UNIT 10 SPECIATION 10 5 PATTERNS OF EVOLUTION

UNIT 10: SPECIATION 10. 5 PATTERNS OF EVOLUTION

EVOLUTION OCCURS IN PATTERNS • Evolution through natural selection is not random. – Natural selection can have direction – The effects of natural selection add up over time.

PATTERNS OF EVOLUTION • Convergent Evolution: evolution towards similar traits in unrelated species due to a similar environment. – Example: Tuna (fish) and dolphins (mammals). Because they lived in the ocean (a similar environment) both faced similar evolutionary pressures and developed fins to navigate the water.

PATTERNS OF EVOLUTION • Divergent Evolution: evolution towards different traits in closely related species – Caused by different environments Red Fox Kit Fox Ancestor

PATTERNS OF EVOLUTION • Coevolution: two or more species evolve in response to changes in each other. – Evolutionary paths become connected – Both species receive benefits from the other as a result of adaptations. • Example: Plants and Insects – Plants: provide insects with nectar – Insect: transfers pollen from one plant to another

COEVOLUTION (CONT. ) • Coevolution can occur in competitive relationships, sometimes called an evolutionary arms race. – Example: Crab vs. Snail

PATTERNS OF EVOLUTION: EXTINCTION BACKG ROUND EXTINCTIONS MASS EXTINCTION S • Cause: local changes in the environment. • Cause: catastrophic events – Forest fires, habitat destruction • Affects a few species in a small area – Less severe • Occurs at roughly the same rate as speciation – Ice ages, meteorites • Destroys many species at a global level – Very severe • Rare but much more intense – At least 5 mass extinctions in

HOW FAST DOES EVOLUTION OCCUR? NO EXACT TIME FRAME! GRADUALISM PUN CTUA TED EQU ILI BRIUM • Slow and steady change of one species into another • Long periods of little change are interrupted by shorter periods of rapid change. – Small changes continually build over time – Due to sudden environment change • Example: Mammal diversity exploded after the dinosaur extinction.

GRADUALISM OF THE HORSE

HOW FAST DOES EVOLUTION OCCUR? • Adaptive Radiation: a process of evolution where one species can split into a number of different species. – Ancestral species diversifies into many descendent species – Each adapted to a different environment • Example: mammals