Transcript Endemism and dispers..

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
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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
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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