Spatial Interactions between the Hemiparasitic Angiosperm Rhinanthus minor and its Host are Species-Specific

1. Effects of organisms that obtain resources from others (e.g. herbivores) can depend on the location of resource removal with respect to their 'prey'. We investigated whether such an effect can be seen in hemiparasitic plant-host plant interactions. 2. We conducted rhizotron studies of the interactions between Rhinanthus minor and individuals of two common host species, Festuca rubra and Festuca ovina. Parasites were grown at two distances from the host, and growth characteristics of hosts and parasites measured over time. 3. Parasites close to their host suffered reduced survival as a result of shading. Without shading these parasites attached earlier, produced more haustoria, grew larger and had a greater fecundity than those planted further away. This effect was significant for parasites infecting the fast-growing F. rubra, but not for parasites infecting the less vigorous F. ovina. Effect of parasite position on host biomass was significant only for F. rubra, which showed a greater reduction when infected by more proximal parasites. 4. Differences in the response of hosts to infection, and parasite growth, suggest the effect of the position of R. minor is host-species specific.