Change in Ecosystems

Question 1

Succession

Answer 1

• Succession is a process of change in community composition and structure, usually towards the establishment of a stable ecosystem.
• It includes changes in both the biotic and abiotic factors in an ecosystem over time.
• When a stable community is established, it is known as a climax community.

Question 2

Primary succession

Answer 2

• Primary succession is an ecological succession where a newly formed area is inhabited for the first time by a group of species or a community.

Question 3

Secondary succession

Answer 3

• Change in ecosystem when previous established community is taken over by a new group of organisms
• The changes leading up to secondary succession:
  □ Fire, flood, land clearing
  □ Interrupts cycling of matter and flow of energy
• Secondary succession follows to regain equilibrium but the numbers and kinds of organisms may be different from original ecosystem

Question 4

Stages of primary succession

Answer 4

○ Catastrophic events (e.g. volcanoes, cyclones, earthquakes, tsunamis)
- Leaves barren sites with no soil and no organisms inhabiting the affected area
○ Pioneer species colonise
- Autotrophs (e.g. lichens)
□ Lichens break down rocks, windblown dust can settle in cracks
○ Soil formation
- Shallow soil
□ Pioneer species/plants die decompose and form a thin layer of soil
□ Mosses can grow
□ Mosses die and add nutrients to soil leading to establishment of simple community consisting of bacteria, fungi, invertebrates
- Deeper soil
□ Grasses, ferns and herbaceous plants can grow
□ New plants provide shade
□ Roots of new plants speed up weathering of rocks
○ New community formation
- Autotrophs attract small herbivores such as insects – becoming the next link in the food chain
- More immigrant species join from surrounding areas and remain if they can survive on available resources

Question 5

Stages of secondary succession

Answer 5

○ A natural disturbance occurs
○ Soil formation
- Soil is still present with some organic matter
- A few organisms may be present
○ New plants
- Fast growing pioneer species colonise area and invertebrates enter ecosystem
○ Slower-growing trees begin to grow and stabilise community
○ New herbivores, then carnivores and omnivores arrive and become part of food web
○ A new community forms and eventually becomes a climax community

Question 6

Compare primary and secondary succession

Answer 6

○ Beginning conditions - A new area with no life (barren) and Begins with disturbance of an already established ecosystem
○ Soil - No soil to start with and Soil is present at beginning
○ Plants - Pioneer species such as lichen first to establish and Seeds and roots of established vegetation already present
○ Biodiversity - Low biodiversity for a long time and Faster development of wider biodiversity
○ Time taken to reach climax community - Hundreds to thousands of years and 50 - 100 years