Download Macroevolution and Speciation

Macroevolution and Speciation
Evolution creates (and destroys) new species, but …
What is a species?
Its not as straightforward a question as most believe.
These are members of different species - eastern (left) and western (right) meadowlark.
What is a Species?
There is only one extant (existing) human species.
What is a Species?
And these are all members of a single species.
Determining What Is and What Isn’t a Distinct Species Can Have
Economic Consequences
Northern spotted owl (left) and barred owl (right).
What is a Species?
The definition we’ll use is this: A species is a group of individuals capable of
interbreeding to produce fertile offspring.
This is the biological species
concept. Like all attempts to
define a species, it has many
problems.
One Problem in the Biological Species Concept
For asexually-reproducing organisms, like these bacteria, what constitutes a species?
…and another
problem with the
Biological Species
Concept…
Where do you draw the
line between different
‘species’?
How Many Species Are There?
We don’t know.
About 2 million species have been described.
Estimates of existing species number range from 4 million to 100 million
(with 10-15 million being a more commonly considered upper estimate).
How did this diversity of life come to be?
Species = basic unit
Continuous lineage - information
passed through genes
Speciation - rise of new species
Two Patterns of Speciation
How Do
Species Arise?
The key to speciation
is reproductive
isolation of
populations.
There are extrinsic
and intrinsic
reproductive isolating
mechanisms.
Geographic isolation is
the primary extrinsic
reproductive isolating
mechanism.
Process of speciation:
Parent
species
I. Barrier
2 separate species
II. Diverge
III. Don’t interbreed
Reproductive Isolation May Occur With or Without
Geographic Isolation
Allopatric speciation occurs
when geographic isolation
creates a reproductive
barrier (an extrinsic
mechanism).
Sympatric speciation occurs
when a reproductive barrier
is created by something
other than geographic
isolation (intrinsic
mechanisms).
Allopatric Speciation
Harris’ antelope squirrel
White-tailed antelope squirrel
Two species of ground squirrel are postulated to have descended from a common
ancestral population that was separated by formation of the Grand Canyon.
Many Intrinsic Reproductive Isolating Mechanisms Drive
Speciation
(different habits within an overlapping range)
Many Intrinsic Reproductive Isolating Mechanisms Drive
Speciation
Courtship rituals, like
these, are critical for
mating within a species,
but ineffective for
attracting members of
other species.
Many Intrinsic Reproductive Isolating Mechanisms Drive
Speciation
Many Intrinsic Reproductive Isolating Mechanisms Drive
Speciation
Hybrid Infertility Was
the Impetus for
Cloning a Mule
Speciation Dynamics - Gradualism or Punctuated Equilibrium?
Gradualism-species is
constantly making small
changes over a long period of
time until they are a new
species
Punctuated equilibrium: new
species evolve fairly rapidly
and then stay the same for a
long time
Punctuated equilibrium appears
to be a more accurate view of
speciation dynamics.
Does Evolution Create the Perfect Organism?
No, only better organisms as evolution is
constrained by history and buffeted by random
events.
Essentially, every organism on earth is in
significant part a sum of accidents.
Species Come and Go
Best estimates from the fossil record indicate that greater than 99% of species that
have existed are now extinct.
A typical “lifetime” for a species is
about 1 million years.
Mass Extinctions Are a Fact of Life
90% of all species that have ever existed are now extinct …
The Cretaceous/Tertiary Mass Extinction
Gary Larson
Are We Now Causing a Mass Extinction?