Endemism

Endemism describes a state where a species is found only in one specific geographic location.

This location can be quite large, like a country or a continent. It can also be very small, such as a single island or a specific sinkhole. For example, the orange-breasted sunbird lives exclusively in South Africa.

The bicolored frog is found only in the Western Ghats of India.

In Arizona, Montezuma Well contains at least five species found nowhere else on Earth. This concept is vital for conservation biology. Scientists use it to measure biodiversity in specific areas. It also helps them evaluate how much risk a species faces from extinction.

Endemism occurs through several different biological and geological processes. One major process is allopatric speciation, also known as geographic speciation. This happens when two populations of the same species become physically separated.

A mountain range or an ocean might act as a barrier between them. Once separated, these groups evolve differently over time. Eventually, they become entirely different species through reproductive isolation. This is why remote islands like Hawaii or the Galápagos Islands have high rates of endemism.

In these isolated places, organisms have little chance to receive new genes from outside groups. Other species might become endemic by using specific areas as refuges. During climate changes like ice ages, some regions remain stable. Species stay in these stable areas while dying out elsewhere.

Scientists use specialized terms to categorize species based on their evolutionary history. One important distinction is between paleoendemics and neoendemics. A paleoendemic is a species that was once widespread but is now restricted to a small area. The ginkgo tree is a famous example of a paleoendemic species. In contrast, a neoendemic is a relatively new species. These species have recently evolved and have not yet spread beyond their original range.

There are also even more specific categories. Schizoendemics arise from a wider species that becomes reproductively isolated but keeps the same chromosome count. Apoendemics are polyploids, meaning they have extra sets of chromosomes. Patroendemics have a lower chromosome count than their related polyploid ancestors. Mikio Ono also introduced the term aneuendemics in 1991 for species with unusual chromosome numbers.

Researchers also look at how species are distributed across a landscape. Some scientists use the term phylogenetic endemism to measure uniqueness. This method weights species based on how distant they are from their living relatives on the evolutionary tree. This helps capture how much unique biological history is present in an area. Some species are called holoendemics if they have stayed in a restricted area for a very long time. Others might be called pseudoendemics if they possibly evolved from a recent mutation. These different categories help experts decide how to allocate resources for protecting biodiversity hotspots.

The history of the word "endemic" provides interesting context. The term comes from the Neo-Latin and Greek word endēmos, which means "native." It is formed from the Greek words for "in" and "the people."

When it first entered the English language via French, it described diseases. It referred to diseases that stayed at a constant level in a country. In 1872, Charles Darwin began using the term in a biological sense. He used it to describe species restricted to specific locations. In 1900, David Sharp coined the term "precinctive" for insects in Hawaii. He chose this word because he felt "endemic" was too closely associated with sickness.

Endemism is the opposite of having a cosmopolitan distribution. A cosmopolitan species has a global or very widespread range. It is a common mistake to think all endemic species are rare. Some endemic species can actually be quite common within their specific home. However, they are still considered endemic because they do not exist anywhere else. Even microorganisms were once thought to be cosmopolitan. The hypothesis "everything is everywhere" suggests that organisms smaller than 2 mm are found wherever habitats support them. This theory suggests that small organisms might not follow the same rules as larger animals.

Certain environments are much more likely to produce endemic species. One such environment involves serpentine soils.

These soils have low fertility and act like "edaphic islands." They are found in places like the Balkan Peninsula, South Africa, and parts of California. Because the soil is so different, plants must adapt to it. This creates high rates of endemism. Caves also create unique conditions for species. Animals that live only in caves are called troglobites. These specialized environments provide the isolation necessary for new, unique species to develop.