Evolution of Biological Communities

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Evolution of Biological Communities
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Outline

• I. Evolution by Natural Selection
• A. Background
• B. Elements of Theory
• C. Examples
• II. Population Genetics

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Background

• Charles Darwin was not the first scientist to
  think about lifes origins or about how species
  might change over time.
• Lamarck
• Study of fossils suggested life evolves
• Inheritance of acquired characteristics

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Charles Darwin (1809-1882)

• Even as a boy, interested in nature
• Accumulated observations leading to theory
• Lyells geology
• Galapagos Islands
• Artificial breeding programs
• Malthus theories of population growth
• Through these observations, Darwin began to see
  adaptation and the origin of new species as
  closely related processes
• Descent with modification

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Evolution by Natural Selection

• Observation In any species, more offspring are
  born into a population than actually survive to
  reproduce
• Observation Resources in any environment are
  limited
• Inference production of more individuals than
  the environment can support leads to a struggle
  for existence between individuals of a
  population, with only a fraction of their
  offspring surviving each generation

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Evolution by Natural Selection

• Observation Members of a population vary in
  their characteristics
• Observation Much of this variation is heritable
• Inference Survival depends in part on inherited
  traits. Individuals whose inherited traits give
  them a high probability of surviving and
  reproducing will leave more offspring than those
  without these inherited traits
• Inference leads to gradual accumulation of
  these favorable characteristics in the population
  over generations

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Natural Selection

• Adaptations traits which give a selective
  advantage to some individuals in a population ie.
  traits which increase an organisms chances of
  survival and reproduction
• Selective Agent/Pressure environmental factors
  that influence which individuals leave more
  offspring (favor certain adaptations within the
  population)
• Natural Selection is the name given to the
  process of differential reproduction-the
  mechanism by which evolution takes place

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Important Points

• Being fit is relative, if the environment
  changes, new traits may be favored and
  individuals suited to one environment may not be
  suited anymore
• It is not survival of the fittest but survival
  and reproduction of the fittest!
• Natural selection does not have foresight-no
  direction toward the perfect organism-blind
  process whereby existing variation is sorted out
  by fitness.

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Population Genetics

• Variation
• Heredity an important and necessary part of the
  theory, not well understood in Darwins time
• As study of heredity and genetics developed, the
  underlying control of an organisms traits has
  become better understood
• 2 types of variation
• Non-heritable no genetic basis, cant be passed
  down, often of environmental origin
• Heritable actual change in the DNA of an
  organism via mutation or mutagen, passed down via
  egg or sperm

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Non-heritable Variation
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Heritable Variation
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Population Genetics

• Gene specific sequence of nucleotides in DNA
  which code for a particular protein
• Allele alternate forms of a gene
• Examples
• More precise definition of evolution
• Evolution is a change in the allele frequencies
  of a population of organisms over time
• Population a group of interbreeding
  individuals, live in the same area at the same
  time