Match the columns:

Column-$I$	Column-$II$
$(a)$ Earthworm	$(i)$ Birth-rate
$(b)$ Succession	$(ii)$ Pioneer species
$(c)$ Population rise	$(iii)$ Pollination
$(d)$ Ecological services	$(iv)$ Saprotrophs

(A-IV, B-II, C-I, D-III) The correct matches are as follows:
$(a)$ Earthworm is a saprotroph,which helps in the breakdown of detritus $(a-iv)$.
$(b)$ Succession involves pioneer species that colonize a barren area $(b-ii)$.
$(c)$ Population rise is directly influenced by the birth-rate $(c-i)$.
$(d)$ Ecological services include processes like pollination provided by ecosystems $(d-iii)$.
Therefore,the correct sequence is $(a-iv, b-ii, c-i, d-iii)$.