The EvolutionEcology Connection

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• The Evolution-Ecology Connection

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• How are evolution and ecology related?
• Ecology involves understanding of relationships
  of organisms with each other and with their
  environment
• Evolution involves changes in species in response
  to interactions with each other and with their
  environment

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• Contributions to Modern Evolutionary Thought
• Malthusian catastrophe
• Thomas Malthus economist, social philosopher
  populations of all organisms eventually out-grow
  available resources

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• Gregor Mendel (1822-1884) concepts and patterns
  of inheritance

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Catastrophism Vs Uniformitarianism.

• Catastrophism- he Earths surface has been
  scarred by catastrophic natural disasters
• Charles Lyell theory of uniformity surface of
  earth has gradually changed, earth much older
  than previously recognized
• "The Present is the Key to the Past"

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Fig. 2.3
Darwins Voyage
Charles Darwin synthesis of theory of evolution
based on natural selection
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Out of this study grew several related theories

• one, evolution did occur
• two, evolutionary change was gradual, requiring
  thousands to millions of years
• three, the primary mechanism for evolution was a
  process called natural selection and
• four, the millions of species alive today arose
  from a single original life form through a
  branching process called "speciation."

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• Forces driving evolution
• over-reproduction
• genetic variability
• selective pressure
• environment (food, temperature, etc.)
• disease
• predators
• survival and reproduction of organisms best
  suited to their environment

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• Read Scot Norris paper Evolution's "Driving
  Force" Shifts Based on Behavior, Study Says
• http//news.nationalgeographic.com/news/2006/11/0
  61116-lizard-evolution.html
• Read Jonathan Losos' paper "Adaptation and
  speciation in Greater Antillean anoles"
• http//biosgi.wustl.edu/7Elososlab/losos.2004.ad
  aptivespeciationbook.pdf

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• Genetics and Evolution
• Trait appearance/ability to carry out some
  process
• Phenotype appearance of an organism due to a
  specific trait or combination of traits
• Gene genetic information (region on a
  chromosome) which codes for a specific trait.
• Allele variant form of a gene

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• Natural selection can favor, disfavor, or
  conserve the genetic make-up of a population
• Stabilizing Selection
• Directional Selection
• Disruptive Selection

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Stabilizing Selection- also known as Purifying
Selection

• Stabilizing selection acts to impede changes in a
  population by acting against extreme phenotypes
  and favoring average phenotypes.- prevents
  divergence from form and function but genetic
  diversity decreases

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Directional Selection

• Directional selection leads to changes in
  phenotypes by favoring an extreme phenotype over
  other phenotypes in the population. Increase
  frequency independent of dominance

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Disruptive Selection- also called Diversifying
selection

• Disruptive selection creates bimodal
  distributions by favoring two or more extreme
  phenotypes over the average phenotype in a
  population.- driving force of sympatric
  speciation- (Finch population Darwin)

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Fig. 2.18
Ecosystems ability to absorb shocks and
disturbances
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• What is a species?
• A group of similar appearing organisms which
  share the same gene pool
• Species evolve to fill different niches
• Example Finch evolution in Galapagos Islands
• Result Radial Evolution
• Single ancestral form
• Many generations ? unique species for different
  niches

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Fig. 2.10
Speciation of Finch on Galapagos Islands- C.
Darwin
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• How do new species arise?
• Sympatric speciation
• Allopatric speciation

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Sympatric speciation

• occurs as a species fills different niches within
  the same habitat or geographic area
• Spread of species into new areas
• Founding population in isolated location
• Geologic changes gradual process

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Allopatric speciation

• spatial isolation occurs due to geographic
  isolation
• Genetic changes (as ploidy levels in plants)
• Disruptive selection divergent genotypes favored

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• Geographic Variation Within Species
• Cline measurable, gradual change in a trait over
  geographic region
• Ecotype Population adapted to particular local
  environment
• Geographic isolate reproductively isolated
  populations
• subspecies

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Gauses Law- competative exclusive principle

• Georgii Frantsevitch Gause
• a theory which states that two species competing
  for the same resources cannot stably coexist, if
  the ecological factors are constant. Either of
  the two competitors will always have an advantage
  over the other that leads to either the
  extinction of the inferior competitor or its
  evolutionary shift towards a different ecological
  niche.

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• Geographic Isolation of Ensatina escholtzii
  populations in CA
• ring species geographically isolated
  populations surround uninhabitable area
• Adjacent populations can interbreed
• Reproductively incompatible at extremes (black)

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Local E.escholtzii
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• Changes within a species are due to changes in
  its gene pool causes
• Selective pressures
• Genetic drift and bottleneck effects
• Isolated populations
• Effect greater in small populations

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Variation Within Populations

• Variation in Plant Populations
• Many plant species differ dramatically in form
  from one elevation to another.
• Clausen et.al. found evidence of adaptation by
  ecotypes to local environmental conditions in
  Potentilla glandulosa.
• Distinctive ecotypes- distinct entity of animal
  or plant or organism closely linked to its
  ecological surroundings

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Variation in Plant Populations

• Molecular and Morphological Information
• Hansen et. al. used randomly amplified
  polymorphic DNA (RAPD) along with morphological
  data to support separation of three species of
  Potentilla.

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• Ecotypes Potentilla glandulosa sticky
  cinquefoil
• 3 ecotypes
• Alpine
• Midelevation
• lowland

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• How genetically different are ecotypes?
• Work with Potentilla nivea (a species complex)
• Morphological (appearance) observations suggest
  three species
• Molecular analysis via RAPID study supports
  morphological species distinction

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Fig. 8.6
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• Summary
• Organisms become tailor made for their role
  niche within an environment by processes of
  evolution
• New species arise from preexisting species
• New species arise as organisms become
  reproductively isolated
• Reproductive isolation may often result in
  genetically different populations

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Questions

• How do we know that a species is a species if we
  do not directly observe whether it can interbreed
  with other organisms? 
• If one population is the ancestor to another, how
  do we decide if they are more than one species? 
• Does extinction imply mistakes by an "intelligent
  designer"?
• How, in terms of Gause's law, does a catastrophic
  event influence subsequent evolutionary events.
• Which (and why) are more likely to become
  extinct, a highly specialized species extremely
  well adapted to a particular niche, or a less
  specialized generalist?