Hostcommensalism

Hostcommensalism is a biological interaction where one organism, the commensal, benefits from another organism, the host, without the host being significantly harmed or benefited. This relationship is characterized by the commensal deriving resources, shelter, or transport from the host. A common example is the relationship between barnacles and whales. Barnacles attach themselves to the skin of whales, gaining a stable substrate and access to nutrient-rich water as the whale moves. The whale, for its part, experiences minimal to no negative impact from the barnacles, and the barnacles do not provide any discernible advantage.

Another instance can be observed with certain species of mites that live on birds. These mites feed on dead skin cells or accumulated debris on the bird's feathers. The mites obtain a food source and a habitat, while the bird is generally unaffected by their presence. Similarly, many epiphytic plants, such as orchids and bromeliads, grow on the branches of trees. They use the tree for physical support, allowing them to reach sunlight, but they do not absorb nutrients directly from the tree, thus not harming it.

The distinction between hostcommensalism and other symbiotic relationships like mutualism (where both organisms benefit) and parasitism (where one benefits at the expense of the other) lies in the neutral impact on the host. In true hostcommensalism, the host is neither helped nor hurt. However, in practice, it can sometimes be challenging to definitively prove the absence of any subtle effect on the host, and some relationships initially classified as commensalism may later be re-evaluated as having minor benefits or harms for the host.