Endemic is a term used to indicate that a plant or animal taxon is restricted, in its geographical range, to a particular region.

It has been recognised since the time of Wallace and Darwin that islands are particularly rich in endemic species. The study of island enedemism has been very important to the understanding of the processes of evolution (e.g. Darwin’s finches).

Endemism may arise by several mechanisms but underlying them all is the principle of geographical ISOLATION.

• A small population with limited genetic diversity is isolated. After many generations genetic drift leads to the formation of a distinct species or subspecies.
   
• A population arriving on an island adapts to fill different ecological niches. Many generations of natural selection result in the formation of several distinct species.
   
• A species that was originally widespread in its distribution suffers extinction over most of its range. The island becomes a “refugia”. This is certainly the origin of several species of Macaronesian endemic “laurels” which were widespread in the Mediterranean region in the Tertiary period.

Canarina canariensis : a Canary-endemic climber

There are many different “levels” of endemism and the term will often be qualified with the region and the taxonomic level. For example the blackbirds to be seen in Tenerife are a Macaronesion endemic subspecies of the familiar European bird. At the other end of the scale there are two genera of Harvestmen (like long-legged spiders) that are endemic to The Canary Islands and several plant species are endemic to the Caldera of Tenerife.