Cosmopolitan distribution

Killer whales (orcas) are among the most well-known cosmopolitan species on the planet, as they maintain several different resident and transient (migratory) populations in every major oceanic body on Earth, from the Arctic Circle to Antarctica and every coastal and open-water region in-between.

[1] The caveat "in appropriate habitat" is used to qualify the term "cosmopolitan distribution", excluding in most instances polar regions, extreme altitudes, oceans, deserts, or small, isolated islands.

A species that is apparently cosmopolitan because it occurs in all oceans might in fact occupy only littoral zones, or only particular ranges of depths, or only estuaries, for example.

Other complications of cosmopolitanism on a planet too large for local populations to interbreed routinely with each other include genetic effects such as ring species, such as in the Larus gulls,[9] and the formation of clines such as in Drosophila.

[11] In the modern world, the orca, the blue whale, and the great white shark all have cosmopolitan distribution, extending over most of the Earth's oceans.

Other examples, including species which have gained a cosmopolitan distribution as a result of human assistance, include humans, cats, dogs, the western honey bee, brown rats, the mushroom Amanita muscaria,[12] the foliose lichen Parmelia sulcata, and the mollusc genus Mytilus.

It may result from a broad range of environmental tolerances[14][15] or from rapid dispersal compared to the time needed for speciation.