Understanding the factors shaping species distributions is essential for predicting their responses to environmental change. The genus Hemorrhois (horseshoe whip snakes) comprises ecologically diverse colubrid snakes found across the Mediterranean Basin, North Africa, the Middle East, and Central Asia. Despite this broad range, their ecological niches and distributional dynamics remain understudied. This study employs ecological niche modeling (ENM) to assess the biogeography, niche differentiation, and potential climate-driven range shifts of H. algirus, H. hippocrepis, H. nummifer, and H. ravergieri under future climate scenarios. Using species occurrence data and bioclimatic variables, I constructed ensemble models to predict suitable habitats, evaluate niche overlap, and quantify potential range changes. Results indicate significant variation in climate-driven distributional responses among species. Hemorrhois algirus is projected to expand across North Africa, whereas H. hippocrepis, H. nummifer, and H. ravergieri may face range contractions under high-emission scenarios. Niche analyses suggest moderate overlap between H. algirus and H. hippocrepis, implying historical and ecological connectivity, while H. nummifer and H. ravergieri display distinct environmental preferences. Climatic and geographic barriers—such as the Sahara Desert, the Dardanelles and Istanbul Straits, the Alps, and the Pyrenees Mountains—play crucial roles in shaping their evolutionary trajectories. Given the increasing threats of climate change and habitat loss, this study underscores the need for conservation strategies prioritizing habitat connectivity, species-specific management, and climate refugia. By integrating ecological and evolutionary perspectives, this research contributes to understanding Mediterranean and Western Palearctic reptile biogeography and their responses to environmental change.

climate change, habitat loss, niche differentiation, Squamata, Western Palearctic

Species distributions and their ecological niches are shaped by a combination of historical biological and geological events, climatic fluctuations, and biotic interactions (Franklin 2009). Continental drift, glaciations, and environmental shifts have profoundly influenced present-day biodiversity by driving speciation and dispersal (Wiens 2011; Pelegrin et al. 2021). Within these frameworks, interspecific competition, environmental pressures, and selective forces further shape evolutionary trajectories (Angert and Schemske 2005; Sexton et al. 2009). Understanding the processes governing species’ ecological niches is critical for predicting their responses to environmental change and informing conservation efforts (Soberon and Peterson 2005; Franklin 2009; Vaissi and Mohammadi 2024).

Climate change represents a significant threat to many reptilian taxa, particularly those with narrow ecological tolerances or fragmented distributions (Vaissi et al. 2023; Şahin 2024). Recent advances in ecological modeling, coupled with global climate and land cover datasets, now allow researchers to forecast species distributions under different environmental scenarios. Ecological niche models (ENMs) integrate occurrence data and environmental variables to predict potential species range shifts under climate change (Phillips and Dudík 2008; Peterson et al. 2011). However, significant conceptual and statistical challenges exist in niche modeling using occurrence records that encompass a geographically representative range of species. For example, most ENMs exhibit spatial correlation among environmental variables, such as temperature, which may lead to misinterpretation of significant niche modeling results as a consequence of geographical distance (McCormack et al. 2010).

The genus Hemorrhois (Colubridae), commonly referred to as the horseshoe whip snakes, comprises four currently recognized species: Hemorrhois algirus, H. hippocrepis, H. nummifer, and H. ravergieri (Abreu 2017; Faraone et al. 2020; Kazemi et al. 2023). This genus exhibits a broad yet regionally distinct distribution, primarily spanning the Mediterranean Basin, North Africa, the Middle East, and parts of Central and South Asia (Carranza et al. 2006; Abreu 2017; Bülbül et al. 2019; Faraone et al. 2020). Hemorrhois snakes display notable ecological adaptability, occupying diverse habitats including arid and semi-arid landscapes, rocky terrains, and anthropogenically modified environments (Montes et al. 2020). The broad distribution and ecological plasticity of Hemorrhois make this genus an ideal model system for testing biogeographic and ecological hypotheses. Such studies could elucidate how ecological niches and climate-driven range shifts have shaped their current distributions while also providing insights into potential future range dynamics under contemporary climate change scenarios (Winter et al. 2016; Veverková 2021).

Despite their broad distributions, Hemorrhois snakes generally remain relatively understudied with regard to their ecological interactions and responses to environmental changes. The integration of species distribution modeling and niche differentiation assessments will clarify the role of climate in their speciation and habitat requirements for conservation planning. Given the increasing pressures of habitat destruction and climate change, future research should prioritize identifying key refugia, assessing population viability, and implementing conservation strategies that account for both regional and global threats to these snakes (Bombi et al. 2011).

This study provides a comprehensive assessment of the biogeography and ecological niches of the genus Hemorrhois by integrating occurrence records, climatic variables, and predictive modeling techniques. I hypothesize that Hemorrhois species exhibit significant climatic niche differentiation corresponding to their ecological and biogeographic diversity and that climate change will drive species-specific range shifts. To test this hypothesis, I developed ENMs based on climatic variables and species occurrence data to (i) evaluate the relationship between current Hemorrhois distributions and observed climate and forecast potential future species distributions under different climate change scenarios (2081–2100) and (ii) measure and compare climatic niche divergence within the genus. These findings will contribute to a better understanding of Mediterranean and Palearctic reptile biogeography and offer insights into the resilience and adaptability of Hemorrhois species in the face of ongoing environmental transformations.

Ecological niche models predicted distinct environmental suitability patterns among Hemorrhois species, with consistent outputs across algorithms. The performance evaluation of the models—based on AUC, AICc, partial ROC, and omission rates—indicated that all selected models demonstrated high predictive accuracy and statistical significance, supporting their reliability for subsequent analyses (Tables 1, 2). The regions projected to be suitable for Hemorrhois species demonstrated significant model performance: H. algirus (AUC = 0.955, omission rate at 5% = 0.044), H. hippocrepis (AUC = 0.943, omission rate at 5% = 0.049), H. nummifer (AUC = 0.959, omission rate at 5% = 0.039), and H. ravergieri (AUC = 0.915, omission rate at 5% = 0.090). Although several statistically significant models were identified for each Hemorrhois species, only one per species met the AICc criterion of ≤ 2. The relative contributions of bioclimatic variables to the ecological niche models of Hemorrhois species are summarized in Table 3.

Model projections under future climate scenarios suggest heterogeneous responses among Hemorrhois species, with some showing potential range expansions, others contractions, and a few maintaining relatively stable distributions (Figs 2–5). Projected patterns of range stability, expansion, and contraction for each Hemorrhois species are summarized in Suppl. material 6 and Table 4. The following results describe species-specific responses of Hemorrhois taxa to future climate scenarios, highlighting patterns of range expansion, contraction, and stability.

For H. algirus, Bio_3 (31.9%) and Bio_18 (31.4%) were the two most important variables affecting its potential distribution (Table 3). The habitat suitability map under recent climatic conditions indicates that North Africa—particularly Morocco and northern Algeria—has high suitability (Fig. 2a). While the species occurs in arid environments such as Tunisia and Western Sahara, it is projected to occupy these regions with relatively limited suitable habitat (Fig. 2b–k). In the future, the distribution range of H. algirus may expand further in North Africa. For example, under the SSP585 scenario, the GFDL (Fig. 2c) and IPSL (Fig. 2e) models predict range expansions of approximately 50.3% and 18.9%, respectively, compared to the current distribution (Table 4). Based on the SRC analysis, range expansion is expected under all optimistic and pessimistic future climate scenarios, except for MPI SSP585 (–13.8%) (Suppl. material 6: fig. S5A).

For H. hippocrepis, Bio_4 (29.8%) and Bio_18 (17.7%) were identified as the most influential variables shaping its potential distribution (Table 3). The habitat suitability map under current climatic conditions indicates a broad and continuous distribution across southern Europe and the western Mediterranean coast. In particular, the Iberian Peninsula (Spain and Portugal) and parts of Italy exhibit high suitability (Fig. 3a). The species shows a notable preference for coastal regions over inland areas (Fig. 3b–k). In the future, a significant range contraction is projected under high-emission scenarios. For instance, under the SSP585 scenario in the MPI model, a loss of approximately 70.2% of suitable habitat is predicted within the species’ current distribution range (Fig. 3g, Table 4). SRC analysis further supports this trend, indicating range contraction under all future climate scenarios—except expansions in MPI SSP126 (11.5%) and both UKESM scenarios (25.4% under SSP126 and 21.7% under SSP585) (Suppl. material 6: fig. S5B).

For H. nummifer, Bio_15 (25.1%) and Bio_8 (19.5%) were the most influential variables contributing to its potential distribution (Table 3). The habitat suitability map under current climatic conditions shows a wide distribution primarily across the Levantine corridor, extending into parts of western Anatolia and the Middle East (Fig. 4a). This pattern suggests adaptation to semi-arid and Mediterranean environments. Under future climate scenarios, a notable range contraction is projected, particularly under high-emission conditions. For example, under the SSP585 scenario, the MPI model predicts a loss of approximately 87.4% of suitable habitat, especially in surrounding countries of the Levantine corridor and western Anatolia (Fig. 4f, Table 4). According to the SRC analysis, habitat loss is expected under nearly all future scenarios—specifically 4 out of 5 under SSP126 and all 5 models under SSP585—except for MPI SSP126, which predicts a limited expansion (5%) (Suppl. material 6: fig. S5C).

For H. ravergieri, Bio_4 (34.1%) and Bio_5 (18.3%) were the most influential variables shaping its potential distribution (Table 3). The habitat suitability map under current climatic conditions highlights high suitability across South-Central Asia—particularly northwestern Kazakhstan and Mongolia—as well as western Asia (Türkiye) and the Caucasus region (Fig. 5a). In future climate scenarios, areas at higher elevations are projected to become increasingly suitable (Fig. 5b–k). However, under the SSP585 scenario, both the MPI and UKESM models predict notable range contractions, with losses of 42.1% and 39.5% of suitable habitat, respectively, particularly in the Caucasus and western Asia (Table 4, Suppl. material 6: fig. S5D).

The comparative analysis of range shift patterns among Hemorrhois species revealed contrasting responses to projected climate change. Hemorrhois algirus is generally expected to expand its suitable range across North Africa, while H. hippocrepis, H. nummifer, and H. ravergieri are projected to experience significant range contractions under pessimistic climate scenarios. The degree of projected range loss was highest for H. nummifer and H. ravergieri, particularly in regions of complex topography and aridification, suggesting species-specific sensitivity to climatic variables and geographic constraints.

The measured niche overlaps among all species are presented in Table 5. The null hypothesis regarding niche overlap among Hemorrhois species (excluding nummifer vs. ravergieri and hippocrepis vs. algirus) was rejected, as the empirical values for Schoener’s D and Hellinger’s I test statistics differed significantly from the null distribution of overlap tests for each species comparison (Suppl. material 7: fig. S6A–F) (t test, df = 99, P < 0.05). The ecological niche models of the majority of these species were not equivalent. The asymmetric and symmetric background tests for the parapatric H. algirus and H. hippocrepis, as well as H. nummifer and H. ravergieri, confirmed partial niche overlap between these species with respect to global bioclimatic variables (Suppl. material 8: fig. S7A–D).

This study provides a comprehensive examination of the ecological niche attributes and future range dynamics of four Hemorrhois species. The biogeographical patterns of these species are influenced by both historical and contemporary ecological processes. The presence of H. hippocrepis in the western Mediterranean, for instance, suggests a complex history of dispersal and vicariance events (Bombi et al. 2011). Specifically, physical barriers such as the Sahara Desert, the Alps, the Pyrenees, and the Dardanelles and Istanbul straits have historically limited gene flow and contributed to speciation through allopatric divergence (Machado et al. 2021). The initial divergence between H. algirus and H. hippocrepis has been estimated to have occurred during the late Miocene to early Pliocene, approximately 4–7 million years ago (Carranza et al. 2006). Subsequent climatic events during the Pleistocene, including sea-level fluctuations at the Strait of Gibraltar, likely influenced the secondary contact, distributional shifts, or population structure of Hemorrhois species. Based on current distributions and phylogenetic inference, H. algirus and H. hippocrepis may have originated in North Africa, with H. hippocrepis subsequently dispersing into the Iberian Peninsula (Carranza et al. 2006). Instead of direct transmarine migration following the opening of the Strait of Gibraltar at the end of the Messinian, climatic events during the Pleistocene glaciations resulted in a sea-level drop of approximately 130 m (Anderson and Borns Jr. 1997) at Camarinal Sill, where water depths range from 40 to 150 m (Brandt et al. 1996). Consequently, some elevated areas in this region temporarily became small islands, potentially allowing certain terrestrial vertebrates—such as the snakes examined here—to traverse the Strait of Gibraltar relatively recently (Carranza et al. 2006). In addition, the Alps (Central Europe) and Pyrenees (between France and Spain) may act as major dispersal barriers due to their cold temperatures, steep terrain, and limited prey availability for H. hippocrepis, which prefers lower elevations with stable temperatures. High-altitude mountain zones often present unsuitable conditions (e.g., frost, low prey density) (Pleguezuelos and Feriche 2002). These findings suggest that climatic conditions and geographic features may have significantly shaped the historical distributions of Hemorrhois species in the region. Notably, physical barriers such as the Dardanelles and Istanbul straits to the north—and the Sahara Desert to the south—could have influenced dispersal and population structure, especially for H. nummifer and H. ravergieri. The Sahara, with its extreme heat, scarce water, and limited prey, likely served as an inhospitable barrier. Likewise, although the Dardanelles and Istanbul straits are narrow, they probably acted as persistent water barriers between Europe and Asia, restricting gene flow in low-dispersal species—particularly given the absence of land bridges during glaciations, unlike the Strait of Gibraltar. Importantly, similar patterns have been documented in other colubrid snakes. For example, the dice snake (Natrix tessellata) exhibits ancestral area reconstruction findings indicating that deserts and mountain corridors in Central Asia and Anatolia significantly shaped lineage distributions (beginning ~3.7 Ma), with Pleistocene glacial refugia emerging as key range modifiers (Salvi et al. 2018; Liz et al. 2021; Romero-Iraola et al. 2023; Jablonski et al. 2024). This supports the idea that both climatic events and geographic barriers have historically constrained colubrid dispersal. Incorporating a similar ancestral-area framework for Hemorrhois could further substantiate these biogeographic inferences. Consequently, the current distribution patterns of Hemorrhois may also result from allopatric speciation influenced by vicariance, wherein physical barriers caused the separation and divergence of populations.

These contrasting responses to climate change may reflect differences in environmental plasticity, which influence each species’ ability to tolerate or adapt to changing conditions. Species occupying broader climatic niches (H. algirus) are more resilient, while those reliant on mesic or montane habitats (H. nummifer, H. ravergieri) show heightened vulnerability. Insular and coastal specialists (H. hippocrepis) are additionally constrained by limited dispersal options. These findings highlight that ecological generalists may fare better under climate change, whereas specialists are at greater risk.

Hemorrhois algirus occupies broad arid and semi-arid habitats in North Africa and is projected to expand its range under future climate scenarios. Its adaptation to harsh environmental conditions, along with ecological flexibility, likely confers resilience to increasing temperatures and habitat changes. In contrast, H. hippocrepis, which inhabits coastal and insular Mediterranean regions, is expected to experience moderate range contraction. Geographic isolation on islands and shorelines, coupled with limited dispersal ability, may make this species more vulnerable to habitat loss and climate-driven shifts.

Hemorrhois nummifer, distributed across mesic habitats in the Levant, shows the highest projected range contraction. Its dependence on relatively humid conditions renders it particularly sensitive to the aridification trends forecasted under future scenarios. Similarly, H. ravergieri, which occupies montane and steppe habitats in Western and Central Asia, is projected to lose a substantial portion of its range—especially in high-altitude regions, which are disproportionately affected by temperature increases.

These observed patterns are consistent with findings in other reptilian taxa. Genera Timon and Lacerta exhibit niche conservatism and gradual phenotypic shifts linked to historical climatic stability (Enriquez‐Urzelai et al. 2022). Similarly, Tarentola mauritanica and genus Anatololacerta demonstrate niche divergence and conservatism depending on environmental pressures (Rato et al. 2015; Şahin et al. 2022). Studies on rat snakes (Zamenis spp.) revealed both niche divergence and conservatism among lineages (Vaissi et al. 2024). Such comparisons reinforce the generality of the mechanisms driving niche evolution and distributional dynamics observed in Hemorrhois.

Given the projections of range contraction for several Hemorrhois species, conservation strategies must prioritize habitat connectivity, preservation of climatic refugia, and management of cross-border habitats. Adaptive conservation planning tailored to each species’ ecological needs will be crucial. Species like H. algirus may benefit from proactive habitat expansion opportunities, whereas H. nummifer and H. ravergieri will require strategies to mitigate habitat fragmentation and loss.

This study also conducted niche analyses to assess the ecological niche overlap among four Hemorrhois species. The results demonstrated a range of niche differentiation—from low to moderate to substantial—reflecting varying degrees of ecological specialization within the genus. The identity and background tests provide insights into niche dynamics, revealing statistical support for niche overlap in only 2 of 8 pairwise comparisons (Table 5; Suppl. materials 7, 8). The comparisons among allopatric Hemorrhois species indicated that their niches are not more similar than expected by chance, yet they are not equivalent (Suppl. material 3). Studies on allopatric Neurergus species in Anatolia (Gül 2019) and the speciation dynamics of endemic lizards in Madagascar (Nunes et al. 2022) indicate that variations in their climatic niches align with the abiotic environmental conditions of the geographical regions occupied by these allopatric species. Species that are adapted to specific climatic or local conditions experience niche differentiation due to the unique adaptations required for survival and reproduction (Nakazato et al. 2010).

The case of niche overlap in parapatric speciation, as illustrated by the comparisons between H. hippocrepis and H. algirus and between H. nummifer and H. ravergieri, requires further discussion due to the restricted distributions of southern Europe and North Africa for H. hippocrepis and H. algirus and the Eastern Mediterranean and Western Asia for H. nummifer and H. hippocrepis. The utilization of the niche is significantly influenced by various ecological interactions. Therefore, incorporating data on diverse selective regimes may aid in analyzing the speciation dynamics of these parapatric species (Gavrilets et al. 2000; Mammola et al. 2018).

These findings suggest that, although certain species have established unique ecological niches, a general pattern of niche conservatism is evident within the Hemorrhois genus. This tendency toward niche conservatism supports the theory that speciation in Hemorrhois may be influenced by the preservation of ancestral ecological features, in line with results reported for other reptile groups (e.g., Morales-Castilla et al. 2011; Pomara et al. 2014; Vaissi et al. 2024).

It is important to interpret these findings with caution, given the inherent limitations of correlative ENMs, which do not incorporate factors such as dispersal constraints, physiological tolerances, or species interactions (Kearney and Porter 2009; Peterson et al. 2015). These limitations underscore the potential value of future research integrating mechanistic or hybrid models.

This study presents a species-level evaluation of ecological niches and projected future distributions for Hemorrhois snakes using correlative ecological niche models based on bioclimatic variables. The projections indicate that H. algirus may experience range expansion under future climate conditions, whereas H. nummifer and H. ravergieri are likely to face substantial habitat reductions. These outcomes should be interpreted within the scope of the modeling framework, as correlative ENMs do not incorporate physiological tolerances, dispersal limitations, or biotic interactions. The results suggest that niche differentiation has occurred among species within the genus, with varied ecological preferences likely shaped by historical isolation and climatic gradients. The evolutionary history of Hemorrhois species appears to have been influenced by past climatic fluctuations and geographic obstacles such as deserts, mountain systems, and sea barriers. Areas identified as climatically stable under both current and future scenarios may represent important climate refugia that could support long-term population persistence. These findings support the prioritization of such regions in conservation planning and emphasize the need to integrate ecological modeling with physiological, genetic, and dispersal-based approaches in future research.

I thank Mr. Hanley Garner for proofreading and Assoc. Prof. Muammer Kurnaz, the respected anonymous reviewers, and the section editor for their valuable suggestions.