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13 The Changing Biosphere
When we finish this chapter you should be
able to:
Define natural selection
Explain how geographical isolation and
reproductive isolation lead to the evolution
of new species
Discuss how mutations increase diversity
13.1 Clues from the past: The fossil record
Biosphere is constantly changing (slowly)
Abiotic: Geologic and Atmospheric (climate) changes
ex: oxygen added to atmosphere over time
warming and cooling cycles (ice ages)
Biotic: Fossil record shows how a
organisms have changed over
time.  Evolution
Old species become adapted
(evolve) to new conditions or
become extinct. Ex: dinosaurs
New species arise under new
climate conditions to replace
old
Ex: Horse: from forest browser to
grassland grazer
Well adapted species can survive for
long periods of time
Ex: Opossum – only marsupial
(pouched) animal left in N. America
Living fossils – well adapted species
survive unchanged for long periods of
time
Ex: Coelacanth (lobed fin fish)
unchanged for 100 million years
is missing link between fish and four
legged animals (amphibians, etc.)
13.1 Section Review
1. Describe some of earth’s ongoing changes
that affect the abiotic part of the biosphere
2. Compare the composition of earth’s
primitive atmosphere with our present-day
atmosphere
3. How does horse evolution show
adaptations to a changing environment
13.2 Evolution through Natural Selection
Population- organisms of a
species – that interbreed
in nature
Members have Variations:
differences in their traits
due to their different
genes, that help them
survive and reproduce
Over production (compared to
limited resources - food,
etc.) leads to natural
selection of best adapted
ones, to pass on their genes
Adaptations – traits which help an organism
to survive – new traits arise through
mutation: change in the genes
Pandas thumb
Isolation - New species arise when some of
the individuals become isolated and stop
interbreeding with the rest
Geographic isolation – separation of a
population by mountain range, river, etc.
separated group changes differently from
original group
ex: grand canyon: Abert squirrel and
kaibab squirrel (north rim)
Leads to Reproductive Isolation
(new species can’t breed with old)
Convergent Evolution
Different animals adapted to
similar lifestyles
ex: mouse deer (goat)
agouti (rodent)
royal antelope (deer)
each is small, brown
– live in tropical rainforest
Also Auk (north pole)
and penguin (south pole)
13.2 section review
1. Explain how natural selection is similar to
people breeding animals.
2. List 3 adaptations that help mammals, like
us, survive in their environment.
3. Compare the terms geographic isolation
and reproductive isolation.
4. Explain convergent evolution by
comparing fish and whales
13.3 diversity and mutations
Gene pool – the collection of all
variations for different genes
for traits in a population – get
mixed during sexual
reproduction
Mutation – change in a gene,
creates new or variation in
traits
- only mutations in egg cells
can be passed on
- usually negative and fatal –
occasionally beneficial
Peppered Moth
England / Industrial revolution
– darkening of trees from soot
Moth population evolved from
light color to dark color over
100 years.
(Now evolving back)
Human Adaptation
Quechua Indians of the high
Andes in S. America have
larger lungs, and more red
blood cells to carry O2 in the
thin air at high altitude
In what type of environment
would webbed feet be an
advantage?
Rate of Evolutionary Change
Two theories:
Gradualism – gradual changes over a long
period of time.
Vs.
Punctuated Equilibrium – long stable periods
with brief periods of changes (1000 years)
How would climate change contribute to
these?
Preserving Diversity
Greater diversity (variety) in traits allows
populations to adapt to changes, rather than
become extinct.
Ex: Cheetah – endangered with little genetic
diversity - one disease could wipe out entire
species
Ex: Depleted Fish stocks – due to overfishing
– cod, blue-fin tuna, swordfish
Avoid also – grouper, snapper, Chilean sea
bass
Better – salmon, mahi-mahi, tilapia, striped
bass, halibut
13.3 section review
1. How do mutations affect species
diversity?
2. What role do mutations play in natural
selection?
3. Describe the main difference between
gradualism and punctuated equilibrium
4. What can you do at the supermarket top
preserve the diversity of the marine
ecosystem?