Patterns of EvolutionPatterns of Evolution

The Rate of EvolutionThe Rate of Evolution► Scientists use two Scientists use two

basic terms to basic terms to describe the rate of describe the rate of evolution:evolution: Punctuated Punctuated

equilibriumequilibrium – – describes pattern of describes pattern of longlong stable periods stable periods interrupted by interrupted by briefbrief periods of more rapid periods of more rapid change.change.

GradualismGradualism – describes a – describes a slowslow, steady , steady change in a population over timechange in a population over time

http://www.ideacenter.org/stuff/contentmgr/files/34ba8a8b571e676d2e06742b48603094/misc/gradualism.gif

Genus and speciesGenus and species

• Genus: group of closely related Genus: group of closely related species, and the first part of the species, and the first part of the scientific name in binomial scientific name in binomial nomenclaturenomenclature

• Species: group of organisms that can Species: group of organisms that can breed and produce fertile offspringbreed and produce fertile offspring

http://www.evcforum.net/RefLib/LigersWolphins_files/223liger.jpg

A liger can not mate with another liger and have offspring!

Review: What is a niche?Review: What is a niche?

NicheNiche – the full range of physical and – the full range of physical and biological conditions in which an organism biological conditions in which an organism lives and the way an organism used those lives and the way an organism used those conditions. (Where it lives and its role in conditions. (Where it lives and its role in

the environment).the environment).

An organism’s fitness is higher An organism’s fitness is higher withinwithin its niche its niche than outsidethan outside of its niche.of its niche.

Ex.: A penguin’s fitness is higher in Antarctica Ex.: A penguin’s fitness is higher in Antarctica than in Chapel Hill.than in Chapel Hill.

► No two species can have the same niche.No two species can have the same niche. Species compete for the food and resources within a Species compete for the food and resources within a

niche.niche. The The most competitivemost competitive species survives and species survives and

maintains the niche.maintains the niche. The The less competitiveless competitive species either dies out or finds species either dies out or finds

a new niche.a new niche.

http://www.paklinks.com/gsmedia/files/18Plus/2a.jpg

SpeciationSpeciation► Speciation is the Speciation is the

development of development of a new a new species.species.

► It occurs when a species It occurs when a species moves into an moves into an unoccupied niche. unoccupied niche.

► Populations evolve and Populations evolve and become reproductively become reproductively isolated from each other. isolated from each other. (Cannot interbreed and (Cannot interbreed and produce fertile offspring)produce fertile offspring)

► Over time, the species Over time, the species evolves evolves adaptationsadaptations that are more suitable to that are more suitable to its new niche.its new niche. http://taxonomy.zoology.gla.ac.uk/~rdmp1c/teaching/L1/

Evolution/l6/speciation.jpg

Different Niches for Different Different Niches for Different BeaksBeaks

When does speciation occur?When does speciation occur?

►Speciation can only occur when Speciation can only occur when populations are reproductively populations are reproductively isolated isolated from one another.from one another. Reproductive isolation – means a Reproductive isolation – means a

population can no longer interbreed with a population can no longer interbreed with a population in another area.population in another area.

Only happens when the Only happens when the gene poolsgene pools are are separate.separate.

Maintaining Reproductive Maintaining Reproductive IsolationIsolation

►There are three basic factors that There are three basic factors that maintain reproductive isolation.:maintain reproductive isolation.: Geographic Isolation: populations Geographic Isolation: populations

separated by physical barriers (rivers, separated by physical barriers (rivers, mountains, bodies of water).mountains, bodies of water).

Behavioral Isolation: capable of Behavioral Isolation: capable of interbreeding, but have different courtship interbreeding, but have different courtship rituals..rituals..

Temporal Isolation: reproduce at different Temporal Isolation: reproduce at different times.times.

Geographic Geographic BarriersBarriers

►When a land formation, When a land formation, such as a mountain, such as a mountain, canyon, river, etc. canyon, river, etc. prevent populations prevent populations from breeding.from breeding. Ex. Beetles divided by a Ex. Beetles divided by a

river.river.

http://evolution.berkeley.edu/evolibrary/images/history/geog_isolation.gif

Behavioral Behavioral IsolationIsolationWhen differences in When differences in

mating rituals.mating rituals. Ex.: Peacock mating Ex.: Peacock mating

dance.dance.

Temporal Temporal IsolationIsolation

Ex.: When plants Ex.: When plants release pollen at release pollen at different times.different times.

http://biology.clc.uc.edu/graphics/bio303/sexualselection.jpg

http://pinker.wjh.harvard.edu/photos/cambridge_boston/images/trees%20in%20Cambridge%20Common.jpg

Speciation via Reproductive Speciation via Reproductive IsolationIsolation

Reproductive isolation occurs between two Reproductive isolation occurs between two populations of the same species.populations of the same species.

Populations become Populations become adaptedadapted to different to different environments.environments.

Separate gene pools become Separate gene pools become less similarless similar..

Eventually reproductive isolation becomes Eventually reproductive isolation becomes permanent.permanent.

Two different species form.Two different species form.

Speciation doesn’t always Speciation doesn’t always happen.happen.

►When the gene pool for a population is When the gene pool for a population is very small, there is less very small, there is less variationvariation..

►This makes it difficult for populations This makes it difficult for populations to adapt to a new niche.to adapt to a new niche.

►These populations often become These populations often become extinct.extinct.

Patterns of EvolutionPatterns of Evolution

►There are several different ways that There are several different ways that evolution can occur:evolution can occur:1. 1. Adaptive radiationAdaptive radiation – One species gives – One species gives

rise to several different forms (new species) rise to several different forms (new species) that appear different externally, live in that appear different externally, live in different ways, but are similar internally. different ways, but are similar internally.

►This is an example of This is an example of divergent evolutiondivergent evolution..►Often occurs when there are empty niches in a Often occurs when there are empty niches in a

community, following an event of mass community, following an event of mass extinction.extinction.

►The adaptive radiation of mammals occurred The adaptive radiation of mammals occurred after the extinction of dinosaurs.after the extinction of dinosaurs.

2. 2. Convergent evolutionConvergent evolution – different – different groups developing similar adaptations groups developing similar adaptations because they live in the same type of because they live in the same type of environmentenvironment

►Ex: Ex: sharks, dolphins, and penguins.sharks, dolphins, and penguins.

http://www.dolphindreamteam.com/pictures/pics/swimdolphin.jpg

http://www.aqua-firma.co.uk/editorfiles/Image/Antarctica/uw-penguin-upload1.jpg

http://www.flmnh.ufl.edu/fish/gallery/descript/TigerShark/scars.JPG

3. 3. CoevolutionCoevolution – two species evolve together, – two species evolve together, responding to changes in each other and responding to changes in each other and becoming uniquely adapted to one anotherbecoming uniquely adapted to one another

► Ex. Ex. Mitochondria and the Eukaryotic CellMitochondria and the Eukaryotic Cell► Ex. Ex. Plants and their PollinatorsPlants and their Pollinators► Ex. Flowers and plant eating insects.Ex. Flowers and plant eating insects.

http://streaming.wcp.muohio.edu/western/insects/butterfly_proboscis.jpg

http://www.olympusmicro.com/micd/galleries/darkfield/butterflyproboscis.html