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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
Douglas-fir
Shade-tolerant secondary
succession species, e.g.,
western hemlock,
Pacific yew
Forest floor species, e.g.,
bryophytes
What about introduced species?
Sitka spruce
Alaska & PNW
Sitka spruce works at its profession
in both regions of the world the
niche is realized in both places
Scotland
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
phenotypes.
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
Number of individuals
in the population
The effects of pollution on the
selection of Peppered moths.
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
Range of values for the trait at time 3
Page 286
Artificial Selection
Examples of directional selection
Stabilizing selection – insect induction of galls
Number of individuals
in the population
Larvae of Eurosta solidaginis
induce gall formation
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
Range of values for the trait at time 3
Stabilizing selection is responsible for
the long term existence of some types of
organisms that have origins hundreds
Page 288
of millions of years ago
in the population
Number of individuals
Disruptive (diversifying) selection
in the population
Number of individuals
Range of values for the trait at time 1
in the population
Number of individuals
Range of values for the trait at time 2
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!
Bacteriophage
T4 injects DNA
into the E. coli cell
DNA replicates,
new phage is
produced and
released when
the cell dies
Log10 density, numbers/ml
Diversifying selection
E coli
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
Cactaceae Mexico and Texas
Euphorbia valida
Euphorbiaceae South Africa
Ecological Niche
1.
Plants accumulate matter
and make growth
The amount of growth depends
upon ecological conditions
2.
Plant growth is an
organized process
following rules of anatomy
and morphology
Plant form determines plant
function and varies with
ecological niche
3.
Plants maintain their heat
and water balance
Physical conditions of water supply,
temperature and radiation vary
between ecological conditions and
pose different problems for plants
4.
Plants have a life cycle with
reproduction and dispersal
5.
Evolution is a constant
process
Life cycles are adapted to suit
ecological conditions
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
NAME:
corn
vanilla orchid
Page 320
Constructing a cladogram
Lamprey
Taxon
Jaws Limbs Hair Lungs Tail Shell
Turtle
Cat
Traits (Characters)
Lamprey
-
-
-
-
+
-
Turtle
+
+
-
+
+
+
Cat
Gorilla
Lungfish
Trout
Human
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
-
-
Gorilla
Taxon
Human
Using the lamprey
as the outgroup
Jaws Limbs Hair Lungs Tail Shell
Lungfish
Trout
Traits (Characters)
Presence/Absence
of characters
Lamprey
0
0
0
0
0
0
Turtle
1
1
0
1
0
1
Cat
Gorilla
Lungfish
Trout
Human
1
1
1
1
1
1
1
0
0
1
1
1
0
0
1
1
1
1
0
1
0
1
0
0
1
0
0
0
0
0
Organise by shared
derived traits
Fig. 20.14, p. 324
Cladistic Analysis
turtle, gorilla, trout,
cat, lugfish, human
lamprey
lamprey trout
turtle, gorilla, cat,
lugfish, human
lungs
jaws
jaws
Relative relatedness
lamprey
trout
gorilla human
lungfish
turtle
cat
In-group and out-group
Primitive characters
Derived characters
node 1
Parsimony
node 2
Use of molecular methods
Fig. 20.15, p. 324-25
Any Questions ?
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