Lecture 2 CM

Question 1

Ecosystems are…

Answer 1

they are changeable. Earth is a dynamic system and has the capacity to recover

Question 2

Agents of change can be…
What do they vary in?

Answer 2

• abiotic or biotic
• they vary in their intensity, frequency and extent

Question 3

What are the two categories of abiotic factors? And what do they play a critical role in?

Answer 3

• disturbances
• stress
• they play a critical role in driving succession

Question 4

Disturbance

Answer 4

an abiotic event that physically injures or kills some individuals and creates opportunities for individuals to grow or reproduce

Question 5

Stress

Answer 5

occurs when some abiotic factor reduces the growth, reproduction, or survival of individuals and creates opportunities for other individuals

Question 6

What is succession?

Answer 6

the process by which species composition of a community changes over time. involves colonisation and extinction due to abiotic and biotic agents of change

Question 7

Primary succession

Answer 7

involves colonisation of habitats that are devoid of life due to catastrophic disturbance or because they are newly created habitats.

Question 8

Why can primary succession be slow?

Answer 8

can be slow as the first arrivals (pioneer/early successional species) typically face harsh conditions

Question 9

Secondary succession

Answer 9

involves the reestablishment of a community in which most but not all of the organisms or organic constituents have been destroyed

Question 10

Where does primary succession occur?

Answer 10

Glacier Bay, Alaska
- the melting of glaciers has led to a sequence of community change that reflects succession over many centuries

Question 11

What are the stages of primary succession?

Answer 11

• in the first years after a new habitat is exposed, a primary or pioneer stage develops, dominated by lichens, mosses, horsetails, willows and cottonwoods
• a second community develops called the dryas stage (roughly 30 yrs after exposure)
• Alders dominate the third community aka Alder stage
• then mature sitica spruce forest comes into place

Question 12

Where does secondary succession occur?

Answer 12

Forests of New England

Question 13

What are the key findings after secondary succession in Mt.St.Helen’s eruption?

Answer 13

1. eruption survivors are key drivers of ecosystem rebirth, and initiate major changes early in the post-eruption period
2. animal disturbance disturbs seed bank beneath the ash layer which triggers seedling germination
3. nitrogen-fixing plants with deep rhizomes provide nutrient cycling service for new seedlings