Which of the following levels is conceptual in terms of size?

Which one of the following statements is correct for secondary succession?

What will be the $P/R$ ratio of a climax community and a pioneer community? What explanation could you offer for the changes seen in the $P/R$ ratio of a pioneer community and the climax community?

What is formed by the interaction between biotic communities and their environment?

Phytoplankton $\rightarrow$ Submerged plant stage $\rightarrow$ Floating plant stage $\rightarrow$ Reed-swamp stage $\rightarrow$ Marsh-meadow stage $\rightarrow$ Scrub $\rightarrow$ Forest. What type of succession does this sequence represent?

What does primary succession indicate in the development of a community?