Ontogenetic niche shift

The ontogenetic niche shift is thought to be determined genetically, while also being irreversible. One of the studies suggests that differences in the ONS across species could be (at least to some degree) explained by the diversity of traits and functional roles of a species. As a consequence, differences in ontogenetic niche shifting are thought to follow some general patterns. == Importance ==

For communities of the same species into distinct life-history stages, can affect the food web of a community. It is thought that almost every organism shows some kind of ontogenetic niche shift. The ONS, which is responsible for causing a noticeable phenotypic variation among individuals of the same species, plays an important role in structuring communities and influencing their inside dynamics. A stage structure of a population can result in various stages interacting with different representatives of a community, or even with individuals of other communities, thus having a distinct ecological role from other life-history stages of the same population. Theoretical models, where communities are stage-structured, propose the ontogenetic niche shifting of studied organisms is influencing the whole community (especially its resilience and disturbance responses). For population The most apparent consequence of the ontogenetic niche shift is a reduction of competition between different stages of the same population, because it causes individuals of different age or size to not have to compete for food, materials, and/or other habitat resources. Different stages of the same population also have different trophic effects on food web of a community. A division of a population on distinct life-history stages is useful and evident, when there is a lack of resources for one stage (for example when juveniles do not get enough resources for themselves). In that case, a lacking stage will have a higher mortality rate. The ONS is of great importance for the survival of populations. Researchers noticed that many species exhibit an ontogenetic niche shift at different times, and in a lot of examples, the ONS occurred as a response to various abiotic and biotic environmental factors. It is thought that the ontogenetic niche shift could be an adaptive response to changing conditions in an individual's habitat. Authors of the life history theory predicted that organisms can affect the time of their ontogenetic niche shifting. While individuals living in favorable conditions would usually delay their ONS to a successive ecological niche, organisms living in a niche with poor conditions typically advance to a further niche. Understanding the ontogenetic niche shifting in different species and its impact on the whole community is important when studying biodiversity and ecosystem functioning. It is thought to be useful when dealing with populations threatened by anthropogenic disturbances and environmental changes. == Representative taxa ==

. On the picture above are shown a pupa and an imago of Rhopalomyia solidaginis.|289x289px '') is an anadromous fish species that exhibits a drastic habitat niche shift. ''. Juveniles of megatheropods proposedly occupied the mesocarnivoran ecological niche. Even though the occurrence of ontogenetic niche shifting is thought to be widely distributed, the best known representative taxa with extensively studied ONS are insects and a few groups of vertebrates, especially fish and amphibians, where individuals often change their habitat as well as a lot of other aspects of their niche during the development. The less pronounced ontogenetic niche shifting can be seen in many other taxa, where their habitat stays the same. Usually the ONS in those species is evident when looking at the resources being used by organisms of the same species, but which are of various ages or size classes (for example, a change in their diet). Nutritional niches and their shifting during an ontogeny can be accurately measured by using a stable isotopic signature of animals. Such a method has been used in studying the ONS in gastropods, such as field slugs. Tadpoles exhibit many differences that distinguish them from the adult stage of a frog; most species' tadpoles are aquatic, they usually possess external gills, and primarily feed on plant material (though there are some exceptions that consume dead animal flesh or a mixed diet). Another well studied example of the ONS occurs in fish that exhibit diadromous behaviour. Diadromous fish species drastically change their habitat when they set out on a journey from sea (saltwater) to rivers (freshwater), and vice versa. The ontogenetic niche shift is a concept widely studied in paleontology and paleozoology. Large non-avian dinosaurs are known to have had exhibited one of the most intensive forms of ontogenetic niche shifting, as they were hatched from an egg and had to experience very significant size shifts during their ontogeny. One of the problems, connected with understanding Mesozoic dinosaur fauna, was a lack of so-called mesocarnivores. It is predicted the ontogenetic niche shift is an answer, because carnivorous dinosaurs started out as small hatchlings and progressed towards adult size, while occupying different successive niches and limiting trophic species diversity. Juvenile individuals of megatheropods are thought to occupy the mesocarnivore niche. Plants The ontogenetic niche shift is primarily studied in animals, but there are some studies that deal with the ONS in plants. One of the ONSes studied in plants is the changing of a regeneration niche. Authors of the paper noticed that during the ontogeny, the regeneration niche of Acer opalus (the Italian maple) had shrunk. It is thought such an ontogenetic niche shift was mainly a consequence of herbivory, the depth of the litter layer, and presence of other plants (especially adult trees and shrubs). == See also ==