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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: Water-surface temperature variation across the LOMA.

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 ]
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