Succession/variation bio aqa

What is the difference between succession and variation?

Succession - replacement of one dominant species by another until a climax community is reached.
Pioneer community -> pioneer species (autotrophic, high reproduction, extremophile, N2 fixing…) -> intermediate community (pioneer species die, humus in soil, able to support secondary coloniser)… -> until climax community (stable).

Biodiversity is greatest in the intermediate community - in the climax community, the most adapted species would have outcompeted the less adapted.
Primary succession - new area of land that has become accessible. Secondary succession - only soil present, no living organisms (forest fire…)

Deflected succession - reach plagioclimax community due to human action (e.g continually mowing grass halts succession in your garden).

What do you mean by variation?