AP Biology Macroevolution Part 2. Modes of Speciation Allopatric speciation Sympatric speciation.
Balance Between Speciation and extinction
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Transcript of Balance Between Speciation and extinction
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Biodiversity
BalanceBetween
Speciation and extinction
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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
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Total number of species
• What patterns do you see?• How do you think scientists estimate the ``unnamed species’’?
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Genetic biodiversity
•
European sheep breeders protecting genetic diversity of their breeds.
These are all one species
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• 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
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Ecosystem biodiversity
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What is an ecosystem??
• A community of organisms, its abiotic environment, and their interactions
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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
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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
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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
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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
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Evolution is NOT• Just a process of getting better
• Something that organisms TRY to do
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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:
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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
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Logic of natural selection
• Individuals vary in their characteristics
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Logic of natural selection
• Often, these differences are due to differences in the genes and therefore can be inherited
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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
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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’’
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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.
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Natural Selection
• Often MIScharacterized as ``evolution by random chance’’
• What IS random about natural selection?– The production of variation by mutation and
genetic recombination
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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
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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
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Adaptation examples: more mimicry
• • Katydids have evolved a body form that looks like a leaf.
• Why? What is the advantage to the katydid?
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Adaptation examples: still more mimicry
• • Non-poisonous king
snakes mimic poisonous coral snakes
• Many examples of mimicry in nature
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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
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Extinction
• The disappearance of a species from Earth• Local disappearance is called extirpation
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