Abstract
Some small invertebrates use other larger sessile organisms as hosts that have defenses against predators and other natural enemies. Patterns of host use are quite different between marine and terrestrial systems. The difference is expected to indicate differences of mechanisms in the evolution of host use between those systems. In this review, major similarities and dissimilarities in evolutional and ecological factors of host use are discussed. Requirements for host as a food source have long been considered as an important factor of the evolution of host use, such as chemical coevolution theory. On the other hand, tri-trophic interaction involving impacts by predators has recently been recognized as ecological factors of host use range. Additionally, host range is affected by availability of host and dispersal ability. Differences between marine and terrestrial host use mechanisms are found in the all factors above, particularly in the availability of food source and taxonomical characteristics.
