assumed that some of the occurrence records for those species were misallocated.

Although individuals of Testudo hermanni were reported from south-east Romania (Iftime 2002, Sós et al. 2008), we chose not to map the respective occurrences, considering them a case of vagrancy (Rozylowicz and Dobre 2010). The presence report of Testudo hermanni from Hunedoara county (Togănel 1993) was also not considered since it was the case of a recent human introduction into the wild (Rozylowicz 2008).

The analysis of sampling effort revealed a significantly higher number of sightings per grid cell within certain areas, mostly protected areas, such as the Jiului Gorges National Park, the Iron Gates Natural Park or the Măcin Mountains National Park. That was a common pattern previously reported from other countries and for different taxa (e.g., Loureiro et al. 2010, Botts et al. 2011). Despite those hotspots, the sampling effort was balanced across the country; therefore the dataset might be useful for additional analyses with only a simple trimming procedure required (Peterson et al. 2011). In the case of amphibians (Cogălniceanu et al. 2013), the sampling effort was biased towards the same hotspots but their number was significantly less numerous for reptiles. Nevertheless, the patterns in species richness support a similar statement revealing a higher richness in the warmer and drier climate in the south-west and the south-east parts of Romania (e.g., Rodríguez et al. 2005) and a constant richness in the rest of the country. Two gaps that require further investigations were revealed in the southern part of Romania (Oltenia and Bărăgan plains), probably being determined by the lack of research interest in those regions, due to their dominant agricultural landscape (Rey et al. 2007, Iojă et al. 2011). The gaps in reptile richness were similar to those of amphibian richness (Cogălniceanu et al. 2013).

The number of reptile species observed in Romania might increase in the near future with two species, namely Pseudopus apodus (Lepşi 1926, Cogălniceanu et al. 2008) and Mediodactylus kotschyi, bothpresent in Bulgaria and near the Romanian border (Gasc et al. 1997).

Several species were widespread across the country (e.g., Emys orbicularis, Lacerta viridis, Lacerta agilis, Natrix natrix, Natrix tessellata, Zamenis longissimus, Vipera berus), while others occurred only in the south of Romania (e.g., Testudo hermanni, Testudo graeca, Eremias arguta, Lacerta trilineata, Eryx jaculus, Elaphe sauromates, Dolichophis caspius). Lacerta viridis had the largest number of sightings mainly because it is a highly detectable species. Its AOO was surpassed only by Lacerta agilis and Natrix natrix, two other highly detectable species. Eryx jaculus is the rarest reptile in the country (see Table 1) with a single new report after 1990, based on a road-kill specimen (Covaciu-Marcov et al. 2012).

The different biogeographic regions overlapping in Romania will face different types and levels of these changes (Popescu et al. in press). Climate change may cause a shift in reptile ranges, although the Carpathian Mountains and the Steppic and Black Sea province of Dobrogea will act as a refuge, being considered critical areas for conservation (Araújo et al. 2006, Popescu et al. in press). To alleviate these threats by conservation activities (e.g., by establishing new protected areas), a key step is predicting the range responses to different climate change scenarios (Franklin 2009, Araújo et al. 2011). Our dataset provides a robust starting point for such analyses. Climate change alone does not result in a rapid range shift; instead, additionally, habitat loss due to the abandonment of traditional agricultural activities such as manual mowing, low-intensity grazing, small-size orchards and vineyards (Plieninger et al. 2006, Angelstam et al. 2013) might lead to a rapid contraction of the reptiles ranges (e.g., Testudo hermanni, Rozylowicz and Popescu 2013). Thus, our database also allows for further investigations resulting in concrete conservation activities.