Endemic --a taxon with a distribution restricted to a particular geographic area
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Endemic--a taxon with a distribution restricted to a
particular geographic area
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Levels of endemism
• The rodent family Heteromyidae is endemic to the Nearctic and Neotropical regions
• The genus Dipodomys, the kangaroos rats, is restricted to North America and Mexico
• The species Dipodomys stephensi is endemic to southern California.
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• The hoatzin is the only species in the avian family Opisthocomidae--found only in northern South America
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• Devil's Hole pupfish population is 38 individuals (as of April 2006) which live in one pool of 60 square meters in the Mohave Desert of Nevada
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Endemics may be classified by place of origin
• autochthonous endemics exist today where they originated; silversword subspecies of Hawaii
• allochthonous endemics exist today in an area apart from where they originated. Ex. tuatara
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Biogeographic relict--a surviving taxon from a group that was once widespread and/or
diverse • evolutionary (or taxonomic) relict--the only
survivor of a once more-diverse taxonomic group (ex. tuatara)
• climatic relict--species whose geographic ranges have constricted due to recent climatic changes (ex. musk ox)
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Often organisms are both evolutionary and climatic--
coelacanth
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Some groups are not endemic and are considered cosmopolitan--widely distributed
throughout the world • Homo sapiens
• Falco peregrinus
• Daphnia genus (water fleas)
• Vespertilionidae family
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Cosmopolitan mammal families
• Soricids (shrews)• Sciurids (squirrels and chipmunks)• Cricetids (hamsters and lemmings)• Cervids (deer)• Ursids• Felids• Mustelids (weasels and badgers)• Bovids (cows)
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• Murids (rats)
• Canids
• Leporids (rabbits)
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51 mammal families are endemic to only one biogeographic region
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• Cosmopolitan groups are likely to be:
• Eurytopic—ecologically tolerant, with efficient dispersal mechanisms
• Endemics with very restricted ranges are likely to be:
• Stenotopic—specific preferences and limited ecological tolerance
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Rapoport made further distinctions
• Endemics--species found in only one biogeographic region
• Characteristic species--species found in two biogeographic regions
• Semicosmopolitan species--species found in three or four biogeographic regions
• Cosmopolitan species--found in five or more biogeographic regions
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Areas with high degrees of endemism are typically isolated
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Cosmopolitan species are often better dispersers and have
broader ecological tolerances than endemic species
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Lake Baikal
• Largest freshwater lake in world
• Deepest lake
• May be oldest lake
• Lake is in a rift valley
• Huge percentage of endemic forms (of 1550 and 1085 animals and plants in lake, 1000 are endemic)
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Krakatau—island located between Sumatra and Java, was destroyed August 27, 1883, by
several volcanic eruptions
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Opportunity to watch the assemblage of a
community from nothing • May 1884—one tiny spider, spinning a web• Fall 1884-a few shoots of grass, probably two
species• 1886—15 species of grasses and shrubs• 1897—49 species of plants• 1928—nearly 300 species of plants• 1984-85—600 invertebrate species, nine bat
species, two rat species, nine reptiles species, 30 land bird species
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Physiognomy of the island has also changed
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Dispersal--the movement of organisms away
from their point of origin
• Organisms balance need to avoid competition/mating with relatives with need to stay in environment they are adapted to
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Dispersal infrequently results in range changes but these are important events
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1. Jump dispersal-long-distance dispersal over a relatively short time period
• Easier for some organisms than others• Great element of chance in which species
reach an area
Three types of dispersal events that may causerange expansion
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2. Diffusion—individuals spreading out from the margins of a species’ range over several
generationsInvasion and establishment
Very fast range expansion
Slowing of range expansion as barriers are reached
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Cattle egrets in New World
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3. Secular migration
• Range expansion over hundreds of generations
• Evolution of species
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Mechanisms of dispersal
• Active—flying, swimming
• Passive—phoresy, wind, water currents, rafting
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Dispersal routes—classified on their likelihood of being traversed
1. Corridors—Bering landbridge
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Dispersal routes
2. Filters—dry lowlands between Rockies and Sierra Madre in Mexico
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Dispersal routes
3. Sweepstakes—colonization of oceanic islands
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Other types of movements
• Seasonal migrations
• Irruptions