Mistletoe host diversity decreases with elevation in a temperate rainforest of southern Chile: implications for frugivory

Abstract

Mistletoes are aerial parasitic plants that constitute key elements of the forest ecosystem, representing an important source of fleshy fruits for many frugivorous species. Additionally, mistletoes rely on their host plants to obtain water and nutrients, exhibiting a wide range of variability in the number of plant species they can parasitize. Those host plants can also provide fleshy fruits for frugivores. However, vegetation composition changes with elevation, which reduces host availability and diversity for mistletoes. We assessed how mistletoe–host interactions changed along an altitudinal gradient in a rainforest of southern Chile, focusing on two Loranthaceae species: Tristerix corymbosus, a hemiparasitic mistletoe capable of parasitizing ~ 30 species, and Desmaria mutabilis, which only parasitizes Nothofagus trees. We found that T. corymbosus is the only mistletoe present in lowland forests (0–400 m), and D. mutabilis is the only mistletoe present above 1265 m a.s.l., up to the forest treeline. Both species coexist in sympatry between 400 and 1265 m. We found a host plant species turnover along elevation, which reduces fleshy fruit diversity and abundance as forest composition changes from evergreen to deciduous trees, explaining why T. corymbosus is gradually replaced by D. mutabilis. As fleshy-fruited species become less abundant and diverse in mountain forests, the relative importance of mistletoe fruits increases with elevation. Above 1265 m, D. mutabilis represents the major source of fleshy fruits for frugivores. Therefore, plant–plant interactions along the elevation gradient increase the relative importance of mistletoes as fleshy-fruited species become less diverse and abundant, making them of paramount importance for sustaining frugivory interactions in highland forests.