Endemism is one of the most important concepts in biology. It is an important term with regards to conservation efforts.
What’s In a Name?
The use of the term ‘endemic’ was criticized by David Sharp, a biogeographer. The word had originally arisen as an antonym of the word ‘epidemic’, in terms of pathogens that affected humans. Sharp proposed the use of the word ‘precinctive’ instead of ‘endemic’ in the ecological sense. Though his reasoning and criticism was accurate, his terminology never caught on, and the word ‘endemic’ remained in use.
Endemism is the state of an organism being confined to a particular geographic area. The geographical area in question can be variable, ranging from a single mountain to a whole country. The organism in question could be any plant, animal, or microbe species. This is in direct contrast to the term ‘cosmopolitan’, which―in the ecological sense―signifies a widespread, possibly global population.
A species being endemic is often an indicator of it being endangered, although it is also possible that the species has always been endemic to a particular region, and has never been found elsewhere. For example, the Galápagos tortoise has always been endemic to Galápagos, and it would be stupid to claim that this means it is endangered.
The term ‘endemic’ is often confused with ‘indigenous’. The latter simply means that the species in question originated there, and makes no commentary on its present habitat. A species indigenous to a region may be found elsewhere, and is thus, not endemic to the region of its origin.
Let’s delve deeper into what this term stands for.
Types of Endemism
Endemic species can be classified into two categories: paleoendemic and neoendemic.
Species that used to be found in numerous areas but are now confined to a particular location are called paleoendemic.
The reasons for the change can be numerous and varied. Human encroachment and the consequent habitat loss is the most common reason for most species becoming extirpated (extinct in terms of a particular region), if not completely extinct. Other causes include pollution, which is another example of human intervention, or changes in the local environment. The entry of new predators, often brought about by humans, can wreak havoc with local ecosystems, thus eliminating particular plants or animals from the region.
The Asiatic lion is the perfect example of a paleoendemic species. Once found from the Middle East to the Sundarbans in Bengal (the two kings of the jungle actually coexisted in the Gangetic plains for a long time), it was actively hunted down in much of its range.
The British rule in India declared wild animals as vermin, and placed rewards on their hunts. The poor animal was also hunted indiscriminately in the rest of its range. This, in addition to other, more passive forms of human intervention, such as habitat loss due to growing urbanization and agriculture, contributed to it becoming extirpated in the huge majority of its range, and it is now only found in the scrublands of western India (the state of Gujarat, to be particular). Though African lions thrive in Africa, the Asiatic lion is now endemic. These terms are equally applicable to plant species.
Redwood trees, once found in abundance all over the U.S., but now largely limited to California, are an example of paleoendemic plants.
A misuse of this term would be to quote the cheetah as an example of paleoendemism. It was eliminated from the vast majority of its habitat in Asia, and now survives primarily in Africa, but extending the limits of endemism to the second largest continent in the world would render the term absolutely meaningless. Similarly, the Bengal tiger can be said to be endemic to the Indian Subcontinent, but since it has numerous populations in various areas of the region, it is not considered so. It may be endangered, but that doesn’t necessitate it being endemic. It would also be erroneous to consider the Siberian tiger as a paleoendemic species; even though it only has one contiguous region of existence (like the Asiatic lion), it is spread across national borders, and also encompasses various types of forests, making it difficult to pigeonhole the species in political or ecological terms.
A species that has never been found outside its place of origin is known as neoendemic.
This occurs mainly because of geographical isolation of the species from the rest of the global ecosphere. Thus, such secluded regions of the world, for instance Australia, Madagascar, and the Galápagos Islands, are home to the widest varieties of neoendemic species.
Due to the geographic isolation and consequent independence from the evolutionary processes going on elsewhere, the organisms in these regions may evolve to look nothing like any other species in the world, and only a deep study into their evolutionary history reveals their link with other, more widespread species.
The perfect example of the latter phenomenon is Australia, which, cut off from the rest of the world, gave rise to animals such as kangaroos, koalas, and wallabies.
These animals look nothing like any found on other continents, since much of their phenotypic (appearance-related) evolution and speciation occurred after plate tectonics separated Australia from the rest of the world.
Apart from the aforementioned Aussie examples, other examples of endemic species that have always been confined to their place of origin are the Galápagos giant tortoise, the marine iguana―also found on Galápagos, and the only lizard in the world to lead a marine lifestyle―and the lemurs on Madagascar. Both of these, being islands, are conducive to the rise of endemic species.
Regions such as Madagascar, Australia, the forests of New Caledonia, the pine-oak forests in Mexico, and the Luzon rainforests in the Philippines are hotspots for neoendemic species, due to their geographic isolation and independent evolution.