Stenobiont

an animal or plant that can live only under relatively constant environmental conditions. Stenobionts tolerate only small fluctuations in temperature, salinity, moisture, or hydrostatic or atmospheric pressure.

For some stenobionts, a single factor, such as the type of food, may be the limiting factor. For example, some South American species of hummingbirds feed on the nectar of flowers of one particular species of plants, and their range is limited by the narrow area of distribution of that plant. The Australian koala feeds only on the leaves of certain species of eucalyptus.

The existence and range of other stenobionts are limited by several factors simultaneously. For example, the fish Pseudo-liparis amblystomopsis is found only at depths of 6–7 km, where it lives in total darkness in water having hydrostatic pressures of 600–700 atm, a constant low temperature, and unchanging salinity.

Stenobionts include many parasites and symbionts that are capable of existing only together with representatives of one certain species; they also include many animals that inhabit the ocean depths, caves, tropical rain forests, alpine regions, and isolated oceanic islands. Stenobionts, owing to limited possibilities of resettlement, have narrow areas of distribution. They contrast with eurybionts, which are capable of surviving wide fluctuations in environmental conditions.