Transcript Topic 5: Ecology and Evolution

Topic 5: Ecology and
Evolution
5.4: Evolution
Evolution slider
The Big Bang
The Simpsons
Earth’s evolutionary past:
• Life from more than 500 million years ago
was greatly different from life today.
• Fish fossils have only been found in rocks
500 million years old or younger. (less than
15% of history of life)
• None of todays top predators existed at
the time of dinosaurs or before.
• Few organisms today have identical forms
in the fossil record. (Exceptions:
cockroaches, ferns, certain sharks)
Charles Darwin
1809 - 1882
Attenborough on
Darwin
“……can we doubt (remembering that many more individuals are born than can
possibly survive) that individuals having any advantage, however slight, over
others, would have the best chance of surviving and procreating their kind? On
the other hand, we may feel sure that any variation in the lease injurious would
be rigidly destroyed. This preservation of favourable variations and the rejection
of injurious variations, I call NATURAL SELECTION.” – On the Origin of Species
How Fossils Form
 Organism dies and gets buried.
 as layers of sediment are added, pressure increases, causing the sediments to
compact into rock.
 As body decays, minerals seep into the it, filling spaces where gases or fluids
used to be — this is known as permineralization.
 Alternately, the minerals in it chemically break down and are reformed or
replaced.
 Eventually, most or all of what is left is a rock-like copy of the body.
Sometimes, organisms are preserved in substances such as amber, ice or tar, as
well.
Occasionally, imprints get filled with sediments that harden into rock, creating
natural molds or casts. A good example is animal footprints
Life 500 million years ago was very
different from life today
 Fish fossils only date back to 500 million
years ago or younger. (< 15% of history
of life)
 None of the top predators today existed at
the time of the dinosaurs or before
 Other than some sharks, cockroaches and
ferns, most living organisms have no
identical form in fossil record

Evidence for Evolution: fossil
record
Whales in the desert
Whale evolution: http://www.youtube.com/watch?v=I2C-3PjNGok
Heike’s crabs
http://www.youtube.com/watch?v=nVSJNhUhV4&feature=related
*Structures which are similar in form and
function but are found in dissimilar species.
Example: pentadactyl limbs are fivefingered limbs which differ in shape,
number of bones and function.
*Evidence for a common ancestor. –
different uses, but basic shape and
placement are the same
Homologous structures
Homologous Structures
1. Population produces more offspring
than the environment can support.
Utilize nutrients/energy of parents
Force competition: food, mates, space
Disease, predation, parasitism
Leads to adaptive behaviors
Ex. Cuckoo bird
Ex. Flowers & insects
2. Variation
Sexual Reproduction
Evolutionary Mechanisms
Competition
for food
• finding
• catching
• opening
• digesting
Predation
• catching
• fighting
• avoiding
• escaping
Competition
for mates
• attracting
• fighting
• fertilising
• providing for
Parasitism
• invading
• avoiding
• removing
• tolerating
Disease
• invading
• avoiding
• removing
• tolerating
Competition
for spaces
• living
space/shelter
• nesting
• reproductive
space
Examples
 Camouflage
 Shapes of body parts such as beaks
 Mating preferences
Variation & survival
1.


DNA mutation
May produce disease
May produce advantage
Each generation only a few mutations.
Most are not useful or harmful. Result is a
wide array of variation
Causes of variety
as a result of
Random Mutation
DNA
Replication
Viral
infection
Sexual Reproduction
Meiosis
Crossing over
(recombination)
prophase I
Random
fertilisation
Random
assortment of
chromosomes
metaphase 1
Evolution lab
When too many individuals exist for limited
resources, survival is determined by
surroundings & compatibility of
characteristics w/ surroundings.
Natural Selection
Over production of offspring w/ variation
 Useful increase/harmful decrease
survival chance
2. Genetic characteristics poorly adapted to
environment - Less successful at
accessing resources
3. Genetic characteristics well adapted to
environment – more successful at
surviving
1.
Natural Selection Steps
4. Organisms that survive to adulthood
more likely to reproduce & pass on
successful characteristics
5. Over many generations, accumulation of
heritable changes results in evolution.
Gene pool has changed.
Steps cont.
Staphylococcus aureus - bacteria
Variation: MRSA – Methycillin-resistant
MSSA – Methycillin susceptible
Environmental change: application of
methycillin
Result: MSSA is killed
MRSA survives & reproduces
MRSA population increases, dominant strain
Methycillin no longer effective against infection
Antibiotic resistance in bacteria
Bacteria can continue to change and
become resistant to all antibiotics –
superbacteria
Bacteria reproduce asexually. Little
variation.
Sources: mutation, plasmid transfer.
Variation: Most individuals are susceptible to
pesticide. Some carry a gene for resistance
Environmental change: pesticide sprayed
Result: Susceptible population reduced.
Resistant population survives and
reproduces
Gene for resistance increases in frequency
Resistant population dominates
Examples: resistance of malaria to DDT, Rats
to poison
Pesticide resistance
Not artificial selection:
Humans are responsible for environmental
changes- creating environmental changes
– pressure organism to adapt or parish.
*adaptations not “chosen” – results of
environmental conditions.
*solution at individual level- significant to a
specific population
Other examples of evolution in action include resistance to pesticides