2.5 Zonation, succession and change

Objective notes

13 learning objectives

2.5.1Zonation definition

• Changes in community along environmental gradient

• Factors: elevation, latitude, tidal level, soil, distance from water

2.5.2Transect use

• Measure biotic and abiotic factors along gradient

• Determine variables affecting species distribution

2.5.3Succession definition

• Replacement of one community by another over time

• Due to biotic and abiotic variable changes

• Zonation: spatial; succession: temporal

2.5.4Seral communities

• Each sere changes conditions for next community

• Competition until stable climax community reached

• Example: mosses → soil formation → larger plants

2.5.5Primary succession

• On newly formed substratum without soil

• Examples: volcanic rock, retreating glaciers, wind-blown sand

2.5.6Secondary succession

• On bare soil with pre-existing community

• Examples: abandoned agriculture, post-fire forest

2.5.7Succession changes over time

• Energy flow, productivity, species diversity, soil depth, nutrient cycling

2.5.8Ecosystem disturbance tolerance

• Depends on diversity and resilience

• Succession increases diversity → resilience and stability

2.5.9(HL)—Community development influences

• Climatic factors, bedrock, soil properties, geomorphology

• Fire, weather events

• Top-down influences from consumers (e.g., wolves, elephants)

2.5.10(HL)—Productivity patterns in succession

• Early stages: low GP, high NP (biomass accumulating)

• Later stages: high GP, NP approaches zero (balanced respiration)

2.5.11(HL)—r- and K-strategist species

• r-strategists: many offspring, pioneer communities

• K-strategists: few offspring, climax communities

2.5.12(HL)—Climax community concept

• Challenged and uncertain

• Alternative stable states due to random events

2.5.13(HL)—Plagioclimax

• Human activity diverts succession progression

• Examples: removal of carnivores, domesticated livestock grazing