Habitat selection in the fossorial toad Pelobates fuscus insubricus (Amphibia: Pelobatidae): does the soil affect species occurrence?

Abstract

For their rapid and alarming decline, the Italian populations of the Italian spadefoot toad ( Pelobates fuscus insubricus ) are of high conservation importance. In this study we examined habitat use by the spadefoot toads in north-west Italy, where one of the largest remaining populations lives. We used compositional analysis and logistic regression models to elaborate land-use and soil composition in order to determine the habitat preferences of the spadefoot toads. We found that the two main variables predicting the occurrence of spadefoot toads in the study area were the percentages of sandy-loam soil texture and the presence of Entisols. Our results showed that spadefoot toads preferred soils that keep soft and malleable structure: Entisols with sand texture, where sand represents the major component, and mature soils, with a high degree of pedogenesis and a relatively high natural fertility and humidity. Conversely, Pelobates fuscus avoids Inceptisols, probably too hard to be dug by the species. This study demonstrates that, at least in the Italian range, the choice of areas in which to reintroduce P. fuscus , or where re-create favourable habitats for it, must take into account the soil types, which, in intensely cultivated areas, seems to be decisive for the possibility of survival of the species in the medium and long time.