2.5 Zonation, Succession and Change in Ecosystems

Guiding question

How do ecological systems change over time and over space?

SL and HL knowledge statements

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

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.

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.

This video explains the changes from an aquatic pond ecosystem to a climax forest community over time. You do not need to know the names or types of organisms at each stage – just know the process.

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.

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

Birth of an Island shows the process of primary succession from vulcanism.

2.5.6 Secondary succession happens on bare soil where there has been a preexisting community, such as a field where agriculture has ceased or a forest after an intense firestorm.

The 1988 Yellowstone fires were a significant disturbance to a famous ecosystem that provided a great opportunity to study secondary succession as it happens.

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

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

Knowledge statements for HL only

Here’s my video for the HL content in topic 2.5.

2.5.9 The type of community that develops in a succession is influenced by climatic factors, the properties of the local bedrock and soil, geomorphology, together with fire and weather-related events that can occur. There can also be top-down influences from primary consumers or higher trophic levels.

2.5.10 Patterns of net productivity (NP) and gross productivity (GP) change over time in a community undergoing succession.

2.5.11 r- and K-strategist species have reproductive strategies that are better adapted to pioneer and climax communities, respectively.

2.5.12 The concept of a climax community has been challenged, and there is uncertainty over what ecosystems would develop naturally were there no human influences.

2.5.13 Human activity can divert and change the progression of succession leading to a plagioclimax.

Practical activities

Practical 2.5.1 – Investigate zonation along an environmental gradient
Practical 2.5.2 – Map changes through stages of succession
HL Practical 2.5.11 – Sample populations of r- and K-strategist species in different successional seres

Possible engagement opportunities

Produce an infographic, poster, or social media for the school to document the fieldwork in which the students have participated.

Happy learning!