13 The Changing Biosphere

When we finish this chapter you should be able to:Define natural selectionExplain how geographical isolation and reproductive isolation lead to the evolution of new speciesDiscuss 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 timewarming 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)

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?

Human Adaptation

Rate of Evolutionary ChangeTwo 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?