What is a species?

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What is a species?

• a group of interbreeding populations that are
  reproductively isolated from other groups
• Appearance can be misleading in determining a
  species.

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Members of Different Species May Be Similar in
Appearance
Fig. 16-1
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Members of SAME Species May Differ in Appearance
Fig. 16-2
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How Do New Species Form?

• Speciation is the process by which new species
  form
• Speciation depends on two factors
• The isolation of populations must prevent gene
  flow and thus keep them similar
• Genetic divergence must occur, driven by genetic
  drift or natural selection

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• the different pathways to speciation fall into
  two broad categories
• allopatric speciation, the isolating mechanism is
  a physical barrier
• sympatric speciation, isolation occurs without
  geographical separation

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• Geographical separation of a population can lead
  to allopatric speciation (as in the web quest
  example)
• 5e Geological changes caused by such factors
  as volcanoes, earthquakes, continental drift, and
  change of course by rivers can lead to the
  separation of populations
• Allopatric speciation is believed to be the most
  common type of speciation, especially among
  animals

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Allopatric Isolation and Divergence
Part of a mainland population reaches to an
isolated island
The isolated populations begin to diverge due to
genetic drift and natural selection
Divergence may eventually become sufficient to
cause reproductive isolation
Fig. 16-9
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• isolation without geographical separation can
  lead to sympatric speciation too! (not in your
  web quest!)
• Sympatric speciation may occur when a
  geographical area contains two distinctly
  different habitats.
• Through natural selection, individuals of the
  species specialize in one habitat or the other
• Ex apple vs. hawthorn tree

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Sympatric Isolation and Divergence
Part of a fly population that lives only on
hawthorne trees moves to an apple tree
The flies living on the apple tree do not
encounter the flies living on the hawthorne
tree, so the populations diverge
Fig. 16-10
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• Now that we have defined a species how they
  come abouthow do we maintain a species?

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Types of isolation?

• 1) Behavioral Isolation occurs when two
  populations are capable of interbreeding but have
  differences in courtship rituals or other
  behaviors.

Birds of Paradise! http//www.youtube.com/watch?v
nS1tEnfkk6M
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• 2) Geographic Isolation occurs when two
  populations are separated by geographic barriers.
• Ex Canyon, mountain, body of water.

http//www.teachersdomain.org/asset/rr10_vid_repro
iso/
http//www.teachersdomain.org/asset/rr10_vid_repro
iso/
Salamanders http//video.pbs.org/video/1300397304/
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• 3) Temporal Isolation
• occurs when two populations reproduce at
  different times.
• Ex orchids

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• Mechanical isolation structure of reproductive
  organs is different enough that mating cannot
  occur.

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• Gametic isolation gametes are incompatible
  even if act of mating occurs, sperm cannot
  fertilize egg.

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HybridsThe Grey area

• This typically happens when a geographical
  barrier is removed. Animals that are closely
  related can mate and produce offspring.
• These offspring are typically sterile and/or weak

• A great example that works are mules. Strong and
  docile its a mix of the fragile horse (but
  easily trainable) and strong willed (but sturdy)
  donkey

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The infamous Liger
Fig. 16-8
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• There is also observed and experimental evidence
  of speciation. One example was in your web quest!

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• So, Darwins BIG IDEA was that natural selection
  takes place in populations that are isolated from
  one another and over LONG periods of time, small
  changes in allele frequencies from generation to
  generation can add up to BIG changes in species.
  This leads us to the idea of a universal common
  ancestor.

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• We can represent this idea with a diagram such as
  this. This only depicts MAJOR living categories
  of organisms and doesnt even include extinct
  organisms and their relationships!

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Why do species disappear?

• Species have a cycle!
• 1. New species
• 2. Stable species w/ many sub species
• THIS can then lead to 1. new species OR
• 3. stable species with few sub species
• 4. reduction in range and numbers
• 5. extinction!

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What Causes Extinction?

• Extinction is the death of all members of a
  species
• At least 99.9 of all species that ever existed
  are now extinct! WHA!!!
• The immediate cause of extinction is probably
  environmental change
• habitat destruction and increased competition
  among species

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• Small range
• Species inhabiting extremely limited ranges may
  become extinct if the area is disturbed
• The Devils Hole pupfish is found in only one
  spring-fed waterhole in the Nevada desert
• http//www.youtube.com/watch?vR_dP4ENjcL0
• Wide-ranging species normally do not succumb to
  local environmental catastrophes

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Very Localized Distribution Can Endanger a
Species
Fig. 16-13
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• Overspecialization
• Species that develop adaptations that favor
  survival in a specific environment are at risk of
  becoming extinct
• The Karner blue butterfly feeds only on the blue
  lupine plant
• The habitat of the lupine has been significantly
  reduced by development
• Loss of the lupine will lead to extinction of the
  Karner blue butterfly

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Extreme Specialization Places Species at Risk
Fig. 16-14
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• Other species
• Species that are unable to exploit resources more
  efficiently and effectively than their
  competitors may become extinct

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• Habitat change and destruction
• Extinctions due to prehistoric habitat change
  have had a significant effect on the evolution of
  organisms
• Human activities are the primary cause of
  present-day habitat destruction
• Clearing of tropical rainforests could lead to
  loss of up to half of all current species over
  the next 50 years

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MACROEVOLUTION

• Macroevolution is BIG changes in evolution

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Macroevolution

• Is concerned without how new taxonomic groups
  came to be
• I.e. how did mammals evolve from ancestral
  reptiles

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Microevolution? Macroevolution

• Usually a population gets separated
• Different populations encounter different
  environments and accumulate different traits
• When they are so different they cant reproduce-
  they are considered a new species

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Patterns of Evolution

• Adaptive Radiation
• A single species or a small group of species
  evolving into several different species that live
  in different ways.
• Example Darwins Finches on the Galapagos
  Islands one species from the mainland evolved
  into at least 12 different species

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Adaptive Radiations

• Frequently one really advantageous trait leads to
  the development of many new species
• i.e. wings allowed birds to fly- and many species
  of bird evolved from one ancestor

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Interpreting Evolutionary Trees
present
Each line represents a species
In an adaptive radiation, multiple speciation
events may occur rapidly enough that biologists
cannot be certain of their order
time
Forks represent speciation events
past
(a) Evolutionary tree
(b) Evolutionary tree representing adaptive
radiation
Fig. 16-11
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• Convergent Evolution
• Results in similarities in body structures among
  animals that DO NOT share a RECENT common
  ancestor. This occurs due to similar
  environmental demands.
• Examples Shark, whale, seal, penguin. Have
  fins, flippers, and paddles they are all
  streamlined to reduce drag in water. Look
  similar due to common environmental history
• Analogous structures look similar but have
  different structure

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• Coevolution
• Process in which two species evolve together in
  response to change in each other
• Examples Orchid and moth, insects and plant
  poison, hummingbird flower structure.

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• How Quickly Does Evolution Happen?
• Gradualism
• Slow and steady. Small changes in populations
  over time.

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• Punctuated Equilibrium
• long stable periods followed by brief periods of
  rapid change

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• Note in geologic time short and rapid can
  mean hundreds of thousands to millions of years!
  The fossil record shows both of these theories as
  possibilities.

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• The Role of developmental
• Genes called hox genes
• Small changes in developmental genes during the
  embryonic stage can have a huge effect on an
  organism. This adds to the variation involved in
  natural selection

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• http//www.pbs.org/wgbh/evolution/library/03/4/l_0
  34_04.html
• Hox gene video (5 min)