Download Ch. 21-Forces within Populations Notesheet

Name ____________________________________ Date ____________ Period _____
Evolutionary Forces within Populations
Raven Ch. 21
Big Idea 1: THE PROCESS OF EVOLUTION DRIVES THE DIVERSITY AND UNITY OF LIFE.
It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to
change.
― Charles Darwin (1859)
Essential Knowledge:
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Natural selection is a major mechanism of evolution
Natural selection acts on phenotypic variations within populations.
Evolutionary change is also driven by random processes.
Biological evolution is supported by scientific evidence from many disciplines including mathematics
Organisms share many conserved core processes and features that evolved and are widely distributed among
organisms today.
Phylogenetic trees and cladograms are graphical representations (models) of evolutionary history that can be
tested
Speciation and extinction have occurred throughout the Earth’s history.
Speciation may occur when two populations become reproductively isolated from each other.
Populations of organisms continue to evolve.
There are several hypotheses about the origin of life on Earth, each with supporting scientific evidence.
Scientific evidence from many different disciplines supports models of the origin of life.
Natural selection is a major mechanism of evolution
Natural Selection- traits that improve ___________________ or _____________________ will
accumulate in the _________________________
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_____________________ change-?? ________________________________________
______________________________________________________________________
Genetic drift- frequency of traits can change in a population due to ____________________ events
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_____________________ change-??________________________________________
______________________________________________________________________
Example: ______________________________________________________________
Types of Natural Selection:
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Selection acts on any trait that affects survival or reproduction
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___________________ selection
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___________________ selection
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___________________ selection
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Predation selection
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act on both ____________________ & _____________________
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speed (ex. _______________________________________________)
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behaviors (ex. _______________________________________________)
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camouflage & mimicry (ex. _____________________________________________)
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defenses (physical & chemical) (ex. ______________________________________)
Physiological Selection
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Acting on body functions
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disease resistance (ex. _______________________________________________)
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physiology efficiency (using oxygen, food, water)
(ex. _______________________________________________)
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biochemical versatility (ex. _____________________________________________)
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protection from injury (ex. ______________________________________________)
One critter’s trash is another critter’s treasure!
Sexual Selection
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Acting on reproductive success
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attractiveness to potential mate (ex. ______________________________________)
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fertility of gametes (ex. _______________________________________________)
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successful rearing of offspring (ex. _______________________________________)
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Survival doesn’t matter if you don’t reproduce!
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Sexual dimorphism- _______________________________________________________
_________________________________________________________________________
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Fitness markers- __________________________________________________________
_________________________________________________________________________
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Acts in all _____________________ reproducing species
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influences both _________________________ & ___________________________
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Effects of Selection
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Changes in the _________________________________ of a ______________________
Genetic Drift
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________________________ events ________________________ frequency of traits in a
population
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____________________ adaptation to environmental conditions
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____________ selection
Examples:
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_______________________ effect
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small group splinters off & starts a new colony
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it’s __________________ who joins the group
_________________________
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a ______________________ reduces population to _________________
number & then population ________________________ & expands again
but from a _______________________who survives disaster may be
random.
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Gene Pool: ___________________________________________________
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Founder effect
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When a new population is started by only a ____________________ of individuals
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just by _______________________ some rare alleles may be at high frequency;
others may be missing
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__________________________ the gene pool of new population
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human populations that started from small group of colonists
Example:
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__________________________________________________________
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__________________________________________________________
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__________________________________________________________
Bottleneck effect
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When large population is drastically _______________________________________________
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____________________, _________________________, ________________…
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loss of _________________________ by chance event
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________________ lost from gene pool
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________________ due to fitness
narrows the gene pool
Cheetahs
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All cheetahs share a small number of alleles
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less than 1% diversity
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as if all cheetahs are
identical twins
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2 bottlenecks
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10,000 years ago
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Ice Age
last 100 years
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poaching & loss of habitat
Conservation issues
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Bottlenecking is an important concept in conservation biology of endangered species
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loss of alleles from gene pool
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reduces variation
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reduces adaptability
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