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Endemic--a taxon with a distribution restricted to a particular geographic area 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. • The hoatzin is the only species in the avian family Opisthocomidae--found only in northern South America • 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 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 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) Often organisms are both evolutionary and climatic-coelacanth Some groups are not endemic and are considered cosmopolitan--widely distributed throughout the world • Homo sapiens • Falco peregrinus • Daphnia genus (water fleas) • Vespertilionidae family Cosmopolitan mammal families • • • • • • • • Soricids (shrews) Sciurids (squirrels and chipmunks) Cricetids (hamsters and lemmings) Cervids (deer) Ursids Felids Mustelids (weasels and badgers) Bovids (cows) • Murids (rats) • Canids • Leporids (rabbits) 51 mammal families are endemic to only one biogeographic region • 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 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 Areas with high degrees of endemism are typically isolated Cosmopolitan species are often better dispersers and have broader ecological tolerances than endemic species 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) Krakatau—island located between Sumatra and Java, was destroyed August 27, 1883, by several volcanic eruptions 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 Physiognomy of the island has also changed 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 Dispersal infrequently results in range changes but these are important events Three types of dispersal events that may cause range expansion 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 2. Diffusion—individuals spreading out from the margins of a species’ range over several generations Invasion and establishment Very fast range expansion Slowing of range expansion as barriers are reached Cattle egrets in New World 3. Secular migration • Range expansion over hundreds of generations • Evolution of species Mechanisms of dispersal • Active—flying, swimming • Passive—phoresy, wind, water currents, rafting Dispersal routes—classified on their likelihood of being traversed 1. Corridors—Bering landbridge Dispersal routes 2. Filters—dry lowlands between Rockies and Sierra Madre in Mexico Dispersal routes 3. Sweepstakes—colonization of oceanic islands Other types of movements • Seasonal migrations • Irruptions