Transcript Geography of Diversification

• Endemism – taxa occuring in one
geographic place and nowhere else
Cosmopolitan – taxa that widely distributed
throughout the world
• Disjunction – closely related taxa that occur
in widely separated areas with no
individuals in region between
• Note use of “taxa” – part of perspective of
hierarchical scale applied in examining
distribution
Heteromyidae – kangaroo rats
and mice. Family endemic to New
World.
Genus Didymops broad
distribution but Microdipodops
endemic to Great Basin
Two species of Didymops
(kangaroo rats). D. ordii covers
most of genus range.
D. ingens endemic to San Joaquin
Valley
Hotspots of Endemism
• Australia, southern Africa, Madagascar,
New Zealand, New Caledonia
• Other islands
• Distinctive habitats (e.g., Devil’s Hole
pupfish – Fig. 10.3)
• Not so hotspots
• Europe, North America, southern Atlantic
Ocean
Cosmopolitanism
• No truly cosmopolitan species although
some come close
• Key is ability to disperse and adaptability
• Peregrine falcon
• Bat Family Vespertilionidae
• Aquatic – Daphnia, water milfoil
(Myriophyllum), duckweed (Lemna sp.)
• Very few genera found in all oceans
Relict Endemics
• Taxonomic relicts – sole survivor of once
diverse group
• Biogeographic relict – species with a narrow
geographic range for a group once diverse
Paleozoic
Mesozoic
Terrestrial Regions and Provinces
• Distinctive biogeographic areas are
arranged hierarchically
• Regions – largest of biogeographic areas;
continental in scope; 10 regions
• Subregions – smaller scale within regions;
distinctive within regions
• Provinces – distinct areas with subregions
• District – smallest scale; distinct within
provinces
Australian Region
• Two subregions
– Eyrean – central 2/3 of
continent;
arid/semiarid; no mtn.
ranges or internal
barriers
– Torresian – wetter
fringes
• Torresian – 3 provinces
– Torresian – tropical belt
with plants and animals
with affinities for New
Guinea and some SE
Asia; many from
Pleistocene land bridge
– Bassian – animals and
plants adapted to cool,
mesic climate; relict
species dating to
Gondwanaland
– Westralia – many
endemics; shares taxa
with South Africa
Australian Region
Plants – more regions but fits well with divisions of animal
regions
Provinces of NA
freshwater fishes;
#s are: families,
species, %
endemic species
Provinces
correspond to
major basins
Are Boundaries Clear Separations
• Many biogeographic lines originally drawn
to mark limits of species
• Are significant
– Wallace’s line – follows Sunda Shelf (exposed
during Pleistocene)
– Isthmus of Panama – last area formed for
Nearctic-Neotropical land bridge
• Obvious overlap due to dispersal
• Still see that most species do not venture far
past
Lines are reversed
Disjunctions
• Closely related organisms living in widely
separated areas
• Three likely scenarios leading to
disjunctions
• Tectonic – once on a joined land mass (e.g.,
Gondwanaland
• Extinction of species in the area between
current ranges
• Disjunction by dispersal
Large flightless birds originating on Gondwanaland
Same genus found in California and Europe
Disjunction by dispersal
Pupfish of SW US are another example
Maintenance of Distinct Biota
• Plenty of examples of biotic exchanges
• How have biogeographic regions been able
to maintain distinct biota?
• Limitations of dispersal
• Ecological barriers – species already present
• Physiological barriers – needed to cross
unfavorable habitats to get to favorable
habitats in another region
Biotic Exchange
• Introduction of non-natives shows it is
possible
• Other examples already discussed
• Fossil evidence limited – example
Gondwanaland biota of India; all Eurasian;
were they pushed to extinction or
adaptation?
Great American Interchange
• Mammalian exchange provides excellent
example
• Mammals evolved ~220 mya; Pangaea still
intact
• Taxa dispersed across land mass before
began to break up
• K-T mass extinction lead to rapid
diversification
• S. America separated ~160 mya, largely
isolated until 3.5 mya
Great American Interchange
• Was imbalance in exchange
• 10% of N. Amer. species of South American
ancestry
• Almost 50% of S. American species of N.
American ancestry
• Filtering of some sort
Possible Reasons Northern Species Held Fast
• Better migraters
– Only three extent S. Amer. sp. in N. Amer.
– Several survive in tropical forests of southern
Mexico
• Better survivors and speciators
– Many N. American species diversified in S.
Amer.; example - camel
• Better competitors
– Radiation of genera and species from N. Amer.
Ancestors shows strong evidence