Host preference of the hemiparasite Struthanthus flexicaulis (Loranthaceae) in ironstone outcrop plant communities, southeast Brazil

Abstract

Struthanthus flexicaulis is a hemiparasite abundant in ironstone outcrops in southeast Brazil. We evaluated its host preference among species of the plant community, taking into account the abundance and foliage cover of the hosts. The importance of each species in the community and the mortality caused by the parasite were assessed based on a quantitative survey in 10 strips measuring 1m x 50m. The 10,290 individuals belonged to 42 species. Only 15 had a relative abundance in the plant community greater than 1%, of which 12 showed vestiges of parasitism. More than 80% of deaths in the community were associated with parasitism. Non-infected individuals had significantly less mortality rates (7%) than those infected (83%) (χ²= 1102.4, df = 1, p < 0.001). The observed infestation was different from the expected both regarding relative host abundance (χ²= 714.2, df = 11, p<0.001) and foliage cover (χ²= 209.2, df = 11, p<0.001). Struthanthus flexicaulis preferred Mimosa calodendron, a legume attractive to avian seed dispersers. The interaction is maintained and intensified not only by the birds, who deposit innumerous seeds on the hosts branches, but also very likely by the ability of M. calodendron to fix nitrogen, thereby enhancing the mistletoe’s development.