endemic --a taxon with a distribution restricted to a particular geographic area

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

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

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

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