Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 814–819 of the course textbook. Image credits are on slide 10.
Succession is a directional change in the species of a community over time, driven by abiotic changes such as water, temperature and soil, and by biotic changes such as competition. Primary succession starts without soil; secondary succession starts where soil remains.
Pioneers such as lichens begin to form soil, which lets larger plants root. Plant size, primary production, species diversity, food-web complexity and nutrient cycling all increase.
Some ecosystems repeat a cycle of communities with no fixed climax. On some New Zealand rocky shores, barnacles, algae and then mussels settle in turn, and when the mussels detach the rock is bare again.
A climax community is stable and in balance with its climate and soil. Human activity can arrest succession: livestock eat tree seedlings, and draining wetlands removes the waterlogged conditions their species need.
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Print this guide and complete it as you work through the slides and videos. It asks for your own explanations, so close the notes while you try each section.
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A printable worksheet covering all four statements, from quick recall to data questions and a longer answer. It has 30 marks and takes about 30 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
You will need: Hay or dried grass, pond water, clear jars, microscope, slides
Safety: Wash hands after handling. Keep lids loose, and dispose of it all according to school procedures.
Carry this out with your teacher's supervision and follow your school's lab rules.
In the early 1900s, Clements saw succession as ordered and predictable, while Gleason emphasised chance. Each view still shapes ecology.
Both drew on real plant communities. Consider how scientists decide between competing interpretations.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
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