Habitat connectivity supports the local abundance of fire salamanders (Salamandra salamandra) but also the spread of Batrachochytrium salamandrivorans

Context: Habitat connectivity can stabilise animal populations by facilitating immigration and genetic exchange, but it increases the risk of infectious diseases being spread by hosts. Chytridiomycosis caused by Batrachochytrium salamandrivorans (Bsal) threatens European salamander diversity. The extent to which the connectivity of populations of fire salamanders (Salamandra salamandra) contributes to the spread of Bsal remains unclear. Objectives: We analysed the impact of habitat connectivity of fire salamanders on the spread of Bsal. Moreover, we show how local salamander abundance is associated with habitat connectivity over a five-year period. Methods: We developed fire salamander habitat suitability models (HSMs) for the Eifel area (Germany), currently considered the core of the range of Bsal in Europe. Habitat models were used to calculate pairwise resistance between salamander occurrences to test whether Bsal presence and salamander abundance were associated with habitat connectivity. Results: Fire salamanders are widely distributed in the Eifel. Solid bedrock and topographic positioning were important predictors of stream suitability as breeding habitats, while deciduous forests and grassland cover determined overall fire salamander habitat suitability along with breeding habitat suitability. Bsal-positive salamander occurrences were better-connected than Bsal-negative or untested occurrences. Nevertheless, fire salamander larvae were more abundant in well-connected sites. Conclusion: The connection of salamander populations by suitable habitat seems to support local salamander abundance while facilitating the spread of Bsal. In situ conservation measures counteracting host species connectivity to interrupt Bsal transmission pathways must be implemented with caution, as they may weaken the demographic advantages of connectivity.