Conservation implications of host use for rare parasitic plants

Both the study and management of parasites have historically focused on the control and even elimination, of parasite populations. In contrast, rare parasitic plants represent an uncommon challenge for conservation biologists and managers who often wish to bolster populations of these parasites. Although parasitic plants may suffer any of the maladies known to affect small populations of plants, parasitic plants may also be limited by the additional suite of factors of host availability, host quality, host resistance to parasitism, and parasite preference. We describe studies that have examined parasite growth and reproductive performance with a variety of host species to argue that consideration of the host needs of parasitic plants is necessary for successful conservation of rare species using this mode of resource acquisition. Although it is clear that parasite performance varies greatly with the availability of different host species little is known about the host requirements of most parasitic plants, and the relative importance of particular host species may not immediately be obvious. Further, because published host lists generally do not distinguish minor hosts from those that sustain parasite populations such lists may be misleading for conservation efforts. We argue that successful conservation and restoration of parasitic plants may necessitate the management of thoughtfully selected host populations.