Glossary: I

IUCN categories

International Union for Conservation of Nature and Natural Resources (IUCN) maintains a Redlist of species that are threatened internationally. For more information, see:

The IUCN categories and criteria are: EXTINCT (EX) - A taxon is Extinct when there is no reasonable doubt that the last individual has died. EXTINCT IN THE WILD (EW) - A taxon is Extinct in the wild when it is known only to survive in cultivation, in captivity or as a naturalised population (or populations) well outside the past range. A taxon is presumed extinct in the wild when exhaustive surveys in known and/or expected habitat, at appropriate times (diurnal, seasonal, annual), throughout its historic range have failed to record an individual. Surveys should be over a time frame appropriate to the taxon's life cycle and life form. CRITICALLY ENDANGERED (CR) - A taxon is Critically Endangered when it is facing an extremely high risk of extinction in the wild in the immediate future, as defined by any of the criteria (A to E) as described below. ENDANGERED (EN) - A taxon is Endangered when it is not Critically Endangered but is facing a very high risk of extinction in the wild in the near future, as defined by any of the criteria (A to E) as described below. VULNERABLE (VU) - A taxon is Vulnerable when it is not Critically Endangered or Endangered but is facing a high risk of extinction in the wild in the medium-term future LOWER RISK (LR) - A taxon is Lower Risk when it has been evaluated, does not satisfy the criteria for any of the categories Critically Endangered, Endangered or Vulnerable. Taxa included in the Lower Risk category can be separated into three subcategories:

Conservation Dependent (cd). Taxa which are the focus of a continuing taxon-specific or habitat-specific conservation programme targeted towards the taxon in question, the cessation of which would result in the taxon qualifying for one of the threatened categories above within a period of five years. Near Threatened (nt). Taxa which do not qualify for Conservation Dependent, but which are close to qualifying for Vulnerable. Least Concern (lc). Taxa which do not qualify for Conservation Dependent or Near Threatened. DATA DEFICIENT (DD) A taxon is Data Deficient when there is inadequate information to make a direct, or indirect, assessment of its risk of extinction based on its distribution and/or population status. A taxon in this category may be well studied, and its biology well known, but appropriate data on abundance and/or distribution is lacking. Data Deficient is therefore not a category of threat or Lower Risk. Listing of taxa in this category indicates that more information is required and acknowledges the possibility that future research will show that threatened classification is appropriate. It is important to make positive use of whatever data are available. In many cases great care should be exercised in choosing between DD and threatened status. If the range of a taxon is suspected to be relatively circumscribed, if a considerable period of time has elapsed since the last record of the taxon, threatened status may well be justified. NOT EVALUATED (NE) A taxon is Not Evaluated when it is has not yet been assessed against the criteria.

ice cap

a large body of land ice that forms when large snowfalls and low temperatures encourage the transformation of snow into ice, often persisting throughout many years. Ice caps are typically less than 50,000 km2 in area but are large enough to submerge the underlying topography.

ice shelf

thick, floating layers of ice formed when glaciers or ice sheets flow onto coastlines and over bodies of water


The study of fishes, which includes bony fishes (Osteichthyes), cartilaginous fishes (Chondrichthyes) and jawless fishes (Agnatha). It is a branch of zoology and, with the extraordinary geographic and taxonomic diversity of fishes, covers a broad range of disciplines.


with parts that overlap each other, such as scales.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.


Native to a particular country or area.

indirect development

development from egg to adult form occurs through intermediate phases in which the animals are very different, morphologically, ecologically, and etc. from the adult. Any development which involves a larval stage, as in insects and many amphibians, is a form of indirect development.

induced ovulation

ovulation is stimulated by the act of copulation (does not occur spontaneously)


(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.


An animal that eats mainly insects or spiders.


those areas of an echinoderms body that lie between the ambulacra (areas with tube feet)

internal fertilization

fertilization takes place within the female's body


referring to the space between cells, atoms or molecules, or soil particles. Interstitial cells are those cells that exist in the connective tissues between other tissues and structures. This term is most often used to refer to the insterstitial cells of the testes that lie between the seminiferous tubules.

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.


referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

introduced range

any areas in which an animal now occurs outside of its native range.


An animal which lacks a backbone (such as insects, spiders and crustaceans).

island endemic

animals that live only on an island or set of islands.


A line on a map that connects places with equal rainfall.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).