Balance Between Speciation and extinction

Biodiversity

BalanceBetween

Speciation and extinction

What is biodiversity?

• Type 1: Total number of species in world• Type 2: Genetic variation within and

between species. • Type 3: Ecosystem biodiversity: huge

variety of ecosystems and habitats

Total number of species

• What patterns do you see?• How do you think scientists estimate the ``unnamed species’’?

Genetic biodiversity

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                                      European sheep breeders protecting genetic diversity of their breeds.

These are all one species

• These are all different species

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Genetic biodiversity

• For example, humans are one species, but we have a great variety of variation in many genes, such as blood type

• Each species has thousands of genes

Ecosystem biodiversity

What is an ecosystem??

• A community of organisms, its abiotic environment, and their interactions

Levels of ecological organization

• Biosphere: all life on Earth and the life-supporting region of Earth

• Ecosystem• Community?

– Populations of different species in the same area or habitat

• Population?– Group of individuals of same species in same area or

habitat

Origin of biodiversity

• EVOLUTION• Simple definition: Descent with modification

– Includes microevolution: changes in gene frequency from one generation to the next

• Includes macroevolution: descent of different species from a common ancestor

Natural Selection• Darwin’s big contribution• Inherently logical:

– Organisms produce more offspring than survive– Individuals vary in important characteristics– Many characteristics are inherited– SO:

• some individuals will be better suited to the environment• Those individuals will be more likely to survive and reproduce• Their offspring likely to be more suited to the environment

Definition of evolution

• Descent with modification– KEY: Evolution proceeds by changes in genes

• NOT JUST: ``Change over time’’– Lots of things change over time:

• Trees change color• Mountains erode• Continents move

– These are NOT evolution

Evolution is NOT• Just a process of getting better

• Something that organisms TRY to do

Geneology: sharing a common ancestor

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Evolution: sharing acommon ancestor

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Natural Selection

• Darwin’s big idea• HOW evolution can happen• Follows logically from some simple ideas:

Logic of natural selection

• Organisms produce more offspring than can survive.– Even elephants—if all survived . . .

• Often, these differences are due to differences in the genes and therefore can be inherited

Logic of natural selection

• Individuals vary in their characteristics

Logic of natural selection

• Often, these differences are due to differences in the genes and therefore can be inherited

Logic of natural selection -2

• As a result of individuals inheriting characteristics from parents:– Some individuals will be better suited to their

environment than others– These better-suited individuals produce more

offspring that survive• They may survive longer to reproduce• They may produce more offspring• They may produce offspring of higher quality

Logic of natural selection - 3

• As a result of some individuals producing more fit offspring:– Future generations will contain more genes, and

more characteristics, of the better-suited individuals.

– Better suited are called ``more fit’’

Natural selection doesn’t mean:

• Only the strong survive NO– Sometimes, other ways of being fit (e.g., hiding)

• Only the best-suited individuals survive NO– Many types may survive. Over long periods, the

more fit will leave more offspring.

Natural Selection

• Often MIScharacterized as ``evolution by random chance’’

• What IS random about natural selection?– The production of variation by mutation and

genetic recombination

Adaptations

• Traits that are successful in their environment

• An adaptation to one environment may be NEUTRAL or UNFAVORABLE in another environment

• May be simple—heavier coat in colder climate—or complex—the mammalian eye

Again:

• Adaptations are specific to the environment.– A zebra’s coat pattern is camouflage in the

African savannah. It would not be advantageous in a North American grassland.

– Running speed is advantageous for a cheetah on the savannah. But cats in the rainforest (e.g., jaguar) are not fast. Strength and stealth are more important than speed there.

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Adaptation examples: mimicry

• Some orchids have evolved to mimic wasps, fooling other wasps to ``mate’’ with them and thus transfer their pollen

Adaptation examples: more mimicry

• • Katydids have evolved a body form that looks like a leaf.

• Why? What is the advantage to the katydid?

Adaptation examples: still more mimicry

• • Non-poisonous king

snakes mimic poisonous coral snakes

• Many examples of mimicry in nature

Speciation

• One species evolves into another OR splits into two.

• How can this happen?– Geographic isolationallopatric speciation

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History of life

• As previous picture shows:– Complex creatures and structures have evolved– But simple life forms still common and

dominate in many habitats ``Earth still belongs to the bacteria’’

– Speciation generates diversity; extinction reduces it

Extinction

• The disappearance of a species from Earth• Local disappearance is called extirpation

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