Host Specificity, Dispersion and Persistence Through Drought of Two Arid Zone Mistletoes

Abstract

In the Whyalla region of South Australia, the loranthaceous mistletoe Amyema quandang (Lindl.) Tiegh. is virtually host-specific to Acacia papyrocarpa Benth., whereas Lysiana exocarpi (Behr.) Tiegh. (Loranthaceae) frequently parasitises 12 species in seven families, and less commonly infects seven other species. Amyema quandang is contagiously distributed with respect to Acacia papyrocarpa, larger trees supporting higher numbers of mistletoes. Host branch diameter (HBD) is assumed to index the age of individual mistletoes of Amyema quandang since seedlings only establish on thin host branches. The age distribution of A. quandang is skewed towards young plants since almost half the population para- sitises host branches Ͱ4 15 mm in diameter, within the range infected by seedlings. HBD is correlated with canopy size and the number of haustorial branches. The proportion of reproductive mistletoes increases with HBD and hyperparasitic L. exocarpi are confined to older plants of A. quandang with HBD Ͱ5 31 mm. As a result of the severe drought in 1982, 25% of large plants of A. quandang lost one or two main haustorial branches and suffered reductions in canopy volume, but only 4% died; by contrast, 31% of large L. exocarpi died and a further 19% lost most of their foliage. In the A. quandang population as a whole, recruitment balanced mortality (19%) over a 40 month period, but in the L. exocarpi popu- lation recruitment compensated for only half the mortality. None of the xerophytic shrub and tree hosts of either mistletoe died.