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

Juana Romero and Raimundo RealRomero J and Real R 1996 Macroenvironmental factors as ultimate determinantsof distribution of common toad and natterjack toad in the south of SpainEcography 19 305-312We have analysed the relations between the distribution areas of Bulo hulo and Bufocalanma in the south of the Iberian Peninsula In order to characterise the localitieswhere the species were found we used 24 environmental variables and we testedtheir influence on the distribution of both species by nonparametnc methods Bvmeans of logistic regression we calculated the odds of hnding one or other species ina locality The environmental parameters that increase the probability ol presence ofeach species and of both species together are related with the climatic stability andwith the climatic subregions Bufo biifo is more likely to be found in areas where theclimate is more predictable probably because in these areas it may exert itscompetitive superiority over B calainita In zones with very low climatic stability Bcalatmta is more likely to be found than B hufo probably because B hufo lacks theability to adapt to unpredictable conditions In areas with intermediate climaticpredictability B hufo is present, but it would be prevented from removing Bcalatmta and so the odds of finding each species are equilibrated ln these areas therewould be a balance between the supenor competitiveness of B hufo and the higheradaptability of B calatmta With the same logistic equation we characterise thetypical habitats of each species and also the environments shared by both speciesJ Romero and R Real, Dept of Ammal Biology Fac of Sciences Inn of MalagaE-29071 Malaga Spam