Download Speciation PP - Blue Valley Schools

Species & Speciation
Morphological Species
Concept
• Species are based on comparison and
differences existing in the physical
characteristic between organism
Morphological Problems
• Two organisms that appear to be different species
may be the same species
• Likewise, organism with similar characteristics may
be place in the same taxonomic groups when they
shouldn’t be (fish and whales)
Evolution & Phylogeny
• After the publication of On the Origin of
Species in 1859 by Charles Darwin
classification took on new meaning.
• Phylogeny is a form of classification
with the goal of representing the
evolutionary relationships and history of
living organisms
Biological Species Concept
• Species are groups of actually or potentially
interbreeding natural populations that are
reproductively isolated from other such
groups. (Mayr, 1942)
• A species is a group of individuals fully fertile,
but barred from interbreeding with other
similar groups by its physiological properties.
(Dobzhansky, 1935)
Speciation
• Process by which:
a) subpopulations of one species diverge
becoming adapted to different
environments and reproductively isolated
b) descendants of a species become adapted
to an environment different than the one
in which it was originally adapted such
that they are qualitatively distinct from
their ancestor
Allopatric Speciation
• Mode of speciation in which the
subpopulations diverge because they
are ‘separated by a geographic barrier’
• Common barriers include water (oceans
to rivers), landforms (canyons and
mountains), climate (glacial periods),
and habitats (deserts, tropics, etc…).
Geographic Separation
• Once populations of a species are geographically
separated the genes that determine their
characteristics can no longer be shared (gene flow
stops).
• If the environment in the different geographic regions
is not the same, then each population may diverge in
their characters through natural selection.
• If these populations are segregated long enough the
populations may become new species.
Reproductive Isolation
• Pre-Zygotic
Mechanisms
1) Temporal
2) Behavioral
3) Mechanical
4) Ecological
5) Gametic Mortality
• Post-Zygotic
Mechanisms
1) Hybrid Inviability
2) Hybrid Sterility
3) Low Fitness Hybrids
Continental Drift & Speciation
• Alfred Wegener
• In the 1930’s suggested
that continents were
(and are currently)
moving relative to each
other and that at some
time in the past they
were joined together
forming a super
continent Pangea
Evidence for Continent Drift
• Continental Geography
• Paleontology and Climate
• Past Glacial Events
Continental Geography
• The eastern coast of
South America and
the western coast of
Africa appear to fit
nicely together like
pieces of a puzzle
Paleontology & Climate
• The ranges of fossil
plant and animal
specimens of similar
age appear to correlate
well across current
continental boundaries
• Tropical fossils exist in
Antarctic sediment
suggesting that this
continent has not
always existed in its
current location
Past Glacial Events
• Mapping of the
extent of glacial rock
remains on the
different continent
suggests particular
connections
between the
continents in the
past
Plate Tectonics
• Continental Drift was not taken seriously by
the geological community until a mechanism
that could explain the movement of the
continents could be developed
• Technical developments associated with
WWII allowed a better understanding of the
Ocean Floor and subsequent development of
the mechanism of Plate Tectonics in the
1970’s
Evidence for Plate Tectonics
• Ruggedness and Age of the Ocean
Floor
• Oceanic Ridges and the process of Sea
Floor Spreading
• Oceanic Trenches and the process of
Mountain Formation, Volcanoes, and
Earthquakes
Ruggedness of the Ocean
Floor
• Through development of sonar and
more extensive use of submarines a
picture of a rugged sea floor emerged
(previously it was thought that the
ocean floor was flat)
• In fact, the Earth’s largest feature is the
Mid-Atlantic Ridge running down the
middle of the Atlantic Ocean
Oceanic Ridges
• At ocean ridges new
crust arises from
magma within the
Earth forcing the
existing plate out
while a new border
for the plate is being
made
Magnetic Striping
• As new magma
cools magnetic
crystals within it line
up with the magnetic
poles of the Earth
• The north end facing
north and the south
end facing south
• As magma in the
Earth’s core circulates
“magnetic or polar
reversals” occur
• Our current north and
south flip such that the
magnetic crystal line up
opposite of what they
would be normally.
Oceanic Trenches
• Where two plates
come together one is
subducted under the
other forming a trench
• Tension builds up in
the plate laying on top
while heat may
generate magma
below (Mts &
Volcanoes)
• Mapping of the
distribution of
Earthquakes across
the globe correlates
well with places
were plates are
coming together
• http://pubs.usgs.gov/publications/text/
Information on Continental Drift and
Plate Tectonics