Practice question

Inquilinism is a form of commensalism in which one species uses another organism, its body, or its constructed space as shelter or a place to live without significantly harming it. A bird nesting in a tree gains support and a protected site for eggs and young, while the tree is ordinarily treated as unaffected. Phoresy would require the tree to transport the bird, and metabiosis usually involves using a structure or environmental modification after its producer has finished with it, such as a hermit crab occupying an abandoned snail shell. Parasitism would require a net cost to the tree caused by exploitation. The classification is an idealization: a heavy nest may break a branch, birds may fertilize soil with droppings, or they may remove herbivores, creating negative or positive effects. For a typical nest, however, these effects are negligible relative to the bird’s clear benefit. The key mechanism is use of living space rather than extraction of nutrients or reciprocal exchange of services.