Transcript ENVI 30 Environmental Issues

Time of Day
Time of Year
Flowers
Snails
Courtship
Sounds/Songs
Bullfrog x
Leopard Frog
Plants
Broadcast Spawners
Horse (2n=64) x
Donkey (2n=62) 
Mule (2n=63)
Fig. 24.3
I.
Reproductive Isolation
C.
Limitations of Biological Species Concept
•
Mayr’s definition emphasizes reproductive
isolation; may not work in all situations
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Ex: Classifying fossil organisms
Ex: Species that reproduce asexually [prokaryotes,
some protists, fungi, plants (e.g. bananas), animals
(e.g. fishes, lizards)]
Ex: Multiple species are inter-fertile but remain
distinct (e.g. orchids)
II.
Speciation
•
Occurs when a population becomes
reproductively isolated from rest of
species
May be allopatric or sympatric
Allopatric Speciation
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A.
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Population becomes geographically separated
Over time, mutation, genetic drift, natural
selection  genetic divergence
Thought to be responsible for development of
most new animal species
How do populations become isolated?
Fig. 24.5
II.
Speciation
A.
Allopatric Speciation
1.
Geographical barriers
a.
b.
c.
d.
e.
f.
g.
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Land bridges form, separating aquatic populations (e.g.
Isthmus of Panama)
Land masses separate or split off from continents (e.g.
South America & Africa)
Mountain ranges form
Water levels in water bodies become lower, creating
multiple smaller pools
Rivers change course (Ex: oxbow lakes)
Glaciation occurs
Islands form and are colonized (e.g. Galàpagos, Hawaii,
Madagascar)
Note: Geographic barriers for some species aren’t barriers
for others
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Ex: Birds and many insects can fly between isolated
patches of habitat
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Ex: Some fishes can swim long distances
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Ex: Airborne pollen and drifting gametes in the ocean
can be transported long distances
II.
Speciation
A.
Allopatric Speciation
2.
Conditions Favoring Allopatric Speciation
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•
a.
b.
c.
Fig. 24.6
Typically occurs at edges of parent population’s range
Splinter population (peripheral isolate) may be good
candidate for speciation because:
Gene pool different from parent population
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Likely to represent extreme of genotypic range
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Speciation more likely if founder population small
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Ex: Harris’ and white-tailed antelope squirrels on rims
of Grand Canyon
Genetic drift within peripheral isolate
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Can lead to rapid divergence from parent population
Natural selection
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Diversifying or directional selection under conditions
at extremes tolerated by parent population
Fig. 24.10
II.
Speciation
B.
Sympatric Speciation
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•
1.
Population becomes reproductively isolated
without geographic separation
May be common in plants; importance in
animals less clear
Plants
a.
Autopolyploidy
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Results from error in mitosis
II.
Speciation
B.
Sympatric Speciation
1.
Plants
a.
Autopolyploidy
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Results from error in mitosis
b. Allopolyploidy
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Error in meiosis + hybridization
Fig. 24.11
II.
Speciation
B.
Sympatric Speciation
1.
Plants
b.
Allopolyploidy
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Allopolyploids typically can’t produce fertile
offspring with either parent (incompatible
chromosome numbers)
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If population of allopolyploids becomes
established, typically one of three outcomes:
1) New species unable to compete successfully;
goes extinct
2) New species competes successfully; coexists
with parent species
3) New species competes very successfully;
causes extinction of one or both parent species
II.
Speciation
B.
Sympatric Speciation
1.
Plants
b.
Allopolyploidy
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May be very common in plants
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Up to 80% of flowering plant species are
polyploid
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May account for 25-50% of plant species
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Mechanism for very rapid speciation (single
generation)
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May account for rapid radiation of plants in fossil
record and high diversity of flowering plants
(>290,000 species)
II.
Speciation
B.
Sympatric Speciation
2.
Animals
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Mechanisms of sympatric speciation less well
understood than in plants
Polyploidy usually lethal
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Habitat differentiation
Ex: North American apple maggot fly (article)
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Mutation  short-term isolation reinforced by nonrandom mating (sexual selection)
Ex: African cichlids
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Fig. 24.12
II.
Speciation
C.
Allopatric vs. Sympatric Speciation
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Animals (usu. allopatric)
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Isolating mechanisms?
Plants (usu. sympatric)
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Isolating mechanisms?
Time of Day
Time of Year
Flowers
Snails
Courtship
Sounds/Songs
Bullfrog x
Leopard Frog
Plants
Broadcast Spawners
Horse (2n=64) x
Donkey (2n=62) 
Mule (2n=63)
Fig. 24.3
II.
Speciation
D.
Adaptive Radiation
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Evolution of many diversely adapted species
from common ancestor
Island chains offer unutilized habitat and open
ecological niches
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Ex: Colonization of Hawaii by honeycreepers
Ex: Silversword alliance in Hawaii
Fig. 25.20
II.
Speciation
C.
Adaptive Radiation
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Occurs when niche space is available
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Ex: Radiation of mammals after K/T extinction
Radiation events often are associated with the
appearance of novel features
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Why?
Ex: Shells & skeletons first appeared at beginning of
Paleozoic (may have facilitated radiation)