Dual roles of terrestrial isopods in seed predation and seed dispersal in Phacellanthus tubiflorus (Orobancheaceae)

Terrestrial isopods are known to play significant roles in litter decomposition and seed predation. The present study examines the function of terrestrial isopods, particularly Armadillidium vulgare and Armadillidium nasatum, in the seed dispersal of a nonphotosynthetic plant, Phacellanthus tubiflorus. These isopods were observed ingesting seeds in the natural habitat of P. tubiflorus in Hyogo Prefecture, Japan. Contrary to the prevailing belief that invertebrates do not serve as effective internal seed dispersers, our analysis demonstrated that some seeds ingested by A. vulgare and A. nasatum were excreted whole, with viability rates comparable to those of seeds directly sourced from fruits. This indicates that these isopods could act not only as seed predators but also as seed dispersers. The research highlights the importance of further exploration into the ecological contributions of isopods and other invertebrates as seed dispersers.