Favourable areas for co‐occurrence of parapatric species: niche conservatism and niche divergence in Iberian tree frogs and midwife toads

Abstract

AbstractAimThe study of areas of sympatry of species with predominantly parapatric distributions can provide valuable insights into their evolutionary history and the factors shaping patterns of species co‐occurrence. This information is key in biogeography, evolutionary biology and conservation planning. In this study we analyse the distributions of two pairs of partially co‐occurring congeneric amphibian species: tree frogs (Hyla molleri and H. meridionalis) and midwife toads (Alytes obstetricans and A. cisternasii).LocationIberian Peninsula (SW Europe).MethodsWe obtained distribution data from the herpetological atlases of Portugal and Spain, consisting of presences and absences on UTM 10 × 10 km grid cells. We built an environmental favourability model for each species, using 24 potential predictor variables representative of physiography, climate and human activity. Variables were selected for each model using both information and significance criteria. Models were evaluated using both calibration and discrimination measures. Models were then combined using fuzzy intersection, and compared using correlation analysis (accounting for spatial autocorrelation), niche comparison metrics and fuzzy similarity indices.ResultsWe found significant dissimilarity between the favourability patterns for A. obstetricans and A. cisternasii, indicating environmental segregation of these two midwife toad species. In tree frogs, we found significant similarity between favourability for H. meridionalis and for its co‐occurrence with H. molleri – that is, sympatry occurs mainly in areas that are favourable for H. meridionalis.Main conclusionsThese results provide clues to understand the evolutionary history of these four species, including the evolution of reproductive isolation, and suggest that conservation efforts for tree frogs may be focused on the areas that are favourable for both species, whereas midwife toads will require specific measures tailored for each species.