Evolution Part IIIEvolution Part III““Speciation through Isolation, Speciation through Isolation, Patterns in Evolution, Fossil Patterns in Evolution, Fossil record, Geologic Time, and record, Geologic Time, and

Cladistics”Cladistics”

Speciation through Speciation through IsolationIsolation

Main IdeaMain Idea: : New species can arise when New species can arise when populations are isolatedpopulations are isolated– IsolationIsolation – if – if gene flowgene flow between species between species

stops for any reason, the populations are stops for any reason, the populations are “isolated”“isolated”

– SpeciationSpeciation – is the rise of two or more – is the rise of two or more species from one existing speciesspecies from one existing species

– Four types of IsolationFour types of Isolation:: Reproductive isolationReproductive isolation Behavioral isolationBehavioral isolation Geographic isolationGeographic isolation Temporal isolationTemporal isolation

Reproductive IsolationReproductive Isolation Reproductive isolation occurs when Reproductive isolation occurs when

members of different populations are no members of different populations are no longer able to mate successfully with longer able to mate successfully with each othereach other

Two cases:Two cases:– Not physically able to mateNot physically able to mate– They cannot produce offspring able to They cannot produce offspring able to

survivesurvive Reproductive isolation between Reproductive isolation between

populations is the final step in populations is the final step in speciationspeciation

Behavioral IsolationBehavioral Isolation A large part of the mating A large part of the mating

process involves rituals, process involves rituals, chemical signals, songs, and chemical signals, songs, and courtship dancescourtship dances

Behavioral isolationBehavioral isolation occurs occurs when members of a population when members of a population are not “accepted” because of are not “accepted” because of their behavior or improper their behavior or improper courtship ritualscourtship rituals– Example – the flashing patterns Example – the flashing patterns

in male and female fireflies in male and female fireflies– Example – the courtship song and Example – the courtship song and

dance of the lyre bird in South dance of the lyre bird in South AustraliaAustralia

Geographic IsolationGeographic Isolation In In geographic isolationgeographic isolation

there are physical there are physical barriers that divide a barriers that divide a population into two or population into two or more groupsmore groups– Rivers, mountains, dried Rivers, mountains, dried

lake beds, or man-made lake beds, or man-made barriers barriers

– When populations are When populations are separated long enough, separated long enough, they may evolve they may evolve different adaptations and different adaptations and undergo undergo speciationspeciation

Temporal IsolationTemporal Isolation A A temporal barriertemporal barrier is one is one

that prevents that prevents reproduction because of reproduction because of “timing”“timing”– Bird migrations are often Bird migrations are often

governed by changing of governed by changing of the seasons and food the seasons and food availability for their youngavailability for their young

Patterns in EvolutionPatterns in Evolution As new species arise they are under As new species arise they are under

pressure to survive. pressure to survive. Adaptive traitsAdaptive traits are are kept in a population through natural kept in a population through natural selection but, sudden changes in an selection but, sudden changes in an environment can eliminate one or more environment can eliminate one or more speciesspecies

In science, the terms In science, the terms chancechance and and randomrandom refer to how easily an outcome can be refer to how easily an outcome can be predictedpredicted– MutationMutation and and genetic driftgenetic drift cannotcannot be predicted be predicted

so they are considered random eventsso they are considered random events

Patterns in EvolutionPatterns in Evolution Natural selectionNatural selection, which acts on , which acts on

diversity, is diversity, is not not randomrandom. Individuals . Individuals with traits that adapt them to their with traits that adapt them to their environment better have a better environment better have a better chance of surviving and passing on chance of surviving and passing on those adaptations to future those adaptations to future generations.generations.

It is important to remember that It is important to remember that it is it is thethe environment that controls the environment that controls the direction of natural selectiondirection of natural selection

Convergent EvolutionConvergent Evolution Different species Different species

around the world adapt around the world adapt to similar environmentsto similar environments

When evolution When evolution towards similar traits in towards similar traits in unrelated organisms unrelated organisms develops it is called develops it is called convergent evolutionconvergent evolution– The habitat will favor The habitat will favor

those best adapted for those best adapted for survival (natural survival (natural selection)selection)

Divergent EvolutionDivergent Evolution When When closely closely

related speciesrelated species evolve in evolve in different different directionsdirections, they , they become increasingly become increasingly different through different through divergent evolutiondivergent evolution

As time passed in As time passed in different habitats, different habitats, several species of several species of primates evolved primates evolved from a common from a common ancestor ancestor

Species EvolutionSpecies Evolution Main Idea: Main Idea: Species Species cancan shape each other over time shape each other over time

– As species interact they form relationships As species interact they form relationships – Close species interaction is called Close species interaction is called symbiosissymbiosis– As species compete, cooperate, and interact in various As species compete, cooperate, and interact in various

ways their evolutionary paths ways their evolutionary paths may become connectedmay become connected

Two types of these interactions:Two types of these interactions:– Coevolution Coevolution – the process by which two or more – the process by which two or more

species evolve in response to changes in the otherspecies evolve in response to changes in the other– ““Evolutionary arms race”Evolutionary arms race” – a type of coevolution – a type of coevolution

where species respond to other species they are where species respond to other species they are competing withcompeting with Often times this occurs in predator-prey relationships Often times this occurs in predator-prey relationships

where the prey evolves to escape the evolving predator where the prey evolves to escape the evolving predator as the predator evolves to better catch its preyas the predator evolves to better catch its prey

Species CoevolutionSpecies Coevolution One such relationship in One such relationship in

nature is between ants and nature is between ants and aphidsaphids– Ants prefer nectar and “herd” Ants prefer nectar and “herd”

the aphids like sheep to the the aphids like sheep to the most succulent parts of a plant most succulent parts of a plant for the aphids to eatfor the aphids to eat

– The aphids produce a nectar The aphids produce a nectar from their abdomen which the from their abdomen which the ants love!ants love!

– In return for the nectar, the In return for the nectar, the ants protect the aphids from ants protect the aphids from their most feared predator – their most feared predator – the ladybug!the ladybug!

Species ExtinctionSpecies Extinction ExtinctionExtinction – the – the

elimination of a elimination of a species from the species from the EarthEarth– Background Background

extinctionsextinctions - - extinctions that occur extinctions that occur continuously at a very continuously at a very low rate caused by low rate caused by many reasonsmany reasons

– Mass extinctionsMass extinctions – – sudden, rare events sudden, rare events that cause hundreds, that cause hundreds, thousands, and thousands, and sometimes millions of sometimes millions of species to become species to become extinct extinct

Adaptive RadiationAdaptive Radiation As one species As one species

diversifies into diversifies into manymany descendent species it is descendent species it is called called adaptive adaptive radiationradiation– This type of speciation This type of speciation

usually follows a mass usually follows a mass extinction and creates a extinction and creates a Huge diversity of species Huge diversity of species in a relatively short in a relatively short period of timeperiod of time

The diagram shows a Species A that moves to an island displaying the founder effect and Species A

undergoes adaptive radiation inhabiting a range ofislands and habitats.

Geologic TimeGeologic Time Scientific evidence shows us Scientific evidence shows us

that the Earth is about 4.5 that the Earth is about 4.5 billion years old!billion years old!

There are many tools There are many tools scientists use to discover scientists use to discover thisthis

Index fossilsIndex fossils are fossils of are fossils of organisms that existed organisms that existed onlyonly during a specific time periodduring a specific time period– The trilobite to the right is one The trilobite to the right is one

of the most abundant fossils of the most abundant fossils during the Paleozoic Eraduring the Paleozoic Era

Geologic TimeGeologic Time There are a couple methods for There are a couple methods for

determining the determining the age age of fossilsof fossils– Relative datingRelative dating gives you an estimate of gives you an estimate of

the time period of an organism based upon the time period of an organism based upon the rock layer in which it is foundthe rock layer in which it is found This method is not very accurate for exact This method is not very accurate for exact

measurementsmeasurements

– Radiometric datingRadiometric dating uses uses isotopesisotopes of organic of organic elements to determine a fairly exact age of elements to determine a fairly exact age of a substance relative to the decay of the a substance relative to the decay of the organic elements found in a sample organic elements found in a sample (usually Carbon-14)(usually Carbon-14) This is accurate to a few hundred years or lessThis is accurate to a few hundred years or less

Radiometric DatingRadiometric Dating

Species Classification based Species Classification based uponupon

Evolutionary RelationshipsEvolutionary Relationships As we look at animals it is As we look at animals it is apparent that similar animals apparent that similar animals have a lot in commonhave a lot in common– Example: modern dogs and wolves Example: modern dogs and wolves

share a share a common ancestorcommon ancestor The The phylogenyphylogeny of a species is of a species is

the evolutionary history of that the evolutionary history of that speciesspecies

The most common way to make The most common way to make an evolutionary tree is through an evolutionary tree is through cladisticscladistics which is which is a a classification based on common classification based on common ancestryancestry

CladisticsCladistics A A cladogramcladogram is an is an

evolutionary tree that evolutionary tree that proposes how species proposes how species may be related may be related through a common through a common ancestorancestor

CladeCladeGroup of organisms that share traits derived from a common ancestor

Derived Derived CharacterCharacter

Trait that organisms share AFTER the hash

mark showing a new trait

NodeNodeBranch that represents the most recent common ancestor