Myrmecophily is considered a form of indirect plant defense against herbivory, though ants often provide other services in addition to protection. Some ants provide hygienic services to keep leaf surfaces clean and deter disease, and defense against fungal pathogens has also been demonstrated. Ants commonly prune epiphytes, vines, and parasitic plants from their host plant, and they sometimes thin the shoots of neighboring plants, as well. In doing so, ants reduce plant-plant competition for space, light, nutrients, and water. Finally, current work focusing on ants' role in nutrient supplementation for plants has shown that in many ant-plant relationships, nutrient flow is bidirectional. One study has estimated that while 80% of the carbon in the bodies of "Azteca" spp. workers is supplied by the host tree ("Cecropia" spp.), 90% of the "Cecropia" tree's nitrogen was supplied by ant debris carried to the tree as a result of external foraging. In light of these services, myrmecophily has been considered advantageous in ensuring a plant's survival and ecological success, although the costs to the plant of providing for the ants can sufficiently high to offsets benefits.