CourseCourseConceptConcept

IB ESS HL 2.5 Zonation Succession and Change Questions

Analyse transect and succession evidence, explain productivity and community development, and assess climax and plagioclimax concepts.

Syllabus
First assessment 2026
Course
ESS HL
Level
HL

Exam points

  • distinguish and interpret spatial zonation versus temporal succession using environmental-gradient, transect and primary/secondary examples
  • describe transect sampling of abiotic and biotic factors using suitable instruments, regular intervals, repeated measurements, species identification and diversity indices
  • identify primary or secondary succession and explain how pioneer colonisation, weathering, soil formation and retained soil or biological legacies enable later communities
  • explain or compare changes in soil quality, nutrient cycling, food-web complexity, species diversity and ecosystem stability or resilience across successional stages
  • explain how climate, bedrock, soil, geomorphology, weather events, disturbance, dispersal and human activity influence community development and colonisation
  • explain how gross/net and primary/secondary productivity change across successional stages after respiration and transfer losses
  • classify r- and K-strategists from life-history evidence and explain their fit with pioneer or climax communities
  • define a climax community and describe how human activities divert succession and maintain an earlier plagioclimax stage

Covered syllabus points

2.5.1—Zonation definition2.5.2—Transect use2.5.3—Succession definition2.5.4—Seral communities2.5.5—Primary succession2.5.6—Secondary succession2.5.7—Succession changes over time2.5.8—Ecosystem disturbance tolerance2.5.9 (HL)—Community development influences2.5.10 (HL)—Productivity patterns in succession2.5.11 (HL)—r- and K-strategist species2.5.12 (HL)—Climax community concept2.5.13 (HL)—Plagioclimax

Question 1

[Maximum number: 1]
Salinity variation in the Large Ocean Management Area

Figure:Salinity variation in the Large Ocean Management Area

Water-surface temperature variation across the LOMA

Figure:Water-surface temperature variation across the LOMA

temperature scale

Figure:temperature scale

Suggest one reason for the zonation seen in Figure 5(b).

Question 2

[Maximum number: 3]
Beaver-dam succession sequence — panel A

Figure:Beaver-dam succession sequence — panel A

Beaver-dam succession sequence — panel B

Figure:Beaver-dam succession sequence — panel B

Beaver-dam succession sequence — panel C

Figure:Beaver-dam succession sequence — panel C

Beaver-dam succession sequence — panel D

Figure:Beaver-dam succession sequence — panel D

Suggest how an ecologist might measure the changes in one abiotic factor along a transect from a beaver marsh, through beaver meadow to the adjoining forest.

Question 3

[Maximum number: 9]
Stages of ecological succession after fire

Figure:Stages of ecological succession after fire

Question (a)

(a)

Outline two reasons why the species within pioneer communities in the succession model shown above are more likely to be r-strategists than K-strategists.

[ 2 ]

Question (b)

(b)

Outline two reasons why the climax community in the succession model shown above is more stable than the intermediate community.

[ 2 ]

Question (c)

(c)

Distinguish between zonation and succession.

[ 1 ]

Question (d)

(d)

Outline two ways in which the food web is likely to change as a result of succession.

[ 2 ]

Question (e)

(e)

Outline two ways in which the soil quality in the pioneer stages of the succession model shown above will differ from that in the climax ecosystem.

[ 2 ]

Question 4

[Maximum number: 1]
Stages of ecological succession after fire

Figure:Stages of ecological succession after fire

Distinguish between zonation and succession.

Question 5

[Maximum number: 4]

Identify four differences between a climax community and a pioneer community.

Question 6

[Maximum number: 2]
Figure 4(c): An example of a retreating glacier in the Swiss Alps, 1891 (left) and 2019 (right)

Figure:An example of a retreating glacier in the Swiss Alps, 1891 (left) and 2019 (right)

Figure 4(d): Average percent cover vegetation near a glacier

Figure:Average percent cover vegetation near a glacier

Describe the processes leading to the development of a pioneer community as the glacier retreats, as shown in Figures 4(c) and 4(d).

Question 7

[Maximum number: 3]
Figure:Fact file on giant sequoia trees

Figure 4(a): Fact file on giant sequoia (Sequoiadendron giganteum) trees
Giant sequoias are legally protected in California. They are adapted to periodic fire; historically, wildfires have occurred in California every 6-35 years. They have thick bark up to 46 cm to protect the core from fire. Fire dries cones and releases seeds, while ash creates nutrient-rich soils. Seeds can also be released by the long-horned beetle, which lays eggs in cones; larvae eat the cone, releasing seeds.

Describe the process of succession after a wildfire has occurred in the forest.

Question 8

[Maximum number: 2]
Distribution of birch forest in Iceland in 874 and 2015

Figure:Distribution of birch forest in Iceland in 874 and 2015

Soil erosion in Iceland in 2007

Figure:Soil erosion in Iceland in 2007

Stages of soil degradation and vegetation-cover change in Iceland

Figure:Stages of soil degradation and vegetation-cover change in Iceland

Known distribution of Nootka lupin in 2010

Figure:Known distribution of Nootka lupin in 2010

With reference to Figures: Distribution of birch forest in Iceland in 874 and 2015, Soil erosion in Iceland in 2007, Stages of soil degradation and vegetation-cover change in Iceland and Known distribution of Nootka lupin in 2010 identify two ways in which vegetation cover has changed over time in Iceland.

Question 9

[Maximum number: 2]
Stages of ecological succession after fire

Figure:Stages of ecological succession after fire

Outline two reasons why the climax community in the succession model shown above is more stable than the intermediate community.

Question 10

[Maximum number: 4]

Outline one climatic and one edaphic (soil) factor which affect the final climax community in an ecosystem.

Question 11

[Maximum number: 7]

Explain how the process of succession leads to changes in productivity.

Question 12

[Maximum number: 1]
Figure 9(b): Round goby (Neogobius melanostomus)

Figure A:Round goby (Neogobius melanostomus)

Figure 9(b): Mottled sculpin (Cottus bairdii)

Figure B:Mottled sculpin (Cottus bairdii)

Figure:Fact file on the round goby (Neogobius melanostomus)

• An invasive species from Asia.
• First discovered in the St Lawrence River in 1990.
• Females lay eggs three times a year; up to 5000 eggs at a time.
• Young fish mature quickly.
• Can eat up to 4000 eggs of other fish in 15 minutes.
• Aggressively defend the best egg-laying sites, out-competing the native mottled sculpin (Cottus bairdii).
• Eat invasive zebra mussels.
• Eaten by native fish, such as lake trout and yellow perch.

Using Figures 9(a) and 9(b), identify one feature of the round goby that shows it is an r-selected species.

Question 13

[Maximum number: 1]
Rainforest environmental cartoon

Figure:Rainforest environmental cartoon

Figure 5 shows an environmental cartoon about rainforests.

Define the term climax community.

Question 14

[Maximum number: 2]

A group of researchers want to investigate succession in an ecosystem.

Describe how two human factors could affect succession.

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