What is Speciation? -how new species evolve from old ones Section 5.6 Speciation and Evolution ( p 157 – 161) Some background info: If two species occupy the same niche, they will compete for each other for food and space If one species is more efficient than the other, it will survive to reproduce (the less efficient species will be driven to extinction)

If two species occupy different niches, then competition is reduced. Thus, any species that occupies an unoccupied niche will be better able to survive. New Species may arise when populations are isolated or separated. ALLOPATRIC SPECIATION: physical barriers such as rivers, mountains, or roads prevent interbreeding ALLOPATRIC SPECIATION: physical barriers such as rivers, mountains, or roads prevent interbreeding REPRODUCTIVE ISOLATION: a mutation may cause individuals with double the number of chromosomes. They may only be able to mate with similar individuals. EXAMPLE: stickle back species in some BC lakes REPRODUCTIVE ISOLATION: a mutation may cause individuals with double the number of chromosomes. They may only be able to mate with similar individuals. EXAMPLE: stickle back species in some BC lakes

Allopatric speciation: (also called geographic isolation) Note: Natural selection works on the separated groups independently

DARWIN’S FINCHES: An example of divergent evolution: a number of different species diverge (‘move away’) from a common ancestral form. 1. A few finches from the South American Mainland found their way to island A of the Galapagos Islands and reproduced. 2. Some birds from A accidentally got isolated on island B (perhaps helped by a storm).

3.Over time population A and B became adapted to their environment. EXAMPLE: A: beaks which can crack small thin shelled seeds B: larger heavier beaks to crack open thick- shelled seeds

4. What happens if birds from island A accidentally make it to island B? -if beak size affects mating behaviour then the two gene pools do not mix THE POPULATIONS HAVE BECOME TWO SEPARATE SPECIES 5.If the two species occupy different niches, they can co-exist If their niches are too similar, they will compete. This could cause extinction of one species, or further evolution.

EVIDENCE OF PAST Divergent Evolution: HOMOLOGOUS STRUCTURES: similar body parts of related organisms evolved to perform different tasks ANALOGOUS: - different origins - different internal structures

Speciation  How rapidly does it occur? Gradualism model Occurs by accumulation of small changes by natural selection Darwinian idea

Speciation  How rapidly does it occur? Punctuated Equilibrium model Speciation occurs more rapidly Species diverge, then change little over time

What does the fossil record show?  Generally, geologically abrupt appearance of species  Little obvious change in species over time  Abruptly disappear  Supports punctuated equilibrium model Why might the fossil record have a discontinuous appearance?

Rapid Evolution may result from dramatic changes in the Earth caused by - global climate change - tidal waves - earthquakes - volcanoes - large asteroid hitting the earth This may have lead to MASS EXTINCTION

-many species die - many niches are left unoccupied -Pre-adaptations -Pre-adaptations (mutations that didn't previously have survival advantages) may now allow an organism to survive such a dramatic change in the environment. MASS EXTINCTION:

Why the Dinosaurs Really Went Extinct From the Farside by Gary Larson

Gary Larson The extinction of a species means that the species was unfit for continued survival. Its gene pool is removed from nature.

“Boom” and “bust” pattern  Mass extinctions, followed by…  Explosive diversifications of surviving groups Diversification follows mass extinction… why? - Groups of animals with enough genetic variability can diverge to fill empty niches

See inside front cover of textbook Cambrian Explosion: - Burgess Shale in BC....evidence of divergent evolution Mass Extinction

Speciation Dynamics - Gradualism or Punctuated Equilibrium? Punctuated equilibrium appears to be a more accurate view of speciation dynamics. Or perhaps a little bit of both models?