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Evolution in Action

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Going on in populations today

Can be observed, recorded & tested

Interactions between species, including humans affect ongoing evolution

I.

Patterns in Progress

A.

DIVERGENT EVOLUTION

i.

A species, which once was similar, is separated. The species diverges, or separates becoming distinct.

a) Species becomes separated by geographic isolation, adapts over time to new environments, adapting size, body shape and even how they live

b) Two Types…

ADAPTIVE RADIATION

Pattern of divergent evolution which many related species evolve from a single ancestral species in a common geographical area.

Occurs when a species of orgs successfully invades an

isolated region where few competing species exist.

If new habitats are available, new species will evolve

Galapagos Finch beaks based on environmental conditions of islands

Marine vs. Land

Galapagos Iguanas

B.

CONVERGENT EVOLUTION

i.

Pattern of evolution in which different organisms evolve similar traits

a) Occurs when unrelated species occupy similar environments in different parts of the world.

b) Because of similar environmental pressures, orgs share same pressures of natural selection

II.

A.

ARTIFICIAL SELECTION

Human breeder chooses individuals to mate

B.

Steers evolution in a direction predetermined by humans

i.

Dog breeds

a) Protection, hunting, companionship

ii.

Agriculture

a) Produce more crops, healthier crops, bigger crops

III.

A.

COEVOLUTION

Joint change in two or more species in close

B.

interaction with each other

2 or more evolve

adaptations to each others’ influence...

i.

Predators & prey

ii.

Parasites & hosts

Pt 2 - Natural Selection and

Species Formation Patterns

I.

Natural Selection (3 Types)

A.

STABILIZING SELECTION

i.

Individuals with the average form of a trait have the highest fitness

a) Average = Optimum balance of good/bad

b) Extreme traits = lower fitness

ii.

Example: Lizards

a) Average size tails are best

Fast enough and small enough to avoid predators

Larger lizards easily spotted, small lizards not fast enough

iii.

**Most common form of natural selection in most traits of most species

B.

DISRUPTIVE SELECTION

i.

Individuals with either extreme variations of a trait have greater fitness than the average form

ii.

Example: Limpets

a) Limpets (marine shellfish) are found in variety of colors from dark brown to nearly white

Dark brown blend with dark rocks, avoiding predators

White blend with barnacles, avoiding predators

Intermediate colors are easily seen and eaten

C.

DIRECTIONAL SELECTION

i.

Individuals that display a more extreme form of a trait have a greater fitness than any other form

a) Example: Anteaters

Longer tongues are at an advantage for eating termites

Shorter and average tongues, not as good

Over time, long tongues are naturally favored

II.

Species Formation

A.

MORPHOLOGICAL CONCEPT OF SPECIES

i.

Species are defined according to structure and appearance

a) Very limited application due to phenotypic differences btwn members of same species

B.

BIOLOGICAL SPECIES CONCEPT

i.

Species is a population of orgs that can successfully interbreed but cannot breed with other groups

a) Limited to only defining species that are currently alive.

b) Also limited to species that reproduce sexually

Cannot test breeding of extinct species

C.

Modern scientists use a combination of both concepts to truly define a species.

D.

Isolation & Speciation

i.

GEOGRAPHIC ISOLATION

a)

b)

Physical separation of members of a population

Causes a stop in gene flow between isolated members of population, eventually drifting genetics far enough apart to become incompatible for mating

c) ALLOPATRIC SPECIATION

Occurs when species arise as a result of geographic

isolation

Allopatric = “Different Homelands”

ii.

REPRODUCTIVE ISOLATION

a) Isolation due to reproductive barrier preventing successful

b) breeding

Often due to disruptive selection in which extreme traits are favored for fitness

c) Two types...

PREZYGOTIC ISOLATION

Species are incompatible before birth

POSTZYGOTIC ISOLATION

Species become incompatible after birth

d) SYMPATRIC SPECIATION

Occurs when two sub-populations become reproductively

isolated within the same geographic area

III.

A.

B.

C.

Rates of Speciation

Most speciation occurs over millions of years

Some species can form more rapidly (1000's of years)

GRADUALISM

i.

Idea that speciation occurs at a regular, gradual rate

ii.

New species are formed are regular intervals throughout time

iii.

This theory is not accepted as scientifically sound

D.

PUNCTUATED EQUILIBRIUM

i.

Idea that speciation occurs in bursts, relative to the geologic

time scale

ii.

Much evidence in fossil record to support this

a) Fossils show long periods of time where species go

without change, as well as short periods of time with tons of change

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