Inbiogeography, acosmopolitan distribution is therange of ataxon that extends across most or all of the surface of the Earth, in appropriatehabitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and environmental conditions, though this is not always so. Killer whales (orcas) are among the most well-known cosmopolitan species on the planet, as they maintain several differentresident andtransient populations in every major oceanic body on Earth, from theArctic Circle toAntarctica and every coastal and open-water region in-between. Such a taxon (usually aspecies) is said to have acosmopolitan distribution, or exhibitcosmopolitanism, as a species; another example, therock dove (commonly referred to as a 'pigeon'), in addition to having beenbred domestically for centuries, now occurs in most urban areas around the world.
The extreme opposite of a cosmopolitan species is anendemic (native) species, or one found only in a single geographical location. Endemism usually results in organisms with specific adaptations to one particular climate or region, and the species would likely face challenges if placed in a different environment. There are far more examples of endemic species than cosmopolitan species; one example being thesnow leopard, a species found only inCentral Asian mountain ranges, an environment to which the cats have adapted over millions of years.[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.[2] For example, thehousefly is highly cosmopolitan, yet is neither oceanic nor polar in its distribution.[3]
The termpandemism also is in use, but not all authors are consistent in the sense in which they use the term; some speak of pandemism mainly in referring to diseases andpandemics, and some as a term intermediate between endemism and cosmopolitanism, in effect regarding pandemism assubcosmopolitanism. This means near cosmopolitanism, but with major gaps in thedistribution, say, complete absence from Australia.[4][5] Terminology varies, and there is some debate whether the true opposite of endemism is pandemism or cosmopolitanism.[6]
A related concept inbiogeography is that ofoceanic cosmopolitanism and endemism. Rather than allow ubiquitous travel, theWorld Ocean is complicated by physical obstacles such as temperature gradients.[7] These prevent migration of tropical species between the Atlantic and Indian/Pacific oceans.[8] Conversely, the Northern marine regions andSouthern Ocean are separated by thetropics, too warm for many species to traverse.
Another aspect of cosmopolitanism is that of ecological limitations. A species that is apparently cosmopolitan because it occurs in all oceans might in fact occupy onlylittoral zones, or only particular ranges of depths, or onlyestuaries, for example. Analogously,terrestrial species might be present only in forests, or mountainous regions, or sandyarid regions or the like. Such distributions might be patchy, or extended, but narrow. Factors of such a nature are taken widely for granted, so they seldom are mentioned explicitly in mentioning cosmopolitan distributions.
Cosmopolitanism of a particular species or variety should not be confused with cosmopolitanism of higher taxa. For example, the familyMyrmeleontidae is cosmopolitan in the sense that every continent except Antarctica is home to some indigenous species within the Myrmeleontidae, but nonetheless no one species, nor even genus, of the Myrmeleontidae is cosmopolitan. Conversely, partly as a result of human introduction of unnaturalapiculture to the New World,Apis mellifera probably is the only cosmopolitan member of its family; the rest of the familyApidae have modest distributions.
Even where a cosmopolitan population is recognised as a single species, such as indeedApis mellifera, there generally will be variation between regional sub-populations. Such variation commonly is at the level ofsubspecies,varieties ormorphs, whereas some variation is too slight or inconsistent for formal recognition.
For an example of subspecific variation, consider theAfrican honey bee (Apis mellifera scutellata)—best known for being hybridized with various European subspecies of thewestern honey bee to create the so-called "killer bee"—and theCape honey bee, which is the subspeciesApis mellifera capensis; both of them are in the same cosmopolitan speciesApis mellifera, but their ranges barely overlap.
Other cosmopolitan species, such as thehouse sparrow andosprey, present similar examples, but in yet other species there are less familiar complications: some migratory birds such as theArctic tern occur from the Arctic to theSouthern Ocean, but at any one season of the year they are likely to be largely in passage or concentrated at only one end of the range. Also, some such species breed only at one end of the range. Seen purely as an aspect of cosmopolitanism, such distributions could be seen as temporal, seasonal variations.
Other complications of cosmopolitanism on a planet too large for local populations to interbreed routinely with each other include genetic effects such asring species, such as in theLarus gulls,[9] and the formation ofclines such as inDrosophila.[10]
Cosmopolitan distributions can be observed both in extinct and extant species. For example,Lystrosaurus was cosmopolitan in the Early Triassic after thePermian-Triassic extinction event.[11]
In the modern world, theorca, theblue whale, and thegreat white shark all have cosmopolitan distribution, extending over most of the Earth'soceans. The waspCopidosoma floridanum is another example, as it is found around the world. Other examples, including species which have gained a cosmopolitan distribution as a result of human assistance, includehumans,cats,dogs, thewestern honey bee,brown rats, themushroomAmanita muscaria,[12] the folioselichenParmelia sulcata, and themollusc genusMytilus.[13] The term can also apply to some diseases. It may result from a broad range of environmental tolerances[14][15] or from rapiddispersal compared to the time needed forspeciation.[16] Cosmopolitan species of birds include themallard andperegrine falcon.
The dictionary definition ofcosmopolitan at Wiktionary
