Ontogenetic niche shift (abbreviated ONS)[1] is an ecological phenomenon where an organism (usually an animal) changes its diet or habitat during its ontogeny (development).[2] During the ontogenetic niche shifting an ecological niche of an individual changes its breadth and position.[3] The best known representatives of taxa that exhibit some kind of the ontogenetic niche shift are fish (e.g. migration of so-called diadromous fish between saltwater and freshwater for purpose of breeding[2]), insects (e.g. metamorphosis between different life stages; such as larva, pupa and imago[2]) and amphibians (e.g. metamorphosis from tadpole to adult frog[2]).[4] A niche shift is thought to be determined genetically, while also being irreversible.[5] Important aspect of the ONS is the fact, that individuals of different stages of a population (e.g. of various age or size) utilize different kind of resources and habitats.[6][7] The term was introduced in a 1984 paper by biologists Earl E. Werner and James F. Gilliam.[1][8]