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					Diversity and Selection

    What’s wrong!

    Why is it wrong?

 Could this ever happen?
               Ecological niche
The total requirements of a species for all resources
and physical conditions determine where it can live
and how abundant it can be at any point. These
requirements determine the species
ecological niche.
The ecological niche of a plant might be determined by:
   the range of temperatures the species can tolerate,
   the intensity of light it requires for photosynthesis,
   humidity regimes,
   minimum quantities of soil nutrients.
The ecological niche can be thought of as a plants
address and it’s profession (these are not always
the same but often are)
  Ecological niches
in old-growth forest

Long-lived pioneer

Shade-tolerant secondary
succession species, e.g.,
       western hemlock,
       Pacific yew

Forest floor species, e.g.,
      What about introduced species?

Sitka spruce      Sitka spruce works at its profession
  Alaska & PNW    in both regions of the world the
                  niche is realized in both places

                     Humans move plants around –
                     but the plants only thrive if the
                     new environment is a suitable
                     ecological niche.
How do plants become suited to an
        ecological niche?
         Natural Selection
Darwin’s view:
    Natural selection is the outcome of
    variations in shared traits that influence
    which individuals of a population survive
    and reproduce in each generation

    Natural selection can lead to increased
    fitness – that is to an increase in
    adaptation to the environment
                                          Page 285
Darwin’s argument summarized:
Populations have reproductive capacity to increase
But no population can increase indefinitely
            So there will be competition between
            individuals in a population
All individuals in a population have the same genes
But genes occur in different forms resulting in different
            Some phenotypes are better than than
            others at helping the individual compete.
            The alleles producing those phenotypes
            increase over time.                    Page 285

Natural selection can lead to increased fitness –
increased adaptation
      What actually happens is more complicated
      than simply an “increase in fitness”

      Three types of Natural Selection
Directional selection
       An environmental pressure causes a change
       in frequency of alleles

Stabilizing selection
       Multiple environmental pressures constrain
       evolution and may reduce variation in alleles
Disruptive (diversifying) selection
       Environmental variation favors opposite ends
       of a range of natural variation.
                                              Pages 286-289
                                               Directional Selection
                                                                  The effects of pollution on the
Number of individuals

                                                                  selection of Peppered moths.
  in the population

                        Range of values for the trait at time 1
Number of individuals
  in the population

                        Range of values for the trait at time 2
Number of individuals
  in the population

                        Range of values for the trait at time 3
                                                                                                    Page 286
    Artificial Selection
Examples of directional selection
                   Stabilizing selection – insect induction of galls
                                                                  Larvae of Eurosta solidaginis
Number of individuals

                                                                  induce gall formation
in the population

                        Range of values for the trait at time 1

                                                                            Wood peckers eat
                                                                            larvae in big galls.

                        Range of values for the trait at time 2

                                                                               The parasitic wasp penetrates
                                                                               the walls of thin galls

                                                                  Stabilizing selection is responsible for
                                                                  the long term existence of some types of
                        Range of values for the trait at time 3   organisms that have origins hundreds
                                                                  of millions of years ago              Page 288
   Disruptive (diversifying) selection

Number of individuals

                        in the population

                                            Range of values for the trait at time 1
Number of individuals

                        in the population

                                            Range of values for the trait at time 2
Number of individuals

                        in the population

                                            Range of values for the trait at time 3

                                                                                      Page 289
                               Escherichia coli
You’ve got millions of these bacteria inside of you!

                                                              Occasional mutations,
                                                              combined with
                                                              inadequate cooking of
                                                              meat products, can
                                                              cause outbreaks of
                                                              food poisoning.

Kingdom: Eubacterium
Scientific Name: Escherichia coli
Image Courtesy of: Shirley Owens, Center for Electron Optics, MSU
Image Width: 9.5 microns
Image Technology: SEM (Scanning Electron Microscope)
   An experiment: place E. coli in a solution in a chemostat – a
   vessel that has a constant input of glucose …
             … then introduce the T4 bacteriophage!

T4 injects DNA
into the E. coli cell
                                                   DNA replicates,
                                                   new phage is
                                                   produced and
                                                   released when
                                                   the cell dies
                            Diversifying selection
                                                                   E coli
Log10 density, numbers/ml

                             Why did the E. coli increase?

                                                                   T4 phage

                                   How did the virus survive after
                                   emergence of a resistant mutant?

Emergence of an E. coli
resistant mutant
                                It so happened that the phage resistant mutant
                                was less efficient at glucose metabolism than
                                the non-mutant – so some non-mutants
                                continued to survive
               Convergent evolution
     Species from different evolutionary branches
     may come to resemble one another if they live
     in similar environments

Astrophytum asterias                    Euphorbia valida
Cactaceae Mexico and Texas   Euphorbiaceae South Africa
                                           Ecological Niche
1.   Plants accumulate matter        The amount of growth depends
     and make growth
                                     upon ecological conditions

2.   Plant growth is an              Plant form determines plant
     organized process               function and varies with
     following rules of anatomy      ecological niche
     and morphology
3.   Plants maintain their heat      Physical conditions of water supply,
     and water balance               temperature and radiation vary
                                     between ecological conditions and
                                     pose different problems for plants
4.   Plants have a life cycle with
     reproduction and dispersal      Life cycles are adapted to suit
                                     ecological conditions
5.   Evolution is a constant
     process                         Selection occurs that suits plants for
                                     a particular niche
                   Yucca glauca

Yucca brevifolia
Naming organisms and its scientific basis

  Binomial classification for all organisms
       Taxonomy – how organisms are known

  Hierarchical naming system
       Classification systems that organize species
       according to their relationships

  Cladistic analysis
       The method of classifying according to
       similarities and differences
          The hierarchical naming system

KINGDOM   Plantae                         Plantae
PHYLUM    Anthophyta (flowering plants)   Anthophyta
CLASS     Monocotyledonae (monocots)      Monocotyledonae
ORDER     Commelinales                    Orchidales
FAMILY    Poaceae                         Orchidaceae
GENUS     Zea                             Vanilla
SPECIES   Z. mays                         V. planifolia

COMMON              corn                      vanilla orchid
                                                               Page 320
            Constructing a cladogram
             Taxon                 Traits (Characters)

  Turtle                Jaws Limbs Hair Lungs Tail Shell

             Lamprey     -     -     -     -      +      -
             Turtle      +     +     -     +      +      +
                                                              of characters
             Cat         +     +    +      +      +      -
             Gorilla     +     +    +      +      -      -
     Cat     Lungfish    +     -    -      +      +      -
             Trout       +     -    -      -      +      -
             Human       +     +    +      +      -      -
                                                             Using the lamprey
                                                             as the outgroup
             Taxon                 Traits (Characters)

Lungfish                Jaws Limbs Hair Lungs Tail Shell

             Lamprey     0     0     0     0      0      0
             Turtle      1     1     0     1      0      1    Organise by shared
    Trout    Cat         1     1     1     1      0      0    derived traits
             Gorilla     1     1     1     1      1      0
             Lungfish    1     0     0     1      0      0
             Trout       1     0     0     0      0      0
             Human       1     1     1     1      1      0           Fig. 20.14, p. 324
                                     Cladistic Analysis
                   turtle, gorilla, trout,                        turtle, gorilla, cat,
 lamprey                                         lamprey trout
                   cat, lugfish, human                              lugfish, human

                       jaws                                       jaws

           Relative relatedness
                                                                 In-group and out-group
lamprey            lungfish                    gorilla human
           trout              turtle     cat
                                                                 Primitive characters

                                                                 Derived characters
                                             node 1
                                       node 2
                                                                 Use of molecular methods
                                                                                          Fig. 20.15, p. 324-25
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