Natural Selection and Speciation
Biology 305
Natural History Lecture
David Wyatt

Natural Selection
• The process where species adapt to their environment.
• Driving Force = Competition for Resources
• Involves Populations and their Gene Pools
• Gene Pool = All of the Genes/Alleles in a population
• Differential Reproduction results in loss and gain of population characteristics
• Shifting of gene pools occurs due to differential reproduction = biological evolution.

The Peacock’s Tail
Are big tails at an advantage to avoid predators?

If not, then why do peacocks still have really big tails?

Selective Breeding ­ Example...

Selective Breeding ­ Example...

Selective Breeding ­ Example...

Selective Pressures
• These provide the means for change to occur in gene pools.
• Every factor of Environmental Resistance is a selective pressure. ER=the effect of physical & biological factors in preventing a species from reproducing at its maximum rate.
• Those with characteristics that help them survive go on to reproduce when becoming adults.
• Those with the “best adaptations” reproduce at higher rates.
• Due to this difference in reproduction rates, modification of the gene pool occurs.
• Natural Selection occurs due to these Selective Pressures.

Evolution and Natural Selection
Evolution: the change in a population’s genetic makeup (gene pool) through successive generations. Populations evolve.
Microevolution: the small genetic changes that occur in a population.
Macroevolution: long-term, large-scale evolutionary changes that occur in groups of species where new species are formed from ancestral species.

Natural Selection
Charles Darwin

Charles Darwin’s Voyage
British Naval Ship - H.M.S. Beagle
December 27, 1831 to October 2, 1836
He was 22 years old when he left England
Darwin published journey account in 1845

Darwin’s Voyage

The Galapagos Islands

The Galapagos Tortoise

Darwin’s Finches

Darwin’s Observations in the Galapagos Islands

Darwin’s
Finch
Beak
Functions

“Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds on this archipelago, one species had been taken & modified for different ends.”

Natural Selection
Alfred Russel Wallace

1854­1862

Major Theory Assumptions
• All species have tremendous reproductive potential unless somehow checked.
• Natural resources used by the species are limited this provides a check on the reproductive potential.
• Individuals in a population display various characteristics, many of which are inherited.
• The presence of more individuals in a population than can possibly survive limits the number of offspring that will survive in each generation.

Major Theory Assumptions
• Individuals that inherit characteristics best suited for the environment have a better survival chance and better chance of producing surviving offspring.
• This unequal survival ability and reproductive ability gradually changes the characteristics of the population over time - favorable characteristics become more prevalent in the population.

Natural Selection is not deterministic, not directed; it is a matter of chance:
• Variations arise through random processes
– mutation
– environmental change
• Variations result in adaptations that increase or decrease the ability to compete for survival
• Variations result in adaptations that increase or decrease the ability to take advantage of a resource
• Variations result in adaptations that increase or decrease a species’ ability to fit and survive in their niche

Adaptations
• Increase survival fitness of a species.

• Occur due to competition for resources.
• Niche = The Fundamental Role of an Organism in it’s Environment at a particular time.
• Essentially an organism’s “job” and
“address” during a particular “time”
• Interspecific competition can occur for:

Resource Partitioning
• A result of interspecific (and