The influence of population source and species pools on propagule supply in an experimental grassland

Background/Question/Methods

The diversity of plant communities is the result of local and regional processes acting in conjunction on propagule supply during community assembly.  The effect of variation within population source and among local species pools on regeneration dynamics is poorly understood.  The objective of our study was to investigate the similarity of local and regional propagules to the aboveground community and whether population source of dominant grasses and species pools influence propagule supply.  We postulated that species richness of emerged ramets would reflect local sources and be most similar to the aboveground community, whereas the seed rain would be least similar to the aboveground community and reflect regional sources.  We also hypothesized that abundance, species richness, and diversity of emerged ramets, emerged seedlings, and seed rain would be differentially affected by dominant grass population source and local species pools.  We quantified similarity and diversity (richness) of local and regional propagules of emerged ramets and seedlings, seed bank, and seed rain to the aboveground community in prairie established with two dominant grass population sources (cultivar vs. non-cultivar) and three unique pools of subordinate species.  

Results/Conclusions

Based on Sørensen’s similarity index for 2010, species richness of the seed rain was most similar to that of the aboveground community for local and regional propagules.  In 2011, species richness of the seed rain was most similar to that of the aboveground ground community for local sources, but was more reflective of emerged seedlings for regional sources.  Abundance of emerged ramets exhibited an interaction between population source and species pool resulting in differences among emerged ramets in prairie restored with cultivar grasses but not local ecotypes of the grasses among species pools (P = 0.017).  Abundance of emerged seedlings was higher within the non-cultivar dominant grass treatment (P = 0.004) and varied among the species pools (P < 0.001).  Species richness of emerged seedlings was also higher within the non-cultivar dominant grass treatment (P = 0.034), whereas richness of the seed rain was lower within the cultivar source (P < 0.001).  Prairie seeded with the cultivar source of dominant grasses exhibited more ramets, which likely manipulated resources to result in lower abundance and fewer species of emerged seedlings relative to prairie restored with local ecotypes.  These findings demonstrate that population source may act as a filter during community assembly.