Archived content - Cicada (17 of 46)
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C. A Fascinating Fauna
8. Distribution of world genera
Cicadas are essentially tropical and subtropical insects, but with few species in desert regions of the world. There are at least 2,500 species in 347 genera world-wide (2008). Most show strong affinities to adjacent countries, as one would expect from insects that do not fly long distances; but a few have relatives in far-flung portions of the globe. Some of the faunal exchanges (such as in the genus Tibicen) appear to date from more than 10 million years ago when world temperatures were much higher than now, because these genera are northern, across the Bering Strait dividing North America from Asia. Some other genera appear to be southern, spread across what is now vast expanses of ocean and polar ice cap (as in the flightless leafhopper family Myerslopiidae, known only from New Zealand and Chile). Such ancient faunas date back more than 100 million years, when the southern continents were connected into one gigantic, tropical land mass. If verified, such widespread genera would give clear evidence of the antiquity of these cicada genera.
The modern cicada genera are mostly confined to one of nine biogeographic regions of the world. Most cicadas are from southeast Asia (area 6 on map). These represent 850 species in 115 genera. A distant second is Africa south of the Sahara (area 8 on map) with 400 species in 70 genera. South America (area 3 on map) presently has 300 recorded species in 62 genera. The fauna of Australia (area 5 on map) is actively researched and presently stands at 243 species in 45 genera, much more than the 145 species in 20 genera for all of northern Eurasia and north Africa (area 9 on map). But the most concentrated cicada fauna anywhere in the world is in the South Pacific oceanic islands of New Guinea southeast to New Zealand (area 4 on map), with 300 species in 41 genera. Other interesting island faunas are found in the Caribbean (area 2 on map) with 21 endemic species in eight genera (of these three genera are wholly endemic), but more particularly in Madagascar (area 7 on map) and the Mascarene, Comoro, and Seychelles islands to the east and north with 45 species in 24 genera. Of these, a single species Macrotristria madegassa Boulard occurs on Madagascar while the rest of the genus is otherwise restricted to Australia. The highly isolated island of Socotra off the tip of the Horn of Africa has one cicada Abroma socotrana (Distant) apparently more closely related to the Madagascarene fauna than to that of Africa, although the island lies ten times as far from Madagascar as from Africa. This island is truly a Noah's Ark, containing frankincense, myrrh and many other strange plants and animals of seemingly antediluvian origins.
In North America (area 1 on map) including Mexico there are 230 species in 16 genera. Most of these cicadas are confined to the hottest parts of North America. In Canada, there are at least 20 native species. The best areas for these northern cicadas are southern Ontario and the arid intermontane valleys of British Columbia. As might be expected for such a tropical group, most Canadian cicadas are representatives of species widespread in more southerly regions. There is a single exception: the well-named Okanagana canadensis is common across much of southern Canada, and enters the USA only from Maine to New Hampshire, and in local areas of New York, Pennsylvania, Michigan, and the Black Hills of South Dakota. In Canada, it ranges northwest to the Mackenzie River, and has been taken as far north as 63° latitude. This is the most northerly site for any cicada in the world.
"Annual" cicadas are good fliers and disperse widely. Thus, Okanagana species in British Columbia are often the same as ones in California. Three species of Okanagana and one of Tibicen (canicularis) have deeply invaded parts of Canada that were covered by glaciers 10,000 years ago, and a specimen of Okanagana occidentalis (Walker) has been taken from a snow-covered plateau at 1800 m elevation on Vancouver Island.
Periodical cicadas (Magicicada species), on the other hand, disperse scarcely at all. Their adult life is very short and seemingly confined to mating and laying eggs in the vicinity of their emergence. This is probably an adaptation to maintaining heavy, but localized, populations to protect individuals from predation. As a result, many of the "broods" of periodical cicadas cover an area less than 500 km across and some extend across less than 100 km. Only one brood (Brood XIV) of the 17-year locust Magicicada septendecim and only one brood (Brood XIX) of all three 13-year locusts are widespread across the eastern US.
It is therefore surprising to find that many Canadian cicadas, including the 17-year locust, show disjunct distributions. Magicicada septendecim and Tibicen chloromerus used to live in the Ottawa Valley on the Québec-Ontario border well removed from their American populations. Okanagana occidentalis is found in the southern half of British Columbia, Alberta and Saskatchewan to 52° latitude, but also inhabits the Peace River district on the Alberta-BC border north of 55° latitude. Okanagana canadensis ranges continuously as far as the Peace River district, but has an apparently isolated population on the Mackenzie River between Great Slave Lake and the Mackenzie Mountains. Okanagana ornata inhabits the Lilooet vicinity of British Columbia; its next closest population is in Oregon. Perhaps most surprising of all, Okanagana vanduzeei (a common Californian species ranging north to Mt. Ranier in southern Washington) enters Canada in the southernmost portions of the arid Okanagan and Kootenay Valleys, yet has been taken also in the forests at Shushwap Lakes 200 km further north.
These strange patterns apparently reflect historical patterns rather than patterns of choice. Such isolated northern populations were almost certainly part of much more extensive distributions, probably when world temperatures were higher than today (6000-8000 years ago). Similarly, Okanagana canadensis survives on the Cypress Hills of southern Alberta long after postglacial warming drove its parental populations into the northern part of the province.
There are very few regional faunas of the 2,500 species Footnote 1 of cicadas published outside North America, and of those, the only monographs recently compiled included 202 species from Australia Footnote 2, 56 from mainland China Footnote 3 and 51 additional species from Taiwan Footnote 4, 36 from Nepal Footnote 5, 33 from Japan Footnote 6, 26 from Korea Footnote 7, 24 from Fiji, Samoa and Tonga islands Footnote 8, 9 from Micronesia Footnote 9, and 7 from the Russian Far East Footnote 10. Other notable, but badly outdated works include 149 species from India Footnote 11, 47 species from Mexico and Central America Footnote 12, 27 from South Africa Footnote 13 and 13 from New Zealand Footnote 14. The European type-species Footnote 15 of some of the oldest genera were illustrated only once.
The list of the genera provided here indicates the part of the world where the species are found. The numbering scheme follows the regional distribution map. Groups occurring in more than one region marked with an asterisk (*). The smallest faunas are in North America including Mexico (Section 8A), the Caribbean Islands (Section 8B) and northern Eurasia including North Africa (Section 8C). Major faunas are found in Central and South America (Section 8D), Pacific Ocean islands (Section 8E), Australia and Tasmania (Section 8F), Southeast Asia (Section 8G), Madagascar and its offshore islands (Section 8H), and Sub-Saharan Africa (Section 8I). The only species belonging to the genus Sapantanga (Prasiini, an Old World tropical tribe) is from an unknown locality.
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