Competition, contacts, and other factors restricting niches of parasitic helminths.

Mechanisms that restrict the intraintestinal niches of helminths (as indicated by the sites they occupy) can be favored by several selection pressures. These selection pressures act on different scales, and may interact to have different effects in different circumstances. In addition, the end results may not reflect responses to the niche, but be a by-product of other processes, such as the immune responses of the host.