An exotic species, otherwise known as alien species, is an organism that is not indigenous to an area. It could have been transported there from its natural habitat by humans, human activities or other agents. This act of transportation alters the ecological balance that has been established due to the environmental and climatic barriers limiting the geographical range of the particular species. Examples of environmental barriers are mainly climatic in nature, and in specific terms, oceans, rivers and deserts are some of the various boundaries that restrict the movement of species.
These barriers have long been transcended since the pre-industrial era, when humans migrated with cultivated plants and domesticated animals to establish new farming locations and settlements. For example, land mammals of North America, in nature, are incapable of crossing the Pacific Ocean to get to Hawaii. However, the Polynesians who first reached and inhabited the archipelago introduced a rat species, the domestic dog, the domestic pig, as well as cultivated plants to the area.
Exotic species do not always establish a self-sustaining wild population in the area which they are introduced. This is due to an unsuitable environment in which they cannot naturally thrive, or simply an adverse environmental or climatic condition which renders their survival impossible. However, some of these nonindigenous species do establish self-sustaining wild populations and are hence naturalized. Previously domesticated animals such as the domestic dog that has naturalized are known as feral animals.
Many exotic species can go on to cause harm to the ecosystem, with populations expanding dramatically at the expense of indigenous, or native, species. These undesirable alien organisms are aptly termed as invasive species.