Tourism affects microbial assemblages in show caves.

Anthropogenic disturbance on natural ecosystems is growing in frequency and magnitude affecting all ecosystems components. Understanding the response of different types of biocoenosis to human disturbance is urgently needed and it can be achieved by adopting a metacommunity framework. With the aid of advanced molecular techniques, we investigated sediment communities of Fungi, Bacteria and Archaea in four Italian show caves, aiming to disentangle the effects induced by tourism on their diversity and to highlight changes in the driving forces that shape their community composition. We modelled diversity measures against proxies of tourism pressure. With this approach we demonstrate that the cave tourism has a direct effect on the community of Bacteria and an indirect influence on Fungi and Archaea. By analysing the main driving forces influencing the community composition of the three microbial groups, we highlighted that stochastic factors override dispersal-related processes and environmental selection in show caves compared to undisturbed areas. Thanks to this approach, we provide new perspectives on the dynamics of microbial communities under human disturbance suggesting that a proper understanding of the underlying selective mechanisms requires a comprehensive and multi-taxonomic approach.