Dispersal in Time- the role of seed banks in patchy population dynamics of an aquatic plant

Progressive habitat fragmentation increasingly threatens plant species with narrow habitat requirements. While local environmental conditions largely define population growth rates and recruitment success at the patch level, dispersal is critical for population viability at the landscape scale. However, identifying dynamics of plant metapopulations in habitat networks is often confounded by the uncertainty of the extent of dormant population compartments. Here, we combined a landscape-scale assessment of an amphiphytic species’ population structure with detailed measurements of dispersal complexity in time to reveal past and present dispersal events and putative shifts in functional connectivity. Using 13 polymorphic microsatellite markers, we analyzed the genetic structure of extant Oenanthe aquatica populations and their soil seed banks in a kettle hole system to uncover hidden connectivity among subpopulations in both time and space. Considerable spatial genetic structure and isolation-by-distance (IBD) patterns suggest limited gene flow between population sites. In contrast, patch level measures of isolation and habitat availability showed minor effects on genetic diversity levels. Low differentiation along the time gradient highlights the superior role of temporal over spatial dispersal. Though some instances of recent colonisation were observed, our results suggest the actual genetic structure of kettle hole populations to result from multiple local seed rain events. Our findings uncover stepping-stone dynamics with source-sink effects based primarily on dispersal from long-term-persistent local populations to adjacent populations. Overall, spatio-temporal connectivity patterns provide support for metapopulation dynamics in our studied system and highlight the importance of persistent seed banks as long-term source of genetic diversity.