Speciation Through Isolation and Patterns in Evolution

Reproductive Isolation Reproductive Isolation occurs when members of different populations of the same species are no longer able to mate successfully with each other Reproductive Isolation is the final stage of speciation Speciation is the rise of two or more species from one existing species

Reproductive Isolation, cont. Reproductive Isolation can have three causes: 1.Behavioral Isolation Differences in courtship and mating behaviors prevents reproduction between populations Example : Firefly species flash different patterns of light to attract mates of their own species

Reproductive Isolation, cont. 2. Geographic Isolation Physical barriers that divide a population into two or more groups Example: The Isthmus of Panama arose from tectonic plates and separated the Atlantic from Pacific oceans. Species one either side could no longer mate. 3. Temporal Isolation Timing of reproduction prevents reproduction between populations Example: Two pine tree species release pollen at different times – early spring and late spring

Patterns in Natural Selection Natural selection is not random. The response of a species to environmental challenges and opportunities occurs in patterns. 1. Convergent Evolution Different species must adapt to similar environments Convergent evolution is evolution towards similar characteristics in unrelated species Analogous structures are common example of convergent evolution Example: Fins of sharks (fish) and fins of dolphins (mammals)

Patterns in Natural Selection Natural selection is not random. The response of a species to environmental challenges and opportunities occurs in patterns. 2. Divergent Evolution Evolution towards different characteristics in closely related species Example: Types of foxes, though closely related, have different appearances as a result of adapting for different climates

Patterns in Natural Selection Natural selection is not random. The response of a species to environmental challenges and opportunities occurs in patterns. 3. Coevolution The process in which species evolve in response to changes in each other Type 1 – Cooperation – “Beneficial Relationships” Both species receive benefits from the other as a result of adaptations that each species has evolved over many generations Type 2 – Competition -“Evolutionary Arms Race” Both species respond to competitive pressure from the other through adaptations over many generations

Extinction Type 1 – Background Extinction Occur randomly but at a very low rate Usually affect only a few species in a small area Can be caused by local changes in the environment Type 2 – Mass Extinction Rare but intense Can operate at the global level and destroy many species Caused by catastrophic events such as ice age

Patterns in Speciation Pattern 1 – Punctuated Equilibrium Episodes of speciation occur suddenly in geologic time and are followed by long periods of little evolutionary change Pattern 2 – Adaptive Radiation Diversification of one ancestral species into many descendent species Adapted to a wide range of environments