Download - Natural Selection and Speciation
Another way to look at it…
• Directional Selection
Fitn
ess
Trait Trait
Positive Directional Selection Negative Directional Selection
Same birds different study
Open portion of bar – Number hatched
Black portion of bar – Number survived
Two more types of selection
• Correlational – working on combinations of traits at once.
(body size)
(Wing length)
• Frequency Dependent Selection – Level of selection dependent upon most common phenotype (at the time)
GenyochromisScale eater
• Selection can lead to speciation
• Speciation:– Splitting of one species into two or more
species
– Transformation of one species into a new species over time
Anagenetic (gradual) versus Cladistic (punctuated) Speciation
A
AB
TIM
E
PHENOTYPICVARIATION
A
B
TIM
E
PHENOTYPICVARIATION
Species
• Many, many definitions
• Biological species definition: A group of actually or potentially breeding individuals which are reproductively isolated from all other groups.
• Doesn’t work in all situations– Fossils– Asexual organisms
Modes of speciation
• Allopatric – allo = different, patri = fatherland
• Sympatric – sym = together
• Has to do with location or habitat
Adaptive Radiation
• Evolution of ecological (& morphological) diversity within a rapidly speciating lineage.