When something is said to be “endemic,” it means that it is characteristic of an area, and naturally present in the region. Biologists often use this term to describe plants and animals, and it may also be used by epidemiologists. By contrast, the closely-related word “epidemic” means that something is new to the area, and not naturally occurring. “Endemic” comes from the Greek en-, a prefix meaning “in,” and demos, which is used to mean “district” in this sense, although it can also mean “people.”
In the sense of biology, people usually use this term to describe a species that is unique to a particular area. For example, a biologist might say “the Red Breasted Snork is endemic to the Fallacious Islands,” meaning that the Red Breasted Snork is found primarily (or only) in the Fallacious Islands. Endemic plants and animals characterize the region they live in, allowing biologists to identify specific regional zones, and they may be ancient or new residents.
Endemic vegetation and animals are often vulnerable to changes in their natural environment. Unlike organisms with what is known as a “cosmopolitan distribution,” meaning that they are found in many areas, endemic organisms have a limited range. This means that expanded human activities, natural disasters, and climate change can all threaten the well-being of a population. Many endangered organisms are considered endemic, making their preservation even more challenging.
In epidemiology, an endemic disease is a disease which is naturally present in a population, rather than a disease which is introduced. For example, malaria is endemic to many parts of Africa and Southeast Asia, with a fairly steady infection rate among the general population. Sometimes, such diseases can play an active role in evolution; for example, many people of African descent suffer from sickle cell anemia, a disease that is closely linked with malarial regions.
Just because something is naturally present doesn't mean that it is not harmful. Poison ivy, for example, is endemic to the Northeastern regions of North America, and most people regard this plant as extremely irritating. These organisms can also threaten their environment if the environment becomes unbalanced; for example, an endemic deer may experience a population explosion if predators are eliminated, leading to overgrazing and hardship for smaller animals. Often, the balance of native populations of plants and animals is very fragile, and a small disruption can make a huge difference.