Practice question

Epiphytes use tree trunks and branches as physical support while obtaining water and mineral nutrients from rain, dust, atmospheric inputs, and accumulated debris rather than from the host’s vascular tissues. The epiphyte benefits by reaching brighter canopy conditions and gaining a substrate for attachment, whereas the tree is commonly assumed to experience no significant effect. This (+, 0) relationship is therefore classified as commensalism, more specifically inquilinism in broad treatments of organisms using another’s living space. It differs from parasitism because a typical epiphyte does not penetrate the tree to withdraw resources, as mistletoes and other haustorial parasites do. Mutualism would require a demonstrated benefit to the tree, and amensalism would require harm without benefit to the epiphyte’s host. Heavy epiphyte loads can sometimes break branches, shade leaves, or alter water relations, so the interaction is not universally neutral. The classification describes the usual net effect in the simplified example and highlights that ecological interactions can shift with abundance and environmental context.