LECTURE 7

Question 1

What happens in terms of lake zonation in warming temperatures?

Answer 1

Warm temperatures result in surface water heating up (becoming less dense) and floating above cooler waters.

Question 2

What is lake stratification?

Answer 2

Lake stratification is when wind mixing is insufficient to offset buoyancy from surface heating.

Question 3

What is the mechanism that helps to mix up the lake water and prevent stratification?

Answer 3

Wind!

Question 4

Describe lake zonation. Name and define the two zones.

Answer 4

Epilimnion = mixed zone (lost of oxygen; photosynthesis)

Hymnolimnion = unmixed zone (aphotic zone)

Question 5

What is the thermocline?

Answer 5

The division between the epilimnion and hymnolimnion zone.

Question 6

What is lake turnover?

Answer 6

When there is mixing of the lake water

Question 7

Lake stratification can vary. What are the three types of lake turnover?

Answer 7

Monomictic (one mixing: stratified in summer and turnover in fall)

Dimictic (summer + winter, stratified; spring + fall, turnover)

Meromictic (where the deepest layer is always stratified/never mixes)

Question 8

T or F: When there is high seasonality, stratification is very stable.

Answer 8

False. Stratification is not stable when there is high seasonality.

Question 9

In warmer temperatures, describe what happens to cold monomictic lakes.

Answer 9

In warmer temperatures, cold monomictic lakes become dimictic.

Question 10

In warmer temperatures, describe what happens to dimictic lakes.

Answer 10

Dimicdic lakes become warm monomictic

Question 11

In warmer temperatures, describe what happens to warm monomictic lakes.

Answer 11

Warm monomictic become meromictic

Question 12

What happens in terms of lake turnover in warmer temperatures?

Answer 12

Warmer temperatures

• Cold monomictic lakes > dimictic
• Dimictic lakes > warm monomictic
• Warm monomictic > meromictic

Question 13

Which lakes are the most stable in terms of stratification?

Answer 13

Typically, lakes at intermediate latitudes are most stable in terms of stratification

Question 14

Describe how changes in climate affect lake food chains.

Answer 14

Because FW species are largely cold-blooded, they are more sensitive to temperature changes

Therefore, lake food chains are strongly impacted by stratification.

Changes in climate could lead to changes in stratification, and changes in food web dynamics

Question 15

In permanently stratified lakes, how many food chains develop?

Answer 15

Two separate food chains, one in each layer

Question 16

What are the limitation of terrestrial systems and aquatic systems?

Answer 16

Terrestrial systems are nitrogen-limited.

Aquatic systems are nitrogen and phosphate-limited.

Question 17

True or false: Climate change is linked to all five major extinction events.

Answer 17

True - Climate change is linked to the five major extinction events both directly and indirectly.

Question 18

Name the direct causes of climate change that led to a mass extinction.

Answer 18

Rapid temperature changes

Changes in sea level

Question 19

Name indirect causes of climate change that led to a mass extinction.

Answer 19

Asteroid impacts, volcanic eruptions (that lead to rapid temperature changes and changes in sea level)

Question 20

Which two mass extinctions are the causes well understood?

Answer 20

Causes for K-T and O-S are well understood

Question 21

Describe the characteristics of the Ordovicina-Silurian Extinction (O-S Extinction).

What was the possible cause of the O-S?

Answer 21

Ordovicina-Silurian Extinction, 440 MYA

2nd best understood in terms of cause (after K-T)

Life in the seas were dominated by benthic marine organisms

Very old fossils so can only get to a genera level where half of all genera lost

After extinction, surviving lineages diversified and overall marine diversity slowly recovered

Possible cause: rapid cooling (sudden shift from greenhouse to icehouse conditions)

Shift to icehouse conditions:
Gondwanaland passed over pole - INITIATION OF GLACIATION
Sea levels drop due to land ice formation

Question 22

Describe the End-Denovian.

What was the possible cause of the E-D?

Answer 22

End-Denovian, 365 MYA

Land colonization
Land plant diversification
Sharks and bony fishes

Extinctions largely contained within marine organisms (20% of all families disappeared)

May have been a series of smaller scale extinctions occurring in succession

Possible cause: removal of carbon dioxide from atmosphere by terrestrial plants, resulting in global cooling

Triggered by land plants

Question 23

Describe the End-Permian or P-T.

What were the possible causes?

Answer 23

End-Permian (or Permian-Triassic), 250 MYA

Worst mass extinction event ever

90% of species disappeared

First event to really impact terrestrial ecosystems

Marks transition between Permian and Triassic

Possible causes: massive volcanism, methane outgassing from sediments

Switch from icehouse to greenhouse

Question 24

Describe the End-Triassic.

What were the possible causes?

Answer 24

End-Triassic, 200 MYA
~50% of species disappeared; mainly large terrestrial animals, plants, and marine species

Wiped out large amphibians and paved way for evolution of dinosaurs

Marks boundary bt Triassic and Jurassic

Possible causes: unclear; possibly due to gradual climate change, volcanism, or asteroid impacts; inconclusive tho

Question 25

Describe the Cretaceous-Tertiary (K-T).

What was the possible cause?

Answer 25

Cretaceous-Tertiary (K-T), 65 MYA

Most famous; characterized by extinction of most dinosaur lineages

Terrestrial species impacted include: mammals, lizards, dinosaurs, insects

Possible cause: extraterrestrial impact

Debris from asteroid impact > ejected material into space
Larger animals killed by infrared radiation while small ones more likely to survive (shelter under rocks, trees, in lakes)

Plant mortality also very high (high temperature = fires)

Question 26

Which dinosaur lineage remains today?

Answer 26

The avian clade remained; modern birds

Question 27

In K-T, smaller species survived. Why?

Answer 27

The larger species didn’t have shelter to hide form the impacts of the asteroid. Smaller species could find shelter under rocks or in lakes.

Question 28

T or F: In K-T, water-dwelling species survived while strictly terrestrial ones went extinct.

Answer 28

True - In K-T, water-dwelling species survived while strictly terrestrial ones went extinct.

Question 29

In K-T, larger herbivores and top predators disappeared. Why did smaller organisms and omnivores survive?

Answer 29

In the first initial wave of heat, the herbivores were more affected. Omnivores are able to adapt their diet and survive this. (our ancestors)

Question 30

Describe the pattern expected by asteroid impacts.

Answer 30

1. Impact event
2. Particulates enter atmosphere (if ejecta reach far, can return to Eath and release massive amount of infrared radiation)
3. Particulates in atmosphere block sunlight and cool planet for months (even centuries)
4. Climate change + decreased sunlight > large-scale vegetation changes
5. Many animals go extinct (due to loss of food sources) but not all levels of the food web equally impacted

Question 31

True or false: Throughout time, there has only been evidence of mass extinction events.

Answer 31

False - multiple minor extinction events also occurred.

Question 32

Name the three extinction recovery models.

Answer 32

Immediate linear response

Logistic response

Simple-positive feedback response

Question 33

True or false: Climate change always causes extinctions.

Answer 33

False - Climate change does not always cause extinction.

Some climate change (like the Pleistocene ice ages) not really linked to extinctions at all (except for the onset of the cyclic ice ages and the end)

i.e. Length of interglacial periods perhaps too short (10 – 20 ky) to cause extinctions in cold-adapted species

i. e. think about the Younger Dryas
- Where vast majority of plants survived this cold period
- Species may be able to tolerate relatively short, extreme climate changes
- If cold snap lasted longer, would they have gone extinct?

Question 34

Name the three major climate events in the past 100 MY.

Answer 34

1. PETM
2. Onset of major glaciation in Antarctica
3. Onset of Pleistocene ice ages

Question 35

What is commonly referred to as the 6th mass extinction?

Answer 35

The Anthropocene

Current extinction rates are much larger than background extinction events