2.5.1 Zonation refers to changes in community along an environmental gradient.

Zonation occurs due to a range of factors, such as changes in elevation, latitude, tidal level, soil horizons or distance from a water source.

2.5.2 Transects can be used to measure biotic and abiotic factors along an environmental gradient in order to determine the variables that affect the distribution of species.

Consider data in tables or figures related to zonation, including kite graphs.

Application of skills: Investigate zonation along an environmental gradient using a transect sampling technique and a range of relevant abiotic measurements. Create kite diagrams to show distribution.

2.5.3 Succession is the replacement of one community by another in an area over time due to

changes in biotic and abiotic variables.

Changes occur as one community changes the environmental conditions so another community can colonize the area and replace the first through competition. This process may continue for hundreds of years; pollen records in peat provide evidence of such changes.

Zonation is a spatial phenomenon; succession is a temporal phenomenon. 

2.5.4 Each seral community (sere) in a succession causes changes in environmental conditions that allow the next community to replace it through competition until a stable climax community is reached.

For example, mosses start soil formation on bare rock, allowing larger plants to colonize.

2.5.5 Primary successions happen on newly formed substratum where there is no soil or pre-existing community, such as rock newly formed by volcanism, moraines revealed by retreating glaciers, wind-blown sand or waterborne silt.

Consider an example of primary succession, which could be a well-documented example, such as Surtsey, or a local example. 

Use the following terms: seral communities or stages; pioneer and climax communities.

2.5.6 Secondary successions happen on bare soil where there has been a pre-existing community, such as a field where agriculture has ceased or a forest after an intense firestorm.

Consider an example of secondary succession, which could be a well-documented example, such as the Broadbalk Wilderness at Rothamsted, or a local example.

2.5.7 Energy flow, productivity, species diversity, soil depth and nutrient cycling change over time during succession.

Consider data in tables or figures related to succession and the reasons for changes in these factors.

Application of skills: Use secondary data and a mapping database to recreate or map the changes through

succession in a given area.

2.5.8 An ecosystem’s capacity to tolerate disturbances and maintain equilibrium depends on its diversity and resilience.

Consider the links between ecosystem resilience, stability, succession, diversity and human activity. For example, succession increases diversity which adds to resilience and stability, though human interference can cause a reduction in these qualities.