Ecological fitting

Ecological fitting is "the process whereby organisms colonize and persist in novel environments, use novel resources or form novel associations with other species as a result of the suites of traits that they carry at the time they encounter the novel condition".^[2] It can be understood as a situation in which a species' interactions with its biotic and abiotic environment seem to indicate a history of coevolution, when in actuality the relevant traits evolved in response to a different set of biotic and abiotic conditions.^[2]

The simplest form of ecological fitting is resource tracking, in which an organism continues to exploit the same resources, but in a new host or environment. In this framework, the organism occupies a multidimensional operative environment defined by the conditions in which it can persist, similar to the idea of the Hutchinsonian niche.^[3] In this case, a species can colonize new environments (e.g. an area with the same temperature and water regime), form new species interactions (e.g. a parasite infecting a new host), or both, which can lead to the misinterpretation of the relationship as coevolution, although the organism has not evolved and is continuing to exploit the same resources it always has.^[2][4] The more strict definition of ecological fitting requires that a species encounter an environment or host outside of its original operative environment and obtain realized fitness based on traits developed in previous environments that are now co-opted for a new purpose. This strict form of ecological fitting can also be expressed either as colonization of new habitat or the formation of new species interactions.^[2][5]