2.5 Zonation, Succession And Change In Ecosystems

Question 1

Example of zonation: rocky intertidal zone

Answer 1

From high tide mark to low tide mark

Highest point/spray zone:
Usually dry
Dominated by lichen, other hardy plants
- can withstand long term exposure to air+sunlight

High tide zone:
Barnacles, mussels, chitons, limpets, sea snails
- attach to rock and can withstand waves

Low tide zone:
More favorable for marine organisms
- sea stars, anemones, sea urchins
Require constant presence of water

Question 2

Human impact on succession: tropical rainforests

Answer 2

Even resilient ecosystem like rainforest can shift

Deforestation:
Trees removed -> grazing land
Reduced habitat complexity -> biodiversity loss
Disrupt nutrient cycling
Changes hydrological cycle
Soil erosion, loss of topsoil, low soil fertility
Decrease in primary productity
Trigger process of desertification

Mining:
Removal of topsoil and vegetation
Soil erosion and landslides
Chemicals -> pollute water
- negatively impacts aquatic life

-> can lead to tropical rainforest = savanna or grassland
- less resilient -> cannot recover as well
- lower biodiversity and procutity
- different abiotic/biotic factors

Question 3

Secondary succession case study: forest fires
Basic info

Answer 3

• Name of case study: Forest fires in Yellowstone National Park
  
  • Primarily located in Wyoming
• 1988: series of forest fires
  
  • Burned around 793,000 acres (36% of park)
  • One of the most significant wildlife events in the parks history
  • Caused by: dry conditions, strong winds, accumulated dead wood

Show resilience of forest ecosystem
Importance of natural disturbances in keeping biodiversity
Research show that natural fire cycles are necessary

Question 4

Secondary succession case study: forest fires
Phases

Answer 4

1st phase: immediate aftermath (0-1 year post fire):
- fire eliminated most vegetation → barren landscape covered in ash
- Organisms died → others (like insects, burrowing animals) survived
- soil nutrients (esp. nitrogen) depleted → gradually became enriched as organic material decomposed

2nd phase: pioneer species (1-5 years post fire):
- hardy plant species (ex. Fireweed and grasses) → first to colonize burned area
- Wind dispersed seeds + resilient root systems → regrowth of species like aspen and willow
- Some tree species (ex: lodgepole pines) have serotinous cones → require fire to release seed → natural regeneration

3rd phase: intermediate community (5-50 years post fire):
- Shrubs and young trees (ex. Douglas fir, quaking aspen) began to dominate the landscape
- Herbivores (ex. elk and bison) returned, followed by predators (ex. wolves and bears)
- Decomposers (fungi and bacteria) crucial role in nutrient cycling -> further enriching the soil

4th phase: climate community (50-200 years post fire):
- Mature forest ecosystem reestablished itself (lodgepole pines, spruces, firs -> dominate)
- biodiversity -> reached pre-fire levels, complex food webs restored
- Small-scale disturbances continued to shape the landscape

Question 5

Primary succession case study: volcanic eruption
Basic info

Answer 5

Korakatoa, Indonesia
August 27, 1883

Destroyed 70% of island
Pyroclastic flows and tsunami -> wipe out all life
38,417 human deaths
Ash cloud block light -> temperature drop

Gradual return of ecosystem
Show resilience and critical role of pioneer species in primary succession

Question 6

Primary succession case study: volcanic eruption
Phases

Answer 6

Pioneer Species (1886–1910s)
- First colonizers: Blue-green algae, mosses, and lichens detected by 1886.
- Method of arrival: Wind and ocean currents brought spores and seeds.

Early Successional Stage (1910s–1930s)
- Species observed: Grasses (e.g., Imperata cylindrica), ferns, and shrubs.
- Animal arrival: Insects (via wind) and birds (from neighboring islands).

Intermediate Stage (1930s–1970s)
- Trees established: Casuarina equisetifolia (beach she-oak), followed by Terminalia catappa.
- Fauna expansion: Small reptiles and mammals arrived (rats, monitor lizards).

Climax Community (Present Day – 2020s)
- Dense forest growth: Dipterocarps and Ficus trees dominate.
- Diverse fauna: Macaques, pythons, and over 40 bird species recorded.
- Current biodiversity: >600 plant species, >200 animal species.