3.2 Origins of Biodiversity

What does biodiversity arise from?

Evolutionary processes

How can biological variation arise?

Randomly - beneficial/damaging/no impact

Define evolution

A gradual change in the genetic character of populations over many generations, achieved largely through the mechanism of natural selection

What does environmental change give?

• New challenges to species

• Drives evolution of diversity

What is natural selection?

• A process part of the theory of evolution by Darwin

• Where the individuals more adapted to their environment flourish and reproduce, while those not die

What is the process by natural selection?

1. Within a population of species, there is genetic diversity/variation

2. When organisms reproduce, they produce more offspring than environment can support

3. Leads to competition for food and other resources

4. Due to natural variation, some genes will adapt better to environment - these individuals become more fitter

5. Fitter individuals will have an advantage and reproduce more successfully

6. Repeated over generations and the advantageous characteristic will become the norm

7. Offsprings of fitter individuals inherit genes

What does natural selection contribute to?

Evolution of biodiversity over time

What is an example of natural selection?

Variation in fur colour within rabbit populations

Define speciation

The gradual change of a species over time

How does speciation occur?

• When populations of species become genetically isolated, they cannot interbreed

• If the environments they inhabit start to change, they may diverge and form new species altogether

What are examples of physical barriers causing speciation?

• Mountain formation

• Changes in rivers

• Changes in sea level

• Climate change

• Tectonic movements

Why does isolation cause speciation?

They give different selection pressures

What do land bridges allow to do?

Allow species to invade new areas

What do land bridges result from?

Continental drifts and changes in sea levels

What do continental drifts result in?

New and diverse habitats

Why can continental drifts do this?

• Continents move to different climate zones

• Changs in climatic conditions and food supplies, causing the species to adapt and lead to an increase in biodiversity

What is the Earth divided into?

Tectonic plates

What can plates do when they meet?

• Move apart at constructive plate margins (divergent)

• Slide against each other at destructive plate margins

• Collide at collision plate margins

What happens at constructive plate boundaries?

Plates are moving apart

What is an example of a constructive place boundary?

Mid Atlantic Ridge

What can occur at a constructive plate boundary?

Volcanic eruptions and earthquakes

What happens at a destructive plate boundary?

• Plates are moving together

• The denser, heavier oceanic plate subducts under the lighter, less dense continental plate

What is an example of a destructive plate boundary?

The boundary between the Nazca plate and the South American plate

What can occur at a destructive plate boundary?

Volcanic eruptions and earthquakes

What happens at a collision boundary?

Two plates of similar density move towards each other

What is formed and how is it formed at a collision boundary?

• Neither plate is dense enough to subduct so land is pushed upwards

• This forms mountains

What can occur at a collision boundary?

Earthquakes

What can tectonic plate movement cause?

• Land bridges and physical barriers - allows movement of organisms

• Changes in climate and food supply - e.g. separation of Africa and South America led to formation of Atlantic Ocean, creating a drier climate in Africa due to reduced moisture transport

• Genetic isolation

• Conservation implications - land bridges/physical barriers

What is background extinction rate?

The natural extinction rate of all species

What were mass extinctions caused by?

• Tectonic plate movements

• Super-volcanic eruption (Deccan Plateau in India)

• Climatic changes (led to Ice Age)

• Meteorite impacts (led to death of dinosaurs)

• Epidemics

What have mass extinctions led to?

New directions in evolution and increased biodiversity

What is this extinction caused by?

Climate change caused by human activity

How have humans caused ecosystem stress?

• Transforming environment - industry, urbanisation, agriculture

• Exploiting other species - fishing, hunting, harvesting

• Introducing alien species - GMO (may not have natural predators)

• Polluting environment - killing species directly/indirectly

Describe the Ordovician-Sullivan mass extinction

• 443-485 million years

• Series of glaciations caused by global cooling event

  • Led to sea-level fall and the contraction of shallow water habitats

  • Caused widespread extinction of marine life

  • Reduction in oxygen levels

  • Ocean anoxia

Describe the Permian-Triassic

• 251 million years ago

• Massive volcanic activity in Siberia

• Released huge amounts of greenhouse gases and other toxins into atmosphere

• Caused global warming, ocean anoxia, ocean acidification

Describe Late Devonian

• 364-375 million years ago

• Climate change caused by spread of land plants reduced amount of CO₂ in atmosphere

• Led to global cooling, decline in sea levels, widespread marine extinction

Describe the Triassic-Jurassic mass extinction

• 199-214 million years ago

• Climate change caused by massive volcanic activity led to global warming, decline in sea levels, caused widespread marine extinction

• Loss of habitat, changes in temperature, precipitation

Describe Cretaceous-Paleogene mass extinction

• 65 million years ago

• Asteroid impact in the Yucatan Peninsula combined with massive volcanic activity in India caused

  • Global cooling

  • Acid rain

  • Widespread wildfires

• Impact caused global tsunami, triggered earthquakes, which caused widespread destruction

• Loss of habitat, changes in temperature and precipitation