In the given taxonomic hierarchy diagram, what do "$P$" $\rightarrow$ and "$Q$" $\rightarrow$ represent respectively?

• A
  "$P$" $\rightarrow$ Increase in the number of species; "$Q$" $\rightarrow$ Decrease in the number of species.
• B
  "$P$" $\rightarrow$ Decrease in the number of species; "$Q$" $\rightarrow$ Increase in the number of species.
• C
  "$P$" $\rightarrow$ Increase in the number of organisms; "$Q$" $\rightarrow$ Decrease in the number of organisms.
• D
  Both $(a)$ and $(c)$.