Host specificity in parasitic mistletoes (Loranthaceae) in New Zealand

1. We quantify the degree of host specificity for the five extant New Zeala nd loranthaceous mistletoes (Alepis flavida, Ileostylus micranthus, Peraxil la colensoi, Peraxilla tetrapetala and Tupeia antarctica). 2. Host specificity is highest for A. flavida, P. colensoi and P, tetrapeta la which primarily parasitize species of Nothofagus, and lowest for 2: anta rctica and especially I. micranthus which parasitize a wide range of host s pecies. 3. These patterns of host specificity support the suggestion that relative host abundance is a key factor determining the degree of host specializatio n in mistletoes (resource fragmentation hypothesis). While evolutionary his tory may be important in the specificity of the mistletoe-host relationship in some situations, our data suggest that for New Zealand mistletoes evolu tionary history simply reflects the temporal component of relative host abu ndance. 4. We conclude that it is the stability of host availability through time a nd space which is the dominant factor determining host specificity patterns .