Macroevolution

Series of microevolution Speciation – the formation of new species

when one ancestral species evolves more than 1 typical descendant.

Since speciation occurs when one species evolves into more than 1 new species, it increases the number of species that exist.

Patterns of MacroevolutionPatterns of Macroevolution

A. Mass Extinctions

B. Adaptive Radiation

C. Convergent Evolution

D. Coevolution

E. Gradualism

F. Punctuated Equilibrium

These are theories/models of evolution

Patterns of MacroevolutionPatterns of Macroevolution

that are

can undergo can undergo can undergo can undergo can undergo

in underunderform inin

Species

Unrelated Related

Inter-relationships

Similar environments

Intense environmental

pressure

Smallpopulations

Different environments

Coevolution Convergent evolution Extinction

Punctuated equilibrium

Adaptive radiation

Mass ExtinctionsMass Extinctions Event in which manymany types of living

things became extinct at the same timeat the same time.  Period in which huge numbers of

speciesspecies disappeareddisappeared. Whole ecosystemsecosystems were wiped outwiped out Left habitatshabitats/niches openopen Resulted in burst of evolutionburst of evolution of new

species in new habitat Disrupted energy flowenergy flow throughout the

biosphere and caused food websfood webs to collapsecollapse

Mass ExtinctionsMass Extinctions

Possible causes– AsteroidsAsteroids hitting earth– VolcanicVolcanic eruptions– Continental driftdrift– Sea levelsSea levels changing

Adaptive RadiationAdaptive Radiation The evolution of an ancestral speciesancestral species,

which was adaptedadapted to a particular way of life, into many diversemany diverse species, each adapted to a different habitatdifferent habitat

Many new speciesspecies diversify from a common ancestorcommon ancestor .

The branching outbranching out of a population through variationvariation.

The new species livelive in differentdifferent ways thanthan the original original species did.

Adaptive RadiationAdaptive Radiation

Convergent EvolutionConvergent Evolution OppositeOpposite of divergent evolutiondivergent evolution (adaptive

radiation) UnrelatedUnrelated organismsorganisms independently evolve evolve

similaritiessimilarities when adapting to similarsimilar environments, or ecological nichesniches

Analogous structuresAnalogous structures are a result of this process

Example: penguin limb/whale flipperflipper/fish finfin The wings of insects, birds, pterosaurs, and

bats all serve the same functionsame function and are similar similar in structurein structure, but each evolved independently independently

Convergent EvolutionConvergent Evolution

Convergent EvolutionConvergent Evolution

Convergent EvolutionConvergent Evolution

Similar body shapes and structures

have evolved in the North

American cacti...and in

the euphorbias in Southern

Africa

CoevolutionCoevolution The mutual mutual evolutionary influenceinfluence between

two speciesspecies When twotwo species evolveevolve in responseresponse to

changes in each othereach other They are closely connected to one another

by ecological interactionsecological interactions (have a symbiotic relationship) including:– Predator/prey prey – ParasiteParasite/host – PlantPlant/pollinator

EachEach party exerts selective pressurespressures on the otherother, thereby affecting each others' evolution

CoevolutionCoevolution

CoevolutionCoevolution

Praying Mantis simulates plant to protect itself from predators and eats pests that are attracted to and feed on the plant, so it protects the plant.

GradualismGradualism

The evolution of new species by gradual accumulation of small genetic small genetic changeschanges over long periodslong periods of time

Emphasizing slowslow and steady changesteady change in an organism

Occurs at a slow but constant rateconstant rate Over a short period of time it is hard hard

to noticeto notice

GradualismGradualism

GradualismGradualism

Punctuated EquilibriumPunctuated Equilibrium

Stable periodsStable periods of no change (genetic equilibrium) interruptedinterrupted by rapid rapid changeschanges involving many different lines of descent

Opposite of gradualismgradualism It is rare, rapid events of branching branching

speciationspeciation Characterized by long periods of virtual virtual

standstillstandstill ("equilibrium"), "punctuated""punctuated" by episodes of very fast developmentfast development of new forms

Punctuated EquilibriumPunctuated Equilibrium

Gradualism or Punctuated EquilibriumGradualism or Punctuated Equilibrium

Why won’t our lungs evolve to deal with air pollution? Limits to adaptation:

– A change in the environment can only lead to adaptation for traits already present in the gene pool

– Reproductive capacity may limit a population’s ability to adapt

If you reproduce quickly (insects, bacteria) then you can adapt to changes in a short time

If you reproduce slowly (elephants, tigers, corals) then it takes thousands or millions of years to adapt through natural selection

– Most individuals without trait would have to die in order for the trait to predominate and be passed on

When faced with a change in environmental condition, a population of a species can:– Adapt via natural selection– Migrate (if possible) to an area with more favorable

conditions (Mars & Atlantis?)– Become extinct

Natural selection can only act on inherited alleles already present in the population—do not think that the environment creates favorable heritable characteristics!

Three types of Natural Selection Directional

– Allele frequencies shift to favor individuals at one extreme of the normal range

Only one side of the distribution reproduce Population looks different over time

– Peppered moths and genetic resistance to pesticides among insects and antibiotics in bacteria

Stabilizing– Favors individuals with an average genetic makeup

Only the middle reproduce Population looks more similar over time (elim. extremes)

Diversifying – Environmental conditions favor individuals at both ends of the genetic

spectrum Population split into two groups

Coevolution

Interactions between species can cause microevolution– Changes in the gene pool of one species can cause changes in

the gene pool of the other Adaptation follows adaptation in something of a long

term “arms race” between interacting populations of different populations

– The Red Queen Effect Can also be symbiotic coevolution

– Angiosperms and insects (pollinators)– Corals and zooxanthellae – Rhizobium bacteria and legume root nodules

Niches

A species functional role in an ecosystem Involves everything that affects its survival and reproduction

– Includes range of tolerance of all abiotic factors– Trophic characteristics– How it interacts with biotic and abiotic factors– Role it plays in energy flow and matter cycling

Fundamental Niche– Full potential range of physical chemical and biological conditions and

resources it could theoretically use if there was no direct competition from other species

Realized Niche– Part of its niche actually occupied

Generalist vs. Specialist– Lives many different places, eat many foods, tolerate a wide range of

conditions vs few, few, intolerant…– Which strategy is better in a stable environment vs unstable?

Niche Overlap

Region of niche overlap

Generalist specieswith a broad nicheGeneralist species

with a narrow nicheNiche

breadth

Nicheseparation

Num

ber

of in

divi

dual

s

Resource use

Competition Shrinks Niches

Key Concepts:

A species consist of one or more populations of

individuals that can interbreed and produce

offspring

Populations of a species have a shared genetic

history

Speciation is the process by which daughter

species evolve from a parent species

Key Concepts:

Geographic barriers can start the process of

speciation– Allopatric speciation

With sympatric speciation, a species can form

within the range of a parent species

Parapatric speciation has adjacent populations

becoming distinct species while still coming in

contact along a common border

What is a Species?

Morphological Species Concept– Based on appearance alone

Biological Species Concept– A species is one or more populations of individuals that

are interbreeding under natural conditions and

producing fertile offspring, and are reproductively

isolated from other such populations

Speciation

Two species arise from one– Requires Reproductive isolation

Geographic: Physically separated Temporal: Mate at different times Behavioral: Bird calls / mating rituals Anatomical: Picture a mouse and an elephant hooking up Genetic Inviability: Mules

Allopatric– Speciation that occurs when 2 or more populations of a species are

geographically isolated from one another – The allele frequencies in these populations change– Members become so different that that can no no longer interbreed– See animation

Sympatric– Populations evolve with overlapping ranges– Behavioral barrier or hybridization or polyploidy

Reproductive Isolating Mechanisms

Any heritable feature of body, form, functioning, or behavior that prevents breeding between one or more genetically divergent populations

Prezygotic or Postzygotic

Pre-Zygotic Isolation

Mating or zygote formation is blocked– Temporal Isolation

– Behavioral Isolation

– Mechanical Isolation

– Ecological Isolation

– Gamete Mortality

Post-Zygotic Isolation

Hybrids don’t work– Zygotic mortality - Egg is fertilized but zygote or

embryo dies

– Hybrid inviability - First generation hybrid forms

but shows low fitness

– Hybrid infertility - Hybrid is fully or partially

sterile

Speciation

Adapted to heatthrough lightweightfur and long ears, legs, and nose, whichgive off more heat.

Adapted to coldthrough heavierfur, short ears,short legs, shortnose. White furmatches snowfor camouflage.

Gray Fox

Arctic Fox

Different environmentalconditions lead to differentselective pressures and evolutioninto two different species.

Spreadsnorthwardandsouthwardandseparates

Southernpopulation

Northernpopulation

Early foxpopulation

Allopatric Speciation

Physical barrier

prevents gene flow

between populations

of a species– Archipelago hotbed

of speciation

Allopatric Speciation

New arrival in species

– Poor habitats on an

isolated archipelago

– Start of allopatric

speciation

Hawaiian Honeycreepers

Sympatric Speciation

New species forms within home range– Polyploidy leads to speciation in plants– Self-fertilization and asexual reproduction

Extinction

The ultimate fate of all species just as death is for all individual organisms

99.9% of all the species that have ever existed are now extinct

– To a very close approximation, all species are extinct Background vs. Mass Extinction

– Low rate vs. 25-90% of total– Five great mass extinctions in which numerous new species

(including mammals) evolved to fill new or vacated niches in changed environments

– 10 million years or more for adaptive radiations to rebuild biological diversity following a mass extinction

Extinction in the context of Evolution

If the environment changes rapidly and The species living in these environments do

not already possess genes which enable survival in the face of such change and

Random mutations do not accumulate quickly enough then

All members of the unlucky species may die

Ordovician: 50% of animal families,

Devonian: 30% of animal families,

Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites.

Triassic: 35% of animal families, including many reptiles and marine mollusks.

Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including manyforaminiferans and mollusks.

Current extinction crisis causedby human activities.

Species and families experiencing mass extinction

Bar width represents relative number of living species

Extinction

Millions ofyears ago

PeriodEra

Pal

eozo

icM

eso

zoic

Cen

ozo

ic Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

Today

65

180

250

345

500Extinction

Extinction

Extinction

Extinction

Extinction