Aim: To assess if the parapatry of the three viper species present in the Iberian Peninsula is mainly caused by environmental conditions, historical events, interspecific competition among them, or a combination of these factors.

Location: The Iberian Peninsula

Taxon: Vipera aspis, V. latastei, and V. seoanei.

Methods: We applied the concept of favourability of occurrence to produce commensurate distribution units unaffected by the prevalence of different species in the Iberian Peninsula. We compared the favourability of each species individually with the favourability of occurrence of more than one species co-occurring in their overlapping ranges, and identified the areas in which sympatric coexistence, environmental segregation, and competitive exclusion are predicted to occur.

Results: The main driver of the parapatric pattern was competitive exclusion, which was mediated by gradual changes in the environmental conditions favouring each species. The para-Mediterranean V. aspis presented fragmented favourable areas outside its range that seemed to be unoccupied due to competitive exclusion by the other vipers. The Mediterranean V. latastei appeared to be limited by competition with the other viper species and by the environment in northwestern Iberia. V. seoanei prevented the other two species becoming established in the north-western quarter of the Iberian Peninsula due to its better adaption to the humid conditions in this region. Some areas of sustainable coexistence were detected, mainly in the upper reaches of the River Ebro.

Main conclusions: Each species is better adapted to particular conditions. However, the existence of ecotones forces them to occur sympatrically and compete for resources. The parapatric pattern is a result of the evolutionary history of the species and of strong competitive interactions between them, which form ‘competitive-exclusion barriers’. However, these barriers are environmentally dependent, so changes in the environment could rapidly affect the limits of the species distribution.

The Iberian distributions of the three vipers were obtained from the distribution atlases of Spain (Pleguezuelos, Márquez, & Lizana, 2002) and Portugal (Loureiro et al. 2008). This information was digitized and supplemented with new digitized data for Spain provided by the Asociación Herpetológica Española (Spanish Herpetological Association), recently published data (Martínez-Freiría et al., 2015, 2020), and unpublished data that have recently been collected. Species distribution data were latticed using UTM 10×10-km grid cells as operational geographic units.

References:

Asociación Herpetológica Española: http://siare.herpetologica.es/

Loureiro, A., Ferrand de Almeida, N., Carretero, M. A., & Paulo, O. S. (2008). Atlas dos Anfíbios e Répteis de Portugal. Lisboa: Instituto da Conservação da Natureza e da Biodiversidade.

Martínez-Freiría, F., Velo-Antón, G., & Brito, J. C. (2015). Trapped by climate: Interglacial refuge and recent population expansion in the endemic Iberian adder  Vipera seoanei . Diversity and Distributions, 21(3), 331–344. https://doi.org/10.1111/ddi.12265

Martínez-Freiría, F., Freitas, I., Zuffi, M. A. L., Golay, P., Ursenbacher, S., & Velo-Antón, G. (2020). Climatic refugia boosted allopatric diversification in Western Mediterranean vipers. Journal of Biogeography, 47, 1698–1713. https://doi.org/10.1111/jbi.13861

Pleguezuelos, J. M., Márquez, R., & Lizana, M. (2002). Atlas y Libro Rojo de los Anfibios y Reptiles de España. Madrid: Dirección General de Conservación de la Naturaleza-Asociación Herpetologica Española.

These data are the presence/absence matrix used to modelled the three species distribution in a UTM 10x10 km grid cell shapefile (also included). Vipera_spp.csv contains the Iberian vipers distribution (in a CSV format using ";" as separator) and the rest of the documents utm10PI.xxx (.CPG, .dbf, .prj, .sbn, .sbx, . shp, .shp.xml, .shx) are the archives to link the distribution with the Iberian Peninsula shapefile . It is neccessary a GIS software to use this dataset.

CODES:

IBCUADR_ID: Identificator of the cell in the UTM grid cell of the Iberian Peninsula, used to link the species presence/absence matrix to the Iberian shapefile.

V_aspis: cells with presence (1) or absences (0) of Vipera aspis.

V_latastei: cells with presence (1) or absences (0) of Vipera latastei.

V_seoanei: cells with presence (1) or absences (0) of Vipera seoanei.