Connectivity loss in experimental pond networks leads to biodiversity loss in microbial communities
Habitat loss and related connectivity loss are one of the major threats leading to biodiversity decline. Although their negative effects have long been emphasized, most experimental studies have focused on terrestrial biomes or a single group of larger aquatic organisms and our knowledge of aquatic microorganisms in this respect is primarily based on empirical studies. To provide experimental proof for the negative effect of connectivity loss independent of habitat loss on microbial biodiversity, we created six metacommunities in an outdoor setup, each consisting of five mesocosms (artificial ponds). For the first four weeks, we carried out weekly dispersal (water exchange) within each metacommunity, then it was stopped in three metacommunities to simulate connectivity loss (habitat fragmentation), while it continued in the three control metacommunities for a further 12 weeks. The effects of fragmentation on local and regional level biodiversity of aquatic prokaryotes and unicellular microeukaryotes were investigated by applying 16S and 18S gene amplicon sequencing. According to our results, prokaryotes were not affected by the treatment. In microeukaryotes, however, significantly lower alpha (aS - ASV richness, aSPIE - effective number of ASVs of PIE) and gamma richness (?S), and evenness were found in the case of fragmented metacommunities by the end of the experiment. While we found a significant negative effect of fragmentation on local diversity measures both in the case of autotrophic (aS, aSPIE) and heterotrophic microeukaryotes (aS, evenness), its impact on regional diversity (?S) was more pronounced in the case of autotrophs. Our study provided one of the first explicit experimental evidence supporting that habitat fragmentation via connectivity loss independent of any changes of local environmental conditions or habitat amount reduction within a pond-network can lead to a significant loss of microbial biodiversity both at local and regional scales.