Evolution – Formation of New Species
What is a species?
Biological species concept - groups of interbreeding natural populations
that are reproductively isolated from other such groups.
(not quite clear cut... There are problems with this definition, but it’s
the best we have…)
Evolution – Formation of New Species
Organisms that look alike may be different species
Organisms that look very different
may be considered the same species
Evolution – Formation of New Species
Organisms from different species may be able to to interbreed
Some organisms like bacteria simply do not interbreed...
Evolution – Formation of New Species
Sometimes, the transition from
one species to the next is not clear cut
Evolution – Formation of New Species
Speciation depends on two factors:
1. Isolation of populations
2. Genetic divergence
Evolution – Formation of New Species
Mechanisms
Speciation can occur through allopatric or sympatric means.
Evolution – Formation of New Species
Mechanisms
Speciation can occur through allopatric or sympatric means.
Evolution – Formation of New Species
Mechanisms
Speciation can occur through allopatric or sympatric means.
In allopatric speciation, genetic flow is reduced through geographic isolation
In sympatric speciation, genetic flow is reduced through ecological isolation or
chromosomal aberrations
(Chromosomal aberrations are
more common in plants
because they can self fertilize)
Evolution – Formation of New Species
Mechanisms
Speciation occurs over space and time!
Using the fossil record, we can see creation of new species over time,
as well as changes in individual species over time
Note that changes and formations of new species is not a constant process over time – Why?
Evolution – Formation of New Species
Mechanisms
Adaptive Radiation – one species gives rise to many...
occurs when populations of a single species invade a variety
of new habitats and evolve in response to the differing
environmental pressures in those habitats.
Evolution – Formation of New Species
Mechanisms
Mechanisms for reproductive isolation (a general overview):
Pre-mating Isolation 1. Geographic isolation
2. Ecological isolation
3. Temporal isolation
4. Behavioral isolation
5. Mechanical incompatibility
Post-mating Isolation 1. Gametic Incompatibility
2. Hybrid inviablity
3. Hybrid infertility
Evolution – Formation of New Species
Mechanisms
New species are always formed, while others go extinct. Over 99.9% of all species
that have ever existed are now extinct!!
Major causes of extinction:
1. Competition among species
2. Introduction of new predators or parasites
3. Destruction (or rapid change) of habitat