ANTA01H3 Lecture Notes - Lecture 4: Allopatric Speciation, Reproductive Isolation, Character Displacement

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Published on 25 Sep 2015
ANTA01 – Lecture 4 - Continuation of last week (Lecture 3)
Ecological Niche
The area that a species is adapted too / a particular habit that a species is adapted too
oA particular way of surviving
How do new species arise?
oHow species arise: success variations can accumulate within a population over a
long period time
oGeographical isolation sometimes causes speciation
2 groups become isolated & subjected to different selection pressures
(however, they can diverge in the same location as well)
oCadogenesis: One species branches into many new species
oAnagenesis: one species evolves into another new species over time
Hard to say when it/the change actually happens
Types of speciation
oSpeciation: processes where new species arise
Problems with this: it is difficult to study empirically
Allopatric Speciation
If 2 animals are allopatric, it means they don’t occur in the same spot
Allopatric: 2 or more populations of a single species are isolated geographically and then
diverge to form 2 or more new species
2 isolated populations go through changes and randomly develop barriers to interbreed
(no longer able to breed)
Primary form of cladogenesis
Most accepted explanation for how new species arise
oFits well with BSC (Biological species concept)
If reproductive isolation is complete when the populations meet again, they have 2 new
If reproductive isolation is not complete, certain things occur such as:
oCharacter Displacement: when the 2 populations merge, there will be competition
for resources in what may lead too the 2 populations specializing in different
things (their niches); can keep populations apart and may lead to speciation
(even if they’re in the same area)
oReinforcement: the 2 populations have diverged overtime, when they come
together, there might be mechanisms put in place that make interbreeding less
likely; examples: courtship behaviour, coloration, breeding season; can also lead
to speciation (even if they’re in the same area)
Allopatric Speciation Summary
Geographic isolation
Different habitat selects for different adaptations
After recolonization:
oReproductive isolation may be complete -> which also means speciation is
oIsolation may be achieved by reinforcement or character displacement
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Parapatric speciation
Limited overlap in ranges
Differences develop overtime due to geographic isolation
Ecological niches concept
At boundaries of ranges, hybrids will have worse fitness, worse reproductive success I.e.
they will be selected against
Even if reproduction isolation is not complete, speciation can still occur; i.e. natural
selection keeping the populations apart
Fits with ESC (Evolutionary Species Concept)
Sympatric speciation:
Share the same geographical area – sympatric
Speciation (new species can occur) can occur in overlapping ranges
Occurred in history and can occur in species with wide geographical ranges
Tempo & Mode in Evolution
2 kinds
oPhyletic gradualism: tiny changes accumulate gradually via microevolution and a
slow progression of one species to another
oPunctuated equilibrium: Gould & Eldridge produced this idea - there are short
periods of rapid change after a long time of little or no change and occurs when
new species arise through isolation
Adaptive Radiation
When you get a bunch of species adapting to new niches (a species colonizes a new
habitat with many open habitats)
Because of fewer competitors, species will differentiate thus filling available niches
Examples of this in evolutionary record: Galapagos finches
Which of the following Is one of Darwin’s postulates of natural selection?
C: Variation will be passed to the next generation
After a drought, a scientist collects dead birds and finds that most didn’t survive to adulthood
had either small beaks or large beaks. Given this pattern:
A: Selection will not change mean beak size
If you crossed a true breeding green pea plant with a true breeding yellow pea plant, what would
the next generation look like?
B: All the plants would be yellow
WHY: yellow if always dominant (smooth & wrinkled skin, smooth is always dominant)
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