VI. Evolution: How Change Occurs

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VI. Evolution: How ChangeOccurs

The Development of New Species

The Niche

• Niche Thecombination of anorganism’s“profession” and theplace in which it lives.– Example: Clown fish

live in sea anemone’sand are immune to itspoison. The Clown fisheats the seaanemone’s leftovers.

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The Niche• No two species can occupy the same

niche in the same location for anextended period of time!– The more efficient species will survive,

reproduce and drive the less efficientspecies to extinction.

– OR one of the species may further evolve.

Speciation

• Speciation The formation of a newspecies.

• A new species is formed when there isreproductive isolation.

• Reproductive isolation prevents populationsbelonging to two different species frominterbreeding.

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Speciation

• Reproductive barriers whichprevent mating

• Habitat (geographic) isolation Two species that live indifferent habitats within the samearea rarely encounter each other.

Speciation• Reproductive barriers which prevent

mating• Behavioral Isolation Special signals

that attract mates.– Example: Different species of birds have

different songs which attract mates only ofthat species.

– Example: Male fireflies blink their light toattract female mates. The female fireflieswill only respond to the signalscharacteristic to that species of firefly.

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Speciation

• Reproductive barriers which preventmating

• Gametic Isolation Gametes of twodifferent species meet but cannot form azygote.– Example: Many aquatic animals release

their sperm into the surroundingenvironment. The sperm only fertilizes eggsof the same species.

Speciation• Reproductive barriers

which prevent mating• Temporal Isolation Two

species that breed duringdifferent times of day,different seasons, ordifferent years.– Example: The western

spotted skunk mates in thelate summer and the easternspotted skunk mates in thewinter.

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Speciation

• Reproductive barriers which preventmating

• Mechanical Isolation Closely relatedspecies attempt to mate but fail becausethey are anatomically incompatible.– Example: Insects of closely related species

cannot mate because their reproductive organsdo not fit together.

• Reproductive isolation is usually theresult of a combination of more than oneof these barriers!

Darwin’s Galapagos Islands• The Galapagos Islands

contain 14 species ofFinches which evolved froma common ancestor.

• Adaptive Radiation Theevolution of many speciesfrom a single ancestor.

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An Example of Speciation by Adaptive Radiation

• Founding fatherand mothers– Some ancestors

of the finch foundtheir way from themainland of SouthAmerica to theGalapagosisland’s

An Example of Speciation by AdaptiveRadiation

• Separation ofPopulations– Some birds from island

A made their way toisland B.

– Geographic Isolation A geographic barriersuch as a river or anocean which preventstwo populations ofsimilar species frominterbreeding.

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An Example of Speciation by Adaptive Radiation• Changes in the gene pool.

– Over time the populations on each island adapt totheir environment.

• Natural selection causes the birds on island B todevelop larger beaks to crack thick shelled seeds.

• The birds on island A continue to have small beakswhich they use to crack soft shelled seeds.

An Example of Speciation by Adaptive Radiation• Behavioral Isolation

– Birds from both islands prefer to mate with finches thathave the same size beak as they do.

– The two populations of birds have achievedreproductive isolation and are now consideredseparate species!

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Analysis of Speciation by Adaptive Radiation• What if the two new species came in

contact with each other?• If they occupy different niches they will

coexist.• If they occupy the same niche

– One of the species may become extinct.– One of the species may evolve further and

eventually occupy a different niche.