What Is A Species?
• Species = individuals that are capable of
producing viable/fertile offspring
Variations, Differential
Reproduction & Speciation
• Different variations, acted
upon by the selective
pressures of the
environment, cause
differential
reproduction within a
population
• Changes in the variations
of a species or the
selective pressures may
lead to speciation
Types of Speciation
Allopatric Speciation
• A population is split into
two groups due to
geographic isolation
• If the two environments
are different, the selective
pressures on each subpopulation will differ
• Differential reproduction
will result as different
variations are favored in
each environment
Kaibab v. Abert Squirrel =
Allopatric Speciation
Peripatric Speciation
• Like allopatric
speciation, population
is split by geographic
isolation
• However, the second,
new population is
much smaller and has
a more limited range
of variations
• 2nd population more
likely to exhibit
Founder’s Effect
Sympatric Speciation
• Unlike allopatric
speciation, population
is NOT split by
geographic isolation
• Due to variations that
develop within the
population, members
become
reproductively
isolated
• Ex: mating behaviors,
different # chromosomes
Different Models For Rate of
Evolutionary Change
• Gradualism
• Slow, incremental
changes in allele
frequency and
phenotype over time
• Punctuated
Equilibrium
• Long periods of no
change in allele
frequency and/or
phenotype interrupted
by rapid “bursts” of
drastic change
Gradualism
• Species tend not to
diverge drastically,
but modify existing
body plans,
behaviors, etc. to fit
small changes in the
environment
Punctuated Equilibrium
• As mutation and
environmental change
are random, so is the
rate of change in
allele frequencies
• Model supported by
most evidence and
research (i.e. Stephen
Jay Gould)
Lab: Origin of Species
• Purpose: To determine the mode of
evolution affecting a sexually reproducing
population in regard to abiotic and biotic
factors, geographic and reproductive
isolation, differential rates of reproduction
and selective pressures
Protocol
• Research the changes on each part of the archipelago
(Windsor, Norcross, etc.) over the course of 5 million
years
• Record your observations, share your results and
answer the analysis questions on the Google Document
recently shared with you
• Notes:
– For each location, what changes occurred in regard to
the Geospiza’s (i.e. pollenpeepers) variations?
– For each location, what were the primary selective
pressures directing those changes
– Was the evolution divergent to the point of
speciation? Why or why not?
– If so, what type of speciation best describes these
changes: allopatric, peripatric, sympatric?