Transcript On the Origin of Species

Macroevolutionary patterns and the fossil record
Diversity changes
Rates of evolutionary change
Patterns of lineage diversification
Patterns of diversification in the Phanerozoic
-- rapid rise in the number of taxa
-- extinct lineages are replaced
ecologically by many representatives
at lower taxonomic levels (e.g., an
order by several genera);
-- diversification of ecosystems
Patterns of diversity in the Phanerozoic
-- rapid rise in the number of taxa
-- extinct lineages are replace ecologically by many representatives
at lower taxonomic levels (e.g., an order by several genera)
-- diversification of ecosystems
increased diversification of species/genera consequences of:
- increased diversity of physical environment
- continental drift
- latitudinal temperature gradients
- mountain building
- increased biotic diversity
- competition
- predation
- mutualism
- parasitism
Coevolution?
distribution of relative brain size in predators and prey through the Cenozoic
What about other biological interactions:
Did angiosperm diversification facilitate insect diversification?
Labandiera and Sepkowski 1993 Science 261:310
Did angiosperm diversification facilitate insect diversification?
Labandiera and Sepkowski 1993 Science 261:310
Diversity of insect families increases rapidly after the Permian extinction
Organismal diversity can be produced by either
- increased origination (speciation) rates
- decreased extinction rates
origination
extinction
time
time
or
Insect diversity is a result of low extinction rates, not high
origination rates
insect diversity is uncorrelated with angiosperm diversity
Diversification of families is related to mouthpart diversity, which
preceded the angiosperm radiation
Diversity has ~generally increased
As the number of species/taxa has increased what are
the patterns of change?
How does change occur?
How fast does change occur?
What is change associated with?
Rates and patterns of change
fossil record frequently characterized by
-- relatively long periods of stasis
-- sudden appearance/disappearance of taxa
-- few transitional forms
partly explained as incomplete fossil record
-- preservation biases
-- taphonomy
-- morphospecies
-- stratigraphy effects
partly real
puntuated equilibrium (Eldredge and Gould 1972)
phyletic gradualism
How do we measure rates of evolutionary change?
How much change has occurred over this time interval?
ln x2  ln x1
r
t
Units are ‘darwins’
These are real rates
Why does the measured rate change?
Why do the rates change?
This is the rate of change in a particular character
between and ancestor and a descendant
What about the rate of change in a group of organisms?
Evolution of character suites in lungfish
Changes were “rapid” a long time ago
No change “recently”
These are considered ‘living fossils’
Horseshoe crabs
Coelocanths
Gingkos
Amborella
Tuataras
.
.
.
Why?
Two patterns:
Decrease in perceived evolutionary rate through time
Existence of living fossils
Punctuated Equilibrium
Niles Eldredge -- Stephen Jay Gould
Extreme Version
All morphological change occurs at speciation
Thereafter there is no change
Punctuated Equilibrium
Niles Eldredge -- Stephen Jay Gould
Extreme Version
All morphological change occurs at speciation
Thereafter there is no change
More balanced version:
Statement about macroevolutionary change--fossil evidence
The changes seen in the fossil record occur at speciation
behavior
physiology
cryptic species
The changes are rapid, but not instantaneous--’successive bedding planes’
time scale differences
The time interval over which change occurs is small relative to the ‘lifespan’
of the species or group.
Darwin was not a phyletic gradualist !!
“Many species once formed never undergo any further
change…; and the periods during which species have undergone
modification, though long as measured by years, have probably
been short in comparison with the periods during which they
retained the same form”
--from On the Origin of Species
Darwin and subsequent development has been gradualist about
the evolution of adaptation (it proceeds gradually) not
about the rate of evolution. The only requirement is that
macroevolutionary rates not be faster than observed rates in
experiments.
Gradual evolutionary change in trilobites from Wales
punctuated speciation in bryozoans
Erwin and Anstey (1995a,b) 58 tests of punctuated equilibrium
evidence for gradualism, punctuation --> pluralism
Jackson and Cheetham (1999) found 29 of 31 cases supported
punctuated equilibrium
‘Living Fossils’
200 mya
Morphological stasis in
horseshoe crabs
400
280
Punctuated equilibrium
Nobody changes
‘Living fossils’ are just not diverse
clams
The more the diversity the more possibility
for change in the clade.
In some clades there is substantial change
e.g. horses
Balance between origination
and extinction
For change:
Variation among taxa
Taxa don’t change
They produce (via
speciation) other
similar taxa
Differences in speciation
or extinction rates
Species Selection