Animal distribution refers to how animal species are spread across different geographical regions. The distribution of animals is influenced by factors such as climate, habitat availability, competition, predation, geological changes, and evolutionary history.Animal distribution can be classified into several types based on their geographical spread and limitations.
Cosmopolitan Distribution: Species with a cosmopolitan distribution are found almost worldwide, across multiple continents and environmental conditions. These species have a wide ecological tolerance and can adapt to diverse habitats.
Examples
• Humans (Homo sapiens) – Found across all continents.
• Pigeons (Columba livia) – Distributed in cities and rural areas worldwide.
• Rats (Rattus species) – Present in almost all human settlements.
• Orcas (Orcinus orca) – Found in oceans worldwide, from polar to tropical waters.
Factors Contributing to Cosmopolitanism
• High adaptability to different climates and habitats.
• Ability to migrate or disperse over long distances.
• Human activities (such as trade and transportation) spreading species unintentionally.
2. Discontinuous Distribution: Species with discontinuous (disjunct) distribution are found in two or more geographically separate areas, with no continuous populations in between. This occurs due to geographic barriers, climate changes, or historical migration patterns.
Examples
• Alligator species – American alligator (Alligator mississippiensis) in the U.S. and Chinese alligator (Alligator sinensis) in China, but no populations in between.
• Lungfishes – Found in South America, Africa, and Australia, but not in other continents.
• Tapirs – Distributed in South America and Southeast Asia, but absent in the intervening regions.
Causes of Discontinuous Distribution
• Continental Drift – Species that were once widespread became isolated as continents moved.
• Climate Change – Ice ages and environmental shifts fragmented populations.
• Human Activities – Habitat destruction or introduction of species to new areas.
3. Isolated Distribution: An isolated distribution occurs when a species is found in a single, restricted location, often separated from similar species. These species have very limited movement or dispersal abilities.
Examples
• Komodo dragon (Varanus komodoensis) – Found only on a few Indonesian islands.
• Lemurs – Restricted to Madagascar.
• Kiwi birds (Apteryx spp.) – Found only in New Zealand.
Causes of Isolated Distribution: Geographic barriers such as mountains, deserts, or water bodies prevent movement.Evolution in isolation, leading to endemism (species unique to one location).Low dispersal ability of the species.
4. Bipolar Distribution: Species with bipolar distribution are found in both the Northern and Southern Hemispheres but are absent in the tropical regions between them.
Examples
• Arctic and Antarctic terns (Sterna paradisaea) – Found in polar regions but not in the tropics.
• Certain fish species (e.g., Gadidae family) – Found in cold-water regions of both hemispheres.
• Mosses and lichens – Some species are found in Arctic and Antarctic regions but absent in equatorial zones.
Causes of Bipolar Distribution
• Climate Preferences – Some species are adapted to cold conditions and cannot survive in warm equatorial regions.
• Past Glaciation – During ice ages, species expanded across a larger area, but as temperatures warmed, populations were pushed to the poles.
• Ocean Currents and Winds – Assist in the transport of some marine and airborne species between poles.
5. Endemic Distribution: Species with endemic distribution are found only in a specific geographic area and nowhere else in the world. These species often evolve in isolated conditions, leading to unique adaptations.
Examples
• Kangaroos (Macropus spp.) – Endemic to Australia.
• Galápagos tortoise (Chelonoidis nigra) – Found only on the Galápagos Islands.
• Baobab trees (Adansonia grandidieri) – Native only to Madagascar.
• Axolotl (Ambystoma mexicanum) – Found only in certain lakes in Mexico.
Types of Endemic
1. Neoendemic Species – Recently evolved species found in a specific area (e.g., cichlid fish in African lakes).
2. Paleoendemic Species – Ancient species that once had a wider distribution but are now restricted (e.g., the coelacanth fish).
Causes of Endemic
• Geographical Isolation – Islands, mountains, or deserts prevent species migration.
• Climate and Habitat Specialization – Some species adapt to specific conditions not found elsewhere.
• Evolutionary Factors – Unique evolutionary paths due to lack of gene flow from outside populations.
The distribution of animal species is shaped by environmental, geographical, evolutionary, and human-influenced factors. Understanding these different types of distributions helps scientists in conservation efforts, biodiversity studies, and evolutionary research.