Regional γ Diversity of Diatoms in Mediterranean and Alpine Temporary Ponds

Temporary ponds, characterized by periodic or intermittent hydroperiods, are globally widespread in all the biogeographical regions and host peculiar biotic communities. Here we investigated shifts in diatom community assemblages across two contrasting biogeographical regions in Italy, the Mediterranean and the Alpine. The study focused on 24 temporary ponds, with 12 ponds sampled at Castelporziano (CP) and 12 at Campo Imperatore (GS). Our results highlighted that γ diversity varied significantly between the two study sites, indicating a notably greater species richness in GS compared to CP. In GS, functional richness values were generally higher, whereas no significant differences were detected for functional distance and functional divergence. Species composition differed significantly between CP and GS indicating that the two sites host distinct communities, with species turnover (0.904) which contributed most to total beta diversity (0.926), while nestedness (0.021) was negligible. CP communities were characterized by pronounced functional clustering in specific sites while GS exhibited both clustering and slight overdispersion. However, although GS communities occupy slightly larger trait space, both regions shared most functional strategies, reflecting substantial redundancy in functional traits across the two environments. Overall, diatom communities in the GS were characterized by higher frequencies of small, mobile, low-profile, and mucilaginous-tube taxa, whereas CP ponds displayed relatively higher representation of larger or motile forms. Although our study is a starting point, large-scale analyses of diatom communities are crucial, as climate change may rapidly and irreversibly alter taxonomic and functional diversity, profoundly affecting the ecology of these temporary habitats and surrounding landscapes.