UW-Madison BIOLOGY 101 - Adaptive radiation and mass extinctions (2 pages)

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Adaptive radiation and mass extinctions

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Adaptive radiation and mass extinctions


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University of Wisconsin, Madison
Biology 101 - Zoology 101: Animal Biology
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Zoology101 Animal Biology Last Lecture Outline 1 Evolutionary trap 2 Speciation and Macroevolution Lecture 37 Current Lecture 1 Allopatric and Sympatric Speciation 2 Adaptive Radiation and Mass extinctions Allopatric and Sympatric Speciation Allopatric geographic separation of population rivers islands Divergence greatly reduced gene flow genetic drift founder effect Natural selection Even if population is restored interbreeding may no longer be possible Channel Islands Founder effect likely help set the stage Isolation from gene flow migration greatly reduced Unique selective environment on island probably helps promote divergence Islands and conservation islands usually have most biodiversity for species to form geographic isolation must be followed by reproductive isolation Sympatric speciation speciation without geographic isolation most common mechanism Polyplpoidy many chromosomes Error during meiosis changes number of chromosomes in gametes offspring offspring may be viable and fertile divergence occurs within one generation Most common in plants wheat oat potatoes cotton Can occur in animals less common reproductive isolation with in the same population different mating preference habitat preference disruptive selection How much genetic change is required for speciation Impossible to generalize cumulative divergence slow single few mutations leading to reproductive isolation How quickly does speciation occur Patterns can often be inferred from fossil records morphological or molecular data Punctuated equilibrium theory in evolutionary biology which proposes that most species will exhibit little net evolutionary change for most of their geological history remaining in an extended state called stasis Gradualism continued divergence until reproductive isolation is complete The interval between speciation events can range from 4 000 to 40 million years Ave 6 5 million years Adaptive radiation and Mass extinction Adaptive radiation periods of evolutionary change in which groups of organisms form many new species can occur when species colonize in new environments silversword on Hawaiian islands Can arise due to evolution of a key adaptation hard body parts flowers Key events in earth s history Life is old and it has taken a long time to get where we are today On an hour scale humans have been around 2 seconds Several key events are linked with evolution of novel adaptations photosynthesis eukaryotic organisms colonization on land Boundaries between geological divisions are often marked by big changes in dominant organisms Mass extinctions Boundaries between geological divisions often marked by mass extinction events 5 mass extinctions loss of 50 or more of the population often associated with big environmental changes onset of ice age meteor volcanic activity Cretaceous mass extinction event 65 million years ago lost 50 80 of marine species several hypothesis asteroid impact collisions volcanic activity climate change took 5 10 million years to restore diversity Reduction in competition brought rise to mammals

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