Macroenvironmental factors as ultimate determinants of distribution of common toad and natterjack toad in the south of Spain

We have analysed the relations between the distribution areas of Bufo bufo and Bufo calamita in the south of the Iberian Peninsula. In order to characterise the localities where the species were found, we used 24 environmental variables, and we tested their influence on the distribution of both species by nonparametric methods. By means of logistic regression we calculated the odds of finding one or other species in a locality. The environmental parameters that increase the probability of presence of each species and of both species together are related with the climatic stability and with the climatic subregions. Bufo bufo is more likely to be found in areas where the climate is more predictable, probably because in these areas it may exert its competitive superiority over B. calamita. In zones with very low climatic stability B. calamita is more likely to be found than B. bufo, probably because B. bufo lacks the ability to adapt to unpredictable conditions. In areas with intermediate climatic predictability B. bufo is present, but it would be prevented from removing B. calamita, and so the odds of finding each species are equilibrated. In these areas there would be a balance between the superior competitiveness of B. bufo and the higher adaptability of B. calamita. With the same logistic equation we characterise the typical habitats of each species, and also the environments shared by both species.